Article (Scientific journals)
Factors controlling the distribution of diatoms and Phaeocystis in the Ross Sea
Goffart, Anne; Catalano, Guilio; Hecq, Jean-Henri
2000In Journal of Marine Systems, 27, p. 161-175
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Keywords :
Antarctica; Ross Sea; Phytoplankton; Diatoms; Phaeocystis; stratification
Abstract :
[en] The spatial and temporal distributions of phytoplankton pigments were investigated in the western and south central Ross Sea during austral spring 1994 and summer 1990. Large gradients in biomass and phytoplankton community composition were observed both in the east-west and south-north directions, in relation to differences in water column structure and stability, which themselves depend on the processes of ice retreat within the different areas. Important are melting in the western Ross Sea, which induces strong stratification, and ice breakup and wind stress in the south central Ross Sea, which result in deep mixing and weakly stratified waters. In the western Ross Sea, the highest chl a concentrations observed in this study (129 - 358 mg m-2 in the upper 100 m) were tightly coupled to the stratified region of meltwater influence and were dominated by diatoms, as indicated by elevated fucoxanthin concentrations (89 - 239 mg m-2 in the upper 100 m). In the diatom bloom area, high levels of phaeophorbides a (maximum value of 192 mg . m-2 in the upper 100 m) indicated that the dominant grazers, identified as Limacina helecina and copepods (Hecq et al., 1992), transferred a sustained part of the diatom production to the herbivore trophic level. Synthesis of our data with published information suggests that the diatom bloom we observed in the western Ross Sea was dominated by the species Fragilariopsis curta, and occurs annually off the coast of Victoria Land from 72°30'S to 77°S within 100 to 250 km from the coastal ice edge. It is assumed to persist on the order of 2.5 - 3 months during summer. In the south central Ross Sea, which was characterized by a poorly or unstratified water column, moderate chl a concentrations (55 - 186 mg m-2 in the upper 100 m) were found in the polynya and in the ice edge area in early spring. 19'-hexanoyloxyfucoxanthin, a biomarker for Phaeocystis, was the major contributor to the total carotenoid abundance (29 - 132 mg m-2 in the upper 100 m), corroborating the hypothesis that Phaeocystis are well adapted to develop in a relatively mixed water column. At the northern limit of the polynya, a quite narrow (c. a. 30 km) diatom bloom (31 - 67 mg fucoxanthin m-2 in the upper 100 m) overlapped with the Phaeocystis bloom in the slightly stratified marginal ice zone. This was an area of increased grazing pressure by various types of herbivorous zooplankton, among which very large amounts of krill were observed.
Research center :
MARE - Centre Interfacultaire de Recherches en Océanologie - ULiège
Disciplines :
Aquatic sciences & oceanology
Author, co-author :
Goffart, Anne  ;  Université de Liège - ULiège > Département des sciences et gestion de l'environnement > Océanologie
Catalano, Guilio;  CNR, Italy > Istituto Talassografico di Trieste
Hecq, Jean-Henri ;  Université de Liège - ULiège > Département des sciences et gestion de l'environnement > Océanologie
Language :
English
Title :
Factors controlling the distribution of diatoms and Phaeocystis in the Ross Sea
Publication date :
2000
Journal title :
Journal of Marine Systems
ISSN :
0924-7963
Publisher :
Elsevier Science, Amsterdam, Netherlands
Volume :
27
Pages :
161-175
Peer reviewed :
Peer Reviewed verified by ORBi
Name of the research project :
Antar A4/DD/B21
Funders :
BELSPO - SPP Politique scientifique - Service Public Fédéral de Programmation Politique scientifique
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