Distribution and ecology of benthic foraminifera in McMurdo sound, antarctica

Abstract

Foraminifera from modern sediments in McMurdo Sound have been studied to provide a basis for interpreting fossil assemblages there. The sound is 50 km across, more than 900 m deep, and ice-covered for at least nine months of the year. The salinity and temperature of the bottom water are nearly constant (33.96–34.99%, and −1.95°C − −1.4°C). Sea floor sediment is mainly fine sand and mud with a little ice-rafted gravel. Nearly 40,000 specimens of foraminifers (2334 living and 36,875 dead) were identified from 28 samples collected by gravity corer and grab from sites varying in depth between 79 and 856 m. Three present day assemblages can be recognised: 1. (1) Shallow open water assemblage (SWA) from 110 to 560 m, found in shallower areas of the open sound, dominated by calcareous species; 2. (2) Deep open water assemblage (DWA) from 620 to 856 m, found in deeper areas of central McMurdo Sound; dominated by agglutinated species; and 3. (3) Harbour assemblages (HA) from 79 to 796 m in the enclosed basins and harbours of the area, dominated by agglutinates species. The composition of the assemblages is controlled chiefly by the calcium carbonate compensaion depth (CCD). Calcareous species are abundant and varied (84 calcareous species) in the SWA above 620 m, but are almost absent from the DWA. The dominance of agglutinated foraminifera in the HA indicates a shallower CCD (about 230 m) in restricted coastal settings. Comparison of McMurdo Sound assemblages to those from other areas of the Antarctic, the Arctic and the deep-ocean indicates that there are grpss similarities in the over-all faunas, but actual species in commin range from 6 to 41% of the McMurdo Sound total assemblage (124 species). Death assemblages have a similar species diversity to corresponding life assemblages from 620 (the CCD) to 420 m, where death assembalges are representative of them, except for open water assemblages from 620 (the CCD) to 420 m, where death assemblages are depleted in calcareous taxa. The diversity of the agglutinated component of each assemblage remains nearly constant in all habitats and at all water depths.