Modeling the seasonal distribution of planktonic foraminifera during the Last Glacial Maximum

[1] We studied the seasonality of planktonic foraminifera during the Last Glacial Maximum using a foraminifera model coupled to an ecosystem model. The model suggests that the timing of the maximum seasonal production of planktonic foraminifera during the Last Glacial Maximum occurred at a different time of the year from present day. The assumption of ‘‘stable’’ seasonality through time, one of the underlying assumptions in paleoceanographical studies that utilize monospecific samples of planktic foraminifera, is thus mistaken. This finding entails implications for foraminifera-based paleotemperature reconstructions. The change in the timing of maximum foraminiferal production could lead to a bias in estimated paleotemperature if the change in seasonality is not taken into account. The existence of the potential seasonal bias is not a new concept in paleoceanography, but here we assess this bias for the first time from a comprehensive modeling approach. In tropical waters, where temperature seasonality has a relatively small amplitude, the estimated sea surface temperature is close to the annual mean. Thus, variations in foraminiferal seasonality do not cause a significant change in the recorded temperature. By contrast, changes in seasonality have the largest influence on the temperature signal at high latitudes and midlatitudes. Our model prediction suggests that because of the temperature sensitivity of the considered species, during the Last Glacial Maximum, the largest production of foraminifera occurred during a warmer season of the year. In some regions, the maximum foraminiferal production month shifted by up to 6 months. Our findings may help to reconcile low glacial planktonic dO values with proxy evidence for deep-water formation in the Nordic Seas.