The role of tides in bottom water export from the western Ross Sea

Abstract

Approximately 25% of Antarctic Bottom Water has its origin as dense water exiting the western Ross Sea, but little is known about what controls the release of dense water plumes from the Drygalski Trough. We deployed two moorings on the slope to investigate the water properties of the bottom water exiting the region at Cape Adare. Salinity of the bottom water has increased in 2018 from the previous measurements in 2008–2010, consistent with the observed salinity increase in the Ross Sea. We find High Salinity Shelf Water from the Drygalski Trough contributes to two pulses of dense water at Cape Adare. The timing and magnitude of the pulses is largely explained by an inverse relationship with the tidal velocity in the Ross Sea. We suggest that the diurnal and low frequency tides in the western Ross Sea may control the magnitude and timing of the dense water outflow.

Improving Antarctic Bottom Water precursors in NEMO for climate applications

“…AABW plays a crucial role in the global overturning circulation, in abyssal ventilation and in the cross-basin transport of heat, salt, carbon, nutrients and numerous other tracers (Killworth, 1983;Johnson, 2008;Orsi, 2010). The principal locations for the formation of the source waters of AABW are the Weddell and Ross Seas adjacent to the large ice shelves (Orsi et al, 1999;van Caspel et al, 2015;Kerr et al, 2018;Bowen et al, 2021). Filchner Ronne Ice Shelf (FRIS) is located at the southern boundary of the Weddell Sea and represents 28% of the total Antarctic ice shelf area (Fig.…”

“…We choose to keep all other ice shelves closed with prescribed melt rates injected at the mouth of the front using the method described by Mathiot et al (2017). RIS, FRIS and LCIS were chosen due to their role in the formation and setting of properties of the parent waters of AABW (Kerr et al, 2018;Bowen et al, 2021), and due to their large size and thus practicality of realistically simulating their sub-ice shelf cavities in a global ocean 1° setup. We choose to explore the changes in circulation, melt rates, and water mass properties in a forced scenario with fixed cavity geometry as coupling can introduce further biases and obscure the changes attributed to sub-ice shelf circulation.…”

Carbonate system data tracing freshwater inflow into the Ross Sea through the eastern gate and along the Ross Ice Shelf (Antarctica)

“…The AABW is produced by the tidal mixing of the Dense Shelf Water (DSW) with the Circumpolar Deep Water (CDW) along the continental shelf margins in the western sector (Whitworth and Orsi, 2006;Castagno et al, 2017;Bowen et al, 2021) and it contributes significantly to the ventilation of the deep layer of the Southern Ocean (Orsi and Wiederwohl, 2009). Therefore, it plays an important role in sequestering CO 2 from the atmosphere and transferring it into the deep ocean (Caldeira and Duffy, 2000;Sabine et al, 2004;Sandrini et al, 2007).…”

High Salinity Shelf Water production in Terra Nova Bay, Ross Sea from high-resolution near-surface salinity observations

“…HSSW is present at depth year-round in TNB, but new HSSW is produced only during austral winter, when salinification of surface waters via brine rejection has broken down lingering stratification from summer ice melt and solar radiation, allowing full water column convection to occur [23][24][25] . While some of the HSSW produced in TNB is converted to Ice Shelf Water (ISW) through its interaction with the local glaciers 22 or exported southward under the Drygalski Ice Tongue 12,19 , most of it spreads northward through the Drygalski Basin, taking about 8 months to reach the Drygalski Trough 26 . It ultimately exits the continental shelf as dense, tidally-modulated gravity plumes 20,21,[26][27][28] .…”

“…While some of the HSSW produced in TNB is converted to Ice Shelf Water (ISW) through its interaction with the local glaciers 22 or exported southward under the Drygalski Ice Tongue 12,19 , most of it spreads northward through the Drygalski Basin, taking about 8 months to reach the Drygalski Trough 26 . It ultimately exits the continental shelf as dense, tidally-modulated gravity plumes 20,21,[26][27][28] . Though the circulation of HSSW within TNB and its export via the Drygalski Trough are generally understood 12,22 , its production rate is poorly constrained; Previous estimates using net heat fluxes parametrized from reanalysis data 29 and simulated passive tracer experiments in a high-resolution regional model of the Ross Sea 19 differ by ~0.9 𝑆𝑣, a discrepancy on the same order of magnitude as the estimated transport of TNB HSSW northward to the shelf break.…”