Variation in the Distribution and Properties of Circumpolar Deep Water in the Eastern Amundsen Sea, on Seasonal Timescales, Using Seal‐Borne Tags

Abstract

In the Amundsen Sea, warm saline Circumpolar Deep Water (CDW) crosses the continental shelf toward the vulnerable West Antarctic ice shelves, contributing to their basal melting. Due to lack of observations, little is known about the spatial and temporal variability of CDW, particularly seasonally. A new data set of 6,704 seal tag temperature and salinity profiles in the easternmost trough between February and December 2014 reveals a CDW layer on average 49 dbar thicker in late winter (August to October) than in late summer (February to April), the reverse seasonality of that seen at moorings in the western trough. This layer contains more heat in winter, but on the 27.76 kg/m 3 density surface CDW is 0.32 ∘ C warmer in summer than in winter, across the northeastern Amundsen Sea, which may indicate that wintertime shoaling offshelf changes CDW properties onshelf. In Pine Island Bay these seasonal changes on density surfaces are reduced, likely by gyre circulation. Plain Language SummaryIn the Amundsen Sea, Antarctica, warm salty water crosses the continental shelf from the deep open ocean, toward the vulnerable West Antarctic ice shelves, bringing heat to help melt them from underneath. Due to lack of observations, little is known about how this flow of warm water varies in space and time, particularly seasonally. Between February and December 2014, in a trough in the eastern Amundsen Sea, 6,704 profiles were collected by sensors attached to seals, measuring temperature and salinity as the seals return from dives up to 1,200 m deep. These data showed that this warm (∼1 ∘ C) deep layer is on average ∼50 m thicker in late winter (August to October) than in late summer (February to April), the reverse seasonality of that seen within a trough in the western Amundsen Sea. This warm layer contains more heat in winter but on a surface of constant density is 0.32 ∘ C warmer in summer than in winter, across the northeastern Amundsen Sea. This may indicate that in winter the deep waters offshelf rise, allowing different water onto the continental shelf. In Pine Island Bay these seasonal changes on density surfaces are reduced, probably because here the water circulates and mixes.

Oceanic Heat Delivery to the Antarctic Continental Shelf: Large‐Scale, Low‐Frequency Variability

“…The seasonal cycles of the wind stress and the surface heat and buoyancy fluxes suggest that the lateral heat advection across and along isobaths may be coupled to these forcings. Indeed, the water mass structure has been observed to have strong seasonal variability in several segments of the ACS, including the regions off the Adélie Coast in East Antartica (Snow et al, ) and the Central Amundsen (Wåhlin et al, ), East Amundsen (Mallett et al, ), Ross (Castagno et al, ), and East Weddell (e.g., Ryan et al, ) Seas. With the exception of the Adélie Coast, these regions show a greater presence of warm CDW‐influenced water on the shelf during summer and early fall.…”

Upper Ocean Distribution of Glacial Meltwater in the Amundsen Sea, Antarctica

“…Since the 1990s, multiple field campaigns have taken place in this region, operated by the British, U.S., Swedish, German, and Korean research communities (Jacobs et al., ; Heywood et al., ; Kim et al., ; Nakayama et al., ). Within these studies, focus has been placed on identifying the mechanisms for the warm water to access the continental shelf and ice shelf (Arneborg et al., ; Assmann et al., ; Mallett et al., ; Thoma et al., ; Walker et al., ; Wåhlin et al., ), and identification of GMW has mainly occurred directly in front of the ice shelves, with the exception of three more recent studies (Biddle et al., ; Kim et al., ; Nakayama et al., ). This location bias is mainly due to the reliability associated with the tracers used to identify GMW, as it was unknown how reliable conservative tracers (and pseudo conservative tracers such as dissolved oxygen concentration) would be with increasing distance from the ice shelves (Jenkins, ).…”

Phased Response of the Subpolar Southern Ocean to Changes in Circumpolar Winds

“…This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. As a result of the sSO's environmental challenges to conventional observational approaches, our understanding of the regional ocean dynamics remains fragmentary and is founded primarily on a few long-term mooring records (Daae et al, 2018;Graham et al, 2013;Kim et al, 2016;Núñez-Riboni & Fahrbach, 2009;Peña-Molino et al, 2016;Webber et al, 2017) and numerical models (Kimura et al, 2017;Mathiot et al, 2011;Paloczy et al, 2018;Stewart & Thompson, 2015) as well as sparse hydrographic data (Hatterman, 2018;Mallett et al, 2018). These studies indicate that in many areas around Antarctica, the slope frontal system and on-shelf pycnocline exhibit pronounced seasonality, with wind forcing being consistently suggested as the primary causal factor.…”