NOAA/WDS Paleoclimatology - Global Foraminifera Mg/Ca Surface Sediment Database

The Mg/Ca of planktic foraminifera is commonly assumed to be a univariate function of ocean temperature, but recent work suggests that nonthermal variables may have a secondary effect, thereby complicating an inverse approach for paleotemperature reconstructions. However, the significance of secondary variables has not been independently validated, and their inclusion may reflect statistical overfitting. Here we evaluate the significance of seven predictive variables on a global compilation (n = 1,124) of coreuc0u8208 top planktic foraminifera Mg/Ca spanning five species. An additive approach was used to construct models that included only variables with significant validation skill. Optimal models support the use of Mg/Ca as a paleothermometer but also find evidence for nonthermal variables: (a) Mg/Ca (N. pachy+incompta) = 0.186 'b1 0.001 'b7 exp(0.095 'b1 0.002 'b7 T) + 2.95Eu8208 3 'b1 5.4Eu8208 6 'b7 size; (b) Mg/Ca (G. ruber) = 0.685 'b1 0.005 'b7 exp(0.058 'b1 0.001 'b7 T) + 0.928 'b1 0.02 'b7 Omega(deep); (c); Mg/Ca (G. inflata) = 1.737 'b1 0.007 'b7 exp(0.065 'b1 0.001 'b7 T) 'b7 Omega(shallow)^u8208 0.734 'b1 0.003; and (d) Mg/Ca (G. bulloides) = 0.623 'b1 0.007 'b7 exp(0.079 'b1 0.001 'b7 T) + 0.548 'b1 0.007 'b7 Omega(deep). Results highlight the importance of independent validation and suggest that u937 and size dependences may complicate univariate inversions for paleotemperature in some species. This is particularly true over timescales when secondary terms cannot be considered constant. Forward modeling is an attractive alternative, and improved Mg/Ca models may reduce bias in paleoceanographic data assimilation efforts. Salinity is absent from all relationships, suggesting that it may have a smaller influence than previously thought or may not vary sufficiently to be resolved at coreu8208 top sites. The stepwise approach illustrated in this study is widely applicable, and validation exercises should be applied to the calibration of other paleoceanographic proxies.