A continuum model (PSUMEL1) of ice mélange and its role during retreat of the Antarctic Ice Sheet

Abstract

Rapidly retreating thick ice fronts can generate large amounts of mélange (floating ice debris), which may affect episodes of rapid retreat of Antarctic marine ice. In modern Greenland fjords, mélange provides substantial back pressure on calving ice faces, which slows ice front calving rates. On the much larger scales of West Antarctica, it is unknown if mélange could clog seaways and provide enough back pressure to act as a negative feedback slowing retreat. Here we describe a new mélange model, using a continuummechanical formulation that is computationally feasible for long-term continental Antarctic applications. It is tested in an idealized rectangular channel and calibrated very basically using observed modern conditions in Jakobshavn fjord, West Greenland. The model is then applied to drastic retreat of Antarctic ice in response to warm mid-Pliocene climate. With mélange parameter values that yield reasonable modern Jakobshavn results, Antarctic marine ice still retreats drastically in the Pliocene simulations, with little slowdown despite the huge amounts of mélange generated. This holds both for the rapid early collapse of West Antarctica and for later retreat into major East Antarctic basins. If parameter values are changed to make the mélange much more resistive to flow, far outside the range for reasonable Jakobshavn results, West Antarctica still collapses and retreat is slowed or prevented only in a few East Antarctic basins.Published by Copernicus Publications on behalf of the European Geosciences Union.Geosci. Model Dev., 11, 5149-5172, 2018www.geosci-model-dev.net/11/5149/2018/

Formation, flow and break-up of ephemeral ice mélange at LeConte Glacier and Bay, Alaska

“…Some attempts have been made to quantify the transfer of resistive stresses from fjord walls to glacier termini (I and II) (Amundson and others, 2010; Burton and others, 2018; Amundson and Burton, 2018) and the impact of calving events on ice mélange flow (I) (Peters and others, 2015). Building on observations that suggest that ice mélange can affect glacier terminus dynamics, a few studies have used ad-hoc parameterizations of ice mélange in tidewater glacier models (Pollard and others, 2018; Todd and others, 2019). In parallel to this work, recent observations have quantified meltwater fluxes from icebergs and ice mélange (III) (Enderlin and others, 2016; Moon and others, 2018), and related changes in water temperatures to ice mélange rigidity and glacier dynamics (III) (Bevan and others, 2019; Joughin and others, 2020).…”

“…The ability of ice mélange to inhibit iceberg calving depends on sea ice thickness, iceberg packing fraction, fjord geometry and ice mélange extent. Discrete element (Burton and others, 2018) and continuum models (Amundson and Burton, 2018) suggest that resistive forces from ice mélange may become sufficiently large to influence iceberg calving rates when the ice mélange length-to-width ratio is greater than ~3, which may explain why ice mélange appears to be more important in some systems than others (Moon and others, 2015; Fried and others, 2018; Pollard and others, 2018). In situations where ice mélange does not directly affect iceberg calving rates, it still likely indirectly affects glacier dynamics through its effect on fjord water properties and fjord circulation patterns.…”

Improvements in one-dimensional grounding-line parameterizations in an ice-sheet model with lateral variations (PSUICE3D v2.1)

“…In major Greenland fjords today such as Jakobshavn and Helheim, mélange is considered to provide significant back stress on the glacier calving front, at least in winter (e.g., Burton et al, 2018). However, in one study using a heuristic continuum model of mélange (Pollard et al, 2018), its back stress on ice shelves and grounding lines is negligible during West Antarctic retreat. In contrast to the narrow Greenland fjords, mélange in the much wider West Antarctic embayments flows northward into the southern oceans nearly unimpeded.…”

“…However, recent geophysical data indicate very low mantle viscosities below parts of West Antarctica (Heeszel et al, 2016;Barletta et al, 2018), which could produce faster rebound and shallower bathymetry by the time grounding lines retreat into central regions. Work to develop Earthsea level models with laterally varying properties and iceocean gravitational interaction, and couple them with icesheet models, is ongoing (Gomez et al, 2018;Powell et al, 2020). For all new model results in the main paper, the buttressing factor θ is given by Eq.…”

Improvements in one-dimensional grounding-line parameterizations in an ice-sheet model with lateral variations

“…In major Greenland fjords today such as Jakobshavn and Helheim, mélange is considered to provide significant back stress on the glacier calving front, at least in winter (e.g., Burton et al, 2018). However, in one study using a heuristic continuum model of mélange (Pollard et al, 2018), its back https://doi.org/10.5194/gmd-2020-131 Preprint. Discussion started: 25 May 2020 c Author(s) 2020.…”