Cruise Report
TABLE OF CONTENTS
Cruise Location Map ( Fig.1)................................................................................................. 3
NeMO 98 Scientific Party..................................................................................................... 4
1.0 CRUISE OVERVIEW........................................................................................................ 5
1.0.2 Background........................................................................................................................... 5
1.0.3 New Eruption Site................................................................................................................. 6
1.0.4 Mooring Searches.................................................................................................................. 7
1.0.5 Seafloor Experiments............................................................................................................ 7
1.0.6 Studies of ASHES and other Vents....................................................................................... 7
1.0.7 Other Operations................................................................................................................... 8
1.0.8 Outreach................................................................................................................................ 8
NeMO'98 ROPOS Tracks ( Fig. 2)........................................................................................ 10
SE Caldera SRZ, Vent Names and Locations ( Fig. 3).......................................................... 11
Instruments Placed Summer'98 ( Fig. 4)............................................................................... 12
ASHES Vent Field, Vent Names and Locations ( Fig. 5)...................................................... 13
DISCIPLINE SUMMARIES.............................................................................................. 14
2.0 VOLCANOLOGY............................................................................................................... 14
2.1 Principal Findings................................................................................................................. 14
2.2 Acoustic Extensometers........................................................................................................ 15
3.0 CHEMISTRY...................................................................................................................... 16
3.1 Vent Fluid Sampling............................................................................................................. 16
3.1.1 Description of Hot Fluid Sampler......................................................................................... 16
3.1.2 Samples Recovered............................................................................................................... 17
3.1.3 Preliminary Results............................................................................................................... 17
3.2 SUAVE Studies..................................................................................................................... 18
3.2.1 Description of Operations..................................................................................................... 18
3.2.2 SUAVE Summary for Project NeMO (Station List and Preliminary Results)..................... 19
3.3 OsmoSampler and OsmoAnalyzer Operations..................................................................... 20
3.4 Gas Sampling........................................................................................................................ 22
3.5 H2 and CH4 Oxidation........................................................................................................... 22
3.6 Determination of Sulfide, Nitrate and Salinity Concentrations
Without the Use of Reagents................................................................................................. 22
4.0 MICROBIOLOGY.............................................................................................................. 23
4.1 Non-Mat Microbial Ecology................................................................................................. 23
4.2 Microbiological Sampling for Molecular Microbial Ecology Analysis............................... 24
4.2.1 Introduction........................................................................................................................... 24
4.2.2 Shipboard Processing and Storage of Samples..................................................................... 25
4.2.3 Laboratory Processing and Molecular Biological Analysis.................................................. 25
4.3 Biomineralization/Lava Mats................................................................................................ 26
5.0 MACROBIOLOGY............................................................................................................ 27
5.1 High Temperature Chimney Biology.................................................................................... 27
5.2 Stable Isotope Food Web Analyses....................................................................................... 27
5.3 Biology of Low Temperature Sites....................................................................................... 28
5.3.1 Introduction........................................................................................................................... 28
5.3.2 Colonization.......................................................................................................................... 28
5.3.3 Regional Character................................................................................................................ 28
5.3.4 Local Variation...................................................................................................................... 29
5.3.5 Ridgeia piscesae.................................................................................................................... 29
5.3.6 A Final Comment.................................................................................................................. 29
5.3.7 MacroBiological Sample List from Low Temperature Sites................................................ 29
6.0 HYDROTHERMAL MINERALIZATION...................................................................... 30
7.0 NON-ROPOS OPERATIONS............................................................................................ 31
7.1 CTD Operations.................................................................................................................... 31
7.1.1 NeMO'98 CTD Casts............................................................................................................ 31
7.1.2 NeMO'98 CTD Cast Locations and Stations Table.............................................................. 32
7.2 Rock Sampling...................................................................................................................... 33
7.2.1 Operations............................................................................................................................. 33
7.2.2 Rock Core Sample List......................................................................................................... 33
7.3 SeaBeam 2100 Survey of Brown Bear Seamount................................................................. 35
8.0 NeMO '98 New Millennium Observatory WEB SITE.................................................... 35
9.0 NAVIGATION.................................................................................................................... 36
9.1 Navigation Overview............................................................................................................ 36
9.2 Final Calibrated Transponder Positions................................................................................ 37
9.3 Vents/Markers/Targets Location Table................................................................................ 38
9.4 NeMO Observatory Instruments in Place, September'98 Table........................................... 41
10.0 NeMO'98 OPERATIONS - ROPOS DIVES R460 - R480............................................. 42
10.1 ROPOS Dive Dates and Locations Table............................................................................. 42
10.2 NeMO'98 Markers/Experiments Deployed and Recovered
(also includes ALVIN 3245-3247 deployments).................................................................. 44
10.3 Sample Types (Total and per Dive)...................................................................................... 46
10.4 ROPOS Samples, Dives R460 - R480.................................................................................47
10.5 Dive Map Nomenclature....................................................................................................... 57
10.6 ROPOS Dive Logs, Dives R460 - R480 (Dive Log follows Dive Map)............................. 59
R460 Dive Map..................................................................................................................... 58
R461 Dive Map..................................................................................................................... 68
R462 Dive Map..................................................................................................................... 84
R463 Dive Map..................................................................................................................... 89
R464 Dive Map..................................................................................................................... 94
R465 Dive Map......................................................................................................................105
R466 Dive Map ..................................................................................................................... 110
R467 Dive Map ..................................................................................................................... 116
R468 Dive Map..................................................................................................................... 122
R469 Dive Map..................................................................................................................... 126
R470 Dive Map..................................................................................................................... 132
R471 Dive Map..................................................................................................................... 134
R472 Dive Map..................................................................................................................... 138
R473 Dive Map..................................................................................................................... 142
R474 Dive Map..................................................................................................................... 150
R475 Dive Log (no dive map)............................................................................................... 157
R476 Dive Map..................................................................................................................... 158
R477 Dive Map..................................................................................................................... 163
R478 Dive Map..................................................................................................................... 166
R479 Dive Map..................................................................................................................... 172
R480 Dive Map..................................................................................................................... 179
GEOLOGY
Bob Embley, Chief Scientist (PMEL)
Bill Chadwick (CIMRS)
Steve Scott (U. Toronto)
Susan Merle (CIMRS)
Julia Getsiv (Vanderbilt U.)
John Chadwick (U. Florida, Gainesville GS*)
Mike Stapp (PMEL)
CHEMISTRY
Dave Butterfield (JISAO-U. Washington)
Gary Massoth (PMEL)
Kevin Roe (JISAO-U. Washington)
Betsy McLaughlin-West (Rutgers U.)
Stacey Maenner (PMEL)
Jim Gendron (PMEL)
Geoff Wheat (U. Alaska)
Elizabeth Guenther (Moss Landing GS*)
Leigh Evans (CIMRS)
MACROBIOLOGY
Verena Tunnicliffe (U. Victoria)
Jean Marcus (U. Victoria GS*)
Maia Tsurumi (U. Victoria GS*)
Kim Juniper (U. Quebec)
Damien Grelon (U. Quebec GS*)
Christian Levesque (U. Quebec GS*)
MICROBIOLOGY
Jon Kaye (U. Washington GS*)
Julie Huber (U. Washington GS*)
Craig Moyer (Western Washington U.)
Karen Pelletreau (Western Washington U.)
EDUCATION
Gene Williamson
ROPOS CREW
Keith Shepherd
Bob Holland
Keith Tamburri
Kim Wallace
Ian Murdock
Mike Dempsey
*GS = Graduate Student
1.0 CRUISE OVERVIEW (R. Embley)
1.0.1 General Overview
This report details the results of the operations that occurred during the NeMO98 cruise on the NOAA Ship Ronald H. Brown from August 25th to September 20th, 1998. The team of 33 chemists, biologists, geologists, and engineers used the scientific remotely operated vehicle ROPOS (Remotely Operated Platform for Ocean Sciences) (Shepherd and Juniper, 1997) to investigate in detail the aftermath of the diking event and its effect on hydrothermal chemistry and on the seafloor and subseafloor biological communities. This was a highly leveraged expedition, with substantial operational support coming from several portions of NOAA (WCNURC, Sea Grant, PMEL VENTS) and from the Canadian National Science and Engineering Research Council of Canada (NSERC). Twelve principal investigators and eight graduate students from the U.S. and Canada participated in the expedition. Support for the research of the investigators and graduate students came from a variety of sources, including the NOAA Sea Grant Program, the National Science Foundation, NSERC, the NOAA VENTS Program, and MBARI (the Monterey Bay Aquarium Research Institute). More than 200 samples were collected, 40 experiments were deployed (most for a year deployment), and 15 experiments were recovered during the 252 hours (over 21 dives) of bottom time with ROPOS. The extraordinary amount of bottom time (about 100 hours more than an equivalent length submersible dive program) allowed the entire scientific party to participate in a careful exploration of the new eruption site and the other hydrothermal systems on the summit of Axial Volcano.
1.0.2 Background
A major focus of the cruise was the NeMO (New Millennium Observatory) project. The primary goal of NeMO is to investigate the effect of dike intrusions and eruptions on the chemistry and micro- and macrobiology of hydrothermal systems (Haymon et al., 1993; Holden et al., 1998; Tunnicliffe et al., 1997; Butterfield, 1997; Delaney et al., 1998). NeMO was conceived in 1996 as a multiyear effort to perform chemical, biologic, hydrographic (plume), and geologic time series studies of Axial Volcano on the central Juan de Fuca Ridge (Fig. 1) (Johnson and Embley, 1990). Axial was chosen for this study because: (1) its shallow depth and large mass of Axial Volcano implies a long-term frequency and volume of volcanic activity significantly higher than the adjacent mid-ocean ridge [Baker, 1992 #60], and (2) hydroacoustic monitoring using SOSUS (Dziak and Fox, 1997) and an ocean floor pressure gauge (Fox, 1990; Dziak and Fox, 1997) showed that the summit of Axial is the most seismically active site on the Juan de Fuca Ridge (Embley et al., 1990), and (3) intensive seafloor surveys by camera and submersible in the 1980s showed extensive evidence for recent volcanism and hydrothermal activity at its summit.
The approach of NeMO is to combine baseline in situ sampling and high resolution mapping with continuous monitoring of the hydrothermal systems over several years with the expectation of several magmatic perturbations occurring within that interval. Extensive seafloor investigations using deep-towed cameras and submersibles took place in the 1980s (CASM, 1985; Johnson and Embley, 1990) and renewed investigations in 1995-97 provided an excellent baseline for the NeMO program. The continuous monitoring aspect of NeMO reached a critical level by 1997, when the instrument suite was expanded to three complementary components: (1) Volcano System monitors (VSMs) to measure vertical crustal motion and seismic tremor, (2) an array of current meter/temperature recorder moorings along the shallowest portion of the south rift zone within the caldera, and (3) deployment of an array of acoustic extensometers (from the R/V Sonne in 1996) capable of recording horizontal strain over a 400-500 meter distance across the north rift zone (Fig. 2). Long-baseline-navigated towed camera surveys and CTD casts and tows from the Sonne (P. Herzig, Chief Scientist) in 1996 and the Brown in 1997 (G. Massoth, Chief Scientist) and several dives with ROPOS in the caldera in 1997 (V. Tunnicliffe, Chief Scientist) provided important baseline data and set the stage for the extensive surveys and sampling planned for NeMO-98.
