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JPR Advance Access published online on September 13, 2006
Journal of Plankton Research, doi:10.1093/plankt/fbl045
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© The Author 2006. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Received February 22, 2006
Accepted August 31, 2006

Article

Distribution of spring phytoplankton (mainly diatoms) in the upper 50 m of the Southwestern Atlantic Ocean (30° to 61°S)

Héctor F. Olguín 1 *, Demetrio Boltovskoy 2, Carina B. Lange 3, and Frederico Brandini 4

1 Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, C1428EHA-Buenos Aires, Argentina; Museo Argentino de Ciencias Naturales, A. Gallardo 470, C1405DJR-Buenos Aires, Argentina
2 Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, C1428EHA-Buenos Aires, Argentina; Museo Argentino de Ciencias Naturales, A. Gallardo 470, C1405DJR-Buenos Aires, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina
3 Departamento de Oceanografía & Centro de Investigación Oceanográfica en el Pacífico Sur-Oriental (FONDAP-COPAS), Universidad de Concepción, Casilla 160-C-Concepción, Chile
4 Centro de Estudos do Mar, Universidade Federal do Paraná, Av. Beira Mar s/n, Pontal do Sul, PR 83255-000, Brazil

* To whom correspondence should be addressed.
Héctor F. Olguín, E-mail: holguin{at}ege.fcen.uba.ar


  Abstract

This is the first study on diatom spatial patterns in relation to major oceanographic features along a mega-scale transect in the Southwestern Atlantic Ocean, and provides a comparison with diatom distribution in surface sediments. Absolute abundances of diatoms, silicoflagellates and dinoflagellates (>10 µm fraction) were assessed in 80 bottle samples from 5-50 m, retrieved in November 1993 at 20 stations (30°-61°S) along 53°W. Siliceous phytoplankton were scarce in the northern half of the transect and south of 57°S (100-150 cells L-1), with a strong peak in the vicinity of the Polar Front (ca. 200,000 cells L-1), whereas dinoflagellates were more abundant at the northern stations (up to 24,000 cells L-1). South of 50°S phytoplanktonic cell densities were loosely (but significantly, r=0.54, P<0.01) associated with chlorophyll a, whereas north of this latitude this relationship disappeared (r=0.018, P>0.1). In total, 191 diatoms and 4 silicoflagellates were recorded. Changes in diatom assemblage compositions along the transect allowed identification of five discrete areas: Subtropical (29°S), Northern Transitional (34-41°S), Southern Transitional (43-48°S), Subantarctic (49-54°S), and Antarctic (55-59°S), each characterized by a set of typical species. Diversity changed little with latitude but numbers of species were higher north of 40°S. Comparison of diatom assemblage makeup in the plankton and in the surface sediments shows very strong disagreements whereby cold water species are very significantly over-represented in the sedimentary record, suggesting enhanced preservation and strong subsurface equatorward advection of the cold-water taxa.

Communicating Editor: KJ Flynn


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