30 July, 2003

Chief Scientist's Report #4

R/V Nathaniel B. Palmer SBI Survey Cruise

James H. Swift

30 July 2003, ca. 1:00 pm Alaska time - from R/V Nathaniel B. Palmer on the outer Chukchi Shelf

We have now completed 144 stations from R/V Nathaniel B. Palmer during our CTD/hydrographic survey of the US Western Arctic Shelf-Basin Interactions Phase II Field Program study area, including during the past week the final sections of our four cross-section exploration of Barrow Canyon waters, a short section across the Chukchi Shelf near Barrow Canyon, and two high-resolution shelf-slope-basin sections which reached well into the Canada Basin interior, each crossing the slope in the zone between Barrow Canyon and Herald Valley (i.e., west of Barrow Canyon).

The shelf-slope-basin sections were carried out with many of the stations at 3-mile spacing. Because the water column deepens rapidly off the slope - in deep water we use the full sampling capacity of our 24-place rosette at most stations - and because there is a limit on the number of water samples we can analyze each day, these sections represent considerable effort by the onboard science team. That effort has every appearance of having produced a bounty of information for the SBI program. For example, our first long section west of Barrow Canyon uncovered three closely-spaced eddies, including a pair of cold-core halocline eddies, very nicely detailed in the CTD, lowered Acoustic Doppler Current Profiler (thanks to Dr. Eric Johnson, our onboard LADCP expert), dissolved oxygen, and nutrient data. And the return section, closer to Herald Valley, hinted that the boundary over the upper slope was indeed feeding shelf water into the basin.

Weather during the past week has been gray, cold and often foggy, with rain and snow. Winds have been in the 20-25+ knot range much of the time, although in the ice they have little immediate effect on the ship other than increasing its on-station drift. The sea ice cover has varied from very open, with many broad leads, to fairly heavy and close, but only first year ice has been observed, all of it fairly rotten, and Captain Joe and his officers have never found the way impassable.

Weather unfavorable for flying resulted in only one marine mammal survey flight being flown during the past week. Nevertheless, that survey represented a good sample of seals hauled out over basin waters, which added to the growing coverage of the SBI study area the marine mammal team is acquiring. They are hoping that more favorable flying conditions during the coming week will enable them to proceed with their aerial surveys now that we are once again over the shelf.

The central unit of our CTD system celebrated 'hump day' - the halfway mark in the cruise - by self-destructing (an electrical short). But we were ready with a well-calibrated spare. We took the opportunity provided by that repair to re-do the electrical and mechanical terminations to the CTD/rosette package and replace two underwater cables. And our nutrient analyst took advantage of the short gap in the work to replace the pump tubing on the autoanalyzer.

So all ready to go and with plenty of stations on the plan, we are now embarked on the first of three long sections which will together comprise the bulk of our survey of the Chukchi shelf. Here stations are typically 50 meters deep and 10 miles apart, and so if all goes well progress can be rapid.

We have now completed two 'cup casts' - exploiting the compressibility of Styrofoam cups under 360 atmospheres pressure - with many on board providing decorated cups; during the past week we saw polar bears almost daily; snd the galley staff continues to pour on the tasty calories.

The survey goes on and all is well.

Lowered Acoustic Doppler Current Profiler (LADPC) data on Eric's computer.

Watching walrus...

... and watching the watchers.

Dr. Eric Johnson helping us "see" a pair of cold-core halocline eddies.