Impact of West Antarctic ice shelf melting on Southern Ocean hydrography

Yoshihiro Nakayama,Ralph Timmermann,Hartmut H Hellmer

doi:10.5194/tc-14-2205-2020

Abstract

Abstract. Previous studies show accelerations of West Antarctic glaciers, implying that basal melt rates of these glaciers were previously small and increased in the middle of the 20th century. This enhanced melting is a likely source of the observed Ross Sea (RS) freshening, but its long-term impact on the Southern Ocean hydrography has not been well investigated. Here, we conduct coupled sea ice–ice shelf–ocean simulations with different levels of ice shelf melting from West Antarctic glaciers. Freshening of RS shelf and bottom water is simulated with enhanced West Antarctic ice shelf melting, while no significant changes in shelf water properties are simulated when West Antarctic ice shelf melting is small. We further show that the freshening caused by glacial meltwater from ice shelves in the Amundsen and Bellingshausen seas can propagate further downstream along the East Antarctic coast into the Weddell Sea. The freshening signal propagates onto the RS continental shelf within a year of model simulation, while it takes roughly 5–10 and 10–15 years to propagate into the region off Cape Darnley and into the Weddell Sea, respectively. This advection of freshening modulates the shelf water properties and possibly impacts the production of Antarctic Bottom Water if the enhanced melting of West Antarctic ice shelves continues for a longer period.

Highlights

Ice shelves in the Amundsen Sea (AS) and Bellingshausen Sea (BS) are melting and thinning rapidly, shown by satellitebased estimates of the last ∼ 20 years (Depoorter et al, 2013; Rignot et al, 2013; Paolo et al, 2015), contributing significantly to ongoing ocean freshening and sea level rise through a high discharge of grounded ice (Shepherd et al, 2012; Rignot et al, 2013)
We conduct four 32-year simulations with different levels of ice shelf melting in the AS and BS to investigate the impact of glacial meltwater on the Antarctic continental shelf hydrography
We show that the LMELT result represents a quasi-steady state without significant change in Ross Sea (RS) shelf water salinity (Fig. 4), and the PRS result shows an RS continental shelf and deep ocean freshening with some similarities to recent observations (Fig. 4)

Summary

Introduction

Ice shelves in the Amundsen Sea (AS) and Bellingshausen Sea (BS) are melting and thinning rapidly, shown by satellitebased estimates of the last ∼ 20 years (Depoorter et al, 2013; Rignot et al, 2013; Paolo et al, 2015), contributing significantly to ongoing ocean freshening and sea level rise through a high discharge of grounded ice (Shepherd et al, 2012; Rignot et al, 2013). In the Ross Sea (RS), shelf water is freshening, leading to a change in the Antarctic Bottom Water (AABW) properties (Jacobs et al, 2002; Jacobs and Giulivi, 2010). Since the salinity decrease leads to a change in AABW characteristics formed in the RS (Jacobs et al, 2002; Aoki et al, 2005; Rintoul, 2007; Jacobs and Giulivi, 2010) and may influence the global thermohaline circulation, understanding the possible link between the melting of West Antarctic ice shelves and RS freshening is important for assessing long-term changes in the Southern Ocean.

Results

Discussion

Conclusion