Brief communication: The anomalous winter 2019 sea-ice conditions in McMurdo Sound, Antarctica

Greg H Leonard,Inga J Smith,Maren E Richter,Maddy S Whittaker,Kate E Turner

doi:10.5194/tc-15-4999-2021

Greg H Leonard, Inga J Smith + Show 3 more

Open Access

https://doi.org/10.5194/tc-15-4999-2021

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Abstract

Abstract. McMurdo Sound sea ice can generally be partitioned into two regimes: (1) a stable fast-ice cover, forming south of approximately 77.6∘ S around March–April and then breaking out the following January–February, and (2) a more dynamic region north of 77.6∘ S that the McMurdo Sound and Ross Sea polynyas regularly impact. In 2019, a stable fast-ice cover formed unusually late due to repeated break-out events. We analyse the 2019 sea-ice conditions and relate them to a modified storm index (MSI), a proxy for southerly wind events. We find there is a strong correlation between the timing of break-out events and several unusually large MSI events.

Highlights

The sea-ice cover in McMurdo Sound can generally be partitioned into two regimes: (1) a stable fast-ice cover occupying the southeastern and western parts of the sound, south of a latitude of approximately 77.6◦ S, and (2) a more dynamic region in the central part of the sound
The 2019 McMurdo Sound sea-ice cover properties are derived from a combination of manual assessment of Sentinel1 synthetic aperture radar (SAR) and MODIS-derived icesurface temperatures and analysing sea-ice concentrations generated by the ARTIST Sea Ice (ASI) algorithm (Spreen et al, 2008)
This study offers new insights into the mechanisms behind individual break-out events and is one of a few case studies that investigate the stability of a fast-ice cover, an area that is in need of future research to improve the parameterization of fast-ice processes in large-scale sea-ice models

Summary

Introduction

The sea-ice cover in McMurdo Sound can generally be partitioned into two regimes: (1) a stable fast-ice cover occupying the southeastern and western parts of the sound, south of a latitude of approximately 77.6◦ S, and (2) a more dynamic region in the central part of the sound. McMurdo Sound logistical and scientific sea-ice operations depend on the formation of a stable fast-ice cover over the winter months that persists through to late December–early January. We are not aware of any studies directly investigating the causes of delayed formation of stable fast-ice covers in McMurdo Sound. Brunt et al (2006) investigated seaice break-out events in the southwest Ross Sea between 1996 and 2005 using satellite imagery and automatic weather station data. They found that break-out events were correlated with a dimensionless “storm index”, defined as the product of low-pressure anomalies and anomalous temperature (lower temperatures in summer and higher temperatures in winter). The 2019 McMurdo Sound sea-ice cover properties are derived from a combination of manual assessment of Sentinel synthetic aperture radar (SAR) and MODIS-derived icesurface temperatures and analysing sea-ice concentrations generated by the ARTIST Sea Ice (ASI) algorithm (Spreen et al, 2008)

McMurdo Sound sea-ice characteristics

Characterization of winter storms

Impact of mid-winter southerly wind events on the 2019 fast-ice cover

Findings

Discussion

Conclusions