Wintertime (2020-2021) hydrographic measurements in the Northern Bering and Chukchi Seas from USCGC (United States Coast Guard Cutter) Polar Star

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.

2021年北极西部冬季科考（Arctic West Winter 2021，简称AWW21）期间，美国海岸警卫队“极地之星”号（USCGC Polar Star）投放了抛弃式温盐深（expendable conductivity-temperature-depth，简称XCTD）剖面仪探头，以支撑一项针对北白令海与楚科奇海冬季水形成过程的科学考察任务。这类低温水体富含支撑春季初级生产的高浓度营养盐，对区域生态系统的正常运转至关重要。但受限于冬季观测数据的匮乏，学界对该水体的形成方式、形成区域及整个冬季的演化过程仍知之甚少。“极地之星”号采集的数据为探究这些问题提供了难得的契机。

AWW21科考分为两个阶段：第一阶段为2020年12月18日至2021年1月1日，科考团队从白令海峡以南至楚科奇海汉娜浅滩纬度带，主要在美俄约定海域附近，成功投放了28个XCTD探头。第二阶段为2021年1月11日至2月2日，主要在北白令海大陆架区域，成功投放了42个探头。大部分投放作业在覆盖程度不等的厚重浮冰区开展，其中多次在重新结冰的冰间水道内完成投放——这类区域正是冬季水易发生物理改造的场所。科考航次临近结束时，科考船行经边缘冰区进入开阔水域（约北纬59度）期间，连续投放了一批探头。

本次科考整体数据回收率极佳：尽管作业环境恶劣，仅7个探头未成功回收，且采集的数据质量优异。这离不开美国国家海洋和大气管理局（National Oceanic and Atmospheric Administration，简称NOAA）中尉莉迪亚·埃姆斯（Lydia Ames）及其XCTD团队成员的辛勤工作与敬业投入，他们分别是：中尉劳伦·科瓦尔斯基（Lauren Kowalski）、二级潜水员查尔斯·福克斯（Charles Fox）、二级机械技师特德·迈纳斯曼（Tedd Meinersmann），以及国家冰情中心（National Ice Center，简称NIC）海冰分析师埃文·纽沃思（Evan Neuwirth）。

我们还要感谢“极地之星”号船长威廉·沃伊特拉（William Woityra）及其全体船员，在极具挑战性的条件下完成了这套珍贵的冬季科考数据采集；感谢美国海岸警卫队太平洋区域工作组为本次任务策划及科考推进提供的关键支持，包括指挥官罗伯特·金西（Robert Kinsey）、船长罗德里戈·罗哈斯（Rodrigo Rojas）、中尉指挥官安德鲁·丹内利（Andrew Dennelly）以及科学联络官菲利普·麦吉利夫雷（Phillip McGillivary）。最后，我们衷心感谢美国国家科学基金会极地项目办公室，其通过快速响应研究（Rapid Response Research，简称RAPID）项目编号OPP-2110148资助了本次XCTD测量工作。