| Summary: | During Arctic West Winter 2021 (AWW21), USCGC (United States Coast Guard Cutter) Polar Star launched expendable conductivity- temperature-depth (XCTD) probes in support of a science mission to investigate the formation of winter water in the Northern Bering and Chukchi Seas. This cold water is critical to the functioning of the regional ecosystem since it contains high levels of nutrients that spur primary production in the spring. However, due to the dearth of wintertime data, very little is known about how/where the water is formed and how it evolves through the winter. The data collected by Polar Star offered a rare opportunity to investigate these issues. During the first phase of AWW21, 28 XCTD probes were successfully dropped from just south of Bering Strait to the latitude of Hanna Shoal in the Chukchi Sea, mainly in the vicinity of the US (United States)/Russian convention line. This was done over the time period 18 December 2020 – 1 January 2021. During the second phase, 42 probes were successfully launched, predominantly over the northern Bering shelf, from 11 January – 2 February 2021. Most of the drops were done in significant, but varied, ice cover. This included numerous drops within re-freezing leads during which time winter water is readily modified. Near the end of the cruise, a sequence of probes was launched as the ship steamed through the marginal ice zone into open water (near 59°N (North)). The overall data return was excellent; there were only 7 failed probes despite the harsh conditions, and the quality of the data was high. This is a testament to the hard work and dedication of NOAA (National Oceanic and Atmospheric Administration) LT (Lieutenant) Lydia Ames and her fellow XCTD team members: LT Lauren Kowalski, DV2 (Diver Second Class) Charles Fox, MK2 (Machinery Technician Petty Officer Second Class) Tedd Meinersmann, and NIC (National Ice Center) sea-ice analyst Evan Neuwirth. We are indebted to Captain William Woityra and the crew of Polar Star for collecting this rare wintertime data set under such challenging conditions, and to the Coast Guard Pacific Area staff for their critical role in formulating the mission and for facilitating the science, including CDR (Commander) Robert Kinsey, CAPT (Captain) Rodrigo Rojas, LCDR (Lieutenant Commander) Andrew Dennelly, and Science Liaison Phillip McGillivary. Finally, we gratefully acknowledge the National Science Foundation Office of Polar Programs who funded the XCTD measurements with RAPID (Rapid Response Research) grant OPP (Office of Polar Programs) -2110148.
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