| Summary: | Using the relative abundance of the two silicoflagellate genera, Dictyocha and Distephanus, for paleotemperature inferences has failed in the past to yield quantitative results. One of the principle reasons this method has been unsuccessful quantitatively is that discrepancies exist as to the exact temperature range assigned to particular generic abundances. This may be attributed to: 1) differences in the techniques used to obtain the silicoflagellates used as the data base, i.e., surface sediment data vs. surface water plankton samples and 2) other environmental factors in addition to temperature may affect the relative generic abundances. This study, based on cores collected between Wilkes Land, Antarctica and Australia, relates other environmental factors in addition to temperature to the relative abundance of Dictyocha and Distephanus in Recent surface sediments. These other factors include mean annual salinity and the mean annual oxygen level in the surface water. All variables were interpreted graphically and statistically to determine their relative importance. All of the variables behave in a similar manner in this area. They remain fairly consistent with latitude in the Antarctic water mass south of the Antarctic Convergence and change with latitude in the subantarctic water mass north of the Antarctic Convergence. Distephanus is dominate south of the Antarctic Convergence where mean annual surface water temperatures range from -0.5°C - 5.0°C, mean annual salinity is constant at 0 33.90°/oo, and the mean annual oxygen level range 7.0 ml/1 - 7.75 ml/1. Dictyocha is dominate north of the Antarctic Convergence and increases with latitude as mean annual surface water temperatures increase from 7.5°C - 13.5°C, mean annual salinity increases from 33.90°/oo - 35.00°/oo, and mean annual oxygen decreases from 7.25 ml/1 - 6.00 ml/1. To determine the relationship between the environmental variables and the relative generic abundance of silicoflagellates, a Dictyocha/Distephanus ratio was calculated for each core area and plotted against the mean annual surface water temperature, salinity, and oxygen. Because of the effect of the Antarctic Convergence, a curved relationship exists between the Dictyocha/Distephanus ratio and the environmental factors. A multiple regression analysis was used as a statistical method to help quantify the data by providing coefficients for a multiple regression equation to be used for surface water temperature predictions. This equation accounts for the effects of all of the variables, therefore, any factor which influences the silicoflagellates assemblage will be measured in this equation. The Dictyocha/Distephanus ratio was used as the dependent variable and the mean annual surface water temperature, salinity, and oxygen were used as the independent variables. The resultant equation successfully predicts mean surface water temperatures usually to within ±2.0°C of the observed values. However, for this equation to be useful quantitatively with confidence for paleotemperature determinations, it needs to be refined by obtaining additional base data. No embargo
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