Dispatch 26: What We Have Learned     Print

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David Jones and Andrey Proshutinsky

October 1, 2017

Weather:  sunny, 15 knot winds, swells

Temperature: 1 ˚C

Relative humidity: 86%

Location: Beaufort Sea, 70˚ 45’ N; 125˚ 15’ W

News

We arrived mid morning at station AG5 and the sampling went smoothly. It is hard to believe that we are now done and steaming for our take out Kugluktuk aka “Kug” which happens on Wednesday, October 3. There is a lot of anticipation about getting home. For the crew of the Louis, it will have been 6 weeks! For most of the science party it has been a mere 4 weeks. But first, before disembarking we must pack. Lots and lots of packing.

This has been the 15th JOIS research cruise. Today Andrey Proshutinsky, Senior Scientist at WHOI writes about what has been accomplished and learned about the Beaufort Sea and the Beaufort Gyre over the past 15 years.  I have also included several photos of "Stuff on the Walls and in the Halls of the Louis"... Pretty self-explanatory, no captions required.

Beaufort Gyre: Some Accomplishments Since 2003

Today we revisit our first dispatch that described major goals and tasks of the Beaufort Gyre exploration program and Beaufort Gyre Observing system. Our BG observations have included standard (those which have to be repeated annually at the same standard locations) and non-standard, added when we have had time and supported by different other programs of the USA, Canada, Japan, and other countries. Our standard observations include observations of ocean physical parameters (water temperature and salinity, currents and bottom pressure); sea ice (draft and drift); and biogeochemistry (CFC, O2, TCO2, 13C, DOC, Helium & Tritium, 14C, Nutrients, 18-O, Ba, Iodine, Cesium, Chla-T, Chla-10/2, POC, C-DOM, CHO, HCH)

Non-standard observations by other programs based on the BGOS logistics cruises include: lowered ADCP measurements, sediment traps, zooplankton sampling, sea ice physical and chemical properties, wildlife observing, seismology, and turbulence measurements.

Many buoys have been deployed including (some were not discussed in this year dispatches but their descriptions can be found at our project web site): Up-Tempo, IMBs, O-buoys, AOFB, ITPs, SAMs – IBOs, polar profiling floats. Plus, drifting bottles were deployed as well to study surface currents of the Arctic Ocean.

From 2003-2016, numerous institutions have participated in the BGOS program including the USA (13 institutions), Canada (8 institutions), Japan (4 institutions), UK (3 institutions), China, Korea, and Poland with one institution from each country. Several TV and broadcasting companies filmed the BG operations and produced videos, movies, and broadcasts about the Beaufort Gyre studies and results: ABC; Asahi Broadcasting Company, Japan; Educational Broadcasting System (EBS) Korea; USA National Broadcasting Company (NBC); National Television (NTV), Russia.

Scientifically, the first program results were published in the Journal of Geophysical Research special section, “Beaufort Gyre Climate System Exploration Studies” in 2010. To date, over 100 peer-reviewed publications have utilized BGOS data.

Below we summarize some scientific results from these publications (more are available at the program website). Slides 22-26 illustrate 2003-2016 BGEP results.

Hydrography: Hydrographic data indicates that liquid fresh water in the BG in summer increased by 5410 cubic km from 2003 to 2010 and decreased a bit in 2011-2014, in 2015 it reached 22,600 cubic km and in 2016 an absolute maximum of 25,100 cubic km was reached or 6500 cubic km over the climatology of the 1950s-1980s.

Sea Ice:  A negative trend in ice draft was observed, while open water fraction has increased, attesting to the ablation or removal of the older sea ice from the BG region over the observational period.  A shift occurred toward thinner ice after 2007.

Freshwater Composition: During the rapid increase in BG freshwater content over 2005-2007, sea-ice meltwater increased by 2.7 m in the central BG region and low-salinity water from the Mackenzie River was advected to the southern BG region. After 2007 the major contributors to the freshwater increase of the BG freshwater reservoir have been Mackenzie river, fresh water from the Pacific Ocean, and from ice melt and precipitation minus evaporation.

Ocean Acidification:  The surface waters of the BG became under-saturated with respect to aragonite in 2008 - the first sign of acidification in the global deep ocean. Three factors contributed: reduced sea-ice extent (~30%), increased sea-ice melt (~30%), and anthropogenic CO₂ (~40%). The deeper Pacific Winter Water is also under-saturated, due to anthropogenic CO₂, with negative implications for shelled benthic organisms during upwelling to shelf ecosystems.

Organic Carbon Cycle:Sediment traps at BGOS Mooring A shows that, unlike other ocean basins, the bulk of particulate organic carbon entering the deep BG region is supplied by horizontal advection from the surrounding margins and that both the organic and inorganic carbon cycle in the Arctic is inherently linked to ocean dynamics.      

Ecosystem Effects:It was noted that freshwater changes from 2007 to 2009 in the BG depressed the top of the halocline and increased the stratification there by 25%, thus deepening the upper nutricline and associated summertime subsurface chlorophyll maximum, making nutrients less available. These harsher conditions coincided with a shift in near-surface ecosystem structure towards the smallest plankton.