Antarctic sea ice over the past 130 000 years – Part 1: a review of what proxy records tell us
Authors: Crosta Xavier , Kohfeld Karen E. , Bostock Helen C. , Chadwick Matthew , Du Vivier Alice , Esper Oliver , Etourneau Johan , Jones Jacob , Leventer Amy , Müller Juliane , Rhodes Rachael H. , Allen Claire S. , Ghadi Pooja , Lamping Nele , Lange Carina B. , Lawler Kelly-Anne , Lund David , Marzocchi Alice , Meissner Katrin J. , Menviel Laurie , Nair Abhilash , Patterson Molly , Pike Jennifer , Prebble Joseph G. , Riesselman Christina , Sadatzki Henrik , Sime Louise C. , Shukla Sunil K. , Thöle Lena , Vorrath Maria-Elena , Xiao Wenshen , Yang Jiao 
Published: August 2022

Abstract. Antarctic sea ice plays a critical role in the Earth
system, influencing energy, heat and freshwater fluxes, air–sea gas
exchange, ice shelf dynamics, ocean circulation, nutrient cycling, marine
productivity and global carbon cycling. However, accurate simulation of
recent sea-ice changes remains challenging and, therefore, projecting future
sea-ice changes and their influence on the global climate system is
uncertain. Reconstructing past changes in sea-ice cover can provide
additional insights into climate feedbacks within the Earth system at
different timescales. This paper is the first of two review papers from the
Cycles of Sea Ice Dynamics in the Earth system (C-SIDE) working group. In
this first paper, we review marine- and ice core-based sea-ice proxies and
reconstructions of sea-ice changes throughout the last glacial–interglacial
cycle. Antarctic sea-ice reconstructions rely mainly on diatom fossil assemblages
and highly branched isoprenoid (HBI) alkenes in marine sediments, supported
by chemical proxies in Antarctic ice cores. Most reconstructions for the
Last Glacial Maximum (LGM) suggest that winter sea ice expanded all around
Antarctica and covered almost twice its modern surface extent. In contrast,
LGM summer sea ice expanded mainly in the regions off the Weddell and Ross
seas. The difference between winter and summer sea ice during the LGM led to
a larger seasonal cycle than today. More recent efforts have focused on
reconstructing Antarctic sea ice during warm periods, such as the Holocene
and the Last Interglacial (LIG), which may serve as an analogue for the
future. Notwithstanding regional heterogeneities, existing reconstructions
suggest that sea-ice cover increased from the warm mid-Holocene to the
colder Late Holocene with pervasive decadal- to millennial-scale variability throughout the Holocene. Studies, supported by proxy modelling experiments, suggest that sea-ice cover was halved during the
warmer LIG when global average temperatures were ∼2 ∘C above the pre-industrial (PI). There are limited marine (14) and ice core (4) sea-ice proxy records
covering the complete 130 000 year (130 ka) last glacial cycle. The
glacial–interglacial pattern of sea-ice advance and retreat appears
relatively similar in each basin of the Southern Ocean. Rapid retreat of sea
ice occurred during Terminations II and I while the expansion of sea ice
during the last glaciation appears more gradual especially in ice core data
sets. Marine records suggest that the first prominent expansion occurred
during Marine Isotope Stage (MIS) 4 and that sea ice reached maximum extent
during MIS 2. We, however, note that additional sea-ice records and transient
model simulations are required to better identify the underlying drivers and
feedbacks of Antarctic sea-ice changes over the last 130 ka. This
understanding is critical to improve future predictions.