On January 28, 1998, an intense earthquake swarm lasting 11 days began on the summit of Axial. Migration of the seismicity 50 km southward during the first few days revealed the similarity of the event to Icelandic and Hawaiian diking/eruptive events (Dziak and Fox, 1998). After the first two days, virtually all of the events located either on the southwestern part of the summit or at the extreme end of the southern rift zone. In mid-February, a rapid response cruise on the Wecoma by NSF and NOAA investigators (J. Cowen, Chief Scientist) found enormous increases in the hydrothermal discharge from the summit of Axial (Baker et al., 1998). In July, 1998, Alvin made four dives into the caldera during a combined NSF and NOAA effort (J. Cowen, Chief Scientist), confirming an area of new hydrothermal activity within a zone of young lavas in the SE part of the caldera. The Brown completed an extensive plume survey in early August and recovered one VSM (Volcano System Monitor) and two of the three temperature sensor moorings deployed in 1997. Temperature data from two of the water column moorings (Fig. 3) recovered by the Brown showed a large heat pulse coincident with the onset of the earthquake swarm and a pressure gauge on the VSM recovered from the center of the caldera showed a 3 meter subsidence of the seafloor (Fox, 1998). The high probability of a summit eruption indicated from these data set the stage for NeMO-98.
1.0.3 New Eruption Site
Much of the bottom time was used to investigate the eruptive site of a new lava flow in the southeast portion of the caldera which erupted along a fissure system at least 3 km long (Figs. 2 and 3). We had an excellent, state-of-the-art set of tools on ROPOS to accomplish this. These included: (1) an in situ chemical scanner (SUAVE) which measured Fe, H2S, Mn, light scattering, and temperature, (2) a suction device primarily used for taking up to 8 samples of unconsolidated material such as microbial mats, meiofauna, and vent animals, (3) a new vent fluid sampler capable of taking as many as 18 water and particle samples for chemical and microbiological analyses, (4) a pencil beam scanning sonar for detailed mapping, and (5) a 3 chip RGB pan/tilt/zoom video system.
A large percentage of the surface of the lava flow was coated with a brown to tan microbial mat which masked the glassy surface of the new flow and caused some initial uncertainty about the age of the lava. The very recent age of this lava was eventually verified by the partial burial of a seafloor instrument (see below) and a line from a navigation transponder mooring that had been deployed in the summer of 1997. The eruption was in the form of a drained-out sheet flow, in contrast to the (primarily) pillow lava erupted during previously monitored NE Pacific eruptions. Sheet flow morphology is thought to be caused by a higher effusion rate, which is consistent with the enhanced magma supply at Axial. High resolution surveys with the downward-scanning sonar revealed that the source of the eruption was an en echelon series of north-south collapse depressions characterized by lava spires and floored by sheet flow. Camera tows and submersible dives in the 1980s and 1990s found numerous vent communities over several kilometers on the southeast part of the caldera where the south rift zone begins near the eastern wall of the caldera. The ROPOS dives showed dramatic changes in the hydrothermal systems on the southeast part of the caldera, most notably the partial burial of the pre-existing vent communities. The eastern part of the lava flow had numerous sites of diffuse venting with extensive white bacterial mats colonized by small polychaete worms and snails (Fig. 3). These sites were devoid of tubeworms except near the eastern edge, where colonization had begun to occur, probably from surviving communities east of the lava flow contact. At one location, dead tubeworms and clams were found partially buried by the lava flow. Farther south, older vent communities still survived just beyond the limit of the new eruption. In one place an older lava drainout area had been penetrated by the new lava. Here, old tube worm communities barely survived on top of lava spires or were dying or dead after the spires had been toppled, possibly by the impinging lava flow and associated seismic activity.
Accompanying the eruption was an intense microbial bloom that was still ongoing in August/September, seven months following the event. A dramatic manifestation of the bloom was the production of large
amounts of white floc, which filled shallow cavities in the lava flow and flowed out in large amounts when the seafloor was disturbed.
1.0.4 Mooring Searches
ROPOS recovered five "prototype extensometer" (PE) instruments (Chadwick et al., 1995), via an elevator mooring. The PE instruments had been recording acoustic range data since they were deployed across Axial's north rift zone in June 1996, at a site about 4 km north of Axial caldera (Figs. 2 and 4). These data (which are still being analyzed) will show any horizontal strain along the north rift zone caused by the dike injection to the south. During the last ROPOS dive of the NeMO98 cruise four PE instruments (the fifth instrument had not worked) were redeployed near the same location across Axial's north rift zone for another year of continuous strain monitoring. Arrays of these instruments are planned for both north and south rift zones over the next several years.
Another role for ROPOS was a search for two seafloor instruments deployed in 1997 that could not be recovered during a previous attempt by the Brown in early August. A current meter/temperature monitor mooring had not responded to acoustic commands and one of the VSMs ("Rumbleometers") confirmed a release from the deployment weight but subsequent ranging indicated that it remained on the seafloor. ROPOS located this VSM by acoustic ranging (Dive R461) and a careful survey of it revealed that it was apparently overcome by flowing lava which had prevented the package from floating free of its deployment weight (Fig. 3). Subsequent attempts to pry it loose with the ROPOS manipulator (Dive R461) and pull it free with a line attached to the cage (Dives R474 and R477) were unsuccessful. An extensive search for the missing water column mooring on R460 and R461 failed to locate it. A bottom search with ROPOS at the deployment location of the mooring base (R477) revealed that new lava covered the site, so it seems likely that the mooring base was overrun by the lava flow, possibly resulting in the release of the mooring.
1.0.5 Seafloor Experiments
ROPOS deployed short-term and long-term experiments (Fig. 4). Several types of experiments were deployed for a year duration at the eruption site. These include: (1) two osmotic fluid samplers, (2) a time-lapse camera, (3) five temperature probes, and (4) several microbial mat collectors. The camera, one of the osmotic samplers, a temperature probe, and several microbial collectors were placed at the Marker 33 site, at which the highest flow rate was observed and the highest temperatures recorded. A short-term osmotic sampler was deployed and recovered from the same site as the long-term experiments. These experiments complement additional NOAA instrumentation emplaced before and after the ROPOS cruise. A replacement VSM was deployed at the eruption site in early August from the Brown. Following the ROPOS cruise, nine water-column moorings were deployed in and around the caldera from the Brown. These moorings include temperature sensors, optical sensors, and current meters to monitor the hydrothermal plume discharge for the next year. Finally, data from a year-long array of ocean bottom seismometers (beginning in July, 1998) at the summit of Axial by Scripps scientists in July 1998 (R. Sohn, S. Webb, and W. Crawford) should provide very valuable correlations between subsurface activity and effects on the hydrothermal system as recorded on the mooring and the in situ experiments.
1.0.6 Studies of ASHES and other Vents
The ASHES high temperature vent field in the SW portion of the caldera (Butterfield et al., 1990)(Figs. 2 and 5) was also extensively surveyed and sampled by ROPOS. It is not yet clear whether the 1998 diking event induced significant changes at ASHES vent field, but detailed analyses of the chemical samples will reveal any major changes induced since the last sampling effort in 1995. Several temperature probes deployed at both diffuse flow and high-temperature sites were left and will be recovered in the summer of 1999. A short-term osmotic water sampler was deployed and later recovered from a high-temperature site and several microbial mat collectors were left in place until 1999.
ASHES was also the focus of detailed studies of the macrofaunal communities. Intensive studies of the ecology of the tubeworm and polychaete communities at this site used a combination of video observations, chemical scanning, and sampling to better understand the relationships between chemistry, temperature, and biology. ASHES has been the focus of more than a decade of studies of the macrofaunal communities and continues to be an important study site for hydrothermal ecology.
Other long-term venting sites in and near the caldera visited and sampled by ROPOS included the CASM site (CASM, 1995) located at the northernmost end of the caldera near the intersection of the caldera wall and a small diffuse vent about 5 km north of the caldera along the north rift zone. The chemical and biological samples taken during these dives will establish a firm baseline for future magmatic perturbations occurring on the north rift zone.
1.0.7 Other Operations
Between dive operations included rock coring and CTD operations. These operations provided valuable additional data about Axial Volcano and used the valuable shiptime with maximum efficiency. The rock coring program concentrated on the South Rift Zone. Very few previous basalt samples had been collected from this site, and extensive analyses of these samples will help put the chemistry of the 1998 eruption into better regional context. The CTD program represented a continuation of the post-eruption plume time series begun in February.
1.0.8 Outreach
A web site (http://www.pmel.noaa.gov/vents/nemo_cruise98/) was updated (A. Bobbitt) on a daily basis with transmissions of still images, an occasional video clip, and descriptions of the latest results. A secondary school science educator (G. Williamson) provided material to a complementary shore-based educator (Mike Goodrich), who then gave daily public lectures on the seagoing activity at the Hatfield Marine Science Center Public Wing and publicized the web site to the educational community. This program will continue in 1999 with Sea Grant funding (V. Osis and W. Handshumaker).
References
Baker, E. T., J. Cowen, S. Walker, and D. Tennant, The 1998 volcanic eruption at Axial Volcano: Hydrothermal plume monitoring from
moored instruments and shipborne response cruises, Eos Trans. Am. Geophys. Un. (Fall Mtg. Suppl.), 79, F922, 1998.
Butterfield, D. A., G. J. Massoth, R. E. McDuff, J. E. Lupton, and M. D. Lilley, The chemistry of phase-separated hydrothermal fluids from ASHES Vent Field, Juan de Fuca Ridge, J. Geophys. Res., 95, 12,895-12,921, 1990.
Butterfield, D., I.R. Jonasson, G.J. Massoth, R.A. Feely, K.K. Roe, R.W. Embley, J.F. Holden, R.E. McDuff, M.D. Lilley, and J.R. Delaney,
Seafloor eruptions and evolution of hydrothermal fluid chemistry, Phil. Trans. R. Soc. Lon. A, 355, 369-386, 1997.
CASM (Canadian American Seamount Expedition), Hydrothermal vents on an axial seamount on the Juan de Fuca Ridge, Nature, 313, 212-214, 1985
Chadwick, W. W., Jr., H. B. Milburn, and R. W. Embley, Acoustic extensometer: Measuring mid-ocean spreading, Sea Technol., 36, 33-38, 1995.
Delaney, J.R., D.S. Kelley, M.D. Lilley, D.A. Butterfield, J.A. Baross, W.S.D. Wilcock, R.W. Embley, and M. Summit, The quantum event of crustal accretion: Impacts of diking at Mid-Ocean Ridges, Science, 281, 222-230, 1998.
Dziak, R. P., and Fox, G. G., Long-term seismicity and ground deformation at Axial Volcano, Juan de Fuca Ridge,
Eos Trans. Am. Geophys. Un., 78, F641, 1997.
Dziak, R. P., and C. G. Fox, Hydroacoustic detection of submarine volcanic activity at Axial Volcano, Juan de Fuca Ridge, January 1998, Eos Trans. Am. Geophys. Un. (Fall Mtg. Suppl.),79, F922, 1998.
