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Highlights

Bob Embley
Chief Scientist Ron Brown Cruise 1998/Thompson/ROPOS 1999

(Click here for full 1998 science report)

More than 50 scientists attended the second annual NeMO (New Millennium Observatory) workshop at NOAA's Pacific Marine Environmental Laboratory in Seattle, Washington to review results of the first year of field work and to discuss plans for 1999 and beyond The goal of the NeMO project is to establish a realtime observatory at the summit of Axial Volcano, an active volcano on the Juan de Fuca spreading ridge 270 miles west of Oregon. The first major field experiments at NeMO were preceded by a major eruption that occurred at the summit of Axial in early 1998 and set the stage for a full and exciting year.

Data from recovered Rumbleometer showing 3 meters of downdrop Extensometer data showed a decrease in distance across the rift zone

Some of the most exciting results from the first year of the NeMO program came from instruments in place during the January 1998 seismic swarm and eruption . A seafloor pressure gauge on the "rumbleometer" (Chris Fox) recorded more than 3 meters of downdrop (right) in the floor of the caldera as magma moved out of the summit and into the rift zone to the south Fortunately, there were two rumbleometers, because one of them got caught in the new lava flow! Water column temperature moorings ( Ed Baker) showed a large heat pulse that started within hours of the earthquake swarm and signaled the onset of the eruption. Acoustic range meters deployed on the north rift zone of Axial in 1996 (W. Chadwick and others) also showed a distance decrease coincident with the subsidence of the caldera floor as the entire summit of the volcano deflated like a balloon during the eruption.

Results from the mapping program (R. Embley and Bill Chadwick/NOAA/PMEL and Oregon State University) show that lava flows were erupted at the southeast corner of the caldera (upper south rift zone) and about 5 km down rift.

The 1998 surveys with ROPOS did not cover the area between the two sites, so it is still not clear whether the eruption was continuous. However, both water column and seafloor measurements and observations failed to find any measurable hydrothermal activity at the southern site, suggesting that both the lava flow and dike below had rapidly cooled off in the months after the eruption. In contrast, the lava flow site at the summit was still vigorously venting, probably because it lies directly above a zone of partially molten rock (sometimes called the "magma chamber"). There is also a contrast in the type of lavas at the two sites. The southern eruption consists almost entirely of more slowly extruded "pillow" lavas (above), whereas the caldera eruption is almost entirely of the more rapidly extruded "sheet flows" (right). This probably reflects the difference in the distance from the ultimate subsurface source of the lava, i.e., the more rapidly extruded sheet flows have a shorter distance to travel from the magma source lying directly below.

A prediction that NeMO was designed to test is that injections of magma near and onto the seafloor (as eruptions) cause a significant increase in microbial activity within the subsurface. This prediction was borne out from the results of both water column and seafloor observations and sampling, including the discovery of shallow chambers filled with sulfur-rich microbial floc and deeper sources with rich populations of hyperthermophilic Archaea. Some of the new vents had very milky fluids with high amounts of elemental sulfur particles in suspension (above) while other sites had clearer emissions with higher flow rates (below). Surveys of the new vents using the SUAVE (SUbmersible System Used to Assess Vented Emissions) revealed large variations in the amount of H₂S concentrations at the new vents ( Gary Massoth). Those with lower flow rates and "milky" fluids had low H₂S. Based on the analyses of numerous fluid samples, Dave Butterfield (University of Washington and NOAA/PMEL) hypothesized that the milky fluids have a longer residence time in the shallow cavities, where the microbial activity oxidizes the hydrogen sulfide to elemental sulfur Julie Huber and Jon Kaye (U. Washington) reported on culturing large numbers of hyperthermophilic microbes (probably Archaea) in almost all of the warm fluids taken by ROPOS. Initial results from molecular analyses of samples taken at the marker 33 vents reveal a high diversity of hitherto unknown types of Archaea and bacteria (Julie Huber and John Baross).

