AV俱乐部

Two hundred and fifty grab samples from the continental margin off Nova Scotia were examined for total (live+dead) foraminiferal content. One hundred and twenty species were recognised, seventy five of which occur with an abundance greater than 3% in any one sample. Q-Mode factor analysis of the raw abundance data (total population) determined 8 shelf and 4 slope factor assemblages, accounting for 87.5% and 77% of the original raw data respectively. Comparison of the live data with the factor assemblages enabled the detection of anomalous assemblages which are un-representative in respect to present day environments.

In the north east of the study area (around Misaine, Canso and Banquereau) an exclusively agglutinated assemblage dominated by Adercotryma glomerata occupies both banks and basins. In the LaHave and Emerald Basins of the central shelf, a predominantly calcareous assemblage occurs with maximum amounts of Globobulimina auriculata and Nonionellina labradorica. Transitional between these two shelf assemblages is an agglutinating assemblage dominated by Saccammina antlantica. Consistently present along the shelf edge is a Trifarina angulosa assemblage. Present in Chedabucto and Gaberous bays and in a few samples near Sable Island is an agglutinating Eggerella advena assemblage. A relict and in some areas a transport affected assemblage is recognised in the south western approaches to Emerald Basin on the Scotian Gulf; this is dominated by Elphidium escavatum. Occupying the hard, rough bedrock, and sandy/gravelly areas of the inner shelf and outer bank regions is a Cibicides lobatulus assemblage.

Four assemblages lie seaward of the shelf break. An upper slope assemblage is dominated by Bulimina exilis, with a local variation dominated by Trifarina occidentalis. A lower slope assemblage is dominated by Uvigerina peregrina. Also present in slope regions is another Elphidium excavatum assemblage which is thought to be the down slope equivalent of the shelf assemblage.

The statistical relationship of these defined assemblages to various aspects of the marine environment (depth, temperature, salinity, percent gravel, sand and mud) were investigated through multiple regression techniques. This indicates that the present foraminiferal distribution patterns off Nova Scotia are mainly a response to the prevailing hydrography. The Adercotryma glomerata assemblage is influenced by the presence of cold, less than normal salinity waters of arctic, Labrador current origin. The central basin assemblage (G. auriculata) is related to warmer more saline waters of slope origin. The transition between these two bottom waters is marked by the Saccammina atlantica assemblage. The primary influence of the hydrography on assemblage distribution patterns on the shelf off Nova Scotia is probably related to calcium carbonate availability which is a function of temperature, salinity, and carbon dioxide content within each water type. Preferred substrate character is found to determine the occurrence of the Cibicides lobatulus assemblage.

Diversity trends within the study area were examined (S,H(s),x,E). Each index used produced similar patterns which indicate relationships to hydrography and environmental stability.

Implications of the present study for further work on Pleistocene to Recent climatic changes are discussed with reference to a piston core from Canso Basin. On the basis of this study the down core changes in foraminiferal populations indicate several distinct variations in temperature and salinity since the last glaciation; these variations are probably a result of the varying degree of influence that Labrador derived waters have had in this area and is in turn a function of changing ice volumes to the north.

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Supervisor:聽 Franco Medioli