Abstract
Abstract. 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 0.28 m in February/March and 0.21 m 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 10 120 ± 1280 km3 in October/November and 13 250 ± 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.
Highlights
Sensed estimates of sea ice area and thickness reveal a dramatic decline in Arctic sea ice volume in the last decades (Kwok et al, 2009; Laxon et al, 2013)
We further show uncertainties in effective sea ice thickness due to sea ice area, density and snow depth, and how they are distributed over space and time
We show that the mean sea ice thickness is strongly influenced by the choice of sea ice density, while the trend and the annual cycle are hardly affected
Summary
Sensed estimates of sea ice area and thickness reveal a dramatic decline in Arctic sea ice volume in the last decades (Kwok et al, 2009; Laxon et al, 2013). This decline mirrors changes in the Arctic heat budget (e.g. Kurtz et al, 2011b; Perovich et al, 2011) and alters the exchange of freshwater between sea ice and the ocean Many of the studies lack a detailed estimate of uncertainties We fill this gap and quantify total uncertainties in sea ice thickness and volume in the Arctic basin. We provide uncertainties averaged over the Arctic basin and analyse the spatial and seasonal variability
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