[OANNES Foro] Eddy-Driven Stratification Initiates North Atlantic Spring Phytoplankton Blooms

[Mario Cabrejos]

Science 6 July 2012: 
Vol. 337 no. 6090 pp. 46-47 
DOI: 10.1126/science.1223881 

The Seasonal Smorgasbord of the Seas
Adrian Martin National Oceanography Centre, Southampton SO14 3ZH, UK. E-mail: adrian.martin en noc.ac.uk
Summary
The spring bloom of phytoplankton-an annual population explosion that propagates poleward across much of the open ocean and spills across the continental shelves-is a seasonal bounty for the marine ecosystem. As it wanes, its annual legacy is a flux of carbon out of the atmosphere as the organic material, containing newly fixed carbon, sinks. On page 54 of this issue, Mahadevan et al. (1) suggest that the bloom can be triggered by instabilities in surface currents that trap phytoplankton near the sunlit surface. In another study, Teeling et al. (2) recently suggested that the bloom itself may help to explain the "paradox of the plankton" (3); how can a seemingly homogeneous ocean sustain thousands of species? 

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Science 6 July 2012: 
Vol. 337 no. 6090 pp. 54-58 
DOI: 10.1126/science.1218740 

Eddy-Driven Stratification Initiates North Atlantic Spring Phytoplankton Blooms
Amala Mahadevan1, Eric D'Asaro2,*, Craig Lee2, Mary Jane Perry3 1Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA. 2Applied Physics Laboratory, University of Washington, Seattle, WA 98105, USA. 3Darling Marine Center, University of Maine, Walpole, ME 04573, USA. E-mail: dasaro en apl.washington.edu
Abstract
Springtime phytoplankton blooms photosynthetically fix carbon and export it from the surface ocean at globally important rates. These blooms are triggered by increased light exposure of the phytoplankton due to both seasonal light increase and the development of a near-surface vertical density gradient (stratification) that inhibits vertical mixing of the phytoplankton. Classically and in current climate models, that stratification is ascribed to a springtime warming of the sea surface. Here, using observations from the subpolar North Atlantic and a three-dimensional biophysical model, we show that the initial stratification and resulting bloom are instead caused by eddy-driven slumping of the basin-scale north-south density gradient, resulting in a patchy bloom beginning 20 to 30 days earlier than would occur by warming. 



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