Embley, R.W., and J. W. W. Chadwick, Volcanic and hydrothermal processes on the southern Juan de Fuca Ridge, J. Geophys. Res., 99, 4741-4760, 1994.
Fox, C. G., Evidence of active ground deformation on the Mid-ocean Ridge: Axial Seamount, Juan de Fuca Ridge, J. Geophys. Res., 95, 12813-12823, 1990.
Fox, C. G., In situ deformation measurements from the summit of Axial Volcano during the 1998 volcanic episode, Eos Trans. Am. Geophys. Un. (Fall Mtg. Suppl.),79, F921, 1998.
Haymon, R.M., D.J. Fornari, K.L. Von Damm, M.D. Lilley, M.R. Perfit, J.M. Edmond, W.C. Shanks III, R.A. Lutz, J.M. Grebmeier, S. Carbotte, D. Wright, E. McLaughlin, M. Smith, N. Beedle, and E. Olson, Volcanic eruption of the mid-ocean ridge along the East Pacific Rise crest at 945-52'N: Direct submersible observations of seafloor phenomena associated with an eruption eventin April, 1991, Earth Planet. Sci. Lett., 119, 85-101, 1993.
Holden, J.F., M. Summit, and J.A. Baross, Thermophilic and hyperthermophilic microorganisms in 3-30° C hydrothermal fluids following a
deep-sea volcanic eruption, FEMS Microbiol. Ecol., 25, 33-41, 1998.
Johnson, H.P., and R.W. Embley, Axial Seamount - An active ridge-axis volcano on the central Juan de Fuca Ridge, J. Geophys. Res., 95, 12,689-12,696, 1990.
Shepherd, K., and S. K. Juniper, ROPOS, creating a scientific tool from an industrial ROV, Mar. Tech. Soc. J., 31, 48-54, 1997.
Tunnicliffe, V., R.W. Embley, J.F. Holden, D.A. Butterfield, G.J. Massoth, and S.K. Juniper, Biological Colonization of New Hydrothermal Vents Following an Eruption on Juan de Fuca Ridge, Deep-Sea Res., 1997.
DISCIPLINE SUMMARIES
2.0 VOLCANOLOGY
2.1 Principal Findings (Bill Chadwick, Bob Embley)
One of the principle findings of the NeMO98 expedition is that the January 1998 earthquake swarm resulted in the eruption of new lavas along the upper south rift zone of Axial volcano. We know that new lava was erupted from the rift zone in at least two locations, 1) the upper most south rift zone between 4555.3' and 4557.2' (129 59.0'), on the SE edge of the caldera where many 1998 ROPOS dives took place, and 2) at a location where a prominent SeaBeam anomaly was found at 4552.0'/130 00.0', about 4 miles south of the caldera where one ROPOS dive was made. It should be emphasized that while we mapped the eastern and western lava contacts in both areas, we never defined the northern or southern limits of the new lava flows in either of these areas. Therefore, the full extent of the 1998 eruption is not yet known, and it is entirely possible that new lava was erupted continuously between the northern and southern study areas. For example, a second, smaller SeaBeam anomaly was found between 4554.5' to 4555.0'. This area was not visited by ROPOS during this cruise, but observations from Alvin dive 3247 in July 1998 suggest that new lava in the northern study area extends at least as far south as 4554.8'.
In the northern study area, it took a while for us to be convinced that new lava had indeed erupted, because in many areas it is covered by a tan/orange deposit of bacterial mat and does not look as fresh and pristine as we have observed at other recent eruption sites. However, by the end of the NeMO98 cruise the cumulative evidence for recent eruption was unequivocal. This evidence includes, 1) the mapping of new/old lava contacts and collapse features in the interior of the new flow in a geologically meaningful pattern from both bottom traverses and Imagenex sonar mapping, 2) a transponder mooring line that was deployed in 1996-97 found to be overrun by new lava along one of the new/old lava contacts, 3) the consistent absence of macrofauna on the new lavas except in new hydrothermal vent areas (contrasted with abundant sponges and other sessile animals on most of the surrounding older lavas), 4) the complete absence of "missing" tubeworm communities that had been photographed by camera tows in 1996 and visited by ROPOS in 1997 and were apparently buried by new lava, 5) the consistent distribution of new hydrothermal vent sites near the center of the new lava flow, and 6) the consistent (and virtually exclusive) association of the tan/orange bacterial mat coatings within the new lavas.
The new lava flow in the northern study area is narrow (300-600 m) and long (at least 3.5 km, but probably more than 4.5 km), and appears to be up to ~5 m thick. It was apparently erupted from a fissure on the rift zone, probably along the entire length of the flow. The lava flow is primarily a lobate sheet flow with extensive areas of roof collapse along its center, where it was thickest before drainout. In the floor of collapse areas are ropy, lineated, and jumbled sheet flows, and many areas with lava pillars up to 4 m in height. Near the margins where the flow is thin it has either lobate morphology or pillows. In places, the new lavas invade and fill in collapse areas in older lavas. The distribution of the tan/orange bacterial mat is variable, but generally it is thinnest near the flow margins and thickest near the center of the flow. The mat distribution is probably related to the way in which heat was dissipated from the new sheet flow as it cooled. The lava flow was hard on instrumentation that had been deployed in the area last summer - it surrounded and partially buried a NOAA/PMEL rumbleometer instrument and apparently buried or caused the premature release of a NOAA/PMEL current meter mooring.
High-resolution bathymetric maps made from data collected during surveys with an Imagenex scanning-sonar over the area show the distribution of collapsed and uncollapsed areas on the new flow, the topographic barriers in surrounding older terrain that limited its lateral extent, and the structural context of vent sites and sample locations. The Imagenex maps show about an order of magnitude higher resolution than hull-mounted multibeam bathymetry and reveal features on the seafloor that would be otherwise impossible to visualize. They will be extraordinarily useful for characterizing the eruption and the distribution of lava types, as well as for assessing the structural interaction between the south rift zone and Axial's eastern caldera wall. Imagenex surveys were also made on the north rift zone of Axial (where the extensometer instruments were recovered) and at ASHES vent field.
Our one ROPOS dive in the southern study area (dive 465) showed that the boundaries of the new lava flow there agreed almost exactly with the edge of the SeaBeam anomaly, which is about 1 mile E-W and 0.5 mile N-S, and is at least 27 m thick. The new flow was clearly erupted along the rift zone and flowed downslope to the east where it increased in thickness. This southern lava flow is primarily formed of pillow lavas, but also has lobate and jumbled sheet morphologies and localized areas of collapse and channelized flow. No active venting was observed on this lava flow, although there was extensive evidence that it had occurred previously.
The volume of lava erupted at Axial in 1998 is definitely larger than that erupted at either the 1993 CoAxial or 1996 Gorda eruptions, judging from the areas we have already mapped. However, we cannot put an upper bound on the eruptive volume until the area between 4552' and 4555' is mapped and the full extent of new lavas is determined.
2.2 Acoustic Extensometers (Bill Chadwick, Bob Embley, Mike Stapp)
The acoustic extensometer instruments were developed by NOAA/PMEL's engineering division with funding from NOAA/NURP and the VENTS Program. They are designed to measure and quantify seafloor spreading events. They do this by acoustically measuring the distance between pairs of instruments very precisely (~1 cm) over a short baseline (100-200 m between instruments). The instruments are deployed in a linear array to span larger distances (up to 1 km). They have enough power and memory to make daily measurements for about a year and a half.
On June 20, 1996 we deployed 5 extensometer instruments on the north rift zone of Axial at about 4601.2'N latitude from the SONNE. We had intended to deploy them with ROPOS that year, but due to the unavailability of the ROPOS winch at the last minute, we were forced to simply drop them from the surface and hope for the best (that they would land in such a way that they would have the required acoustic line-of-sight between them). We had also hoped to recover them in July 1997 from the TULLY, but this was the first shake-down cruise for the new ROPOS and there was not enough dive time available. However, this means they were still deployed when the earthquake swarm occurred on Axial in January 1998, giving us the opportunity to see if the north rift zone was involved in the 1998 eruption.
The five extensometer instruments were recovered by ROPOS and the elevator mooring (equipped with 5 large black plastic tubes) on September 5, 1998, on ROPOS dive 467. By luck, ROPOS landed right on top of instrument #2, after a short test above the bottom with the digital camera. All five instruments were in the elevator with 3.5 hours (surprisingly fast). The instruments had all landed within 9 to 39 m of their drop positions. An Imagenex survey was made of the area where the instruments were located to aid in finding the best sites for their re-deployment and to study the structure of the north rift zone.
Four of the five extensometers recorded data. Instrument #4 would not respond after recovery, and its data could not be retrieved. Of the 4 remaining, one ended up in a hole (#1) and could not see the others for ranging (this is why ROV deployment is so important!). The remaining 3 ranged to each other for about 20 months (until ~March 2, 1998), and luckily spanned the axis of the north rift zone. Of the two range legs between the 3 instruments, one range leg (#5<->#3) spanned the north rift zone and was 300 m in length (the dead instrument was in the middle there) and the other range leg (#3<->#2) was 100 m in length and east of the rift axis.
The good news is that most of the instruments worked. We obtained a good Imagenex sonar survey of the site, and an excellent ROV deployment of the instruments. They will provide an exceptional monitoring baseline for the next year. We deployed the 4 working instruments back on the north rift in about the same location. Future plans call for extensometer arrays on both the north and south rift zones with new instruments that can remain on the bottom for 5 years with annual data retrieval by acoustic modem.
3.0 CHEMISTRY
3.1 Vent Fluid Sampling (Dave Butterfield)
One of the goals of the NeMO 98 Cruise was to understand the connections between microbiology, geology, and chemistry. Specifically, we wanted to address whether fluid chemistry is a controlling factor in the abundance and type of microbes present in hydrothermal vents. This fits in nicely with the studies of vent fauna and how they relate to fluid chemistry. This part of the project requires collecting coordinated samples for fluid chemistry and microbiology, and for that purpose, we constructed the Hot Fluid Sampler (HFS).
3.1.1 Description of the Hot Fluid Sampler
HFS was designed to collect fluid and particle samples from vents with a wide range of temperature and flow rate. The system consists of a titanium intake nozzle with 1mm slits to exclude large particles and a platinum resistance thermometer in a titanium sheath with the sensing tip located about 1 cm above the inlet slits. Hydrothermal fluids are pulled through the intake nozzle, past the temperature sensor, through a ball joint, into a 0.5 inch diameter PEEK plastic tube (~1.5 m long). This flexible tube connects to a 0.5 inch titanium tube (~1.3 m long), which in turn connects to 0.5 inch teflon tubing. A second temperature sensor is located at the junction of the titanium and teflon tubing, in order to assure that the temperature of the fluids has cooled to below 100°C prior to being pulled into the various samplers or passing through the flushing pump. The flushing pump pulls the sample from the intake nozzle past the samplers, and operates at adjustable rates from 1 to 5 liters per minute. The sample pathway is made entirely of titanium, PEEK, and teflon. There are nine teflon cross fittings along the fluid path, allowing a maximum of 18 individual samples to be taken per deployment. By maintaining a constant and smooth inner diameter through the fluid pathway, the system promotes easy flushing of any entrained particles and provides minimal dead spots for particles to accumulate. To protect the flushing pump, we are limited to relatively "clean" samples, i.e. we can't use the fluid sampler as a suction sampler.
