Variability of the marginal sea ice zone in the Nordic Seas in a 1/12°
ocean model forced and coupled to the atmosphere
Abstract
The marginal sea ice zone (MIZ) is a complex interface between the open
ocean and the pack ice, where ocean-ice-atmosphere interactions are
extremely complex. With a width of about 100 km, similar to the grid
size of many climate models, the MIZ is not resolved in CMIP5 climate
scenarios. In recent years, coupled climate models have been developed
with ocean components at higher resolution, such as the high resolution
version of the Met Office Global Coupled Model GC3 based on the GO6
configuration of the ORCA12 1/12° ocean model. We compare the MIZ
representation in a coupled simulation with a simulation using the same
ocean component forced by observed atmospheric data. Biases in the MIZ
position and width are of the same order of magnitude in the coupled and
forced model. The sea ice edge is strongly influenced by the ocean
circulation and is often found at the wrong location, even when an
observed atmospheric state is used to force the model. Despite a
possible mismatch between atmosphere and ice/ocean in the forced model,
due to the absence of feedback between sea ice and atmospheric
temperature, surface heat fluxes in the MIZ are similar in amplitude in
the coupled and forced simulations. Our analysis focuses on the
Greenland Sea because it is region of deep water formation, a major
control of the Atlantic Meridional Overturning Circulation and thus very
important for climate scenarios. The strong interannual variability of
sea ice in the Greenland Sea is examplified by the Odden tongue, a
protrusion of sea ice extending northeastward away from the Greenland
continental slope. The coupled model exhibits such interannual
variability, with a sea ice concentration larger than observed on
average. The relationship between atmosphere, ice concentration and
mixed layer depth is analyzed to assess the performance of both coupled
and forced 1/12° models to represent deep water formation in the Nordic
seas.