Stratiphyt - Changes in vertical stratification and its impacts on phytoplankton communities

Abstract

Global warming will change physical, chemical and biological processes in the oceans. Ocean-climate model predict that heating of the surface layer may yield a stronger vertical stratification, which starts earlier in spring and lasts longer in autumn. This results in suppressed upward mixing of nutrients from the deep ocean. Changes in stratification will have major effects on the production and species composition of phytoplankton (unicellular algae). This will subsequently impact grazing, virally induced mortality and sedimentation rates, with cascading effects on ecosystem functioning and biogeochemical fluxes. Little is known, however, of the exact implications of global warming for these fundamental processes. As part of the Dutch ZKO (Sea, Coast and Ocean) competitive funding program we will investigate how changes in vertical stratification affect phytoplankton communities along a north-south gradient in the Atlantic Ocean. Six institutes and seven PIs are involved in the STRATIPHYT project. The project runs for 4 years (2009-2013). Our study is based on oceanographic cruises from the Canaries to Iceland, advanced models of hydrodynamics and plankton growth, and detailed laboratory experiments with representative phytoplankton species. We have chosen for the Northeast Atlantic Ocean, because it is a key area in global ocean circulation, a large sink for atmospheric CO2, and a major determinant of the climate in Western Europe. Furthermore, the Atlantic Ocean offers a gradient from weak seasonal stratification in the North to strong permanent stratification in the (sub)tropics. This gradient offers ideal opportunities for the comparative study of different stratification regimes. Our integrated approach of physical, chemical, and biological processes, by a new research team, will enable a better understanding of the implications of global warming for plankton growth in the North Atlantic Ocean.