Multi-decadal variability of phytoplankton and related physical forcing in the North Atlantic Ocean

• Main Authors: Martinez, Elodie, Antoine, David, Raitsos, Dionysios
• Other Authors: OPLC, Laboratoire d'océanographie de Villefranche (LOV), Observatoire océanologique de Villefranche-sur-mer (OOVM), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Observatoire océanologique de Villefranche-sur-mer (OOVM), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Red Sea Research Centre (RSRC), King Abdullah University of Science and Technology Saudi Arabia (KAUST), European Project:
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2011
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; North Atlantic
• Online Access: https://hal.science/hal-00749230

International audience The spring, bloom is a renowned feature of many seasonal seas in the global ocean. Perhaps most famous of all is the spring bloom that occurs at middle and high latitudes of the North Atlantic. Since the 1950's the Sverdurp's theory prevails to explain the spring bloom initiation in the North Atlantic subpolar region. Photosynthesis is light limited during winter, so the bloom occurs in spring when the mixed layer shoals sufficiently to allow phytoplankton to remain within the sunlit region and enable net growth. Therefore an increase of stratification, due to global warming for instance, would lead to a strengthened bloom through phytoplankton spending more time in the euphotic zone. In this context, a stepwise increase in biomass has been reported in the mid-1980s correlated with the sea surface temperature (SST), an indicator of stratification, and the Atlantic Multidecadal Oscillation in the North Sea and Northeastern Atlantic. Chlorophyll-a (Chl), a measure of phytoplankton biomass, derived from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) from 1997-2002 was combined with in situ measurements of the Phytoplankton Color Index (PCI) collected by the Continuous Plankton Recorder survey since 1946. Recently, an increase of Chl has also been observed in satellite ocean color observations of the northeastern Atlantic (30°-50°N and 40°-0°W), from the 1980s to the 2000s (Coastal Zone Color Scanner ― CZCS, and SeaWiFS missions respectively) in parallel to an increase of SST. However, this increase of SST appeared to be related with a deepening of the Mixed Layer Depth (MLD) in this region rather than an increase of stratification. This result gives substance to the "dilution-recoupling hypothesis". The Dilution-Recoupling hypothesis suggests, under climate warming conditions, that weaken of winter mixing may lead to decreased net phytoplankton growth rates and vernal biomass (i.e., an opposite conclusion from one based on the Sverdrup's theory). However, because these contradictory ...