Subduction of Pacific Summer Water into sub-surface eddies; coordinated observations from late summer 2018

Jennifer A MacKinnon1, Harper L Simmons2, John T. Hargrove3, Jim Thomson4, Thomas Peacock5, Matthew H Alford6, Marion S Alberty1, Benjamin Iolo Barton7, Samuel Brenner8, Nicole Couto9, Seth L Danielson10, Elizabeth Fine1, Hans Christian Graber3, John Guthrie11, Joanne Hopkins12, Steven R Jayne13, Thilo Klenz14, Craig Lee6, Yueng Djern Lenn15, Andrew J. Lucas16, Madison Smith17, Sinhue Torres-Valdes18, Kevin R Wood19 and John Woods20, (1)Scripps Institution of Oceanography, La Jolla, CA, United States, (2)University of Alaska Fairbanks, Fairbanks, AK, United States, (3)University of Miami, Center for Southeastern Tropical Advanced Remote Sensing, Miami, FL, United States, (4)University of Washington, Seattle, WA, United States, (5)Dept of Mech Eng - RM 1-310, Cambridge, MA, United States, (6)Univ Washington, Seattle, WA, United States, (7)University of Western Brittany, Laboratoire d'Océanographie Physique et Spatiale (LOPS), Plouzané, France, (8)University of Washington Seattle Campus, Oceanography, Seattle, WA, United States, (9)Scripps Institution of Oceanography, La Jolla, United States, (10)Univ Alaska, Fairbanks, AK, United States, (11)Polar Science Center, APL-UW, Seattle, WA, United States, (12)National Oceanography Centre, Liverpool, United Kingdom, (13)WHOI, Department of Physical Oceanography, Woods Hole, MA, United States, (14)University of Alaska Fairbanks, College of Fisheries and Ocean Sciences, Fairbanks, AK, United States, (15)Bangor University, Wales, School of Ocean Sciences, Menai Bridge, United Kingdom, (16)University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States, (17)Applied Physics Laboratory University of Washington, Seattle, WA, United States, (18)Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Bremerhaven, Bremerhaven, Germany, (19)NOAA Pacific Marine Environmental Laboratory, Seattle, WA, United States, (20)U.S. National Ice Center, Washington D.C., DC, United States
Abstract:
Advective heat fluxes in the Pacific Summer Water (PSW) class into the Arctic Ocean have been steadily increasing. Some of this heat is sequestered through subduction into warm intrathermocline eddies and filaments, which are becoming a new normal part of the Arctic halocline. These heat reservoirs can lurk for weeks to years, potentially bringing substantial sub-surface heat into the central gyre that can be, given the right circumstances, mixed upwards towards sea ice. Though evidence of very warm (6+ degrees C) sub-surface eddies is increasing, their formation process has not previously been documented in detail.

Here we present a novel suite of observations from the September 2018 ONR-funded Stratified Ocean Dynamics of the Arctic process cruise. Using a combination of ship-board sampling, autonomous instruments and drifter data, we observed a 50-100 meter deep surface intensified jet of warm PSW heading offshore from Barrow Canyon. The meandering warm jet can also be seen clearly in satellite data. In conjunction with meanders of the jet, energetic subduction resulted in the formation of coherent sub-surface eddies with a 7-10 km radius. Upward turbulent heat fluxes of 10-100+ W/m^2 move heat towards the surface, which was anecdotally associated with melting of remnant multi-year sea ice in this vicinity. Implications of both the heat and nutrient transport of subduction events like this for the central basin will be discussed.