On the Modified Circumpolar Deep Water Upwelling Over the Four Ladies Bank in Prydz Bay, East Antarctica

Abstract

Analyses of hydrographic observation data sets revealed that modified Circumpolar Deep Water (mCDW) tends to flood the western flank (73–78°E, 67–68°S) of the Four Ladies Bank (FLB) in Prydz Bay. In this study, we investigated the mechanism responsible for mCDW upwelling over the FLB based on an eddy‐resolving coupled ocean‐sea ice‐ice shelf model in conjunction with the latest high‐accuracy bathymetry. It was found that zonal step‐like declines in the seabed over the FLB are crucial for the mCDW onshore upwelling, through topographic dynamic effects on the alongshore Antarctic Slope Current. In the presence of meridional cross‐shelf σθ isopycnals, warm mCDW at ~500‐m depth in the deep sea can make its approach to the shallower continental shelf (~200‐ to 500‐m depths), characterized as a warm layer (> −1.8 °C) bounded by the cross‐shelf σθ isopycnal surfaces of 27.5 and 27.7 kg/m3. The simulated outflow of the Prydz Bay gyre is concentrated to the eastern flank of the Prydz Channel. These results suggest that, in addition to the depressions and troughs around the Antarctic, smaller topographic features such as step‐like declines in the seabed near the Antarctic Slope Current are also favorable for onshore mCDW intrusion. This study demonstrates that mCDW onshore transport around the Antarctic continental shelf might be significantly underestimated by numerical models with coarse spatial representations of the topography.

Reduced Sea Ice Production Due to Upwelled Oceanic Heat Flux in Prydz Bay, East Antarctica

“…Although the Antarctic Slope front (ASF) acts as a strong dynamical barrier to the inflow of CDW across the shelf in East Antarctica (Spence et al, ; Thompson et al, ), intrusions of mCDW have been observed in the sea ice growth season (March–August), entering Prydz Bay over Four Ladies Bank (FLB) and occupying the eastern side of the bay following the cyclonic PBG and are directed toward the eastern flank of the AIS (Herraiz‐Borreguero et al, ; Liu et al, ; Williams et al, ). The interaction of the AIS with mCDW heat transport has been clarified by several studies (Herraiz‐Borreguero et al, , ; Wong et al, ), and the AIS net basal melt rate driven by mCDW inflow was estimated at 1.0 ± 0.4 m/year (Herraiz‐Borreguero et al, ), reducing local shelf water density and suppressing its potential contribution to AABW formation (Williams et al, ).…”

Predominant Sea Ice Fracture Zones Around Antarctica and Their Relation to Bathymetric Features

“…Thus, it can be assumed that ocean circulation and tides are key drivers for sea ice stability in the Southern Ocean. According to, for example, Tamsitt et al (2017) and Liu et al (2018), upwelling of deeper water masses can be expected along the shelf break. Tides apparently have a great influence on the stability of the sea ice.…”

Cold Ocean Cavity and Weak Basal Melting of the Sørsdal Ice Shelf Revealed by Surveys Using Autonomous Platforms

“…A narrow Antarctic Coastal Current (ACoC), driven by offshore and easterly winds, flows westwards near to the coast (Smith et al, 1984). Intrusion of Modified Circumpolar Deep Water (MCDW) occurs over Four Ladies Bank and eventually flows into the Prydz Bay Gyre and the AIS cavity (Galton-Fenzi et al, 2012;Liu et al, 2018). This MCDW is an important factor in driving basal melting of the AIS (Herraiz-Borreguero et al, 2015).…”

“…Observations from APRES confirm this and show that a seasonal cycle in basal melting is practically nonexistent at the two sampled sites. However, despite the weak observed melting, observations from moorings, ship, and instrumented seals over many years (Guo et al, 2019;Nunes Vaz & Lennon, 1996;Smith et al, 1984;Williams et al, 2010Williams et al, , 2016Wong et al, 1998) and multiple modeling studies (Galton-Fenzi et al, 2012;Liu et al, 2017Liu et al, , 2018 of the Prydz Bay region have shown that MCDW upwells over the Four Ladies Bank and is present close to the coastline in significant quantity. This MCDW has been shown to (in part) drive melting beneath the AIS (Herraiz-Borreguero et al, 2013;Herraiz-Borreguero et al, 2015) and is known to drive strong melt in other locations around Antarctica (e.g., Walker et al, 2013).…”