Reconstructing Sea Ice Conditions in the Arctic and Sub-Arctic Prior to Human Observations - Arctic Sea Ice Decline: Observations, Projections, Mechanisms, and Implications - page 25

Reconstructing Sea Ice Conditions in the Arctic and
Sub-Arctic Prior to Human Observations

Anne de Vernal, Claude Hillaire-Marcel, Sandrine Solignac, and Taoufik Radi

GEOTOP, Université du Québec à Montréal, Montreal, Quebec, Canada

André Rochon

GEOTOP and ISMER, Université du Québec à Rimouski, Rimouski, Quebec, Canada

Sea ice is a sensitive parameter characterized by a high variability in space and
time that can be reconstructed from paleoclimatological archives. The most direct
indication of past sea ice cover is found in marine sediments, which contain various
tracers or proxies of environments characterized by sea ice. They include sedimentary
tracers of particles entrained and dispersed by sea ice, biogenic remains associated
with production under/within sea ice or with ice-free conditions, in addition to
geochemical and isotopic tracers of brine formation linked to sea ice growth.
Reconstructing the extent of past sea ice is, however, difficult because proxies are
only indirectly related to sea ice and require the use of transfer functions having
inherent uncertainties. In particular, we have to assume a correspondence between
sea ice cover values from modern observations and the sea ice proxies from surface
sediment samples, which is a source of bias since the time intervals represented
by modern observations (here 1954-2000) and surface sediments (10 0 -10 3 years)
are not equivalent. Moreover, suitable sedimentary sequences for reconstructing
sea ice are rare, making the spatial resolution of reconstructions very patchy.
Nevertheless, although fragmentary in time and space and despite uncertainties,
available reconstructions reveal very large amplitude changes of sea ice in response
to natural forcing during the recent geological past. For example, during the early
Holocene, about 8000 years ago, data from dinocyst assemblages suggest reduced
sea ice cover as compared to present in some subarctic basins (Labrador Sea, Baffin
Bay, and Hudson Bay), whereas enhanced sea ice cover is reconstructed along the
eastern Greenland margin and in the western Arctic, showing a pattern not unlike
the dipole anomaly that was observed during the 20th century.

1. INTRODUCTION

Sea ice is a parameter of the climate system that plays
an important role because of its high albedo modulating the
energy budget at the surface of the ocean and because it con-
trols the exchanges of heat and gases at the interface between

27