Eddy Generation and Jet Formation via Dense Water Outflows across the Antarctic Continental Slope

Abstract

Along various stretches of the Antarctic margins, dense Antarctic Bottom Water (AABW) escapes its formation sites and descends the continental slope. This export necessarily raises the isopycnals associated with lighter density classes over the continental slope, resulting in density surfaces that connect the near-freezing waters of the continental shelf to the much warmer circumpolar deep water (CDW) at middepth offshore. In this article, an eddy-resolving process model is used to explore the possibility that AABW export enhances shoreward heat transport by creating a pathway for CDW to access the continental shelf without doing any work against buoyancy forces. In the absence of a net alongshore pressure gradient, the shoreward CDW transport is effected entirely by mesoscale and submesoscale eddy transfer. Eddies are generated partly by instabilities at the pycnocline, sourcing their energy from the alongshore wind stress, but primarily by instabilities at the CDW-AABW interface, sourcing their energy from buoyancy loss on the continental shelf. This combination of processes induces a vertical convergence of eddy kinetic energy and alongshore momentum into the middepth CDW layer, sustaining a local maximum in the eddy kinetic energy over the slope and balancing the Coriolis force associated with the shoreward CDW transport. The resulting slope turbulence self-organizes into a series of alternating along-slope jets with strongly asymmetrical contributions to the slope energy and momentum budgets. Cross-shore variations in the potential vorticity gradient cause the jets to drift continuously offshore, suggesting that fronts observed in regions of AABW down-slope flow may in fact be transient features.

On the effect of topography and wind on warm water inflow—An idealized study of the southern Weddell Sea continental shelf system

“…Warm inflow over the continental shelf is limited by the presence of the ASF. In agreement with Stewart and Thompson [], we find that on‐shelf transport of CDW mainly occurs when dense water formation over the shelf connects the density surfaces between the oceanic CDW and the cold shelf water, and the CDW can access the shelf without doing work against the buoyancy forces.…”

“…Eddy‐mediated transport of WDW to the wide continental shelf is most efficient when dense water on the shelf (HighSSS) is transported offshore, creating V‐shaped isopycnals across the continental slope. The result agrees with Stewart and Thompson [], who find that the establishment of an isopycnal connection between the dense shelf water and the CDW, creates a pathway for CDW to access the continental shelf without doing work against the buoyancy force. For the other scenarios, the main role of eddies is to balance the wind‐driven downwelling, which influence the thermocline depth and the temperature of the WDW interacting with the trough topography.…”

“…In experiments with higher shelf salinity (HighSSS), dense water is exported from the shelf (negative and in Figure f). The isopycnal is lifted over the slope (Figure d) and forms a V‐shape, which connects the cold, dense shelf water to the warmer CDW at middepths over the slope [ Stewart and Thompson , ]. Eddies transport warm water onto the shelf (positive ), and the shelf‐depth temperature increases by 0.1–0.2°C (Figures b and f).…”

Seasonal cycle of hydrography on the eastern shelf of the Filchner Trough, Weddell Sea, Antarctica

“…[] and Stewart et al . []. For comparison, salinities in 2013 when the inflow started even earlier and reached the ice front were at 34.43, while they were about 0.05 lower in 2011 [ Darelius et al ., ], where the MWDW did not reach the ice front [ Årthun et al ., ]; however, no information is available about the start of the inflow.…”

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

“…At mesoscales and submesoscales, evidence has shown that eddies of O(1–5 km) are prime contributors to the onshore mass and heat transports across the continental slope (e.g., Graham et al, ; Nøst et al, ; Stewart & Thompson, , , ; Stewart et al, , hereafter SKM18), likely via eddy stirring of temperature along isopycnals (Stewart & Thompson, ; SKM18). The background Antarctic Slope Current/Undercurrent (ASC/ASUC) flow also plays an important role (Chavanne et al, ; Peña‐Molino et al, ; Walker et al, ).…”