Abstract
Ocean driven melting of Antarctic ice shelves is causing grounded ice to be lost from the Antarctic continent at an accelerating rate. However, the ocean processes governing ice shelf melting are not well understood, contributing to uncertainty in projections of Antarctica's contribution to sea level. Here, we analyse oceanographic data and in situ measurements of ice shelf melt collected from an instrumented mooring beneath the centre of the Amery Ice Shelf, East Antarctica. This is the first direct measurement of basal melting from the Amery Ice Shelf, and was made through the novel application of an upwards-facing Acoustic Doppler Current Profiler (ADCP). ADCP data were also used to map a region of the ice base, revealing a steep topographic feature or “scarp” in the ice with vertical and horizontal scales of ~20 m and ~40 m respectively. The annually-averaged ADCP-derived melt rate of 0.51 ± 0.18 m yr−1 is consistent with previous modelling results and glaciological estimates, and there is significant seasonal variation in melting with a maximum in May and a minimum in September. Melting is driven by temperatures ~0.2 °C above the local freezing point and background and tidal currents, which have typical speeds of ~3.0 cm s−1 and 10.0 cm s−1 respectively. We use the coincident measurements of ice shelf melt and oceanographic forcing to evaluate parameterisations of ice-ocean interactions, and find that parameterisations in which there is an explicit dependence of the melt rate on current speed beneath the ice tend to overestimate the local melt rate at AM06 by between 200 % and 400 %, depending on the choice of drag coefficient. A convective parameterisation in which melting is a function of the slope of the ice base is also evaluated and is shown to under-predict melting by 20 % at this site. Using available observations from other ice shelves, we show that a common current speed-dependent parameterisation overestimates melting at all but the coldest, most energetic cavity conditions.
Highlights
The Antarctic Ice Sheet is losing mass, and raising sea level, at an accelerating rate (Bamber et al, 2018; Shepherd et al, 20 2018; Meredith et al, 2019)
These earlier studies suggested a pathway for High Salinity Shelf Water (HSSW) from the calving front along the eastern flank of the Amery Ice Shelf (AIS), cooling and freshening due to basal melting, with a return 235 flow on the western flank of the ice shelf driven by a buoyant Ice Shelf Water (ISW) plume. 3.4 Acoustic Doppler Current Profiler (ADCP)-derived basal melt rate The ADCP-based approach estimates an annual mean melt rate at AM06 is 0.51±0.18 m yr−1 (Fig. 8)
425 In this paper we examined the relationship between basal melting and ocean conditions beneath the AIS using mooring data from a borehole drilled in 2010
Summary
The Antarctic Ice Sheet is losing mass, and raising sea level, at an accelerating rate (Bamber et al, 2018; Shepherd et al, 20 2018; Meredith et al, 2019). Of critical importance to the magnitude, spatial pattern and seasonality of the melt rate 30 are the properties of the watermasses that intrude into the ice shelf cavity. Intrusion of seasonally warmed Antarctic Surface Water (AASW), a much lighter watermass, into cavities drives elevated melt rates in summertime near the ice shelf front (e.g. Arzeno et al, 2014; Stewart et al, 2019). Relatively warm Circumpolar Deep Water (CDW; T ∼ 1 ◦C) drives extremely rapid melting at intermediate depths (e.g. Cook 35 et al, 2016; Jacobs et al, 2011; Jenkins et al, 2018)
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