Brief communication: PICOP, a new ocean melt parameterization under ice shelves combining PICO and a plume model

Tyler Pelle,Mathieu Morlighem,Johannes H Bondzio

doi:10.5194/tc-13-1043-2019

Abstract

Abstract. Basal melting at the bottom of Antarctic ice shelves is a major control on glacier dynamics, as it modulates the amount of buttressing that floating ice shelves exert onto the ice streams feeding them. Three-dimensional ocean circulation numerical models provide reliable estimates of basal melt rates but remain too computationally expensive for century-scale projections. Ice sheet modelers therefore routinely rely on simplified parameterizations based on either ice shelf depth or more sophisticated box models. However, existing parameterizations do not accurately resolve the complex spatial patterns of sub-shelf melt rates that have been observed over Antarctica's ice shelves, especially in the vicinity of the grounding line, where basal melting is one of the primary drivers of grounding line migration. In this study, we couple the Potsdam Ice-shelf Cavity mOdel (PICO, Reese et al., 2018) to a buoyant plume melt rate parameterization (Lazeroms et al., 2018) to create PICOP, a novel basal melt rate parameterization that is easy to implement in transient ice sheet numerical models and produces a melt rate field that is in excellent agreement with the spatial distribution and magnitude of observations for several ocean basins. We test PICOP on the Amundsen Sea sector of West Antarctica, Totten, and Moscow University ice shelves in East Antarctica and the Filchner-Ronne Ice Shelf and compare the results to PICO. We find that PICOP is able to reproduce inferred high melt rates beneath Pine Island, Thwaites, and Totten glaciers (on the order of 100 m yr−1) and removes the “banding” pattern observed in melt rates produced by PICO over the Filchner-Ronne Ice Shelf. PICOP resolves many of the issues contemporary basal melt rate parameterizations face and is therefore a valuable tool for those looking to make future projections of Antarctic glaciers.

Highlights

Glaciers around the periphery of the Antarctic Ice Sheet (AIS) have undergone dynamic changes due to the spreading of warm modified Circumpolar Deep Water onto the continental shelf and, sometimes, into sub-ice shelf cavities (e.g., Jacobs et al, 2011; Pritchard et al, 2012)
We compare the modeled basal melt rates calculated by PICO and PICOP to melt rates inferred from conservation of mass and satellite interferometry (Rignot et al, 2013), which we refer to as “observations”
We focus on three regions: the Amundsen Sea sector of the West Antarctic Ice Sheet, the Totten and Moscow University ice shelves of the East Antarctic Ice Sheet, and the Filchner-Ronne Ice Shelf (FRIS)

Summary

Introduction

Glaciers around the periphery of the Antarctic Ice Sheet (AIS) have undergone dynamic changes due to the spreading of warm modified Circumpolar Deep Water (mCDW) onto the continental shelf and, sometimes, into sub-ice shelf cavities (e.g., Jacobs et al, 2011; Pritchard et al, 2012) This process drives enhanced basal melting, which has the potential to reduce the buttressing effect that ice shelves exert on grounded ice upstream (e.g., Rignot and Jacobs, 2002). Two of the most recently published melt parameterizations that resolve sub-shelf ocean circulation are the Potsdam Iceshelf Cavity mOdel (PICO, Reese et al, 2018) and one based on the physics of buoyant meltwater plumes (plume model, Lazeroms et al, 2018) Both parameterizations are novel in their own regards, melt rates calculated by PICO suffer from unrealistic “banding” as a product of its box model approach and remain too low near grounding lines.

Methods

Results

Conclusion