Mixing it, Southern Ocean style

Sea water being churned in the ocean off Antarctica may be having a greater effect on global patterns of ocean movement than previously thought, according to new research reported in this week’s edition of the international journal Science (9 January 2004).

The research, lead by scientists from the University of East Anglia (UEA), shows that “remarkably intense and widespread” mixing of water in the Southern Ocean occurs over large regions where the ocean bed is rough.

The main author of the report, Dr Alberto Naveira Garabato, says: “The turbulent mixing that we observed in the Southern Ocean acts as a blender of cold deep waters with warmer surface waters. In doing so, it contributes to driving the global ocean circulation and influences our climate.”

One of the biggest puzzles for oceanographers in recent decades has been in trying to identify where and how the cold water that sinks to the deep ocean in the North Atlantic and near Antarctica warms up through mixing and returns to the surface. Understanding more about the processes of ocean mixing will help improve the accuracy of global climate models.

Dr Naveira Garabato and colleagues used a new technique to estimate ocean mixing, looking at the waves within the ocean between water of different densities and at different depths. When these internal waves ‘break’ they cause turbulence and mixing.

The scientists conclude that their study raises a number of questions about the ‘potentially key contribution of turbulent mixing in the Southern Ocean’ to driving global ocean circulation and call for ‘a large dedicated observational and modelling effort’ to help answer those questions.