The Density‐Driven Winter Intensification of the Ross Sea Circulation

Abstract

The circulation over the Ross Sea continental shelf facilitates the exchange between the Southern Ocean and the Ross Ice Shelf cavity. Here transport and mixing processes control the access of oceanic heat from the Southern Ocean to the ice shelf base, the formation of sea ice, and the production of High Salinity Shelf Water (HSSW) in polynyas and hence the subsequent formation of Antarctic Bottom Water. A climatological ocean‐ice shelf coupled model of the Ross Sea Sector including the cavity, with prescribed sea ice fluxes, was used to examine the details of currents and their seasonal variability over the continental shelf. A system of two cyclonic and three anticyclonic persistent circulation features has been identified. Transports steadily increase throughout winter, with individual currents carrying up to 2 Sv, nearly doubling their minimum. The seasonal modulation is driven by lateral differences in density and subsequent baroclinic pressure gradients, induced through dense shelf water formation in the Ross Sea and the Terra Nova Bay Polynas. Wind plays a minor role in ocean momentum variability. Sensitivity experiments suggest a weakening of transports with increasing wind stress. Horizontal density variations at the ocean surface are smoothed by the wind. The source of momentum in the cavity is the gravity‐driven bottom flow of HSSW, produced in the Ross Sea Polynya as part of the thermohaline overturning circulation. Tracer experiments suggest that HSSW forming in the Terra Nova Bay Polynya has no cavity access, but instead is the main contributor to Antarctic Bottom Water formed in the northwest slope.

Modeling Ocean Eddies on Antarctica's Cold Water Continental Shelves and Their Effects on Ice Shelf Basal Melting

“…In February, this strong barotropic flow under the ice shelf is substantially weaker. Jendersie et al () found a similar seasonality of the flow under the western ice shelf and attributed it to stronger horizontal density gradients driven by winter sea ice formation. North of the ice shelf, the shelf break jet (the Antarctic Slope Current) and intrusions onto the continental shelf are intensified.…”

Variability in the Distribution of Fast Ice and the Sub‐ice Platelet Layer Near McMurdo Ice Shelf

“…The co-occurrence of higher frequencies of strong southerly wind events we observed in the RSP region over winter and the relatively rapid manifestation as thicker SPLs in McMurdo Sound in the following late spring of 2011 and 2017 also suggests a shorter time scale for HSSW and ISW ventilation from the deeper cavity than most modeling studies. Jendersie et al (2018) modeled the circulation within the McMurdo-Ross ice shelf cavity to be weakest from March to May before intensifying continuously until November and December. They attributed this to increased HSSW production in the RSP and resultant inflow to the cavity via McMurdo Sound/Haskell Strait and a channel east of Ross Island.…”

Multidecadal Basal Melt Rates and Structure of the Ross Ice Shelf, Antarctica, Using Airborne Ice Penetrating Radar

“…The amount of basal melting depends on the heat content of the underlying ocean determined by the ocean circulation under the ice shelf, and the intensity of mixing near the ice base to maintain an upward flux of ocean heat against the stabilizing effect of buoyant meltwater production (Holland & Jenkins, 1999). For the Ross Ice Shelf, the sub-ice-shelf circulation is described in detail by Assmann et al (2003), Dinniman et al (2011Dinniman et al ( , 2016, Jendersie et al (2018), Tinto et al (2019), and others. The low basal melt rates, and possible marine ice accumulation, that we estimate under most of the ice shelf (Figure 7a) is consistent with previous satellite-derived estimates (Moholdt et al, 2014;Rignot et al, 2013).…”