Continuous winter oceanic profiling in the Cape Darnley Polynya, East Antarctica
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ORIGINAL ARTICLE
Continuous winter oceanic profiling in the Cape Darnley Polynya, East Antarctica Shigeru Aoki1 · Kazuya Ono1 · Daisuke Hirano1,2 · Takeshi Tamura3,4 Received: 12 December 2019 / Revised: 12 April 2020 / Accepted: 13 May 2020 © The Oceanographic Society of Japan and Springer Nature Singapore Pte Ltd. 2020
Abstract Antarctic coastal polynyas provide extremely dense water to the global abyss, but the dense water formation process has been poorly monitored in winter. This study developed a new tethered profiler to realize time-series observations of the water column in the Cape Darnley Polynya, East Antarctica. The system successfully obtained temperature and salinity profiles at 10-day intervals from March to November 2017. From March to April, significant cooling and vertical mixing started, while stratification collapsed. Salinity increased rapidly from April to late-May and then gradually increased until October. Salinity development was largely consistent with the cumulative salt increase due to sea-ice production at the initial stage, but not at latter stages, indicating the influence of cross-shelf exchange. These results highlighted the potential of the measurement platform to fill the remaining gap in the global ocean monitoring network. Keywords New tethered profiler · Winter oceanic profiling · Sea-ice production · Cape Darnley Polynya · East Antarctica
1 Introduction Antarctic coastal polynyas provide the densest water to the global ocean abyss. Continuous sea ice formation and brine rejection in a coastal polynya leads to the production of Dense Shelf Water (DSW), a precursor to the Antarctic Bottom Water (AABW) that fills the deepest part of the global ocean (Johnson 2008). In addition to well-known productive polynyas such as the Ross Sea and Mertz Glacier Polynyas (Jacobs et al. 1970; Rintoul 1998), research has found an active polynya off Cape Darnley, East Antarctica (Fig. 1), an area that has one of the largest sea ice productions along the circum Antarctic Coast (Tamura et al. 2008). This area is also associated with the outflow of an AABW variety (Ohshima et al. 2013). Recent advances in understanding * Daisuke Hirano [email protected] 1
Institute of Low Temperature Science, Hokkaido University, Kita‑19 Nishi‑8, Kita‑ku, Sapporo 060‑0819, Japan
2
Arctic Research Center, Hokkaido University, Kita‑21 Nishi‑11, Kita‑ku, Sapporo 001‑0021, Japan
3
National Institute of Polar Research, 10‑3, Midori‑cho, Tachikawa 190‑8518, Japan
4
The Graduate University for Advanced Studies, 10‑3, Midori‑cho, Tachikawa 190‑8518, Japan
polynya dynamics have suggested the potential influence of continental meltwater (Williams et al. 2016; Silvano et al. 2018), driven by the intrusion of modified Circumpolar Deep Water (mCDW; Herraiz-Borreguero et al. 2015), to DSW. However, contributions from these processes are still uncertain and dependent on each polynya environment. In coastal polynyas, DSW production is prominent in winter. To fully understand the development of DSW c
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