Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> The Amery Ice Shelf (AIS), East Antarctica, has a layered structure, due to the presence of both meteoric and marine ice. In this study, the thermal structure of the AIS and its spatial pattern are evaluated and analysed through borehole observations and numerical simulations with Elmer/Ice, a full-Stokes ice sheet/shelf model. In the area with marine ice, a near-isothermal basal layer up to 120 m thick is observed, which closely conforms to the pressure-dependent freezing temperature of seawater. In the area experiencing basal melting, large temperature gradients, up to <span class="inline-formula">−</span>0.36 <span class="inline-formula"><sup>∘</sup></span>C m<span class="inline-formula"><sup>−1</sup></span>, are observed at the base. Three-dimensional (3-D) steady-state temperature simulations with four different basal mass balance (BMB) datasets for the AIS reveal a high sensitivity of ice shelf thermal structure to the distribution of BMB. We also construct a one-dimensional (1-D) transient temperature column model to simulate the process of an ice column moving along a flowline with corresponding boundary conditions, which achieves slightly better agreement with borehole observations than the 3-D simulations. Our simulations reveal internal cold ice advected from higher elevations by the AIS's main inlet glaciers, warming downstream along the ice flow, and we suggest the thermal structures dominated by these cold cores may commonly exist among Antarctic ice shelves. For the marine ice, the porous structure of its lower layer and interactions with ocean below determine the local thermal regime and give rise to the near-isothermal phenomenon. The limitations in our simulations identify the need for ice shelf–ocean coupled models with improved thermodynamics and more comprehensive boundary conditions. Given the temperature dependence of ice rheology, the depth-averaged ice stiffness factor <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mover accent="true"><mrow><mi>B</mi><mo>(</mo><msup><mi>T</mi><mo>′</mo></msup><mo>)</mo></mrow><mo mathvariant="normal">‾</mo></mover></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="27pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="e3453d98d88d537f4bcecb4a715f2f34"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="tc-16-1221-2022-ie00001.svg" width="27pt" height="15pt" src="tc-16-1221-2022-ie00001.png"/></svg:svg></span></span> derived from the most realistic simulated temperature field is presented to quantify the influence of the temperature distribution on ice shelf dynamics. The full 3-D temperature field provides a useful input to future modelling studies.

Highlights

  • The Amery Ice Shelf (AIS) (Fig. 1; ~70°S, 70°E) is the largest ice shelf in East Antarctica

  • We present vertical temperature profiles of the Amery Ice Shelf at six borehole sites, AM01–AM06, based on thermistor and distributed temperature sensing (DTS) measurements, indicating distinct thermal structures along flowlines in regions with and without marine ice

  • In AM01, AM04 and AM05 boreholes that have a 695 permeable basal layer of porous marine ice, approximately 100 m thick is present, which appears to conform to the pressuredependent seawater freezing temperature

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Summary

Introduction

The Amery Ice Shelf (AIS) (Fig. 1; ~70°S, 70°E) is the largest ice shelf in East Antarctica. It has an estimated floating ice area of 60,000 km (Galton-Fenzi et al, 2008), extending more than 550 km from its southern grounding zone to the ice front 30 in Prydz Bay. The thickest region of the ice shelf is at the southern grounding zone, with a thickness of ~2,500 m The AIS is fed primarily by the Lambert, Mellor and Fisher Glaciers, which account for 60.5% of the total ice mass flux (Yu et al, 2010). The AIS together with its tributary glaciers and their catchments is referred to as the Lambert-Amery Glacial system (LAGs). The AIS together with its tributary glaciers and their catchments is referred to as the Lambert-Amery Glacial system (LAGs). 35

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