A separate sample pump (100 to 250 ml/min) pulls the fluid into the sampler selected by a 25-port valve. The sample pump pulls the backfill water out of the samplers to draw the fluid in, and does not contact the sample fluid, except in the case of the filter samples for particle collection, when filtered water is pulled through the sample pump. In addition to the dive sample number assigned to every ROPOS sample, we assign a water sample number which is the dive number followed by the type of sample (P for piston, B for bag, F for filter) and the valve position number. Pistons are numbered 8-13, with 8 and 9 used for gas sampling. Bag samples are numbered 2-7 and 23 and 24. Filters occupy positions 16-18.
The sampler uses 4 wires: ground, +26-35V DC, and RS232 transmit and receive. The software used to control the sampler runs on a PC under a DOS window. When data logging is on, we record (once per second) temperature, valve position, pump status (on/off), and volume pumped. By tracking the intake temperature of the sample throughout sampling, we get an average temperature for the water sampled, so we can calculate element/heat ratios.
Part of the philosophy of this sampler was to collect a large number of fluid and particle samples on a single dive dedicated primarily to fluid sampling, alternating with dives serving other purposes. Because the sampler is so large, few other operations are possible when the sampler is in use. The sampler is best utilized when there are a number of known targets to sample, or when replicate sampling of a few sites is desirable.
HFS takes 3 types of samples. There are 6 PVC piston samplers, 4 with teflon check valves for general water chemistry, and 2 with steel check valves with o-ring face seals for gas sampling. The piston samplers can hold up to 800 ml of sample when full. For gas sampling, we take only 150-200 ml so as not to exceed the capacity of the gas extraction line. There are 8 bag samplers, each with a teflon check valve. We have the option of placing filters in front of the bag samplers to remove particles. Our standard configuration took six filtered samples, with the filters going to Feely's group at PMEL for XRF and SEM analysis. The bags themselves are either Tedlar or laminated, high-density polyethylene-lined, and both types are reasonably impermeable to gases. Finally, we use a variety of filters with no fluid collection to trap particles. On this trip we used 3 micron GFF followed by 0.2 micron Sterivex cartridge filters for microbiological work (DNA analysis).
3.1.2 Samples recovered
The fluid sampler was deployed on 4 dives: 468 (shortened by mechanical problem with the 7-function arm), 469, 473, and 479. During these dives, we collected 42 fluid samples. We sampled focused, hot fluids from Virgin Mound, Crack, Mushroom, Inferno, and Hell vents, and diffuse vent fluids distributed throughout the ASHES vent field. We took one sample (20°C) at Tombstone vent located about 500 meters south of the ASHES field. On dive 473, we sampled a wide variety of fluids associated with the new lava flow in the SE corner of the caldera. These samples included the "milky" fluids venting along a line in the northern part (Milky, Easy, Magnesia vents), floc-producing vents (Snowblower near The Pit), clear fluids venting through holes in the roof of drain-back areas (Roof vent), hotter clear-venting fluids (marker 33), and a smoky vent (Cloud). We sampled two of the 3 sites sampled during the July Alvin dives (marker 33 and marker 108). We also found and sampled a hot vent (275°C) near the eastern contact of the new flow. Between the HFS samples, additional water samples collected with the suction sampler and ROV-mounted Niskins, and chemical data from SUAVE scans, we have excellent spatial distribution for vent fluid chemistry. Our assessment of what is actually venting from the recent eruption area at Axial is more comprehensive than the 1993 sampling after the CoAxial eruption.
3.1.3 Preliminary results
Our shipboard analyses included hydrogen sulfide, silica, pH, alkalinity, ammonia, and refractive index for salinity. We found that Virgin Mound still has a very low salinity, and that the salinity at Hell and Inferno has decreased significantly since 1995. This is the first time we have found all the high-temperature fluids to be less than seawater salinity at ASHES. Maximum temperatures measured with the fluid sampler were 297 at Hell, 261 at Virgin, 256 at Inferno, and 179 at Mushroom. (There may be higher temperature fluids venting from other orifices that we did not measure. We did not measure what was the hottest orifice on Inferno, because there was a HOBO temperature probe left in it.)
Many of the samples we collected were very gas-rich. The HFS sample containers hold the gas quite well, so we recovered much more sample than we typically get with the major samplers, which are designed to leak. Castle vent was charged with CO2, with over 5 mM H2S, and low salinity. The present venting at Castle is limited to a small anhydrite chimney near the base of what appears to be a decaying sulfide structure. This gives the impression that the venting at Castle has been rekindled by the recent eruptive activity.
We see a wide range of H2S/heat or H2S/Si ratios in the collected vent fluids. This range is a potential indicator of both differences in the reaction zone temperature and sulfide-consuming reactions in the sub-seafloor. Further study of the vent fluid and particulate chemistry combined with the microbiological results should clarify what processes are involved, and how they relate to the eruptive activity.
Although we saw significant thermal and particle plumes over some distance south of the ASHES field, our one dive there did not turn up much venting. We saw only one large patch of venting with tube worms, anemones, crabs, and other biota, and took one sample there. The sample has a moderate H2S/heat ratio. Because of the length of the transect (over a kilometer) we could not do a thorough search. Overall, we obtained an excellent set of samples that should allow us to learn how the free-living microbes and the mats relate to the vent fluid chemistry.
3.2 SUAVE Studies (Gary Massoth)
3.2.1 Description of Operations
The Submersible System Used to Assess Vented Emissions (SUAVE) was conceived from the need for a better tool to probe the submarine hydrothermal environment. Chemical oceanographers within the NOAA Vents Program require information about the concentration, distribution, and inventory (flux) of key chemical species in seafloor effluents and hydrothermal plumes that has a much higher spatial resolution than that typically afforded by conventional "n-limited" discrete sampling procedures. In situ chemical analyzers or "scanners" of the type first described by Ken Johnson and associates (Johnson et al., 1986) are an ideal solution to this need. By matching high-resolution chemical data provided by scanner technology with continuously-sensed physical property information, unprecedented insights about processes occurring in the submarine hydrothermal environment are in the offering. Similarly, by coordinating in situ chemical measurements with observations of vent field macro- and micro-biology, the effects of chemistry on hydrothermal biota, and vice versa, can be rigorously evaluated (Sarrazin et al., submitted). Finally, chemical analyzer data collectable over the "operational-day" time scale, both on the seafloor and within hydrothermal plumes, provides both the spatial and temporal resolution necessary to discriminate ephemeral processes critical to understanding the evolution of seafloor hydrothermal systems. These attributes plus the species/concentration-range adaptability, multiple-platform compatibility, reduced opportunity for sample contamination, and "quicktime" feedback inherent to chemical analyzers provided extreme incentive to develop a SUAVE capability within the Vents Program.
SUAVE is an integrated instrument system consisting of an evolved chemical analyzer patterned after the original in situ chemical analyzer, the "scanner"(Johnson et al., 1986), and an array of physical property sensors (temperature, conductivity, pressure, light scattering and/or attenuation). Co-funded by the NOAA NURP and Vents Programs, design and fabrication were initiated in 1991, incorporating modifications suggested by Ken Johnson and Kenneth Coale of the Moss Landing Marine Laboratory, based on their experience with the "scanner." Schematic block diagrams of SUAVE electronics and chemical components are shown in Figure 1. The SUAVE chemical analyzer is based on principals of flow analysis and colorimetric detection. For NeMO 98 SUAVE was configured to measure H2S (simultaneously by two methods: nitroprusside over the range ~50 to 2000 æmol/L and molybdenum blue over the range ~1 to 200 æmol/L), Mn(II) and Fe(II+III) dissolved in vent fluids. Sensors data was recorded for temperature (0 to 120øC), pressure (depth), conductivity (salinity), and light scattering. All data channels logged readings each 5 seconds during deployment.
During NeMO 98 SUAVE was deployed on ROPOS-II during 10 of the 21 dives conducted. SUAVE was engaged in thermochemical surveys of seafloor venting for over 67 hours during which 55 scans (extended measurements for over 5 minutes at a single point in space: 30 along the East Rift eruption mound, 22 at ASHES vent field, 2 at CASM and 1 at the 91 vent field on the North Rift Zone of Axial Volcano) were made. The SUAVE measurements will be used to determine the spatial variability in concentration of the various measured chemical species and their ratios to heat for comparison to historical data. The SUAVE data set will be extended both spatially and elementally by merging with vent fluid data collected by Butterfield. Evidence for selective regional exhalation of H2S, a product of magmatic degassing and dike cooling and also a primary microbial nutrient, will be sought to guide studies of temporal variability of hydrothermal effluents. Identification of signature' ratio values indicative of the recent lava intrusion/eruption at Axial Volcano will be characterized. SUAVE H2S data will be merged with micro- and macro-biological data collected by Juniper, Tunnicliffe, and Moyer to help define thermochemical niche values for various biological communities.
References:
Johnson, K. S., C. L. Beehler, and C. M. Sakamoto-Arnold (1986). A submersible flow analysis system, Anal. Chim. Acta, 179:245-257.
Sarrazin, J., K. Juniper, G. Massoth, and Legendre (submitted). Physical and chemical factors controlling hydrothermal species distributions on two sulfide edifices of the Juan de Fuca Ridge, Northeast Pacific, Deep-Sea Res.
Tunnicliffe, V., R.W. Embley, J.F. Holden, D.A Butterfield, G.J. Massoth and S.K. Juniper (1997). Biological colonization of new hydrothermal vents following an eruption on Juan de Fuca Ridge, Deep-Sea Res. 44(9/10):1627-1644.
