Role of microbial and phytoplanktonic communities in the control of seawater viscosity off West Antarctica (30-80°W).

Laurent Seuront (1) , Sc Leterme , Js Seymour , Jg. Mitchell , D. Ashcroft , W. Noble , Pg Thompson , At Davidson , R. van den Enden , Fj Scott , Sw Wright , C. Chapperon , N. Cribb

1 LOG - Laboratoire d’Océanologie et de Géosciences (LOG) - UMR 8187

Despitethelong-standingbeliefthatseawaterviscosityisdrivenbytemperatureandsalinity, biologicallyincreasedseawaterviscosityhasrepeatedlybeenreportedinrelationtophytoplankton exudatesinshallow,productivecoastalwaters.Here,seawaterviscositywasinvestigatedinrelationto microbialandphytoplanktoniccommunitiesoffthecoastofEastAntarcticaalonglatitudinaltransects located between301E and801E insub-surfacewatersandatthedeepchlorophyllmaximum(DCM).The physicalcomponentofseawaterviscosityobservedalongeachtransectsrangedfrom1.80to1.95cP, while theactualseawaterviscosityrangedfrom1.85to3.69cP.Thisresultedinbiologicallyincreased seawaterviscosityreachingupto84.9%insub-surfacewatersand77.6%attheDCM.Significantpositive correlationswerefoundbetweenelevatedseawaterviscosityand(i)bacterialabundanceinsub-surface watersand(ii)chlorophyll a concentrationandtheabundanceofflowcytometrically-definedauto-and heterotrophicprotistsattheDCM.Amongthe12groupsand108speciesofprotistsidentifiedunder light microscopy,dinoflagellatesandmorespecifically Alexandriumtamarense and Prorocentrum sp. were themaincontributorstothepatternsobservedforelevatedseawaterviscosity.Ourobservations, which generalisedthelinkpreviouslyidentifiedbetweenseawaterviscosityandphytoplankton compositionandstandingstocktotheSouthernOcean,arethefirstdemonstrationofincreasesin seawaterviscositylinkedtomarinebacterialcommunities,andsuggestthatthemicrobially-increased viscositymightquantitativelybeatleastasimportantastheonerelatedtophytoplanktonsecretion. & 2009 ElsevierLtd.Allrightsreserved

Domaines: Océanographie

Laurent Seuront, Sc Leterme, Js Seymour, Jg. Mitchell, D. Ashcroft, et al.. Role of microbial and phytoplanktonic communities in the control of seawater viscosity off West Antarctica (30-80°W).. Deep Sea Research, 2010, 57, pp.877-886. ⟨10.1016/j.dsr2.2008.09.018⟩. ⟨hal-00767876⟩