WHY ARE THERE NO POST-PALEOGENE DINOFLAGELLATE CYSTS IN THE SOUTHERN-OCEAN

Dinoflagellates are an important component of Antarctic coastal and se a ice communities but comprise only a relatively minor component of So uthern Ocean oceanic phytoplankton assemblages. However, living specie s capable of producing geologically-preservable cysts have been report ed only rarely from Antarctic waters and no Quaternary cysts have ever been recovered from Southern Ocean surface sediments. The youngest fo ssil dinoflagellate cysts to occur anywhere in the Antarctic - Souther n Ocean region are Oligocene and these predate the period of rapid sea -floor spreading and major continental glaciation. This geographic and thermal isolation has prevented the poleward migration of cyst-produc ing dinoflagellates, which require a continental shelf or slope pathwa y to migrate. The loss of shallow water shelves from the Antarctic con tinent, due to the isostatic effects of ice accumulation, must have co ntributed to the local extinction of the Paleogene cyst-forming groups .