3.2.2 SUAVE Summary for Project NeMO (Station list and preliminary results)
Site Tmax Tave H2S Mn Fe H2S/Q Mn/Q Fe/Q
°C °C M M M nM/J nM/J nM/J
SE Caldera
ROPAX 97@ huge worm field 6.4 6.4 82 ? BDL 4.8 - -
R460-1 bacteria floc by Milky Vent 2.9 6 BDL (45) 3.7 - (37)
R460-2 MKR N2@ Milky Vent 8.0 8.0 175 40 90 7.9 1.8 1.1
R460-3 MKR N3@ hole in basalt 13 11.5 200 40 40 5.5 1.1 1.1
R460-5 MKR N1@ Pit Vent 13.7 13 180 50 15 3.3 0.9 0.3
R461-1 @ MKR 33 bacteria mat, crack 15 8 470 2 47 9.3 0.04 0.9
R461-2 @ MKR 33 over white mat 11 15 5 2 0.4 0.2 0.1
R461-3 @ MKR 33 over hole in above mat~4.5 ~10 BDL BDL ~1.2 - -
R461-6 @ MKR 33 crack with floc flow 37 26 1000 18 40 7.2 0.1 0.3
R461-7 @ MKR 33 mat @ Bag Creature 17 700 2 5 12.0 0.1 0.1
4R61-8 @ MKR 33 Bag Creature 2.8 75 BDL BDL 62 - -
R461-9 @ MKR 33 Baby Bag Creature 3.1 40 BDL BDL 16.5 - -
R461-10 @ MKR N6 Cloud Vent 27 750 5.5 62 7.6 0.1 0.6
R461-11 @ MKR N4 Cloud Vent 24 750 2 55 8.7 0.1 0.6
R461-12 @ MKR 108 8.1 6.0 230 45 25 10.0 2.0 1.1
R461-13 @ MKR 113 flow @ top of pillar 10 237 BDL 7 7.7 - 0.2
R461-14 @ MKR 113@ Vemco probe tip 10.5 307 BDL 8 8.0 - 0.2
R461-17 @ MKR 113@ bacteria trap 23.5 20 500 -BDL 9 13.0 - 0.2
R461-19 @ MKR 113base of tall tubes 5.7 45 -BDL 8 4.5 - 0.1
R461-21 @ Cirque Vent and hole in 6.5 6.5 87 3.0 57 6.2 0.2 3.5
basalt with Fe floc cover
R461-22 @ Castle Vent@ base of 90 60 1400 18 71 6.1 0.1 0.3
Hi-T vent
R461-23 @ Castle Ventprobe in 5.3 5.0 132 BDL BDL 13.0 - -
tubes @ base
R461-24 @ Castle Vent and MKR N5, 21 19 200 6 19 3.0 0.1 0.3
@ healthy tube worms
R478-1 @ MKR 33 17
R478-2 MKR 33 Near OSMO Sampler 42.2
and MTR
R478-4 20 m SW of MKR 33 13.0
at crack venting floc
R478-5 ~5 m NW of CLOUD VENT 18.7
R478-? Scan 5 at Nascent Vent 23.5
R-478-? Scan 6 at MKR N41 22.7
R478-? Scan 7 on old flow just N of N41 9.5
R478-? Scan 8 on old flow and 16.3 16.1
within big tube worms
ASHES Vent Field
ROPAX 97@ Hat Vent 30.5 90 21 15.5 0.8 0.2 0.1
ROPAX 97@ Phoenix 4.9 93 4 12.5 9.9 .4 1.3
ROPAX 97@ Phoenix 19.5 320 4.8
ROPAX 97@ Phoenix 37.2 150 1.1
ROPAX 97@ Crack Vent 61.6 725 13 55 3.1 0.1 0.2
ROPAX 97@ Wall 80 m W 19.5 4 11.5 0.05 0.1 0.2 0.001
R466-20 @ Inferno near palm worms 5.5 4.0 45 10 45 7.4 1.6 7.5
R466-23 @ Hell front edge pork chop 16 12 1690 70 90 2.8 1.8 2.3
R466-24 @ Hell back of pork chop 19 17 420 60 87 7.3 1.0 1.5
R466-25 @ Hell center of chop 19 17 420 45 85 7.3 0.8 1.5
R466-26 @ Hell tip of chop 19.5 18 650 75 90 10.4 1.2 1.4
R466-5 @ Hillock@ bacteria traps, tubes 15.9 120 7.5 5 3.4 0.1 0.1
R466-10 @ Hillock@ Phoenix I, base 20 16 290 22 68 5.3 0.4 1.3
R466-11 @ Hillock@ Phoenix I, higher 15 11 1170 38 75 34 2.2 2.6
R466-12 @ Hillock@ Phoenix I, higher 6 4 360 15 62 59 2.5 10
R466-13 @ Hillock@ Phoenix II 8 4.5 360 17 67 45 2.1 8
R466-14 @ Hillock@ Phoenix II 4.2 3.0 54 1 8 27 0.5 4.0
R466-15 @ Hillock@ Phoenix II 6.1 4.0 67 4 17 11 0.7 2.8
R466-16 @ Hillock@ Phoenix III 80 65 380 25 70 1.5 0.1 0.3
R466-17 @ Hillock@ Phoenix III 24 22 27 BDL 10 0.3 - 0.1
R466-18 @ Hillock@ Phoenix III 3 2.8 81 3 17 67 2.5 14
R466-6 @ ROPOS@ bacteria trap site 29 24 305 40 80 3.4 0.4 0.8
468 Scan #1 early@ Crack Vent 77 70 1260 45 5 4.6 0.16 0.02
468 Scan #1 late@ Crack Vent >125 105 2120 <0 9 5.1 - 0.02
R466-7 @ Hair-doo at top of worms 14 12.5 125 12.5 8 3.1 0.3 0.2
R466-8 @ Hair-doo where worm 14.8 13.5 180 15 10 4.1 0.3 0.2
roots were
CASM
R480-1 @ T&S Vent base diffuse flow 41.9 37 232 73 >91 1.7 0.5 >.7
R480-5 @ T&S Vent top in lush tube 20.3 16 177 40.5 86 3.3 0.8 1.6
worm community
91 Vent (N. Rift) 4.5 4 124 5 2 14 0.8 0.3
in most intense flow near worms, clams
Through R481:
10 SUAVE Dives
55 SUAVE Scans
67 h of bottom time
3.3 OsmoSampler and OsmoAnalyzer Operations (Geoff Wheat)
Changes in the chemical composition of hydrothermal effluent after a tectonic-volcanic event have been documented (e.g., Baker et al., 1987, 1998; Butterfield and Massoth, 1994; Von Damm et al, 1995; Massoth et al., 1995; Massoth et al., in press; Wheat et al., to be submitted) and a conceptual model has been developed that theorizes the chemical evolution of venting fluids (Butterfield et al., 1997). However, the timing of these changes is uncertain. To date observations of temporal variability in the chemical composition of hydrothermal fluids has relied on repeated submersible operations and the collection of discrete samples. While this technique provides some temporal constraints, a continuous water sampler or analyzer allows one to collect more samples with limited need for costly submersible operations. Our goal for this cruise was to deploy two short-term (two weeks) and two long-term (one year) continuous sampling systems to provide temporal constraints for observing hourly to daily and weekly to monthly chemical cycles in the hydrothermal effluent. Data from these samplers and their comparison to samples collected using traditional discrete sampling techniques will allow us to determine the temporal scale of chemical change in the hydrothermal effluent as the hydrothermal system evolves and may provide constraints for understanding the physical and chemical conditions at depth and the path for fluid circulation.
Two sampling systems were deployed, OsmoSamplers and OsmoAnalyzers. OsmoSamplers are continuous water samplers that use the osmotic pressure that is created across a semi-permeable membrane by solutions of differing salinity (Theeuwes and Yum, 1976; Jannasch et al., submitted). This pressure drives water across the membrane at a speed that is dependent on the surface area of the membrane, type of membrane, salt gradient, and temperature. An excess of salt is maintained on one side of the membrane, thus only temperature affects the flow of water in the sampler. Pumps in an OsmoSampler are used to continuously draw sample through a small bore (0.8 mm id) tubing that is attached to a 40-cm-long T-handle. An additional pump was used to add acid to the sample stream in most of the OsmoSamplers. A 1.5-m-long section of tubing separates the sample intake from the pump to allow the pump to be placed in an area void of hydrothermal influence and thus minimizes temperature (pump rate) fluctuations. A temperature recorder with a resolution of 0.0018°C is attached to the T-handle to monitor the same water that is being collected by the OsmoSampler. Chemical data are obtained by retrieving the sampler, cutting the sample tubing into sections, extracting the seawater, and analyzing the seawater for chemical species of interest. Time-stamps for individual samples are determined assuming a uniform temperature at the pump that translates into a uniform rate of pumping.
OsmoAnalyzers, in contrast to OsmoSamplers, use osmotic pumps to deliver reagents into a sample stream for in situ analysis (Jannasch et al., 1994). These analyzers are very similar to the SAUVE, which is described above. OsmoAnalyzers were designed to measure concentrations of dissolved iron and manganese at 30-minute intervals for up to six months. These analyzers thus compliment data collected by the SUAVE, which can measure concentrations continuously but only for a maximum of about three days.
Two long-term acid-addition OsmoSamplers were deployed. One was deployed at Milky vent and the other at Marker 33. Each sampler was positioned away from visual flow to decrease the potential in temperature fluctuations at the pump. For example, the SAUVE measured a temperature of 3.0°C, relative to a bottom temperature of 2.7°C, at the sampler deployed at Marker 33. At both sites the sample input was positioned into the most vigorous flow. Temperature recorders were attached to these inputs and will provide a yearly record of temperature at 30-minute intervals. We expect that these OsmoSamplers will provide four 0.5-mL samples per week for the length of the deployment.
Two short-term deployments were conducted and both samplers were recovered. One sampler package was deployed at Marker 33. During the two-week deployment measured temperatures varied from about 10° to 50°C. This vent was sampled using two OsmoSamplers and two OsmoAnalyzers. One OsmoSampler consisted of an acid addition pump and a Teflon sample tubing for shore-based chemical analyses of the major and minor ions in seawater and several trace metals. 240 0.5-mL samples were collected. The other OsmoSampler had a copper sample tubing. This sampler provided 48 2.5-mL samples for shore-based analyses of dissolved gases. The two OsmoAnalyzers were designed to measure concentrations of dissolved iron and manganese, respectively. On the basis of initial inspection of these analyzers, the iron analyzer work, but the manganese analyzer did not.
The other short-term sampler package was deployed at Hell vent in the ASHES vent field for two weeks. This high temperature black-smoker vent was leveled before the acid addition sampler was deployed. The sampler had a temperature probe attached to the pump and an additional high-temperature (>100°C) probe was placed in the venting hydrothermal fluid. Both probes recorded temperature every 30 seconds for a maximum of about 30 days, however, the high-temperature probe was not recovered. The probe attached to the sampler recorded temperatures of about 3.6°C for the first week, then recorded temperatures of about 10°C for the second week. A total of 301 0.5-mL, one 1.0 mL, and one 1.5 mL samples were collected. Because sulfides were deposited in and on the sample inlet, it is likely that only a portion of these samples are directly from the vent orifice. Altered seawater likely entered through a weak link about 30 cm from the input.
References:
Baker, E. T., G. J. Massoth, and R. A. Feely. 1987. Cataclysmic hydrothermal venting on the Juan de Fuca Ridge. Nature, 329, 149-151.
Baker, E. T., G. J. Massoth, R. A. Feely, G. A. Cannon, and R. E. Thomson. 1998. The rise and fall of the CoAxial hydrothermal site, 1993-1996. J. Geophys. Res., 103, 9791-9806.
Butterfield, D.A., and G. J. Massoth. 1994. Geochemistry of north Cleft segment vent fluids: Temporal changes in chlorinity and their possible relation to recent volcanism. J. Geophys. Res., 99, 4951-4968.
Butterfield, D. A., I. R. Jonasson, G. J. Massoth, R. A. Feely, K. K. Roe, R. E. Embley, J. F. Holden, R. E. McDuff, M. D. Lilley, and J. R. Delaney. 1997. Seafloor eruptions and evolution of hydrothermal fluid chemistry. Phil. Trans. R. Soc. Lond. A, 355, 369-386.
Jannasch, H. W., K. S. Johnson and C. M. Sakamoto. 1994. Submersible, osmotically pumped analyzers for continuous determination of nitrate in situ. Anal. Chem. 66, 3352-3361.
Jannasch, H. W., C. G. Wheat, M. Kastner, and D. Stakes. 1998. Long-term in situ osmotically pumped water samplers. Deep Sea Res., submitted.
