Eighteen-year record of circum-Antarctic landfast-sea-ice distribution allows detailed baseline characterisation and reveals trends and variability

Alexander D Fraser,Jessica Cartwright,Zhaohui Wang,Kay I Ohshima,Phillip Reid,Marilyn N Raphael,Andrew R Klekociuk,Robert A Massom,Richard Porter-Smith,Mark S Handcock

doi:10.5194/tc-15-5061-2021

Abstract

Abstract. Landfast sea ice (fast ice) is an important though poorly understood component of the cryosphere on the Antarctic continental shelf, where it plays a key role in atmosphere–ocean–ice-sheet interaction and coupled ecological and biogeochemical processes. Here, we present a first in-depth baseline analysis of variability and change in circum-Antarctic fast-ice distribution (including its relationship to bathymetry), based on a new high-resolution satellite-derived time series for the period 2000 to 2018. This reveals (a) an overall trend of -882±824 km2 yr−1 (-0.19±0.18 % yr−1) and (b) eight distinct regions in terms of fast-ice coverage and modes of formation. Of these, four exhibit positive trends over the 18-year period and four negative. Positive trends are seen in East Antarctica and in the Bellingshausen Sea, with this region claiming the largest positive trend of +1198±359 km2 yr−1 (+1.10±0.35 % yr−1). The four negative trends predominantly occur in West Antarctica, with the largest negative trend of -1206±277 km2 yr−1 (-1.78±0.41 % yr−1) occurring in the Victoria and Oates Land region in the western Ross Sea. All trends are significant. This new baseline analysis represents a significant advance in our knowledge of the current state of both the global cryosphere and the complex Antarctic coastal system, which are vulnerable to climate variability and change. It will also inform a wide range of other studies.

Highlights

Around Antarctica, landfast or fast ice is a stationary and consolidated form of sea ice which is attached to, and held in place by, the coastline or floating ice shelf fronts (World Meteorological Organization, 1970) and icebergs grounded in waters shallower than approximately 400 m (Giles et al, 2008; Fraser et al, 2012)
When partitioned into appropriate regions, opposing trends are observed in most neighbouring regions (Fig. 5b–i): positive trends in the Dronning Maud Land, Western Indian Ocean, Australia, and Bellingshausen Sea regions and negative trends elsewhere
Using a newly released, long-term (18-year), highquality and high-resolution dataset of circum-Antarctic fast ice, we have for the first time

Summary

Introduction

Around Antarctica, landfast or fast ice is a stationary and consolidated form of sea ice which is attached to, and held in place by, the coastline or floating ice shelf fronts (World Meteorological Organization, 1970) and icebergs grounded in waters shallower than approximately 400 m (Giles et al, 2008; Fraser et al, 2012). Antarctic fast ice can range in persistence from annual through perennial to multi-decadal (e.g. Massom et al, 2010), with certain regions being highly variable and break-. Fraser et al.: Antarctic landfast-ice variability ing out and reforming several times per year Fraser et al.: Antarctic landfast-ice variability ing out and reforming several times per year (e.g. Massom et al, 2009; Fraser et al, 2012)

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