Geometry and dynamics of an East Antarctic Ice Sheet outlet glacier, under past and present climates

Abstract

The behavior of East Antarctic Ice Sheet (EAIS) outlet glaciers both at present and during the recent geological past is of considerable interest both from the point of view of understanding the mechanics of contemporary glacier dynamics, and also with regard to epoch‐scale ice sheet stability during Plio‐Pleistocene climate transitions. Here we use a glacier flowline model that incorporates the effects of longitudinal stresses to numerically simulate Ferrar Glacier, first under present‐day environmental conditions, and subsequently under both colder and warmer climate regimes representing the Last Glacial Maximum (LGM) and mid‐Pliocene peak warmth respectively. Using airborne radar profiles, InSAR‐derived surface velocities, ice core and geological data for empirical constraint, we present a diagnostic simulation that uses an iterative method to closely reproduce observed dynamics. Our model suggests that the glacier is largely cold‐based under present conditions, flows predominantly by way of internal deformation, and ‘cascades’ over bedrock ridges due to the combined action of changes in cross‐sectional valley geometry, local steepening of the glacier surface, and the non‐local effects of longitudinal coupling. Time‐dependent (evolutionary) simulation of a lower‐profile glacier under a colder, drier, LGM climate, predicts flow velocities lower than present with minimal bedrock erosion or basal till flux. Conversely, the warmer‐than‐present mid‐Pliocene climate produces a more dynamic glacier that is warm‐based and sliding along much of its bed. We propose that EAIS outlet glaciers, such as the Ferrar, respond dynamically along their length in response to changing environmental forcings, with most significant changes taking place in their lower reaches. Adjustment to perturbations in upper catchments is more muted.

Ice Velocity Variations of the Polar Record Glacier (East Antarctica) Using a Rotation-Invariant Feature-Tracking Approach

“…Stearns et al [3] provided direct evidence for the acceleration of the ice velocity on the Byrd Glacier in response to two subglacial lake drainage events. Golledge and Levy [4] suggested that the ice velocity of the East Antarctic Ice Sheet outlet glaciers has responded dynamically in response to environmental changes. Miles et al [5] analyzed the calving activity of six outlet glaciers in the Porpoise Bay region (East Antarctica) between November 2002 and March 2012, and investigated the drivers behind …”

Basal conditions of two Transantarctic Mountains outlet glaciers from observation-constrained diagnostic modelling

“…Although a shallow-shelf approximation (SSA) model is not appropriate for mountain glaciers, such as those described here, longitudinal extension and compression in TAM outlets means that gravitational driving stresses, d , alone may not yield a velocity field that accurately replicates observed values (Kavanaugh and others, 2009;Golledge and Levy, 2011). To account for this shortcoming, we implement the scheme of Kamb and Echelmeyer (1986) and Echelmeyer and Kamb (1986), which allows a heuristic adjustment to be made to b , so that they are smoothed according to an icethickness-dependent triangular averaging filter:…”

“…The numerical glacier flowline model we employ is essentially identical to that of Golledge and Levy (2011), but here we use the model in a diagnostic (rather than prognostic, or time-dependent) manner in order to make explicit use of new observational data, as well as recently published gridded data. These data are employed as constraints in an iterative calculation of creep and sliding velocity fields that aim to characterize the present-day behaviour of the two studied glaciers, assuming that each is currently in a state of equilibrium.…”

“…Since our interest lies in establishing likely values of basal ice temperatures, creep and sliding velocities, we hold our prescribed ice geometry constant and iterate only two model parameters: our deformation-rate coefficient, f d , and our sliding coefficient, f s . In the first integration we set f d according to a temperature-dependent relationship (Golledge and Levy, 2011):…”

Neogene tectonic and climatic evolution of the Western Ross Sea, Antarctica — Chronology of events from the AND-1B drill hole

“…Reflector Ri was mapped into the AND-1B succession within the lower part of diatomite unit 4.1, coincident with a~800 ky (4.4-3.6 my) unconformity beneath a thin volcaniclastic interval at~440 mbsf. Clinoform strata above reflector Ri thicken to the east and west and are linked to large-scale regression across the shelf (Fielding et al, 2008) and increased sediment flux to the VLB due to more dynamic EAIS outlet glaciers under warmer-than-present Pliocene climate (Golledge and Levy, 2011;Levy et al, 2012). Reflector Rk mapped into AND-1B at 150 mbsf represents an~500 ky hiatus distributed across two disconformities and may be related to flexural loading from Ross Island (mainly mounts Terror and Erebus).…”