The Ice-Covered Ocean: the Final Challenge for Climate Models?

The polar regions are most sensitive in responding to climate change, and host key processes driving that change. Yet they are the regions where least is known, in part because of the historical paucity of observations. Climate models also find the high latitudes particularly challenging, where length-scales of ocean processes are much smaller than at low latitudes. Modelling the interaction of ocean and cryosphere is an active area of research. This project brings together new observations in the Southern Ocean and around Antarctica with the latest developments in the UK Met Office's IPCC-class climate model HadGEM. It will address how well the IPCC models perform against ocean measurements, and assess the climate impacts of the new ice shelf model being implemented in HadGEM. Melting of the Antarctic ice sheet may be accelerated by interaction of the relatively warm ocean with floating ice shelves, contributing to sea level rise. Both sea ice melt and ice shelf melt cause a freshening on the continental shelf. Subsequent sea ice formation causes an increase in salinity and hence density. These water mass transformation processes create the dense, cold outflow that becomes Antarctic Bottom Water. These processes are poorly represented even in eddy-resolving ocean-ice models; in climate models these processes are sub-gridscale and must be parameterised. The project has two aspects. First, the student will study simulations from the available IPCC climate models of the Southern Ocean and Antarctic shelf, a poorly validated region. The student will quantify how well the water mass properties are represented, and assess where and how dense water forms in the models and observational fields. Observational data will include the meridional hydrographic sections and year-long moorings of SASSI, an International Polar Year project with an intensive field phase (2008-2010) on the Antarctic continental shelf and slope. This will enable assessing circumpolar and seasonal water mass characteristics. Further north, we will exploit the coverage of the upper 2000 m of the Southern Ocean from Argo floats. The second aspect will involve the student in appraisal of a new development of HadGEM. An ice shelf model is being included in HadGEM, as part of a broader model development to couple interactive ice sheets to the oceans and atmosphere. This depends on well validated parameterisations to transport warm mid-depth waters to the base of the ice shelves, so the validation of model water masses will feed directly into this aspect. The student will assess the processes of interaction of ocean with ice shelves, both the upwelling of warm mid-depth waters onto the continental shelf and impact of ice shelf melt water on the ocean. This is a rare opportunity for a student to be involved in assessing a substantial upgrade to one of the major climate models, and whether the consequent ocean and atmosphere components are 'improved'. The student will be trained in handling large datasets; computer programming; numerical modelling and ocean/climate dynamics. They will participate in a Southern Ocean research cruise to learn observational oceanographic techniques and data quality control. They will benefit from embedding in the synthesis phase of the international SASSI project, including attending workshops and conference sessions. All UEA PhD students attend transferable skills training. This project benefits the Met Office through the verification of climate model developments with new observations. The student gains by working closely with those who are developing and running the next generation of IPCC climate models.