Craig Moyer ( Western Washington U.) presented analyses of the microbial mats at the new vents that showed DNA enrichments up to 10x the amounts previously seen at hydrothermal vents. In addition, Dick Feely(NOAA/PMEL) found large increases in elemental sulfur (image below right) over the eruption site during the summer months of 1998, indicating a significant enrichment in the microbial biomass in the months following the eruption . Jim Cowen (University of Hawaii) has reported high concentrations of an unusual metal-depositing bacteria, absent in non-plume samples, from plumes sampled in February.

Results from the water column measurements stimulated a lengthy discussion about the nature of chemical and thermal discharges following a deep-sea eruption. Water samples taken above the lava flow showed enriched ³He relative to the temperature of the plume up to seven months after the eruption (J. Lupton,/NOAA-PMEL). ³He is an isotope derived from the upper mantle of the earth and is a unique and "conservative" (so-called because it doesn't react chemically with anything else) tracer of hydrothermal activity in the oceans. However, except for the samples above the lava flow, the other samples taken immediately after the eruption on the Wecoma contained ratios of ³Ile to heat in the more "normal" range typical of mature vent sites. This result is puzzling, as high ³He/heat ratios found in October 1997 and August 1999 are consistent with the idea that Axial Volcano overlies

Figure showing enriched helium relative the plume temperature after the eruption. (Click for full size)

a deep magma source with a relatively high gas content. A low content of magmatic gas in plumes generated immediately after the eruption is supported by the low CO₂/Mn ratio found in February by Joe Resing (NOAA/PMEL). Betsy McLaughlin-West (Rice University), Marv Lilley, and Eric Olson (both at University of Washington) found high CH₄/Mn ratios in February, but isotopic measurements of the CH₄ indicate its origin was thermogenic decomposition of organic matter (new lava overrunning established vent biology?) or microbial methanogenesis, not magma degassing.

A major surprise was the announcement by Kim Juniper (University of Quebec) that the pervasive tan coating on the new lavas that made it difficult to map its boundaries precisely in 1998 consisted mostly of the skeletal remains of diatoms (tiny plankton made of silica) in some places mixed with bacterial mat.

The probable origin of this material is a spring diatom bloom that is common in the surface waters of the northeast Pacific. Why did this coating only seem to occur on the new lavas? The theory, given by Dr. Juniper is that bottom feeders had not yet colonized the new lavas, so the diatom layer was only "processed" by the endemic bottom feeders (e.g. holothurians) on the older areas. It will be interesting to see what the new lavas' appearance i s when ROPOS revisits it.

Biological observations at the 1998 eruption site suggests that colonization of the new vents was more complex than had been predicted. At some locations, tubeworms had already begun to colonize the new vents (top) while at other sites, polychaete worms grazing on the microbial mats were the dominant fauna. Since all of the new vents were within a few hundred meters of mature communities still surviving east of the lava flow, it is unclear why there was so much variation in their faunal composition. Verena Tunnicliffe, Maia Tsurumi and Jean Marcus of the University of Victoria suggested that much of the variation is due to random chance and to differences in recruitment of larvae due to variations in hydrothermal flow rate and chemistry between the vent sites.

The first year's experience at the NeMO site is laying the groundwork for a long-term realtime observatory at the site. A cruise on the R/V WECOMA June 16-29 (Ed Baker, Chief Scientist) will resurvey and resample the plumes above Axial and will recover and redeploy the array of water column moorings. The R/V T.G. Thompson with ROPOS on board will arrive at Axial the 22nd of June for a three week program of dives. Finally, in mid-September, the remotely operated vehicle JASON (also on T.G. Thompson) will deploy a year-long prototype of a realtime seafloor monitor consisting of a camera and temperature probe. Eventually, these data will be transmitted from the seafloor up through the water column by an acoustic modem and from the surface buoy to a satellite, where it will be sent to a shore station and onto the internet. The world scientific community will, for the first time, have direct, realtime access to data from a deep-sea volcano.

