USCGC Healy Cruise HLY-1502

US Arctic Geotraces

Weekly CTD/Hydrographic Team Report 09

final report from Jim Swift, UCSD/SIO, CTD/hydro team scientific leader at sea

Sunday, 11 October 2015, 3:00 pm, local date and time (2300 11 October UTC)

54.3°N, 166.4°W (about 26 miles north of Dutch Harbor in the Aleutian Islands)

air 6 degC / 43 degF

water 9 degC / 48 degF

wind 26 knots from W

on final approach to Dutch Harbor, Alaska

Note: This is a hydrography-oriented report from Jim Swift, who is working with the SIO Oceanographic Data Facility (ODF) CTD/hydrographic team on the US Geotraces Arctic Ocean expedition led by Dr. David Kadko, FIU, chief scientist. This is not a report from Dr. Kadko or the other science teams.

Dear Colleagues,

Our final days of station work on HLY-1502 continued the wait-for-a-weather- window theme of the previous week, although science operations transpired without incident during the times we were able to work. Working over the stern

  • required at Geotraces stations - was restricted to wind and sea conditions unlikely to result in problems with the oceanographic cables, and with fall storms in the area those times were fewer than hoped. But Geotraces did manage a sequence of three slope stations (≈ 3465, 1000, and 85 meters) and a 35 meter shelf station. Repeat hydrography, which uses the starboard A-frame and could work in a somewhat broader weather window, added casts at 2600, 1600, 500, 300, 160, and 68 meters. These stations sum to a fine hydrographic section across the abrupt Canada Basin - slope - Beaufort shelf transitions.

The ODF CTD/rosette program went well right to the end. Over the course of a 64-day expedition there were very few rosette problems, the analysts maintained outstanding data quality (there were only a few nutrients or oxygen values coded ‘bad’ the entire cruise), and there was excellent attention to data processing. The CTD/hydrographic data the science teams will carry home is ready for initial research use, with little change expected from the few final data processing steps remaining ashore.

Following completion of the CTD/hydrographic work, after waiting a bit for acceptable flying weather, two officials from the Department of Homeland Security (which includes the Coast Guard) were brought out by helicopter from Barrow to ride the ship to Dutch Harbor. The next day a crew member was flown ashore for medical attention, and then the Healy began a fast transit to Dutch Harbor. Winds have often been above 20 knots, and there was a stretch where sustained winds of about 40 knots were recorded, but fortune has smiled upon us: the winds have been behind us, giving us a fast and relatively comfortable “downhill” ride almost all the way.

In the early parts of the past week, there were partly clear nights several times, with active auroras. Even the rarer pinkish aurora was seen (see attached photo).

Last night the science team cooked dinner. The Healy has an excellent galley staff, but we held our own with a meal of coq au vin (for which we used the last of the ship’s onions and carrots), rice, grilled corn, macaroni and cheese, dinner rolls, and ice cream cookie sandwiches. It was a fun time for the science team and all hands seemed to enjoy the dinner.

We should arrive in port early this evening, a half day a‹head of schedule (thanks to those tail winds). The Dutch Harbor port period will be very busy for most on the science team, who are leaving the ship. Nearly all unloading will take place when the ship returns to Seattle in November.

A wide range of scientific inquiry will be made possible by the new repeat hydrography data. Preliminary analyses show that the mean temperatures in the layer defined between the sigma-0 27.8 and 28.05 isopycnals - which corresponds roughly to the density of the northern source of Denmark Strait Overflow Water - warmed considerably between 1994 and 2015 over the Chukchi Borderlands and in Makarov Basin, but there was little change between 2005 and 2015 from the Southern Canada Basin to the crest of the Alpha Ridge.

There were some strong changes in the halocline waters on the outbound section. For example the maximum in dissolved silicate, which lies in the halocline (roughly 150 meters) and well above the DSOW layer, showed large Makarov Basin 1994 to 2015 cruise-to-cruise differences, but small changes over 2005 to 2015 in the Canada Basin. And as is known from other recent studies, surface salinities over the two Canadian sector basins are now much fresher than they were in the past, yet we found that the lower intermediate water salinities are often a little higher now. There are exciting results in the ocean carbon and CFC/SF6 data as well.

All of this would not have been possible without the enthusiastic and capable support provided by Captain Hamilton, the officers & crew of USCGC Healy, and the science teams. I owe them and the US Coast Guard and National Science Foundation my heartfelt thanks for making these outstanding sections across the Makarov and Canada basins possible.

A few reflections in closing…

I have long been interested in the polar regions, and I am also drawn to hydrography, a word oceanographers use to encompass both the measurement of temperature, salinity, and other properties of seawater and also the interpretation of those data to describe aspects of the nature and circulation of ocean waters. A stroke of great good fortune brought me to Knut Aagaard, my graduate advisor at the University of Washington, who remains my oceanographic mentor and stout friend. And Joe Reid generously guided and supported me at the Scripps Institution of Oceanography, providing me not only the opportunity to work with him and his group, but also to study the World Ocean itself. I have since enjoyed an exciting career working with visionary scientists and supportive ship operators, and been honored to participate on great voyages with wonderfully talented technical teams, thinking especially of the SIO Oceanographic Data Facility measurement specialists to whom I owe so much.

The plans for USCGC Healy Cruise 1502 represented a once in a lifetime opportunity to measure and interpret change in some of the world’s waters I love best. To have now sailed the oceanographically-rich track on which we engaged has been a dream come true, and, seeing this is intended to be my final oceanographic cruise, a fitting finale to the seagoing aspect of my career.

That the National Science Foundation and other Federal agencies which support science at sea, the Scripps Institution of Oceanography, and my family have so wholeheartedly supported me on these endeavors for so many years is a great privilege for which I will always be indebted. I enjoy an abiding satisfaction that comes from doing something worthwhile, and doing it well.

Jim Swift

Research Oceanographer

UCSD Scripps Institution of Oceanography