D04: Interaction of meridional ocean heat transports and regional processes in the Arctic Ocean
Atlantic overturning and gyre circulation carry heat from low and mid-latitudes to the Arctic. A part of this heat is released to the sea ice and the atmosphere. At present strong oceanic stratification still inhibits efficient heat release in most parts of the Arctic. Recent observations indicate, however, that in some regions major changes are taking place in the upper layers of the Arctic Ocean. In particular, the cold halocline layer, which separates warm Atlantic water from the upper ocean mixed layer, appears to be affected by Arctic climate change. On the one hand, warming in the shelf regions was found to affect the formation of the cold halocline. On the other hand, warm Atlantic water was suggested to destabilise the cold halocline from below.
This project aims to better understand the oceanic processes that shape the response of the Arctic climate system, especially the ocean-atmosphere heat fluxes, to greenhouse gas warming using regional and global modelling in addition to analysing existing results from global climate models. A focus will be the Barents Sea, where strong surface heat fluxes foster low sea level pressure and shallowdepth export of water and sea ice. The export is compensated for by a corresponding inflow of Atlantic water, which closes a positive feedback loop. Ocean stratification and dense water formation are affected and, as a consequence, these processes can contribute to further Arctic warming.
An initial analysis of model results from the Coupled Model Intercomparison Project Phase 5 (CMIP5) suggests that global climate models simulate an increased breakdown frequency of the cold halocline in a future climate change scenario and that these breakdowns inluence the surface ocean temperature.
Additional work is proposed here to further investigate the potential importance of an increased cold halocline breakdown frequency for Arctic climate change and to evaluate simulations of cold halocline breakdowns in climate models. Earlier experiments with a coupled ocean-sea ice model (North Atlantic Arctic Ocean Sea Ice Model, NAOSIM) show a destabilisation of the halocline due to increased freezing in polynyas of Arctic shelf seas. We are planning to combine global and regional modelling with observations to better quantify and understand the relevant processes.
Regional feedback processes between atmosphere and sea ice–ocean associated with leads and cyclones are critical mechanisms for Arctic amplification.
Specific questions we want to answer:
- What is the influence of a cyclonic wind anomaly over the Barents Sea?
- Under what conditions do cold halocline breakdowns occur and how important are they for Arctic surface warming?
Role within (AC)³
Prof. Dr. Rüdiger Gerdes
Alfred-Wegener-Institute Helmholtz Center for Polar and Marine Research (AWI)