Winter phytoplankton blooms within the
Gironde plume waters in the bay of Biscay
Clairc Labry (1) , Alain Herbland (1) , Daniel Delmas (1) ,
Pierre Laborde
(2) , Pascal Lazure
(3) , Jean-Marie Froidefond (4) ,
Anne-Marie Jégou
(3) , Benoît Sautour (2)
(1) Université du Littoral Côte d’Opale, maison de la recherche en environnement naturel,
32 avenue Foch, 62930 Wimereux, France
(2) Université de Bordeaux 1, laboratoire d’océanographie biologique,
UMR-CNRS-EPOC 5805, 2 rue du Pr Jolyet, 33120 Arcachon, France
(3) Ifremer Brest, Del/ao, BP 70, 29280 Piouzané, France
(4) Umversité de Bordeaux 1, département géologie et océanographie,
UMR-CNRS-EPOC 5805, avenue des Facultés, 33405 Talence Cedex, France
cabry@mren2.univ-littoral.fr
Abstract
Thermostratification and seasonal light increase are generally considered
as the first causcs of phytoplanktonic spring blooms in temperate waters. The objective of this study is to confirm the existence of winter
blooms, responsible for the earlv exhaustion of phosphate, within the
Gironde plume waters (SK of the bay of Biscay), anrl to understand
what mav initiatc them so early
Résumé
La thermostratification et l’augmentation saisonnière de la lumière sont
géncralement considérées commc les premières causes des blooms phytoplanctonic|ues printaniers dans les eaux tempérécs. L’objectif de cette
étude est de confirmer l’existence de blooms hivernaux dans le panache
de la Gironde (sud-est du golfe dc Gascogne), responsable d’un épuisement précoce en phosphate, et de comprendre ce qui les a initié si précocement.
Results and conclusion
Two cruises, Biomet II and Biomet III, were carried out respectively in
early winter (8-21 Januan ) and late winter 1998 (25 Fcbruaty-11 March)
to validate the h\rpothesis.
Between the two cruises nutrtent concentrations decreased, especially
phosphatc which reached very low and non-conservative values. In the
same time, Chl a increased dramatically both within plume and oceanic
waters (mean Chl a values increased from 0.5 to 1.7 µg/1). SeaWifs estimations of surface Chl a between the two cmises agree with that observation.
More than 80% of Chl a belong to microorganisms smaller than
20 gm in early winter with a great part in the size class 3-20 gm (54%).
137
Gironde plume waters in the bay of Biscay
Clairc Labry (1) , Alain Herbland (1) , Daniel Delmas (1) ,
Pierre Laborde
(2) , Pascal Lazure
(3) , Jean-Marie Froidefond (4) ,
Anne-Marie Jégou
(3) , Benoît Sautour (2)
(1) Université du Littoral Côte d’Opale, maison de la recherche en environnement naturel,
32 avenue Foch, 62930 Wimereux, France
(2) Université de Bordeaux 1, laboratoire d’océanographie biologique,
UMR-CNRS-EPOC 5805, 2 rue du Pr Jolyet, 33120 Arcachon, France
(3) Ifremer Brest, Del/ao, BP 70, 29280 Piouzané, France
(4) Umversité de Bordeaux 1, département géologie et océanographie,
UMR-CNRS-EPOC 5805, avenue des Facultés, 33405 Talence Cedex, France
cabry@mren2.univ-littoral.fr
Abstract
Thermostratification and seasonal light increase are generally considered
as the first causcs of phytoplanktonic spring blooms in temperate waters. The objective of this study is to confirm the existence of winter
blooms, responsible for the earlv exhaustion of phosphate, within the
Gironde plume waters (SK of the bay of Biscay), anrl to understand
what mav initiatc them so early
Résumé
La thermostratification et l’augmentation saisonnière de la lumière sont
géncralement considérées commc les premières causes des blooms phytoplanctonic|ues printaniers dans les eaux tempérécs. L’objectif de cette
étude est de confirmer l’existence de blooms hivernaux dans le panache
de la Gironde (sud-est du golfe dc Gascogne), responsable d’un épuisement précoce en phosphate, et de comprendre ce qui les a initié si précocement.
Results and conclusion
Two cruises, Biomet II and Biomet III, were carried out respectively in
early winter (8-21 Januan ) and late winter 1998 (25 Fcbruaty-11 March)
to validate the h\rpothesis.
Between the two cruises nutrtent concentrations decreased, especially
phosphatc which reached very low and non-conservative values. In the
same time, Chl a increased dramatically both within plume and oceanic
waters (mean Chl a values increased from 0.5 to 1.7 µg/1). SeaWifs estimations of surface Chl a between the two cmises agree with that observation.
More than 80% of Chl a belong to microorganisms smaller than
20 gm in early winter with a great part in the size class 3-20 gm (54%).
137