HLY1502 letter 09 from Jim Swift

Sunday, 04 October 2015, 7:30 pm, local date and time (0330 05 October UTC)

73°N, 158.8°W (on the Beaufort slope)

air -4 degC / 25 degF

water -0.5 degC / 31 degF

wind 1-2 knots from ENE

on station 060 (a Geotraces ‘slope’ station)

Dear Family, Friends, and Colleagues,

This week started out rough for the expedition’s science programs, with Geotraces hit especially hard. Reversing the order of the cruise plan worked out well for most of the cruise, enabling excellent Arctic Ocean spatial coverage, for example. But one of the acknowledged risks was the degree to which fall storms would undermine the ability to carry out the final stations when the ship was in open water late in the season, just as we are now. Although we arrived in the southern Canada Basin with equipment working well, and what seemed to be a fine amount of time to do the scheduled work (I am not privy to the cruise time line, however), a series of low pressure systems (fall storms) has disrupted station work and led to damage to two of the three oceanographic cables used on this cruise: the trawl wire experienced damage some hundreds of meters above the termination and the Vectran synthetic cable, required for the trace metal rosette program, had to be inspected for possible damage about 1000 meters above the termination. Both of the damaged cables are used over the stern A-frame and both were involved in very high wire angle situations during casts the same day of worsening weather during the past week. No equipment was lost. The trawl wire was quickly put back into service, and the Vectran cable issue also was not a special problem, but the core issue remains that stormy weather makes for rough conditions, affecting most severely our science operations over the stern. We lost several days of stern operations due to weather, and this has put a dent in plans for the final thrust of the science program, which focuses on examining the basin-to-slope- to-shelf transition in the Southern Canada Basin. By the time of next week’s letter all this will have been settled one way or the other.

One other cable problem, not associated with bad weather, occurred a few hours ago: We lower the big 36x10-liter ODF rosette to within 10 meters of the bottom, take our first water sample (by closing it via remote control from our CTD computer), then haul the rosette up and stop to take other water samples at other levels. When it came time to haul up from near the bottom, the winch went down instead of up and quickly lowered the rosette onto the bottom. No damage was done to the rosette, but when tension is taken off the CTD cable like that, the cable kinks due to accumulated torque, so after the rosette was back on deck we had to cut off the kinked part and make a new termination. As a result all three of our oceanographic cables have had new terminations since I last wrote.

Although we are now in good weather, storms continue to haunt us with the next one due some time Monday. If it is bad enough and lasts long enough, that might be the end of science operations on the Canada Basin section because at some point we must begin heading for Dutch Harbor.

Meanwhile, the CTD/hydrographic measurements and data processing for both Geotraces and repeat hydrography continue to go very well when we are able to work. Deck operations are smooth and quick, the CTD works well in the just- below-freezing (as opposed to deeper cold) weather of the past, and all hydro team lab systems continue excellent performance. The CFC and ocean carbon teams have been able to do full profiles, generating a treasure of data for repeat hydrography. Here in the Canada Basin we have replicated a significant portion of the section done from the Swedish icebreaker Oden in 2005. Temperature comparisons show that the mid-depth layers have warmed since 2005 and that the upper layer has greatly freshened. These results are overall similar to the 2015-minus-1994 Makarov Basin differences reported earlier this cruise, demonstrating the widespread nature of these Arctic Ocean changes.

The fair weather windows can be short, making science planning less orderly than the norm preferred by the Coast Guard, which prefers a firm plan for the next 24 hours at 6:30 pm each day. (This is understandable seeing that they must orchestrate functions for a large crew.) There is also the matter that bathymetric charts for this region are inaccurate whereas we need to stop and do stations at scientifically-chosen isobaths, rather than assign in advance firm positions as favored by the Coast Guard. The Coast Guard has patiently worked this out with us, and now we are working well together on this.

Because we are now in open water and the air is usually sub-freezing, we see a moderate amount of sea ice formation, mostly grease ice but sometimes forming into small pancakes. The pancakes do not interfere significantly with the operation of the Healy’s rapid-launch small boat, which Geotraces uses for near surface trace metal sampling away from the influence of the ship (see photo taken by Chris Marsay, Skidaway Institute of Oceanography).

One way or the other our science work ends in a few days. We are tired, but not tired out. We are certainly not hungry, not with the excellent food the galley continues to provide. We enjoy working with our Coast Guard comrades, who treat us very well indeed. But we are all - Coast Guard and science teams alike - ready to finish up and head for port.

Saving a nice moment for last: We had a clear night with an aurora! Cory Mendenhall, the ship’s public affairs officer, captured a wonderful photo from the Healy’s helicopter pad, looking forward towards the hangar, with the ship’s red night lights glowing and the moon illuminating the sky beyond, auroral drapery shifting, changing, beautiful.

One way or the other our science work ends soon. I will send a final letter in one week.

Jim Swift

Research Oceanographer

UCSD Scripps Institution of Oceanography