Increased Productivity in the Equatorial Pacific During the Deglaciation Inferred From the Ba/Ca Ratios of Non-Spinose Planktic Foraminifera

Abstract

The production and export of organic matter to deep-sea sediments is a key driver in modulating glacial-interglacial carbon cycles. Yet, it remains unsettled whether productivity has increased or decreased over glacial-interglacial transitions, in part because productivity proxies may be complicated by sediment re-deposition and diagenetic alterations. Here, we explore using non-spinose foraminifera Ba/Ca ratios as a proxy for surface ocean productivity. We analyze foraminifera Ba/Ca ratios since the Last Glacial Maximum in cores that span a productivity gradient along the equatorial Pacific. Ba/Ca is low and invariable in the spinose species Trilobatus sacculifer. In contrast, Ba/Ca is higher and more variable in the non-spinose species Neogloboquadrina dutertrei and Pulleniatina obliquiloculata. Ba/Ca enrichment in non-spinose species is hypothesized to be linked to the degradation of organic matter within the species' particulate microhabitat and reflects surface ocean particulate organic matter productivity at the time of shell calcification (Fehrenbacher et al., 2018, https://doi.org/10.1016/j.gca.2018.03.008). Ba/Ca in core-top and sediment trap derived non-spinose foraminifera correlate with organic matter productivity. We reconstruct an increase in non-spinose species Ba/Ca during the deglacial in the western and eastern equatorial Pacific and suggest this may be linked to an increase in productivity, as observed in several other regional records. The 16–17 ka BP peak in non-spinose foraminifera Ba/Ca is evident in specimens obtained from a deep ocean core and from regions that experience sediment focusing, suggesting the Ba/Ca proxy may be useful even in regions where samples are poorly preserved or complicated by sediment re-deposition.