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

• Published in: Journal of Plankton Research
• Main Authors: Olguín, Héctor F., Boltovskoy, Demetrio, Lange, Carina B., Brandini, Frederico
• Format: Text
• Language: English
• Published: Oxford University Press 2006
• Subjects: Article; Antarctic; Strong Peak; Antarc*
• Online Access: http://plankt.oxfordjournals.org/cgi/content/short/fbl045v1; https://doi.org/10.1093/plankt/fbl045

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.