Biogeographic patterns of planktonic diatoms in the south western and Antarctic sectors of the Atlantic Ocean

OLGUÍN SALINAS, H.F..; . ALDER, V.A.; .BOLTOVSKOY, D..

BUENOS AIRES, ARGENTINA

Simposio; 4th OPEN SCIENCE CONFERENCE-SCAR; 2010

Scientific Committee on Antarctic Research y DNA_IAA Argentina

The study describes the biogeographic pattern of diatom species over a broad, hydrographically heterogeneous spatial scale (29-76º S). The analysis was based on 117phytoplankton samples collected during four cruises covering the Brazil-Malvinas Confluence Zone (BMCZ), sub-antarctic (Argentine shelf and adjacent oceanic zone), antarctic waters (Antarctic Peninsula and Weddell Sea), and the Drake Passage. The multivariate analyses performed on the 252 diatom species identified and the Nitzschia bicapitata species complex, revealed the presence of two main groups of stations. One of these groups was found to be clearly oceanic and spatially superimposed with the location of the BMCZ (35-50º S). It was characterized by a high (60 %) contribution of subtropical taxa being transported by the Brazil Current, and its southern limit was represented by the Subantarctic Front (50º S, 55-56º W). The second major group encompassed the rest of the sites and denoted a gradual latitudinal floristic change jointly with the prevalence of cold water species due to expatriation processes from Antarctic to subantarctic shelf waters. Three subzones were identified within this large main group: 1) Argentine shelf waters, with 31, 30 and 16 % contributions of cold, coastal and subtropical diatom species, respectively; b) waters between the Subantarctic Front and the Southern Front of the Antarctic Circumpolar Current, which showed stability during the four cruises probably as a result of the Antarctic Circumpolar Current circulation; 3) the Weddell Sea and waters off Antarctic Peninsula, which are subject to the seasonal dynamics of the sea-ice coverage. .