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

Abstract

An idealized eddy‐resolving numerical model, with topographic features common to the southern Weddell Sea, is constructed to study mechanisms through which warm deep water enters a wide continental shelf with a trough. The open ocean, represented by a 1700 m deep channel, is connected to a 400 m deep shelf with a continental slope. The shelf is narrow (50 km) in the east but widens to 300 km at the center of the model domain. Over the narrow shelf, the slope front is balanced by wind‐driven Ekman downwelling and counteracting eddy overturning, favoring on‐shelf transport of warm water in summer scenarios when fresher surface water is present. Over the wide shelf, the Ekman downwelling ceases, and the mesoscale eddies relax the front. Inflow of warm water is sensitive to along‐shelf salinity gradients and is most efficient when denser water over the wide shelf favors up‐slope eddy transport along isopycnals of the V‐shaped slope front. Inflow along the eastern side of the trough cannot penetrate the sill region due to potential vorticity constraints, while along the western trough flank, eddy‐induced inflow crosses the sill and reaches the ice front. The warm inflow into the trough is sensitive to the density of the outflowing dense shelf water. For weaker winds, absence of the dense water outflow leads to a reversal of the trough circulation and a strong inflow of warm water, while for stronger winds, baroclinic effects become less important and the inflow is similar to experiments including dense water outflow.

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

“…Daae et al . [] find in an idealized model study, that the establishment of an upper eddy overturning cell in summer, which is associated with the fresh water layer due to sea ice melt, leads to a relaxation of the thermocline and thus to a stronger inflow of MWDW onto the continental shelf. Figure a shows the onset of sea ice melt is in November and lasts until February.…”

“…Based on results from idealized modeling, Daae et al . [] suggest that the southward transport of MWDW is increased for denser outflowing ISW and a higher shelf salinity. The denser water exported from the continental shelf lifts the shelf break isopycnals and connects the warmer WDW over the slope with the shelf, forming a v‐shaped front [ Stewart et al ., ].…”

“…We do observe a denser shelf at the beginning of Phase 1 in 2015 ( S = 34.47) and an earlier warming at the upper instrument compared to the previous year ( S = 34.43), which would agree with results of Daae et al . [] and Stewart et al . [].…”

“…The results of Daae et al . [] focus on the Filchner Trough rather than on the eastern shelf which is over 100 m shallower and is likely governed by different dynamics.…”

“…These observations are consistent with the results of Daae et al . [], who suggest that a fresh surface layer in summer leads to a shallow eddy overturning cell that causes a relaxation of the thermocline. Hence, in a year with strong sea ice melt like 2013, a thicker fresh surface layer would develop and cause a stronger lift of the isotherms, leading to the exceptional warm inflow and vice versa.…”