Uncertainties in Arctic sea ice thickness and volume: new estimates and implications for trends
Type
Journal articlePeer reviewed
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Date
2014-04-22
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Sea ice volume has decreased in the last decades,
evoked by changes in sea ice area and thickness. Estimates
of sea ice area and thickness rely on a number of geophysical
parameters which introduce large uncertainties. To quantify
these uncertainties we use freeboard retrievals from ICESat
and investigate different assumptions about snow depth, sea
ice density and area. We find that uncertainties in ice area
are of minor importance for the estimates of sea ice volume
during the cold season in the Arctic basin. The choice
of mean ice density used when converting sea ice freeboard
into thickness mainly influences the resulting mean
sea ice thickness, while snow depth on top of the ice is
the main driver for the year-to-year variability, particularly
in late winter. The absolute uncertainty in the mean sea ice
thickness is 0.28m in February/March and 0.21m in October/
November. The uncertainty in snow depth contributes up
to 70% of the total uncertainty and the ice density 30–35 %,
with higher values in October/November. We find large uncertainties
in the total sea ice volume and trend. The mean total
sea ice volume is 10120±1280 km³ in October/November
and 13250±1860 km³ in February/March for the time period
2005–2007. Based on these uncertainties we obtain
trends in sea ice volume of −1450±530 km³ a−1 in October/
November and −880±260 km³ a−1 in February/March
over the ICESat period (2003–2008). Our results indicate
that, taking into account the uncertainties, the decline in sea
ice volume in the Arctic between the ICESat (2003–2008)
and CryoSat-2 (2010–2012) periods may have been less dramatic
than reported in previous studies. However, more work
and validation is required to quantify these changes and analyse
possible unresolved biases in the freeboard retrievals.
Publisher
Copernicus Publications on behalf of the European Geosciences UnionCollections
Copyright Author(s) 2014