Intercomparison of Antarctic ice-shelf, ocean, and sea-ice interactions simulated by MetROMS-iceshelf and FESOM 1.4

Kaitlin A Naughten,Tore Hattermann,Jens B Debernard,Ralph Timmermann,Benjamin K Galton-Fenzi,Katrin J Meissner,Hartmut H Hellmer,Matthew H England

doi:10.5194/gmd-11-1257-2018

Abstract

Abstract. An increasing number of Southern Ocean models now include Antarctic ice-shelf cavities, and simulate thermodynamics at the ice-shelf/ocean interface. This adds another level of complexity to Southern Ocean simulations, as ice shelves interact directly with the ocean and indirectly with sea ice. Here, we present the first model intercomparison and evaluation of present-day ocean/sea-ice/ice-shelf interactions, as simulated by two models: a circumpolar Antarctic configuration of MetROMS (ROMS: Regional Ocean Modelling System coupled to CICE: Community Ice CodE) and the global model FESOM (Finite Element Sea-ice Ocean Model), where the latter is run at two different levels of horizontal resolution. From a circumpolar Antarctic perspective, we compare and evaluate simulated ice-shelf basal melting and sub-ice-shelf circulation, as well as sea-ice properties and Southern Ocean water mass characteristics as they influence the sub-ice-shelf processes. Despite their differing numerical methods, the two models produce broadly similar results and share similar biases in many cases. Both models reproduce many key features of observations but struggle to reproduce others, such as the high melt rates observed in the small warm-cavity ice shelves of the Amundsen and Bellingshausen seas. Several differences in model design show a particular influence on the simulations. For example, FESOM's greater topographic smoothing can alter the geometry of some ice-shelf cavities enough to affect their melt rates; this improves at higher resolution, since less smoothing is required. In the interior Southern Ocean, the vertical coordinate system affects the degree of water mass erosion due to spurious diapycnal mixing, with MetROMS' terrain-following coordinate leading to more erosion than FESOM's z coordinate. Finally, increased horizontal resolution in FESOM leads to higher basal melt rates for small ice shelves, through a combination of stronger circulation and small-scale intrusions of warm water from offshore.

Highlights

The Antarctic Ice Sheet (AIS) has significant potential to drive sea level rise as climate change continues (Deconto and Pollard, 2016; Golledge et al, 2015; Rignot et al, 2014; Mengel and Levermann, 2014)
While we find that both MetROMS and FESOM underestimate total basal mass loss from ice shelves, this is a regional bias largely confined to small, warm-cavity ice shelves which are not well resolved by the model configurations considered here
With respect to simulated sub-ice-shelf circulation, some ice-shelf cavities show agreement with the direction of transport inferred from observations and others show disagreement

Summary

Introduction

The Antarctic Ice Sheet (AIS) has significant potential to drive sea level rise as climate change continues (Deconto and Pollard, 2016; Golledge et al, 2015; Rignot et al, 2014; Mengel and Levermann, 2014). The ocean is an important driver of AIS retreat (Golledge et al, 2017; Joughin and Alley, 2011), as 40 % of the ice sheet by area is grounded below sea level (Fretwell et al, 2013). The Amundsen sector of West Antarctica has bedrock geometry favourable for a marine ice-sheet instability, and unstable retreat may have already begun (Rignot et al, 2014)

Results

Discussion

Conclusion