Massoth, G. J., E. T. Baker, R. A. Feely, D. A. Butterfield, R. E. Embley, J. E. Lupton, R. E. Thomson, and G. A. Cannon. 1995. Observations of manganese and iron at the CoAxial seafloor eruption site, Juan de Fuca Ridge. Geophys. Res. Lett., 22, 151-154.
Massoth, G. J., E. T. Baker, R. A. Feely, J. E. Lupton, R. W. Collier, J. F. Gendron, K. K. Roe, S. M. Maenner, and J. A. Resing. 1998. Manganese and iron in hydrothermal plumes resulting from the 1996 Gorda Ridge Event. Deep Sea Res., in press.
Theeuwes, F., and S. I. Yum. 1976. Principles of the design and operation of generic osmotic pumps for the delivery of semisolid or liquid drug formulations. Ann. Biomed. Eng., 4, 343-353.
Von Damm, K. L., S. E. Oosting, R. Kozlowski, L. G. Buttermore, D. C. Colodner, H. N. Edmonds, J. M. Edmond, and J. M. Grebmeier. 1995. Evolution of East Pacific Rise hydrothermal fluids following an oceanic eruption. Nature, 375, 47-50.
Wheat, C. G., H. W. Jannasch, F. J. Sansone, J. N. Plant, and C. L. Moyer. 1998. Hydrothermal Fluids From Loihi Seamount After the 1996 Event: A Year of Change Monitored With a Continuous Water Sampler. Earth Planet. Sci. Lett., to be submitted.
3.4 Gas Sampling (Lee Evans)
The primary goal of gas sampling during the NeMO '98 expedition was direct sampling of vent fluids by way of Titanium Gastight Bottles and modified gas pistons on the PMEL Hot Fluid Sampler. Approximately 24 useful samples were gathered and their available gas contents extracted and sealed in glass ampoules for chemical analysis. These ampoules will be used for the analysis of helium concentrations and helium isotopes at PMEL, Newport and other gases such as hydrogen and methane at the University of Washington.
The geographic coverage of vent fluid sampling included the east side of Axial Volcano's caldera, Ashes vent field on the west side and CASM vent field at the north end of the caldera. Samples from the east side were largely low temperature diffuse fluids spanning most of the north to south extents of the known vent field. The one high temperature sample was from Castle Vent. At Ashes Vent Field numerous high temperature chimneys and diffuse sites were sampled. Some repeated sampling from July Alvin dives. Only two diffuse vents were sampled at CASM.
Other samples for helium analysis included about 80 samples in crimped copper tubing from 12 hydrocasts. Most were from just above vents which were sampled directly. They are expected to be useful in conjunction with methane analyses from the same Niskin bottles. One of the Osmosamplers consisted of a reel of thin copper tubing. Forming a time series over about 15 days at Marker 33, the reel was segmented into 48 samples, each of which represents about an 8 hour average of what emerged from the vent.
3.5 H2 and CH4 Oxidation (Betsy McLaughin-West)
A seafloor eruption event can result in any number of effects in existing hydrothermally active areas. The event that occurred at Axial Volcano during February 1998 presented an opportunity for further study of the types of changes that occur as a result of a seafloor eruption. One effect is an elevation of hydrogen concentrations in the venting fluids as a result of increased hot water/rock reactions. This dissolved hydrogen may be a significant energy source for bacteria. Previous work at Loihi Seamount following an eruption showed that microbial hydrogen oxidation rates were elevated in the hydrothermal plumes found above the seamount immediately following the event but dropped to background seawater levels within a few months. The February 1998 eruption event at Axial Volcano offered a second opportunity to study the microbial response to a sudden change in available hydrogen. During the NeMO 98 cruise, samples were collected from the plumes above Axial Volcano approximately 6-7 months after the event. Microbial hydrogen oxidation rates for these fluids will be determined from the results of radioisotopic uptake experiments performed aboard ship. These rates will be compared with a similar set of measurements made during the Axial Rapid Response cruise in February 1998. Microbial hydrogen and methane oxidation rates will also be determined for samples collected directly from the diffuse venting areas and the buoyant portions of the plumes so that the relative importance of these two gases to the microbial communities can be estimated.
3.6 Determination of Sulfide, Nitrate and Salinity Concentrations Without the Use of Reagents (Elizabeth Guenther)
I am a graduate student at Moss Landing Marine Laboratories, my name is Elizabeth Guenther. Gary Massoth invited me on this cruise. I have been working on a project for my thesis work at Moss Landing with the help of my advisor, Ken Johnson. I have been working on a new method for the determination of sulfide, nitrate and salinity concentrations without the use of reagents. I measure the UV absorbance of a seawater sample and various standards and from that information I am able to predict the concentration of nitrate, salinity or sulfide. The purpose of this cruise was to determine if this method could be applied to vent fluids and if so, what are the possible interferences involved, if any?
I have collected samples from the fluid sampler that Dave Butterfield brought on the cruise as well as from the slurp sampler. These samples were analyzed for sulfide concentrations and will be used to determine if salinity and nitrate can also be calculated. The sulfide concentrations were compared to those predicted by the Methylene blue chemistry performed by Kevin Roe on this cruise. Preliminary examination of the data indicates that this new method may provide good estimates of the sulfide concentrations in the vent fluid samples. These data will be used in the MSC thesis and for publication.
4.0 MICROBIOLOGY
4.1 Non-Mat Microbial Ecology (Jon Kaye and Julie Huber)
We focused on several aspects of vent microbial ecology during this cruise, much of which is geared toward defining time point #1 in a multi-year chemistry-microbiology data set with Dave Butterfield. We have used non-mat microbial samples and have cultured from 2-90°C, covering all thermal classes and many metabolic groups of bacteria and archaea, in order to develop a comprehensive picture of non-mat microbial ecology at Axial Seamount. In addition, more narrowly focused goals include obtaining novel physiological classes of hyperthermophiles and quantifying halotolerant microbes in the vent environment and the overlying water column. 36 ml of water from all samples was preserved in 3.7% formaldehyde for microbial enumeration.
Hyperthermophiles were cultured in a 0.6% (w/v) organic medium, with and without native sulfur (yeast extract and peptone, YP, and with sulfur, YPS). Positive enrichments (which require confirmation on land) came from Crack, Gollum, Milky Vent, Mushroom, Bubbler #2, Marshmallow, background water in ASHES, Marker 33, Easy Vent, Roof, Castle, Styx, Magnesia, Old Tubeworms, West Caldera Wall, Snowblower, Medusa, Porkchop, near Cloud, Marker 113 Pandora worm slime, other animal inocula, and sulfide rock from Hell. Methanogens were enriched from many of these same locales. The Slurp Sampler and Dave's Fluid Sampler were equally effective for culturing purposes. Overall, hyperthermophiles are ubiquitous in and around ASHES and found in all sampled diffuse fluids in the caldera. However, no hyperthermophiles were cultured in YPS from a putative buoyant plume hit during hydrocast V-98-002 (Niskin #18) above Cloud.
Quantitative enrichments (MPNs, Most-Probable-Number technique) were performed at 90°C from several sites. The table below contains the 95% confidence interval for the abundance of hyperthermophiles that grow in the given media, given in microbes/liter. These data are preliminary and must be confirmed by microscopy on land.
YPS (likely Thermococcus) YE (likely methanogens)
Marker 33 >48,000 140-4200
Marshmallow 3000-96,000
"Background" in ASHES 300-7600 <60
Caldera Wall, west of ASHES in progress
Total community DNA was captured from various diffuse flow, high-temperature and background sites and split into free-living (0.2-3 m) and particle-attached (>3m) fractions by filtration. Filters were frozen at -80°C. Enrichments for methanogens, heterotrophic hyperthermophiles, sulfur oxidizers, and sulfate- and nitrate-reducing microbes were performed simultaneously from 2 to 90°C, with the majority at 50 and 90°C. Dave Butterfield, Kevin Roe, and Betsy McLaughlin-West made and will make further chemical measurements at the same sites. Likewise, complementary SUAVE data from Gary Massoth will be correlated with this microbial work.
Diffuse fluids, high-temperature fluids, sulfide rock, homogenized Paralvinella specimens, and animal mucus were inoculated into modified high-organic hyperthermophile media (YP and YPS) and incubated at 90°C. Halotolerant hyperthermophiles able to grow in a 5% NaCl YPS medium appear ubiquitous, though media with 0.2% and 8% NaCl did not appear to allow growth. Metal-resistant hyperthermophiles capable of tolerating mM levels of Cd, Hg, Cu and Co were routinely cultured. Confirmation of growth must await phase-contrast microscopy on land.
Eight MPNs for mesophilic halotolerant microbes were performed on diffuse fluids, near-vent bottom water and hydrocast samples. The medium used enriches for heterotrophic bacterial and archaeal aerobes at room temperature. To complement these quantitative enrichments, water was filtered (0.2 m) and the filters frozen for Halomonas (a halotolerant bacterial genus) DNA probe work on land.
4.2 Microbiological Sampling for Molecular Microbial Ecology Analysis (Western Washington University, Biology Department: Craig L. Moyer & Karen Pelletreau.)
4.2.1 Introduction
One of the greatest challenges in microbial ecology is the accurate identification and description of microbial populations within their respective communities. This information is central to determining the extent of global microbial diversity, which remains the least understood of all the biological size classes. To address this challenge, molecular biological techniques using small-subunit ribosomal RNA (SSU rRNA) gene sequences have been applied to describe the structure and diversity of different microbial communities. The current endeavor is to examine specific habitats with known biogeochemical characteristics (e.g., S, Fe, Mn) to learn more about the dominant microorganisms residing therein. The focus of this study at Axial Volcano is to estimate the microbial community structure and diversity to assess the degree of commonality and uniqueness among local hydrothermal vent habitats, (i.e., vent-associated sediments, free-living microbial mats, microbes associated with subsurface floc-ejecta), and to also compare these results with distal hydrothermal vent habitats. This study will also allow for the enhanced development of a comprehensive global perspective regarding the diversity of deep-sea microbial communities.
Selective enrichment culture has severe limitations as an approach to the cultivation of naturally-occurring microorganisms. The majority (typically >90-99%) of microbes in nature have not yet been cultivated using traditional techniques. Consequently, it is very unlikely that collections of microbial isolates are representative of in situ diversity and community structure. Furthermore, because relatively nutrient-rich media are generally used for isolations, "weedy" or opportunistic microorganisms may be selected rather than those dominant in the natural community. The approach, herein, is to ascertain a microbial community's primary members through molecular (i.e., cell component) means and then to attempt to further characterize their respective phylogeny or natural history. Obtaining a better representation of microbial community structure and diversity is crucial to aspects of microbial ecology where Bacteria and Archaea interact with one another and with their environment, e.g., global biogeochemical cycling of matter, succession and disturbance responses, predator-prey relationships, and trophic-level interactions. These lessons can then be used to focus enrichment culture techniques towards ecologically significant taxa. This approach has been successfully used to isolate the dominant iron-oxidizer bacterial taxon found within the microbial community at hydrothermal systems located at Loihi Seamount, North Gorda Ridge, and other habitats (Emerson and Moyer, 1997; unpublished results).
