Science Advances - Ocean Heat Drives Rapid Basal Melt Of The Totten Ice Sheet (Antarctica)

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Abstract

Mass loss from the West Antarctic ice shelves and glaciers has been linked to basal melt by ocean heat flux. The Totten Ice Shelf in East Antarctica, which buttresses a marine-based ice sheet with a volume equivalent to at least 3.5 m of global sea-level rise, also experiences rapid basal melt, but the role of ocean forcing was not known because of a lack of observations near the ice shelf. Observations from the Totten calving front confirm that (0.22 ± 0.07) × 106 m3 s−1 of warm water enters the cavity through a newly discovered deep channel. The ocean heat transport into the cavity is sufficient to support the large basal melt rates inferred from glaciological observations. Change in ocean heat flux is a plausible physical mechanism to explain past and projected changes in this sector of the East Antarctic Ice Sheet and its contribution to sea level.

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RESULTS

We collected oceanographic profiles and bathymetry data from the calving front of the TIS in January 2015 (Fig. 1; Materials and Methods). The heavy sea ice conditions that had prevented previous expeditions from reaching the ice front relaxed briefly during a period of southwest winds, allowing for access through a narrow and short-lived shore lead. Fast ice prevented access to the western 30 km of the ice front, where geophysical data (15) indicate shallower seafloor depths (Fig. 1A). Temperature, salinity, and oxygen were measured from the sea surface to within 8 m of the seafloor at 10 stations along the calving front and fast ice edge.

The shipboard bathymetry data reveal a deep trough in front of the western TIS cavity, with a maximum depth of 1097 m and a maximum width of 10 km at a depth of 600 m (Fig. 2A). Below 600 m, the trough narrows to form two deep channels with widths of 2 to 4 km. These narrow channels are much deeper than the BEDMAP2 estimate of bottom depth at the ice front [<350 m (22)]. Inversion of airborne geophysical data identified a trough in the same location as observed by the ship (Fig. 1A) but with a shallower maximum depth (<680 ± 190 m) as a result of smoothing by the inversion procedure (15). The geophysical data indicate that the trough extends well south of the calving front and connects to the deep cavity beneath the TIS (Fig. 1A).

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The temperature of the mCDW near the seafloor in the deep trough exceeds the in situ freezing point by more than 2.2°C (the in situ freezing point decreases with increasing pressure) (Fig. 3A). If this warm water can access the grounding line at a depth of 2300 m (15), the temperature would exceed the local freezing point at the grounding line by 3.2°C. Velocity measurements collected by a lowered acoustic Doppler current profiler (LADCP) confirm that the warm water at the bottom of stations 35 and 36 flows strongly (>0.2 m s−1) into the sub–ice shelf cavity (Fig. 3B). The velocity profile is highly sheared, with weak flow in the cold water above the thermocline near 600 m depth and maximum inflow near the seafloor, where the warmest water is found. The deep flow in the eastern trough (station 41) also flows into the cavity but is substantially weaker (Fig. 3B).

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http://advances.sciencemag.org/content/2/12/e1601610.full

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