EXPLORING BA/CA RATIOS IN NON-SPINOSE PLANKTIC FORAMINIFERA AS A PROXY FOR PALEOPRODUCTIVITY (Invited Presentation)

The barium-to-calcium (Ba/Ca) ratios of non-spinose foraminifera are highly elevated compared to spinose species obtained from the same sample. Although previously attributed to contaminant phases or preferred diet, the elevated Ba was recently hypothesized to be driven by a particulate organic matter (POM, or marine snow) microhabitat during early ontogeny that is unique to non-spinose species. The interstitial seawater within POM can have higher trace element composition compared to open ocean seawater and can have lower pH and oxygen compared to ambient seawater, providing a unique environment suitable for increased Ba uptake. Non-spinose foraminifera, living within particulates, record the elevated Ba composition within their shells during calcification. Here, we expand upon this POM microhabitat hypothesis and suggest Ba in non-spinose foraminifera may be a useful proxy for paleoproductivity. Under this hypothesis, POM production is lower during periods of low productivity, and this is reflected in the overall lower Ba/Ca ratios of non-spinose species during such time periods. Conversely, POM production is higher during periods of high productivity, and this would be reflected in overall higher Ba/Ca ratios. Using downcore records from the western and eastern equatorial Pacific, we demonstrate that Ba/Ca ratios are higher in two non-spinose species during the Deglaciation, a period of higher productivity in these regions in comparison to the Holocene and Last Glacial Maximum time periods.