Icebergs

Iceberg debris has been used as a tracer for past ocean circulations in the Quaternary since the mid-1970s. However, until the mid-1990s there was little attempt to integrate this information into climate models. I developed a dynamic and thermodynamic model of iceberg movement that can be used in a coupled mode within a larger-scale climate model, or run in a non-feedback mode, to give a dynamical view of how ice-rafted debris distributions came about. This model has been tested in both hemispheres of the modern ocean and used in glacial mode.

Highlights of the work include

  • Discovery that iceberg meltwater may contribute as much as the precipitation budget to freshwater inputs to significant regions of the Southern Ocean. As convection around Antarctica is critically dependent on the salinity of waters following sea-ice formation the iceberg signal acts as a negative feedback on deep water formation.
  • Use of the model to assist interpretation of glacial iceberg-rafted debris signals. Using various palaeoceanographic indicators ranging from carbon isotopes to magnetic strengths of iron fragments in ocean core sediments the iceberg model has been used with various ocean model circulations to narrow down the characteristics of the glacial ocean circulation state. The most compatible ocean state is one with most deep water formation in the Southern Ocean.
  • Discovery of the relationship between large scale iceberg releases Modelling the twentieth century iceberg flux from Greenland, which, from its agreement with observed and marine core data from either side of Greenland, suggests that the dominant calving location of icebergs has shifted north during the century.

Remote sensing has also been used to help validate the iceberg trajectory model, and to move towards an iceberg calving flux for Antarctica, and a sea-ice hazard tool for the Arctic. This work has been carried out in collaboration with Keith Nicholls of the British Antarctic Survey, Barbara Maher of Lancaster University, Rupert Gladstone, Sarah Watkins, Tiago Silva, Richard Levine, Jen King, Clare and Mattias Green from Bangor University, Wales. The work has been funded by NERC and Kongsberg Satellite Services.

Southern Ocean freshwater input