Effects of the marine biota on ocean physics

Cyanobacteria (blue-green algae) are assumed to become more abundant in the future due to their growth optimum at high temperatures. Since these organisms are positively buoyant they form surface mats and thereby alter the light (absorption, albedo) and mechanical (surface roughness) properties of the ocean. Changes in mixed layer dynamics and ocean circulation are therefore expected. To quantify the relative effects of the different feedback mechanisms we have conducted several model simulations. Our model results show that increased cyanobacteria concentrations cause a surface heating (by up to 2◦C) along with a subsurface cooling; this leads to enhanced stratification. The largest effects are due to altered absorption and biologically induced reduction of the wind drag; changes in the surface albedo turned out to have a rather minor impact (Sonntag and Hense 2011).

Completed project

Relevant Publications

Hense I. , H.E.M. Meier and S. Sonntag (2013): Projected climate change impact on Baltic Sea cyanobacteria. Climatic Change, doi:10.1007/s10584-013-0702-y.

Sonntag S. and I. Hense (2011): Phytoplankton behavior affects ocean mixed layer dynamics through biological-physical feedback mechanisms. Geophysical Research Letters, 38, doi:10. 1029/2011GL048205.