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13 Apr 1997

MILLER FREEMAN Cruise MF97-04 Report
28 Mar - 13 Apr 1997
E. D. Cokelet, Chief Scientist

FOCI Cruise No: 4MF97

Operating Area: Shelikof Strait and eastern Bering Sea

Participating organizations:
NOAA - Alaska Fisheries Science Center (AFSC)
NOAA - Pacific Marine Environmental Laboratory (PMEL)

University of Washington -Joint Institute for Study of Atmosphere and Ocean (JISAO)
National Research Council Postdoctoral Fellowship Program (NRC)

University of Alaska, Fairbanks (UAF)


Chief Scientist:

Edward D. (Ned) Cokelet, Ph. D. PMEL

Participating Scientists:

Deborah Blood AFSC
Daniel M. Dougherty JISAO
William Rugen AFSC
Pim Van Meurs, Ph. D. NRC
Paul Simpson UAF
Erik Suring UAF

Cruise Objectives

The cruise had two primary objectives. The first was to study the Bering Slope Current and how it relates to the associated "green belt" of enhanced biological activity. CTD (conductivity-temperature-depth) and ADCP (acoustic Doppler current profiler) observations provided information on the current's speed and location. Water sample analyses will give phytoplankton species composition, standing stock, primary production, and nutrient estimates. The second primary objective was to obtain walleye pollock (Theragra chalcogramma) eggs on the southeastern Bering Sea shelf for a series of controlled, low-temperature incubations on board ship.

There were two secondary objectives. One was to measure the distribution of physical properties and currents in Shelikof Strait through the deployment of one satellite-tracked drifting buoy and the occupation of a CTD transect along Line 8. The last objective was to recover and deploy a temperature mooring near the mouth of Pavlof Bay for crab studies.

This work was part of the Fisheries Oceanography Coordinated Investigations (FOCI) to understand the physical and biological processes that lead to recruitment variability of commercially valuable fish and shellfish stocks in Alaskan waters.

Summary of Operations

The following tables show the overall numbers of samples taken and gear types employed.

Table 1A: Sample Summary

Table 1B: Gear Count

Sum of numsamp
samp Total
A-Genet 110
c/n cpm 339
chl cpm 241


CTD 124
DC cpm 31
Deploy 2
Discard 1
Fluor 63
HPLC cpm 263
nut cpm 359
PAR 63
phyt cpm 192
Strip 3
(blank) 0
Grand Total 1855

Count of Gear
Gear Total
Aleutian 1
CTD 41
Moor 1
Nor 1
SatBuoy 1
Trans 1
(blank) 0
Grand Total 130

Summary of Cruise

The ADCP was an essential instrument for this cruise because we wished to reference geostrophic currents to absolute ADCP velocities rather than to the velocity at an arbitrarily chosen pressure level (e.g. 1500 dbar) as had been done in the past for the Bering Slope Current. However when the scientific party arrived at the ship on 27 March the ADCP did not work owing to cable damage sustained when the ship's centerboard was raised at the end of cruise MF97-02. Pacific Marine Center (PMC) had sent a spare electronics box, cable and transducer for troubleshooting and replacement. Tests by LET Rick Philips indicated a transducer or cable failure, both of which required removing the transducer from the bottom of the centerboard using divers. No attempt at transducer removal could be made on 27 March, as first planned, due high waves at the Homer Spit wooden pier where the ship was berthed.

On 28 March, two of the ship's divers, LTJG Mark Sramek and S/F Bruce Thomassen, began the arduous task of removing the ADCP transducer. Field Operations Officer (FOO) LT Mike Hoshlyk, remained topside providing coordination, logistical support and safety monitoring as the divemaster. The work went slowly in the sediment-laden, near-freezing water. The transducers were not mounted for easy removal and installation. The divers first fastened a basket under the ship as a makeshift working platform. Standing in it and reaching above their heads, they had to weave their hands up into the ADCP well, behind the transducers, and unscrew 8 small half-inch-sized fasteners (6 bolts and 2 nuts) while wearing neopreme gloves as protection against the cold. The space was so small that they could not simultaneously see the bolts and unscrew them. Over several dives that day requiring 6 hours in the water, the dive team managed to remove 4 bolts. LT Hoshlyk looked after his divers well, filling air bottles, logging time at depth, and removing them from the water when cold began to hinder their efficiency. Though disappointed by their slow progress, Sramek and Thomassen maintained their optimism. They vowed to do better on the next day, and they did. Soon after breakfast they had removed 3 more bolts with 1 remaining. Meanwhile the Commanding Officer, CDR John Clary, arranged for a commercial diver, Cecil Cheatwood of C and C Aquatics, to join the diving team. The divers attacked the problem with renewed vigor, removing the last bolt and guiding the ~80-lb transducer head from under the ship and onto the deck. There we hooked up the new cable and tested the old transducer which worked, thus confirming that the old cable was at fault. With the help of the deck crew topside, the divers threaded the ADCP cable back through the centerboard and reinstalled the ADCP head, again spending several hours in the water. The ADCP worked perfectly for the rest of the cruise.

