DISTRIBUTION OF CHAETOCEROS RESTING SPORES IN MODERN PERI-ANTARCTIC SEDIMENTS

One hundred and sixty-five surface sediment samples from the Southern Ocean were examined for distribution and relative abundance of Chaetoc eros resting spores. The contribution of resting spores to the total d iatom assemblage ranges from 0% in the Subantarctic Zone to 95% in the Antarctic Peninsula sector. On the basis of both absolute and relativ e abundances four 'biogeographic' zones are distinguished: (1) the Ant arctic Peninsula sector, (2) the Embayment Systems (Ross Sea and Wedde ll Sea), (3) the Continental Shelf zone (water depth <2000 m) and (4) the Deep Ocean (water depth >2000 m). Chaetoceros resting spores abund ance reaches up to 900 x 10(6) valves/g of dry sediment in the Gerlach e Strait, southwest of the Antarctic Peninsula. The hydrology of this region is characterized by an intense stratification of the water colu mn due to sea-ice meltwater inputs, continental glacial runoffs and th ermal warming of the surface water layer. The availability of nutrient s, the lack of vertical mixing in those surface waters having low sali nity (<30 parts per mil) and relatively high temperature (>2.4 degrees C) is thought to be the main pre-condition for development of large C haetoceros species blooms. We propose that increased relative abundanc es of Chaetoceros resting spores in fossil diatom assemblages from the Southern Ocean can therefore be used as tracers of water-column strat ification due to glacial melt water.