.gif)
Victoria University Antarctic Research Expedition Science and Logistics Reports 1984-85: VUWAE 29
Distribution of modern benthic foraminifera of McMurdo Sound, Antarctica - B.L. Ward (PhD)
Distribution of modern benthic foraminifera of McMurdo Sound, Antarctica - B.L. Ward (PhD).
Abstract:
This thesis presents the results of a study of benthic foraminifera from McMurdo Sound, Antarctica. The sound is 50 km across and more than 900 m deep, and is ice-covered for at least 9 months of the year. However, salinity and temperature of the bottom waters are constant (35%. and −1.8°c). Sea floor sediment is mainly fine sand and mud with a little ice-rafted gravel.
page 65
| 1. | Shallow open water assemblage (SWA): Trochammina glabra, Cribrostomoides jeffreysii, Trifarina earlandi, Ehrenbergina glabra, FursenKoina earlandi and Globocassidulina crassa. |
| 2. | Deep open water assemblage (DWA): Reophax pilulifer, Reophax subdentaliniformis, Portotrochammina antarctica, Textularia antarctica and Miliammina arenacea. |
| 3. | Harbour/enclosed basin assemblage (HA): Reophax subdentaliniformis, Portotrochammina antarctica, Textularia antarctica, Fursenkoina earlandi and Globocassidulina crassa. |
The composition of the assemblages is controlled largely by the calcium carbonate compensation depth (CCD). Calcareous species are abundant and varied (84 calcareous species) in the SWA above 620 m, but are virtually absent from the DWA, which is found in deeper water. The dominance of agglutinated foraminifera in the HA indicates an even shallower CCD (about 230 m) in restricted coastal settings.
Death assemblages have a similar species diversity to corresponding life assemblages and are reasonably respresentative of them, except for the 200 m zone above the offshore CCD, 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, even though shallow water samples include a range of calcareous species. Thus competition from calcareous species appears not to be a stress factor for agglutinated species, which are considered to have reached the limit of their evolutionary potential in these waters.