Preprints
https://doi.org/10.5194/os-2021-111
https://doi.org/10.5194/os-2021-111

  24 Nov 2021

24 Nov 2021

Review status: this preprint is currently under review for the journal OS.

Evaluation of basal melting parameterisations using in situ ocean and melting observations from the Amery Ice Shelf, East Antarctica

Madelaine Gamble Rosevear1,2, Benjamin Keith Galton-Fenzi3,4,5, and Craig Stevens6,7 Madelaine Gamble Rosevear et al.
  • 1Oceans Graduate School, University of Western Australia, Perth, Western Australia
  • 2Institute of Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania
  • 3Australian Antarctic Division, Kingston, Tasmania, Australia
  • 4The Australian Centre for Excellence in Antarctic Science, University of Tasmania, Hobart, Australia
  • 5Australian Antarctic Program Partnership, Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia
  • 6National Institute of Water and Atmospheric Research, Wellington, New Zealand
  • 7Department of Physics, University of Auckland, Auckland, New Zealand

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.

Madelaine Gamble Rosevear et al.

Status: open (until 19 Jan 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on os-2021-111', Carolyn Begeman, 01 Dec 2021 reply

Madelaine Gamble Rosevear et al.

Madelaine Gamble Rosevear et al.

Viewed

Total article views: 124 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
99 24 1 124 0 1
  • HTML: 99
  • PDF: 24
  • XML: 1
  • Total: 124
  • BibTeX: 0
  • EndNote: 1
Views and downloads (calculated since 24 Nov 2021)
Cumulative views and downloads (calculated since 24 Nov 2021)

Viewed (geographical distribution)

Total article views: 118 (including HTML, PDF, and XML) Thereof 118 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 01 Dec 2021
Download
Short summary
Understanding ocean-driven melting of Antarctic ice shelves is a key piece of the future-sea-level puzzle. However, ocean observations beneath an ice shelf are scarce. Here, we present unique ocean- and melting-data from the Amery Ice Shelf, East Antarctica. We use our observations to evaluate common methods of representing melting in ocean/climate models (melting “parameterisations”) and show that these parametrisations overestimate melting when the ocean is warm and/or currents are weak.