Global thermohaline circulation

The possibility of future shut-down of convection in the North Atlantic Ocean, and a consequent reduction in the strength of the Gulf Stream, with associated cooling of western Europe has been much in the news in recent years. While the prospects for this occurring remain limited it is clear that the ocean circulation has changed significantly, and rapidly, at times in the past. I use models to explore the regimes under which change can occur, and the consequences of such change.

Highlights of this work include

  • Discovery of the impact of opening of the sea connection between the Arctic and Atlantic through the Canadian Seaways. Without the freshening influence of Arctic waters on the Labrador Sea the latter becomes much saltier, and more subject to convection, allowing more northward heat transport. An open connection through the Canadian Archipelago therefore acts as a negative feedback on the North Atlantic overturning circulation.
  • Discovery that the location of past injection of massive freshwater or iceberg fluxes to the glacial ocean leads to significantly different climate impact. From this work, it has become clear that a massive iceberg release about 30,000 years ago, known as H3, probably occurred in the European Arctic, rather than from North America, as previously believed.
  • Discovery that variation in sea level over the Quaternary has led to dramatic changes in the thermohaline circulation, due to enhancement of tidal mixing during low sea level stands.

This work has been carried out with Martin Wadley, Richard Levine of the Meteorological Office, and Mattias and Clare Green from Ocean Sciences at Bangor University, Wales, and funded by NERC and the Leverhulme Trust.

Global circulation model grid