JPR Advance Access originally published online on September 13, 2006
Journal of Plankton Research 2006 28(12):1107-1128; doi:10.1093/plankt/fbl045
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Distribution of spring phytoplankton (mainly diatoms) in the upper 50 m of the Southwestern Atlantic Ocean (30–61°S)
1 Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, C1428EHA-Buenos Aires, Argentina 2 Museo Argentino de Ciencias Naturales, A. Gallardo 470, C1405DJR-Buenos Aires, Argentina 3 Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina 4 Departamento de Oceanografía & Centro de Investigación Oceanográfica en el Pacífico Sur-Oriental (FONDAP-COPAS), Universidad de Concepción, Casilla 160-C-Concepción, Chile AND 5 Centro de Estudos do Mar, Universidade Federal do Paraná, Av. Beira Mar s/n, Pontal do Sul, PR 83255-000, Brazil
* Corresponding Author: holguin{at}ege.fcen.uba.ar
Received on February 22, 2006; revised on July 10, 2006; accepted on August 31, 2006
Communicating editor: K.J. Flynn
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Abstract |
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This is the first study on diatom spatial patterns in relation to major oceanographic features along a megascale 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 to 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 in the south of 57°S (100–150 cells L–1), with a strong peak in the vicinity of the Polar Front (
200 000 cells L–1), whereas dinoflagellates were more abundant at the northern stations (up to 24 000 cells L–1). In the south of 50°S phytoplanktonic cell densities were loosely (but significantly, r = 0.54, P < 0.01) associated with chlorophyll a, whereas in the 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 in the 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.