Compilation of d18O data, living planktic foraminifera

Most of the isotopic paleotemperature equations used for paleoceanographic reconstructions have been derived from culture experiments or inorganic precipitates of calcium carbonate. To test these equations in the modern ocean, we measured the oxygen isotope composition of planktonic foraminifera (Globigerinoides ruber, Globigerinoides sacculifer, Globigerina bulloides and Neogloboquadrina pachyderma) collected from Atlantic and Southern Ocean surface waters, and added published plankton tow data from the Pacific, Indian and Arctic Oceans. The resulting species-specific regression equations of the temperature:d18O relationships for G. ruber, G. sacculifer and G. bulloides are statistically indistinguishable. The equations derived for G. sacculifer and G. bulloides agree with relationships obtained from laboratory experiments, in which these species were cultured at pH values close to modern surface waters. The equation derived from N. pachyderma has a significantly lower slope and offset than the other three species but produces a regression equation that is nearly identical to the one for the epifaunal benthic foraminifer Cibicides sp. Our work on plankton tow and pumped samples indicates that culture-derived equations appear to be more appropriate for predicting the absolute d18O of the species examined compared to equations derived from inorganic precipitates. However, over the oceanic temperature range, the slopes of the equations we derive for living species agree with the slopes obtained from inorganic precipitates.

目前用于古海洋重建（paleoceanographic reconstructions）的绝大多数同位素古温度方程（isotopic paleotemperature equations），均源自碳酸钙（calcium carbonate）的培养实验（culture experiments）或碳酸钙无机沉淀物（inorganic precipitates of calcium carbonate）的沉淀实验。为在现代海洋中验证此类方程，我们对采自大西洋与南大洋表层水体的浮游有孔虫（planktonic foraminifera）开展了氧同位素组成（oxygen isotope composition）测定，所涉物种包括Globigerinoides ruber、Globigerinoides sacculifer、Globigerina bulloides以及Neogloboquadrina pachyderma，并补充了已发表的太平洋、印度洋与北冰洋浮游拖网数据（plankton tow data）。针对Globigerinoides ruber、Globigerinoides sacculifer与Globigerina bulloides的温度与d18O关系，我们得到了物种特异性回归方程（species-specific regression equations），三者在统计学上无显著差异。针对Globigerinoides sacculifer与Globigerina bulloides推导得到的方程，与实验室培养实验得到的对应关系一致——此类实验中，受试物种所处的pH环境与现代表层水体近乎一致。针对Neogloboquadrina pachyderma推导得到的方程，其斜率与截距均显著低于其余三个物种，但所得回归方程与表生底栖有孔虫（epifaunal benthic foraminifer）Cibicides sp.的回归方程几乎完全一致。我们针对浮游拖网与泵取样本（pumped samples）的研究表明，相较于基于碳酸钙无机沉淀物推导得到的方程，源自培养实验的方程更适用于预测本次研究所涉物种的绝对d18O值。不过在海洋温度区间内，我们针对现生物种推导得到的方程斜率，与无机沉淀实验得到的斜率基本相符。