13 August, 2003
Chief Scientist's Report #6
R/V Nathaniel B. Palmer SBI Survey Cruise
James H. Swift
13 August 2003, ca. 1:00 pm Alaska time - from R/V Nathaniel B. Palmer in the Arctic Ocean off the Beaufort shelf
Our SBI cruise continues to go very well. The professionalism of the officers, crew, and science team, plus the forgiving ice conditions, have combined to provide rapid progress with our planned work. We have now completed 299 CTD/rosette stations, setting new casts-per-cruise records for the ship and all hands.
Our shelf survey sampled two distinct shelf bottom water regimes, one low in nutrients and high in oxygen, and the other high in nutrients and low in oxygen. Our overall measurements connected the high oxygen regime to the Beaufort slope through Barrow Canyon, but there were several puzzling features about the spatial pattern of the low-oxygen regime. Partly to better study this regime we embarked on a long section along the outer shelf from the Russia/US boundary line to Barrow Canyon, including a crossing of Herald Valley and two spur sections into the Arctic basin. Indications are that the low-oxygen signal, which is strongest in the west, spreads east along the outer shelf, spills into Herald Valley which heads it out along the shelf edge, then spreads around Hanna Shoal into Barrow Canyon. The lowered-ADCP data reveal a shelf edge flow supporting these inferences from water properties. Our earlier deep basin observations of high-nutrient outer reaches on cold core eddies may indicate one mechanism which could move these waters away from the slope into the basin interiors. We followed the shelf section with a rerun of our earlier Barrow Canyon section closest to SBI current meter arrays. The plots from this pair of sections shows them clearly as twins, but to the eye perhaps more nearly fraternal than identical. In sum, this has been a satisfying week of water chasing.
The three graduate students who are working on the rosette program (thanks to NSF!) have been doing a terrific job. They run casts, work in the sampling room, carry out their own research programs, and still make time to work up property-property plots and vertical sections comparing the 2003 data to data from the three 2002 SBI cruises, and excellent plots of the ship's underway data. Together with Eric Johnson's LADCP plots these will comprise a suite of interpretative products which should be useful to the SBI science team.
Weather during the past week began with more of the same gray-cold-foggy conditions, joined by freezing rain which decorated the rails with icicles. But there have also been breaks of good weather.
The marine mammal surveys continue to produce good results, although unfavorable weather has limited use of the helicopter. Across the study area, the team observed lower densities of seals than expected, presumably due to declining haulout rates following the annual molting period. Consistently high densities of walrus have been observed hauled out on a band of ice just inside the outer fringe of the marginal ice zone, where several thousands of walrus were seen over the past week.
Chance observations of marine life continue. One evening as we were on station we came across a polar bear - or rather the bear came by - riding a drifting, isolated chunk of jumbled floes some 30 miles from the main ice field. The bear appeared to be tired, rising to look at us only as we passed. Last night our TEA Jim Rogers saw a bear swimming along in the ocean, many miles from ice or land.
Every now and then the pumps on our CTD ingest some marine life which fouls the sensors - usually for only a few seconds. Otherwise the stations just hum along.
We are now repeating one of our long shelf-slope-basin sections which ran close to another SBI moored array east of Barrow Canyon. The ice cover has all but disappeared during the month between occupations, making for brisk progress. Our final goal - a shelf-slope-basin section east of any yet done for SBI - is in sight.
All is well.
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