Observations of exponential wave attenuation in Antarctic sea ice during the PIPERS campaign

Alison L Kohout,Guy Williams,Lettie A Roach,Madison Smith,Fabien Montiel,Michael J M Williams

doi:10.1017/aog.2020.36

Abstract

AbstractQuantifying the rate of wave attenuation in sea ice is key to understanding trends in the Antarctic marginal ice zone extent. However, a paucity of observations of waves in sea ice limits progress on this front. We deployed 14 waves-in-ice observation systems (WIIOS) on Antarctic sea ice during the Polynyas, Ice Production, and seasonal Evolution in the Ross Sea expedition (PIPERS) in 2017. The WIIOS provide in situ measurement of surface wave characteristics. Two experiments were conducted, one while the ship was inbound and one outbound. The sea ice throughout the experiments generally consisted of pancake and young ice <0.5 m thick. The WIIOS survived a minimum of 4 d and a maximum of 6 weeks. Several large-wave events were captured, with the largest recorded significant wave height over 9 m. We find that the total wave energy measured by the WIIOS generally decays exponentially in the ice and the rate of decay depends on ice concentration.

Highlights

Antarctic sea ice is a key element in the global climate system
7297 were captured by waves-in-ice observation systems (WIIOS) deployed on the way into the sea ice and 16 169 by WIIOS deployed on the way out of the sea ice
Fourteen WIIOS were deployed on Antarctic sea ice during the PIPERS expedition in autumn 2017

Summary

Introduction

Antarctic sea ice is a key element in the global climate system. Its presence contributes to the well-known albedo effect, provides buffering that help sustain Antarctica’s ice sheets (Mossom and others, 2018), promotes an exchange of water with deeper layers of the ocean affecting ocean circulation and affects the rate of global warming by influencing ocean heat uptake in the Southern Ocean (Houghton and others, 2001). The sea ice grew in extent faster than the WIIOS drifted north and nearly 40% of the WIIOS wave records were measured at distances 400–500 km from the ice edge (Figs 5a, 6 and 7a). Exponential decay of total wave energy with distance is represented by a linear relationship between dHs/dx and Hs. Following the method presented in Kohout and others (2014), we assume that the wave field is consistent along the zonal spread of the sensors and that as waves enter the sea ice they refract and travel meridionally south.

Results

Conclusion