Till Andreas Soya Rasmussen – Niels Bohr Institute - University of Copenhagen

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Till Andreas Soya Rasmussen

Title: Modelling of the sea ice and the ocean in the Nares strait

A thesis submitted for the degree of Doctor of Philosophy on December 3rd, 2009 and defended January 22nd, 2009.

The Niels Bohr Institute
The Graduate School
of Science
Faculty of Science
University of Copenhagen
Denmark and The Danish Meteorological Institute

Supervisor:
Eigil Kaas, University of Copenhagen
Nicolai Kliem, The Danish Meteorological Institute

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Abstract

Modelling of the sea ice and the ocean in the Nares strait

This thesis describes a regional high resolution coupled ocean, HYCOM (HYbrid Coordinate Ocean Model), and sea ice, CICE (Community Ice CodE), model setup of the Nares Strait, the Baffin Bay and the Lincoln Sea. Two simulations have been run.

The first simulation is a hindcast simulation with oceanic boundaries from the operational system at the Nansen Center and atmospheric forcing from HIRLAM (HIgh Resolution Limited Area Model), the operational model at the Danish Meteorological Institute. The purpose of the simulation is to test the ability of the model system to describe small scale events like the opening of the North Water Polynya, variation of the sea ice flux etc.

The results have shown, that the North Water Polynya is well described in the model. An opening of the polynya in February is modelled at the same time as the observations. In general an area of thin ice is observed in the model where the polynya is located. It is associated with an ice bridge that forms in the southern part of Kanes Basin. The model shows, that the net surface heat flux is positive into the ocean between May and July; hence the atmospheric forcing keeps the polynya open. The sea ice area flux is in the lower end, between 4x103km2/year and 15x103km2/year. The relative annual variation of the ice cover agrees well.

The second simulation is a climate simulation. The climate change is prescribed by the Intergovernmental Panel on Climate Change (IPCC) scenario A1B, which prescribes a global temperature increase of 2oC. The atmospheric forcing is based on a regional climate simulation with HIRHAM (HIgh Resolution Hamburg Atmospheric Model). The oceanographic lateral boundaries are based on a global ocean simulation with ECHAM5-MPI-OM. The periodof the simulation is 1952 to 2080. The main di erence between a hindcast simulation and a climate simulation is that the statistics of the climate simulation should be correct, but an exact timing of individual events can not be expected.

The ice cover shows a decreasing trend during the entire simulation. The mechanism of the removal of sea ice in spring and return in winter is the same throughout the simulation. The only di erence is that the winter period becomes shorter. The North Water Polynya opens earlier than the rest of the domain. In fall the ice cover returns from north towards south.

The area ice flux agrees well with the observed in the present day climate. The area ice flux generally ranges from 10x103km2/year to 40x103km2/year
in this period. Around 2040 the area ice flux increases and individual years have an area ice flux with a maximum of 90x103km2/year.

The volume ice flux has a large variation, but the 10 year average is constant around 60xkm3/year. A small increase is observed, when the area flux increases around 2040, but it returns to its normal level shortly after.

The sea surface temperature in the Baffin Bay and the temperatures at depths around 200 meters just north of Kanes Basin shows an increase with up to 3oC in summer in the future scenario. The sea surface salinity in the Lincoln Sea is reduced with around 3 psu (practical salinity unit) from a present day value (averaged from 1961-1990) of approximately 32.5.

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