GOALS FOR 1999 FIELD WORK INCLUDE:

(1) Resample the vents at the new lava sites for chemical and microbiologic studies

(2) Observation and sampling of vent biota at all sites

(3) Recover all experiments placed in 1998

(4) Redeploy experiments, some with expanded arrays

(5) Survey seafloor eruption site farther south to complete map of new lava flow

(6) Map and sample CASM vent (not well-sampled last year)

(7) Attempt to recover Rumbleometer embedded in lava

(8) Continue sampling program of Axial Volcano lavas from ROV and by gravity coring

MOST IMPORTANT QUESTIONS FOR THIS YEAR:

(1) How has the thermal output of Axial Volcano changed during the past year (PREDICTION: A POWER LAW DECREASE)?

(2) How has the chemistry of the new hydrothermal vents evolved during the past year (PREDICTION: SIGNIFICANTLY LESS VOLATILE CONTENT, HIGHER CHLORINITY)? (3) Have there been any significant perturbations in temperature and chemistry at the local scale correlated with microseismicity as recorded on ocean floor seismometer array deployed by Scripps Institution of 'Oceanography (i.e., seismicity below the threshold of the realtime hydrophone monitoring system) (NO PREDICTION)?

(4) What was the extent of the eruption between the caldera sheet flow and the southern anomaly and southward (NO PREDICTION)?

(5) How has the mat covering the surface of the new lava flow changed during the past year (PREDICTION: MOST OF DIATOM MAT HAS BEEN "PROCESSED" BY SESSILE GRAZERS)?

(6) What has been the succession of vent biota during the past year (PREDICTION: TUBE WORMS HAVE COLONIZED ALL SITES)?

(7) Are hyperthermophiles still present in culturable level at fluids being emitted from the new lava flows (PREDICTION: SIGNIFICANT REDUCTION IN NUMBERS OF HYPERTHERMOPHILES)?

NOT MENTIONED AB0VE ARE FOLLOWING:

Titles of Manuscripts on results from the 1998 work at Axial Volcano submitted to a Special Section of Geophysical Research Letters (A journal of the American Geophysical Union):

(1) Dziak, R.P., and C.G. Fox,

The January 1998 Earthquake Swarm at Axial Volcano, Juan de Fuca Ridge: Hydroacoustic Evidence of Seafloor Volcanic Activity

(2) Sohn, R., S. Webb, and W. Crawford,

Ocean Bottom hydrophone record of post-volcanic diking event at Axial Volcano

(3) Baker, E.T., C.G. Fox, and J.P. Cowen,

In situ observations of the onset of hydrothermal discharge during the submarine eruption of Axial Volcano, Juan de Fuca Ridge, 1998 submitted

(4) Fox, C.G.,

In situ ground deformation measurements from the summit of Axial Volcano during the 1998 volcanic episode

(5) Chadwick, W.W., Jr., R.W. Embley, H.B. Milburn, C. Meinig, and M. Stapp,

Evidence for deformation associated with the 1998 eruption of Axial Volcano: Juan de Fuca Ridge, from acoustic extensometer measurements

(6) Embley, R.W., W.W. Chadwick, Jr., D. Stakes, and D. Clague,

1998 eruption at Axial Volcano: Multibeam anomalies and seafloor observations

(7) J.E. Lupton, E.T. Baker, R.W. Embley, R. Greene, and L. Evans,

Anomalous helium and heat signatures associated with the 1998 Axial Volcano event, Juan de Fuca Ridge

(8) McLaughlin-West, E.A., E.J. Olson and M.D. Lilley,

Variations in hydrothermal methane and hydrogen following the 1998 eruption at Axial Volcano

(9) Resing, J.A., R. Feely, G. Massoth, and E. Baker,

The chemistry of Fe, Mn and C0₂ in the hydrothermal plumes above Axial Seamount following a volcanic eruption

(10) Feely, R.A., E.T. Baker, G. Lebon, J.F. Gendron, J.A. Resing, and J. P. Cowen,

Evidence for sulfur enrichment in hydrothermal particles at Axial Volcano following the January-February 1998 eruption

(11) Dziak R.P., and C.G. Fox,

Long-term seismicity and Ground Deformation at Axial Volcano, Juan de Fuca Ridge

(12) Cowen, J. P., R. Shackelford, P. Lam, D. McGee, and E. Baker,

Microbial biomass in the hydrothermal plumes associated with the 1998 Axial Volcano eruption

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