LTJG Mark Sramek and S/F Bruce Thomassen deserve special recognition for their unselfish devotion to the task, taking risks and forsaking their own personal comfort to make our scientific research possible. LT Mike Hoshlyk is to be congratulated for looking after the dive team's needs and maintaining a safe diving environment. CDR John Clary had overall command and took a close personal interest in the details of the operation. He was never far from the action, handling the lines on several occasions. His hiring of a commercial diver bolstered the dive team with a fresh, experienced member who helped expedite the repair.

Recommendation: The ADCP repair delayed our departure by 28 hours. Bolt removal and refitting consumed most of the time. The ADCP mounting must be redesigned for easier repair by divers. The transducer head should be placed in a recessed housing with a flange that bolts directly to the bottom of the centerboard via a ring of easily accessible bolts.

The ship departed Homer on 29 March at 1900 hours bound for Shelikof Strait. There we launched a satellite-tracked drifting buoy and occupied 7 CTD stations along Line 8 (Figs. 1 and 2).

We proceeded to the mouth of Pavlof Bay to recover and deploy a temperature measuring crab mooring (Fig. 1). The wind was blowing at 40 kt from the NW with gusts to ~50 kt. The in-place mooring's acoustic release would not respond to enabling commands despite repeated transmissions from both the centerboard-mounted and hand-lowered 12 kHz transducers. By listening inside the centerboard trunk, we determined that the transducer there was transmitting. Disabling commands were sent to the acoustic release. The new mooring was deployed with some difficulty in the strong wind. It was initially placed in water too shallow, but was subsequently lifted, dragged and released in deeper water.

The ship carried on through Unimak Pass into the Bering Sea where we searched for spawning walleye pollock using the EK 500 research echosounder (Fig. 3). When promising fish sign was observed, the Poly Nor'easter bottom trawl with roller gear was fished at mid-depth to catch a small amount of pollock. The first haul was small but contained some spawning females. Eggs were set aside for the Alaska Department of Fish and Game, and fin clips were taken for genetic study. A second haul produced no spawners; therefore the Aleutian wing trawl was used on the third haul providing adequate spawners. Eggs were stripped, fertilized and incubated in 4 refrigerators by Debbie Blood to determine the effects of temperature on egg development.

Following trawling, the ship sailed northwestward to the inward end of section I to begin the Bering Slope Current study (Figs. 3 and 4). There commenced a series of 7 CTD-ADCP sections with stations located nominally at 150, 200, 500, 1000 and 1500 m depth and then every 15 to 30 nm. Usually two CTD casts were taken at each station, one shallow cast limited to 300 m because of the depth range of the ChLAM (chlorophyll light absorbance meter) and one deep cast to the lesser of 1500 m or near bottom. The shallow CTD, operating off the starboard winch, measured the photosynthetically available radiation (PAR), fluorescence and chlorophyll concentrations as well as temperature and salinity. Water samples for nutrients, pigments, algal cells and primary productivity incubations were drawn from Niskin bottles on this CTD for final analysis at the University of Alaska, Fairbanks. The deep CTD off the port winch carried dual temperature and salinity sensors for cross-checking precision. Water bottle samples there were used for salinity calibration and to supplement the biological sampling. CTD data were processed while at sea, and preliminary profiles and sections worked up using EPIC programs.

The ADCP ran continuously while the ship was in the Bering Sea. Using GPS navigation and attitude determination (with an Ashtech 3DF unit), it computed the current velocity which will be used later to reference geostrophic speeds and draw fine-scale current vector maps. Dedicated ADCP transects connected the ends of the CTD sections (Figs. 3 and 4). A portion of the ADCP data was processed preliminarily at sea, but reinstallation of the ADCP heads meant that several sections had to be completed before adequate data were available to compute the transducer misalignment angle and scaling factor. Also because the processing person stood CTD watches and processed CTD data, he lacked time to process the ADCP data as well.

While underway the ship continuously measured PAR on the mast and temperature and salinity from the sea chest whose intake was located 5-5.5 m below the surface. Fluorescence was measured with a Turner Designs 10-AU bench top fluorometer situated in the chem lab and plumbed to the sea chest. The flow-through cell was cleaned every 1-2 day. A DI water blank was run periodically and automatically subtracted from the fluorometer reading. Also the scaled raw fluorescence values were recorded, and reference samples were drawn from the fluorometer stream and run through the calibrated University of Alaska fluorometer.

Specifics of Operations

See Table 2, the Discrete Sample Data Base (DSDB) MF97-04 Cruise Summary.


Figure 1:Shelikof Strait DSDB stations for MF97-04.

Figure 2:Shelikof Strait CTD casts for MF97-04.

Figure 3:Pavlof Bay and Bering Sea DSDB stations for MF97-04.

Figure 4:Pavlof Bay and Bering Sea CTD casts for MF97-04.

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