Response to Filchner–Ronne Ice Shelf cavity warming in a coupled ocean–ice sheet model – Part 1: The ocean perspective

Ralph Timmermann,Sebastian Goeller

doi:10.5194/os-13-765-2017

Abstract

Abstract. The Regional Antarctic ice and Global Ocean (RAnGO) model has been developed to study the interaction between the world ocean and the Antarctic ice sheet. The coupled model is based on a global implementation of the Finite Element Sea-ice Ocean Model (FESOM) with a mesh refinement in the Southern Ocean, particularly in its marginal seas and in the sub-ice-shelf cavities. The cryosphere is represented by a regional setup of the ice flow model RIMBAY comprising the Filchner–Ronne Ice Shelf and the grounded ice in its catchment area up to the ice divides. At the base of the RIMBAY ice shelf, melt rates from FESOM's ice-shelf component are supplied. RIMBAY returns ice thickness and the position of the grounding line. The ocean model uses a pre-computed mesh to allow for an easy adjustment of the model domain to a varying cavity geometry. RAnGO simulations with a 20th-century climate forcing yield realistic basal melt rates and a quasi-stable grounding line position close to the presently observed state. In a centennial-scale warm-water-inflow scenario, the model suggests a substantial thinning of the ice shelf and a local retreat of the grounding line. The potentially negative feedback from ice-shelf thinning through a rising in situ freezing temperature is more than outweighed by the increasing water column thickness in the deepest parts of the cavity. Compared to a control simulation with fixed ice-shelf geometry, the coupled model thus yields a slightly stronger increase in ice-shelf basal melt rates.

Highlights

The mass flux from the Antarctic ice sheet to the Southern Ocean is dominated by iceberg calving and ice-shelf basal melting
Melt rates between 3 and 5 m year−1 are suggested for Evans and Rutford Ice streams in the western sector of Ronne Ice Shelf, which is consistent with estimates based on ice flux divergence (Joughin and Padman, 2003)
We have presented the coupled ice sheet–ice shelf–ocean model Regional Antarctic ice and Global Ocean (RAnGO) which is focused on the Filchner–Ronne Ice Shelf (FRIS) and the grounded ice in its catchment basin

Summary

Introduction

The mass flux from the Antarctic ice sheet to the Southern Ocean is dominated by iceberg calving and ice-shelf basal melting. It was assumed that iceberg calving was the dominant sink of Antarctic ice sheet mass, but ice-shelf basal melting is estimated to outweigh all other processes (Depoorter et al, 2013; Rignot et al, 2013). The acceleration of mass loss from the Antarctic ice sheet since the 1990s (Rignot et al, 2011) has been attributed to enhanced ice-shelf basal melting and related ice-shelf thinning in the Amundsen and Bellingshausen seas (Pritchard et al, 2012). Using atmospheric output from the HadCM3 climate model, Hellmer et al (2012) found the potential of a rapid warming of the southwestern Weddell Sea continental-shelf waters by a redirected coastal current. In the Jacobs et al (1992) terminology, the replacement of cold shelf water by water originating from Warm Deep Water (WDW) leads to a shift from Mode 1 to Mode 2 melting, and to dramatically increased melt rates for the Filchner–Ronne Ice Shelf (FRIS). Timmermann and Hellmer (2013) showed that the surface

Methods

Results

Conclusion