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Spatial and seasonal-variations of diatom assemblages off the argentinian coast (south western atlantic)

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Spatial and seasonal variations of diatom assemblages off the Argentinian coast (South Western Atlantic) OCEANOLOGICA ACTA 1985- VOL. 8 - W 3 ~ -----~- Spatial and seasonal variations of diatom assemblages Phytoplankton Dia toms Distribution South Atlantic Phytoplancton Diatomées Distribution Atlantique Sud off the Argentinian coast (South Western Atlantic) ABSTRACT RÉSUMÉ Karin B. LANGE CONICET-Museo Argentino de Ciencias Naturales «B. Rivadavia>>. Angel Gallardo 470, 1405 Buenos Aires, Argentina. Present address: UCSD, Scripps Institution of Oceanography, Marine Life Research Group, A-027, La Jolla, California 92093, USA. Received 21/1/85, in revised form 20/3/85, accepted 28/3/85. Forty-eight surface netplankton samples were collected between April and December 1981 along a transect off the Argentine coast (38°12'S 57° 15'W to 39°59'S 54° ll'W). In total 158 diatom taxa were recorded, including cosmopolitan (55% of entire inventory), subtropical (18%) and subantarctic (16.5%) forms of neritic and/or oceanic distribution. Two different diatom assemblages and one transitional group were identi- fied along the area transected: 1) A coastal assemblage, mainly represented by warm- water neritic taxa, was related to high water temperatures ( > 10° C) and relatively sharp monthly salinity changes (S x 103: 33.44 to 34.03). This assemblage occupied the area between the coast and ca. 57° W. The complete absence of cold-water diatoms at the westernmost station 1 indicates that this zone is fed from the subtropical Brazil Current throughout the year. 2) An outershelf-oceanic assemblage, comprised of a mixed flora, was dominated by typically antarcticjsubantarctic forms in winter and spring. It was associated with the low temperatures (usually < 9°) and moderate salinities (S x 103 > 33.64) of the Malvinas Current. This complex characterized the area defined by ca. 56° W and 54° ll'W (our easternmost station). 3) A transitional, midshelf assemblage w

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