Impact of Sea-Ice Bottom Topography on the Ekman Pumping - Towards an Interdisciplinary Approach in Earth System Science - page 127

Impact of Sea-Ice Bottom Topography
on the Ekman Pumping

Giulia Castellani, R diger Gerdes, Martin Losch and Christof L pkes

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Abstract Sea-ice elevation pro les and thickness measurements have been col-

lected during summer 2011 in the Central Arctic. These two different data sets have
been combined in order to obtain surface and bottom topography of the sea-ice.
From the bottom pro

le, the keels of ridges are detected. Then, a parameterization

of oceanic drag coef cients that accounts for the keels depth and density is applied.

The calculated oceanic drag coef cients are highly variable (between about

10 − 3 ) within the range of observed values. In order to
estimate the contribution of variable drag coef

10 − 3 and about 8

2 × ×

cients on the Ekman pumping, the

calculated drag coef cients are used in an idealized model experiment, where

sea ice is drifting at constant velocity on an ocean at rest. The resulting variations of
the Ekman vertical velocity are in the same order of magnitude as for variable ice
velocity at the surface. In most state-of-the-art general circulation models, the
variations of drag coef cients are not taken into account. The simple experiment

carried out in the present study suggests that neglecting this contribution can lead to
an incorrect representation of the momentum exchange between ice and ocean and
to an underestimation of the Ekman pumping, with consequences for the large scale
ocean circulation.