Sea-ice freeboard and thickness in the Ross Sea from airborne (IceBridge 2013) and satellite (ICESat 2003–2008) observations

Liuxi Tian,Stephen F. Ackley,Jiakui Tang,Alberto M. Mestas-Nuñez,Hongjie Xie,Xianwei Wang

doi:10.1017/aog.2019.49

Abstract

AbstractNASA's Operation IceBridge mission flew over the Ross Sea, Antarctica (20 and 27 November 2013) and collected data with Airborne Topographic Mapper (ATM) and Digital Mapping System (DMS). Using the DMS and reflectivity of ATM L1B, leads are detected to define local sea level height. The total freeboard is then obtained and converted to ice thickness. The estimated mean sea-ice thickness values are found to be in the 0.48–0.99 m range. Along the N-S track, sea ice was thinner southward rather than northward of the fluxgate, resulting in two peaks of modal thickness: 0.35 m (south) and 0.7 m (north). This supports that new ice produced in coastal polynyas is transported northward by katabatic winds off the ice-shelf. The lowest (2%) elevation method used for freeboard retrieval for ICESat is also tested for ATM data. It is found that the lowest elevation method tends to overestimate freeboard, but mean values are less affected than mode values. Using mean thickness values of ICESat and ATM along the ‘fluxgate’, separating the shelf from the deep ocean, the exported ice volume at this ‘fluxgate’ is found to be higher during the ICESat years (2003–2008) than during the IceBridge year (2013).

Highlights

Sea ice plays an important role in heat exchange between the ocean and atmosphere due to its impact and feedback on the transfer of heat, moisture and momentum across the ocean– atmosphere interface (Rinke and others, 2006; Dieckmann and Hellmer, 2010)
Leads are detected by combining Digital Mapping System (DMS) images and reflectivity of Airborne Topographic Mapper (ATM) L1B, and local sea level are retrieved from ATM L1B shots over leads
Freeboard estimates are obtained from the difference between surface elevation of ATM L2 and the local sea level

Summary

Introduction

Sea ice plays an important role in heat exchange between the ocean and atmosphere due to its impact and feedback on the transfer of heat, moisture and momentum across the ocean– atmosphere interface (Rinke and others, 2006; Dieckmann and Hellmer, 2010). Polar regions show high sensitivity to climate change due to the high reflectivity of ice compared to ocean water. This ice-albedo feedback mechanism is a factor that contributes to high polar sensitivity to warming (Holland and others, 2001; Screen and Simmonds, 2010). Earlier sea-ice advance and later retreat make the summer ice-free season shorter by 2 months (Stammerjohn and others, 2012). It is still unclear, if sea-ice thickness, volume and sea-ice production (SIP) have increased in the Ross Sea

Results

Discussion

Conclusion