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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 speciesTrilobatus sacculifer. In contrast, Ba/Ca is higher and more variable in the non‐spinose speciesNeogloboquadrina dutertreiandPulleniatina 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.
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New Foraminifera-Based Proxies to Trace Changes to the Organic and Inorganic Carbon System Since the Last Glacial Maximum.
The production of carbon and export to deep ocean sediments is linked to carbon partitioning between the ocean and atmosphere and is a key driver of climate change over the glacial-interglacial transition. Yet conflicting reconstructions create barriers to understanding changes to the carbon system over this important climate transition. Production reconstructions conflict in part because commonly used production proxies may be subject to water column and seafloor diagenetic alterations that overprint primary oceanographic signals. In addition, reconstructions of deep ocean carbonate chemistry are complicated by the variable ways that dissolution/preservation affects the proxy. This dissertation explores the utility of new proxies recorded in the shells of planktic foraminifera that have the potential to reconstruct parameters of the carbon system and can be carefully assessed for signs of diagenesis. Proxy developments and reconstructions are made using foraminifera from equatorial Pacific Ocean sediments that span a gradient in surface ocean carbon production and deep ocean carbon preservation.
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- Award ID(s):
- 1737165
- PAR ID:
- 10574141
- Publisher / Repository:
- Oregon State University
- Date Published:
- Format(s):
- Medium: X
- Institution:
- Oregon State University
- Sponsoring Org:
- National Science Foundation
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Geochemical records generated from the calcite shells (tests) of benthic foraminifera, especially those of the genera Cibicidoides and Uvigerina, provide the basis of the majority of long-term climate records in a variety of proxy reconstructions. However, the extent to which benthic foraminifera are affected by post-depositional alteration is poorly constrained in the literature. Furthermore, how diagenesis may alter the geochemical composition of benthic foraminiferal tests, and thereby biasing a variety of proxy-based climate records, is also poorly constrained. We present the Foraminiferal Preservation Index (FPI) as a new metric to quantify preservation quality based on objective, well-defined criteria. The FPI is used to identify and quantify trends in diagenesis temporally, from modern coretop samples to the Mid-Pliocene Warm Period (0.0-3.3 million year ago), and spacially in the deep ocean. The FPI identifies the chemical composition of deep ocean water masses to be the primary driver of diagenesis through time, while also serving as a supplementary method of identifying periods of changing water mass influence at a given site through time. Additionally, we present stable isotope data (d18O, d13C) generated from individual Cibicidoides tests of various preservation quality that demonstrate the likelihood of significant biasing in a variety of geochemical proxy records, especially those used to reconstruct past changes in ice volume and sea level. These single-test data also demonstrate the robustness of paleorecords generated from carefully selected specimens of only the highest quality of preservation.more » « less
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