Project Weddell Sea (2009-2012)

Coastal polynyas play an important role for the coupling between the components of the sea ice-ocean-atmosphere system in polar areas. Locally enhanced surface exchange processes in areas of open water have important consequences for the atmosphere, ocean processes, ice formation (brine release), gas exchange, and biology. In the Weddell Sea, recurrent coastal polynyas form at the Filchner-Ronne ice shelf and in the area of the recently collapsed Larsen ice shelf, both largely triggered by atmospheric forcing. The project aims at an improved understanding of the polynya formation processes, and the quantification of the bottom water formation and ice production associated with coastal polynyas for the Weddell Sea area. A coupled system of the non-hydrostatic weather forecast model COSMO (German Meteorological Service, DWD) and the sea ice-ocean model FESOM (AWI) is being used at a high resolution. Simulations with a resolution of 5 km are used over a whole winter period. The forcing by synoptic-scale cyclones and mesoscale processes (such as katabatic winds and mesocyclones) and their interaction with the polynyas are being investigated. Of particular interest is the possible change of bottom water formation in the former Larsen ice shelf area.

The main scientific questions of the project are:

  • How large is the contribution of coastal polynyas in the Weddell Sea to the deep/bottom water formation?
  • How is the polynya formation related to the development of cyclones and mesocyclones? What are the feedbacks?
  • What is the role of katabatic and barrier winds to the polynya formation near the Antarctic Peninsula?
  • How does the disintegration of Larsen A and B ice shelves affect bottom water formation and water mass properties on the western Weddell continental shelf?
  • What is the benefit using high-resolution atmospheric forcing for sea-ice modelling compared to forcing on the scale of re-analyses?

The main objectives of the project are:

  • Case studies of polynya formation processes using the coupled COSMO-FESOM system
  • Case studies of mesocyclones, katabatic wind and barrier wind events and the investigation of their interaction with coastal polynyas
  • A model-based mesocyclone statistics for a whole winter period including advanced cyclone tracking algorithms Investigations of the effects of increased horizontal resolution in the atmospheric forcing data
  • Quantification of the surface energy and fresh-water budget of coastal polynyas in the southern Weddell Sea and their role for convection and water mass modification for a winter period
Fig. 1: COSMO ~15 km and ~5 km model domain (red box) for the Weddell Sea Region
Fig. 2: FESOM mesh with ~2.5° horizontal resolution and up to ~3 km at the coastlines of the Weddell Sea
Figs. 3: MODIS infrared imageries of the 2nd September of 2008, showing a polynya opening in the south-eastern Weddell Sea. Dark colors indicate warm brightness temperatures (legend in K)
Figs. 4: MODIS infrared imageries of the 3rd September of 2008, showing a polynya opening in the south-eastern Weddell Sea. Dark colors indicate warm brightness temperatures (legend in K)