Cell component analyses provide a culture-independent means of investigating microorganisms as they occur at hydrothermal vent systems (Moyer et al., 1994;1995; 1998). While several types of cell components have been analyzed, the SSU rRNA molecule offers an amount and type of information that makes it one of the best culture-independent descriptors or biomarkers of microorganisms. In recent years a detailed theory of evolutionary relationships among the domains Bacteria, Archaea and Eucarya has emerged from comparisons of SSU rRNA "signature" sequences. For example, each SSU rRNA gene contains highly conserved regions found among all living organisms as well as diagnostic variable regions unique to particular organisms or closely related groups. Additionally, each SSU rRNA gene contains about 1,500 nucleotides of sequence information that can be obtained and utilized to differentiate among closely-related and distantly-related groups of microorganisms. This type of molecular approach allows the autecology of microorganisms to be studied whether or not they can be been cultivated (Moyer et al., 1996). In addition, the phylogenetically described taxa or "phylotypes" can be placed in a synecology context through the examination of SSU rRNA clone libraries generated from a microbial community and habitat diversity can be analyzed through rarefaction (Moyer et al., 1998). These features make SSU rRNAs particularly useful for studies of molecular microbial ecology, where a broad and unknown range diversity of microorganisms is likely to exist. Currently, over 10,000 SSU rRNA sequences from both cultured isolates and environmental phylotypes have been made available for study through the Ribosomal Database Project at NSF's Center for Microbial Ecology at Michigan State University.
4.2.2 Shipboard Processing and Storage of SamplesA dual approach was used for microbial sampling. First, a "slurp" gun suction device was be used in combination with a rotating rosette of sample bottles to "vacuum" and capture free-living microbial mats from the surface of various hydrothermal vent habitats. Slurp gun samples were successfully obtained from the East-Side of Axial at (1) Marker #33 Vent, (2) Snow Blower Vent near Pit, (3) Milky Vent Floc, (4) Cloud Vent Floc, (5) yellow mats near EZ Vent, and (6) red iron-oxides near Milky Vent. Similar samples obtained in and around the ASHES area include, (1) orange oxides near Gollum Vent, (2) white mat from Gollum Vent, and (3) yellow mat from the West Wall to the northwest from ASHES.
Second, the deployment and recovery of bacterial traps using glass wool as a substrate for microbial growth. Bacteria traps were constructed using a cluster of three 3" sections of 4"o.d. Plexiglas tubing, surrounded top and bottom by a 202 µm nylon mesh (Nytex) to exclude macrofauna grazing. These were placed directly into diffuse vents and were used to collect colonizing microorganisms in an effort to examine community succession. These were deployed with the idea of attempting a time-series with both short-term (days) and long-term (annual) time scales. This objective was partially achieved with short-term recoveries made at Marker #33, Cloud Vent, and Milky Vent on the East-Side of Axial Volcano. Long-term deployments were made at these three sites as well as at EZ Vent, Axial Gardens, Castle Mound, and at four sites within the ASHES Vent Field (Gollum, ROPOS, Hillock, Mushroom). Short-term recoveries from these sites (especially at ASHES) will be attempted again next year, in addition to the long-term recoveries from each of the sites listed above.
Microbial samples collected were each independently processed. Microbial biomass preservation was achieved by quick-freezing in liquid nitrogen and storing on dry ice or ultrafreezer (-80C) until return to the laboratory. These samples will be used for the direct extraction of nucleic acids. A series of sub-samples were also (i) cryo-preserved (again using liquid nitrogen quick-freezing) with 40% glycerol, and (ii) aliquots were stored at 4C, both for enrichment culture selection. Another series of sub-samples was fixed with 2.5% EM grade glutaraldehyde for examination with SEM and epifluorescence microscopy.
4.2.3 Laboratory Processing and Molecular Biological Analysis
Initially, all samples will be examined by epifluorescence microscopy in an effort to ascertain biomass estimates and examine morphological diversity. A subset of these will also be examined through SEM and an analysis of extractable lipids, which provides an estimate of microbial biomass and initial clues into community structure. The overall molecular biological strategy used will be essentially that of Moyer et al. (1994, 1995; 1998) with a few technical and logistical improvements. The first step will be the efficient and direct extraction of high molecular weight nucleic acids from quick-frozen samples. This will be followed by PCR amplification of SSU rDNAs using previously defined conditions to maximize the equal representation from each population contained within a respective community. The concept is to proportionally amplify or make several copies using the total genomic DNA from a natural community serving as the template for oligonucleotide primers that are complementary to universally conserved SSU rDNA sequence positions. Representative SSU rDNA amplification products are cloned generating a clone library. Clone libraries will then examined through the use of Amplified Ribosomal DNA Restriction Analysis or ARDRA and by using rarefaction as a metric for organismal diversity (Moyer et al., 1998). This approach, using tetrameric restriction enzymes, has been shown to detect >99% of the taxa (i.e., phylotypes) present within a model dataset with maximized diversity (Moyer et al., 1996). SSU rDNA sequences will also be subjected to phylogenetic analysis (using distance matrix and maximum likelihood algorithms) to estimate the affiliated ancestral lineage for each dominant community member thereby yielding clues as to their respective evolutionary history and potential physiology.
References
Emerson, D., and C. L. Moyer. 1997. Isolation and characterization of novel iron-oxidizing bacteria that grow at circumneutral pH. Appl. Environ. Microbiol. 63:4784-4792.
Moyer, C. L., F. C. Dobbs, and D. M. Karl. 1994. Estimation of diversity and community structure through restriction fragment length polymorphism distribution analysis of bacterial 16S rRNA genes from a microbial mat at an active, hydrothermal vent system, Loihi Seamount, Hawaii. Appl. Environ. Microbiol. 60:871-879.
Moyer, C. L., F. C. Dobbs, and D. M. Karl. 1995. Phylogenetic diversity of the bacterial community from a microbial mat at an active, hydrothermal vent system, Loihi Seamount, Hawaii. Appl. Environ. Microbiol. 61:1555-1562.
Moyer, C. L., J. M. Tiedje, F. C. Dobbs, and D. M. Karl. 1996. A computer-simulated restriction fragment length polymorphism analysis of bacterial SSU rRNA genes: efficacy of selected tetrameric restriction enzymes. Appl. Environ. Microbiol. 62:2501-2507.
Moyer, C. L., J. M. Tiedje, F. C. Dobbs, and D. M. Karl. 1998. Diversity of deep-sea hydrothermal vent Archaea. Deep-Sea Res. II. 45:303-317.
4.3 Biomineralization/Lava Mats (Kim Juniper, University of Quebec, Montreal: Steve Scott, University of Toronto)
Early in the cruise we observed extensive deposits of iron-rich floc of possible microbial origin covering the new lavas in the East Rift Zone. The deposits were heavy enough to mask the normally glassy appearance of the new lavas and actually prevented us from confirming the present of the new flow until early in the second week of the cruise. Similar deposits had been observed and sampled on the new lavas at the FLOW site on CoAxial segment shortly after the June 1993 eruption. However, this coverage was much more extensive and was not the same bright orange color as the CoAxial oxide mats. The extent and thickness oxide deposits on the new Axial lavas varied along an east-west traverse across the flow. Heaviest deposits were in the central part of the lava flow where some bright-orange oxide material was still being deposited at a few active vents. At the edges of the flow, oxide material was brownish in color, and was being reworked by deposit feeding invertebrates such as holothurians (sea cucumbers) that had moved in from adjacent older lavas.
A systematic sampling of the putative microbial floc was undertaken during dives 474 and 476 that conducted a series of East-West and West-East traverses of the new lava from beginning in the south and ending near Milky Vent. Samples (7 in all) were both fixed for electron microscopy and frozen for elemental and mineralogical analyses, and measurements of microbial enzyme activity. This work will be carried out by an M.Sc. student at the University of Toronto who will work under the direction Steve Scott, and who will travel to UQAM in Montreal to work with Kim Juniper on biological aspects. The aim of the study will be to characterize the material mineralogically, confirm its microbial origin and map relative density of the deposits across the lava flow in order to understand the relationship to thickness of the underlying new lavas. The latter information is important to testing a working hypothesis that heating of surface flows by underlying lava caused leaching of reduced iron into the seawater, permitting colonization by iron-oxidizing bacteria.
Samples were also collected of iron-oxide deposits and small oxide mounds near the ASHES field for comparison of mineralogy and microbiology with the oxide material from the East Rift Zone lava flows.
5.0 MACROBIOLOGY
5.1 High Temperature Chimney Biology (Damien Grelon, Christian Levesque & Kim Juniper, University of Quebec, Montreal UQAM)
This work focused on study of the feeding behavior and microbial food resources of the sulfide worm, Paralvinella sulfincola, on newly-formed surfaces of sulfide chimneys in the ASHES field. The worm lives in a mucus tube cemented to the sulfide and appears to feed around the opening of its tube by scraping organic material off the mineral surface. Temperatures in excess of 50C have been measured in this habitat and the worm is a prime candidate for a first-ever identified trophic link between thermophilic/hyperthermophilic bacteria and an animal. Field work concentrated on:
1) Making in situ video recordings of worm behavior for analysis of feeding behavior and territoriality .
2) Collecting samples of worm populations and chimney material for analysis of population structure, organic matter concentration and stable isotope ratios in food and animal tissues.
3) Acquisition of temperature/chemistry information from the worm's habitat to examine environmental controls on feeding behavior and food abundance
The behavioral and environmental data form the core of an M.Sc. thesis by Damien Grelon while the stable isotope study is part of a M.Sc. project on hydrothermal vent trophic links by Christian Levesque.
We obtained 3-4 hours of recordings of worm behavior from 5 sites in the ASHES field. Worms from all but one of the observational sites were sampled using the ROPOS suction sampler, and either frozen or formalin-fixed prior to analysis at UQAM. One site was designated for time series observations and revisited twice during the cruise to follow worm migration and behavioral changes in relation to changes in fluid flow patterns.
In collaboration with Gary Massoth, a total of 15 SUAVE scans were performed among sulfide worm populations after behavioral observations.
The big surprise was the aggressive territoriality of the worms, in relation to each other. Individuals frequently probed and entered the feeding area of others, and physical contact between residents and invaders often resulted rapid, aggressive striking movements. Both feeding and territorial behavior will be systematically analyzed in relation to organism density, site and environmental factors.
5.2 Stable Isotope Food Web Analyses (Christian Levesque, Damien Grelon & Kim Juniper, University of Quebec, Montreal)
The importance of free-living microbes as a food source for deposit feeding and suspension feeding animals at hydrothermal vents is still poorly understood. The intent of the study was to concentrate on identifying the food resources exploited by two co-occurring polychaete worms that colonize sulfide chimneys in the ASHES field. The working hypothesis was that the sulfide worm (Paralvinella sulficola) and the palm worm (Paralvinella palmiformis) manage to share the same space by not competing for food. Preliminary data showed clear differences in stable isotope ratios between the two species, confirming apparent differences in feeding behavior with the sulfide worm seeming to deposit feed on surfaces while the palm worm appeared to mainly feeding by trapping suspended particles in turbulent flow. Several collections were made of both worm species as well as of organic material from chimney surfaces. We were also able to use the ROPOS suction sampler to make 3 collections of suspended particles from above colonies of palm worms. All material will be analyzed for stable isotopes of carbon and nitrogen.
The stable isotope work was also expanded in response to the observation of extensive white bacteria mats at new vents on the lava flow in the East Rift Zone. These mats were being grazed upon by at least two species of scale worm. These first vent animal colonists could be seen to be actively scraping microbial mat from rock surfaces. At a few locations, small vent snails were also abundant and grazing on bacterial mats. Collections of scale worms, snails and bacterial mats were made at several sites for stable isotope analysis to confirm this trophic link. Previous observations at CoAxial suggested the importance of post-eruptive microbial blooms as a resource for vent animals. These samples will permit us to make considerable progress in understanding this early phase of ecosystem development.
5.3 Biology of Low Temperature Sites (Verena Tunnicliffe, Maia Tsurumi and Jean Marcus)
5.3.1 Introduction:
This biology program focused on four study themes: i) evaluation of colonization on the new lavas, ii) nature of the regional distribution of species and populations, iii) the composition of communities in different fluid chemistries, and iv) the biology of the vestimentiferan Ridgeia piscesae. We were most fortunate to receive over a dozen samples that had either SUAVE or fluid sampler information with them. To our knowledge, this is the first such coordination of widespread sampling at low temperature sites. Previously, it has been very difficult to obtain environmental information with biological samples. For us, this information is a triumph for the cruise.
5.3.2 Colonization:
The opportunity to observe colonization of new hydrothermal vents so soon after a known eruption is a rare opportunity. From our limited experience at CoAxial, we had predicted small vestimentiferan recruits with three or four other known species. Our dives, however, identified three types of colonization, one of which was the predicted pattern. The others were dense snails and a mix of scale worm species. The large expanse of new lava created geographic separation among the sites. The cause of three distinct colonization patterns likely relates to either stochastic events governing larval delivery or differing chemical character across the flow. Hopefully, chemical and microbial information will help resolve this issue.
In addition to type of colonization, extent also varied. The most vigorous flows of Milky and Cloud Vents hosted few animals while nearby vents were colonized. To understand more about sources, we were able to sample vents on old lavas. A large field of tubeworms (the SONNE field) was obliterated by the eruption but outlier colonies remained. We can compare composition of these colonies with recruits this year and next. We also have taken samples for a genetic analysis of one species to determine the likely source of the new populations. An interesting complication is that many of the "old" worm colonies are now experiencing rejuvenated fluid flow resulting in morphological changes in the resident worms and new recruitment.
5.3.3 Regional Character:
Axial Volcano is one of the few places on the Ridge that allows us to study discrete well-separated communities. A current question in vent ecology is how populations interchange among sites. We need better description of species distributions in a regional setting. We are finding that some species are curiously patchy and are attempting to apply ecological concepts of metapopulations to model population patterns. To this end, samples from the Eastern Rift (north and south), ASHES, Northern Rift and CASM form five essential contemporaneous points in this model. These samples will be sorted to determine compositional differences as well as including a population genetic analysis of one species.
5.3.4 Local Variation:
Collections at ASHES are to be used in two studies. Firstly, they set the basis for local variability for assessment of regional differences in the study above. Secondly, they provide an important set of samples to complement samples from earlier years in a study of spatial and temporal change. The polychaete species will be examined in detail to relate relative abundances to position and chemical character of the fluids. As little work has been published on "whole communities" this basic step is a useful contribution to understanding vent community dynamics. As part of this work on polychaetes, the unusual scaleworm collected from the new lavas of the Eastern Rift will be examined in detail in conjunction with Juniper's isotope work.
5.3.5 Ridgeia piscesae:
The tubeworm forms the basis for the vent communities of Juan de Fuca. As such, there is considerable interest in understanding more about its requirements and basic biology. Samples that were collected with coordinated fluid data will be examined in a study of size, reproductive condition, trophosome condition and juvenile recruitment. The aim is to understand the chemical conditions that are optimal and marginal for both reproduction and recruitment. Specimens were also processed for ultrastructural examination on the beach. Here, the intent is to collect detailed morphological characters to test models of the evolutionary relationships of vestimentiferans. Lastly, specimens of live tubeworms were transported to the Aquatic Facility of University of Victoria to attempt in vitro fertilization of eggs. Study of embryological characters adds information to both phylogenetic studies and dispersal capabilities.
5.3.6 A Final Comment:
The interdisciplinary nature of this cruise has been of considerable benefit to understanding biological features of the vent communities. It is an important learning environment for experienced researchers and students alike. Particularly welcome, is the opportunity to develop collaborations when new opportunities present themselves.
5.3.7 MacroBiological Sample List from Low-Temperature Sites
S=SUAVE; HFS=Hot Fluid Sampler
ASHES
Tube worm grabs
· R466-3: Mkr L, tube worm grab of hat-like structure (S)
· R466-8: Hairdo vent, huge tube worm grab of bouquet-like structure (S)
· R471-6: Mkr i, tube worm grab, left a marker to SUAVE later
· R471-3: Gollum vent, tube worm grab (HFS)
· R472-3: Medusa vent, tube worm grab (HFS)
EAST RIFT ZONE
Suction Samples from new lavas
· R462-2: mkr 33, suction sample of mat and polynoids (S)
· R462-3: mkr 33, suction sample of mat and polynoids (S)
· R462-4: mkr 33, suction sample of mat and polynoids (S)
· R473-6: easy vent, suction sample of polynoids and mat
· R473-18: mkr 33, suction sample of new polynoids and mat (S)
· R473-21: mkr 108, suction sample for new worm and mat
· R474-3: mkr N41, suction sample of tube worms (S)
Tube worm grabs
· R461-15: mkr 113, tube worm grab from a new vent on old lavas (S)
· R464-9: near mkr 113, tube worm grab of moribund worms on old lavas
· R464-14: mkr N5, tube worm grab of live-looking worms on sulfide structure near Castle (S)
· R476-3: oldworms, tube worm grab of reinvigorated venting on old lavas (HFS)
· R478-8: nascent vent, tube worm grab of new tube worms on new lavas (S)
· R478-11: old flow, tube worm grab of reinvigorated venting on old lavas (S)
· R478-13: large tube worms, tube worm grab of reinvigorated venting on old lavas (stayed in Pacman until surface) (S)
NORTH RIFT ZONE
Tube worm grab
· R467-4: Bob vent, tube worm grab of old venting (S)
CASM
Tube worm grab
· R480-7: T & S vent, tube worm grab of healthy worms on sulfide (S)
6.0 HYDROTHERMAL MINERALIZATION (Steve Scott)
Hydrothermal deposits are known from previous expeditions at the ASHES, Southeastern Rift and CASM Vent fields. During the NeMO expedition, considerable work was done in and around ASHES and USRZ (Upper South Rift Zone). A short visit was made to CASM.
At the ASHES field, Hell, Inferno, ROPOS and Mushroom are sizable hydrothermally active sulfide spires a few meters high. Virgin and Virgin's Daughters are small active anhydrite chimneys. Those who had seen ASHES on previous expeditions commented that Mushroom, Inferno and Hillock had thickened considerably. Hillock, for example, had grown from a small spindle to a much more massive structure. A small chimney and flange were sampled at Hell. The chimney is predominantly iron-rich zinc sulfide (probably wurtzite based on the hexagonal shape of its millimetric crystals) with a central conduit lined by a copper -iron sulfide (probably isocubanite). The flange, although finer grained, appears to have the same mineralogy with the probable isocubanite forming in hot water ponded buoyantly against the underside.
At Southeastern Rift, a sulfide structure that had been seen in a 1996 Sonne camera tow was named "Castle" by the NeMO expedition. The main structure is about 10 m high, 3 m diameter at its base and 5 m at its top. The top is festooned with 50 cm high chimneys which inspired the name Castle. The edifice appears to be sitting on a small pillow mound within what otherwise is a ~5 meter depression. Diffuse venting is occurring in many places on Castle. On its southwest side there is a small anhydrite spire that is actively venting hot water. This was sampled on an early dive and had regrown to its ~50 cm height just 9 days later. About 10 m southeast of Castle there is another sulfide structure of similar size to Castle named "Flat Top" by the NeMO expedition. It, too, has diffuse venting although seemingly not as much as Castle. About 10 m south of Castle is a small spire, about 1 m tall, that appears to be extinct. It could be gathered in its entirety using the elevator.
CASM was a huge surprise. The site is within and adjacent to a 5-10 m wide fissure on the floor of the caldera where the north rift slices the northern wall. When discovered in August 1983 on a Pisces IV dive, there were just a few diffuse vents supporting small colonies of tube worms and other animals. Now, vents such as Shepherd Vent, for example, are much more robust. About 50 m north of Shepherd there are several hydrothermally active spires ~3 m tall and supporting abundant life. Hot focused flow, wide spread diffuse flow and abundant gas bubbles characterize the hydrothermalism. Samples of one spire are predominantly zinc sulfide, with well formed crystals (wurtzite?) in places. Small patches of coarse crystalline copper-iron sulfide are also evident. Despite being very prominent and obvious features within the confines of the fissure, these spires were not seen in 1983 dives nor in 1988 dives (V. Tunnicliffe). They must have formed since 1988.
A quick look was taken at the Lamphere Chimneys about 20 m east of the fissure. The main structure, whose diffuse venting supported abundant life in 1983, is no longer active and is practically devoid of animals.
Is the recent volcanic activity in the caldera reflected in the sulfide deposits? It is tempting to contemplate that the renewed high temperature hydrothermalism at Castle may be a consequence of the nearby volcanism. There is no obvious effect on the deposits at ASHES (although there may be in the vent fluids themselves, see report by Butterfield). The new (since 1988) CASM chimneys are too large to have been formed since the January-February eruptions.
With three sulfide sites now known (and there may be more) in widely separated places within the caldera, there is now the opportunity to study mineralization processes through time in somewhat different settings and to study the interaction of mineralization and biology at different stages of population development. Also, if the petrological studies (see report by J. Chadwick) demonstrate that there are differences in basalt chemistry at the different sites, the opportunity exists to examine the relation, if any, between the composition of sulfides and their host rocks.
7.0 NON-ROPOS OPERATIONS
7.1 CTD Operations (Jim Gendron)
7.1.1 NeMO'98 CTD Casts
During leg IIb of the NeMO98 Vents cruise a total of 11 vertical casts and 2 tows were completed. Samples that were collected included 55 filters for XRF analysis and 53 salinity samples. Other samples that were collected included He, methane, hydrogen, H2S, O2 and bacteria samples. Samples for particulate organic carbon were also taken.
In general, most of the results of the sampling will not be known until the samples are analyzed on shore. The distribution of the particle plumes that were seen by the nephelometer seemed to follow the same patterns as were found on leg 1. Large concentrations of particles were present over the new vent area southeast of the caldera, at ASHES vent field and south of ASHES. The CASM site showed similar plumes and it is possible that a buoyant plume was detected there on the downcast.
7.1.2 NeMO'98 CTD Cast Locations and Stations Table
| Vents98C | Brown leg IIb | cast | latitude | longitude |
| site | SE caldera | cast 1 | 45 55.2' | 129 59' |
| date | Aug 27 | |||
| station | V98c01 |
