Assessing oxygen depletion in the Northeastern Pacific Ocean during the last deglaciation using I/Ca ratios from multiple benthic foraminiferal species

Abstract

Paleo‐redox proxies are crucial for reconstructing past bottom water oxygen concentration changes brought about by ocean circulation and marine productivity shifts in response to climate forcing. Carbonate I/Ca ratios of multiple benthic foraminifera species from Ocean Drilling Program Hole 1017E—a core drilled within the Californian oxygen minimum zone (OMZ), on the continental slope—are employed to reexamine the transition from the well‐oxygenated last glacial into poorly oxygenated modern conditions. The redox and export productivity history of this site is constrained by numerous proxies used to assess sensitivity of I/Ca ratios of benthic foraminifera to changes in bottom and pore water O2 concentrations. Reconstructed iodate (IO3−) availability is from the I/Ca ratio of epifaunal (Cibicidoides sp.), shallow infaunal (Uvigerina peregrina), and deep infaunal (Bolivina spissa) foraminifera. The reconstructed IO3− availability profile is used to determine the contribution of bottom water O2 relative to oxidant demand on pore water O2 concentrations. These results suggest that high export productivity on the California Margin drove low pore water O2 concentrations during the Bølling. In contrast, low bottom water O2 concentrations at 950 m water depth only contributed to reduced sediments during the Allerød. Increased contribution of modified North Pacific Intermediate Water to the California Current System ventilated the California OMZ during the late glacial and the Younger Dryas such that water overlying the site was oxygenated. These results highlight the promising potential of this new proxy for understanding the relative influence of bottom water O2 concentration and pore water oxidant demand on OMZs.

Organic Heterogeneities in Foraminiferal Calcite Traced Through the Distribution of N, S, and I Measured With NanoSIMS: A New Challenge for Element-Ratio-Based Paleoproxies?

“…Our study shows that I and S are certainly associated with organic matter within the foraminiferal calcite. In previous studies, the cleaning procedures for the determination of foraminiferal I/Ca use the same protocols, which have been developed and are routinely applied for the determination of foraminiferal Mg/Ca (Lu et al, 2010(Lu et al, , 2016Glock et al, 2014Glock et al, , 2016Taylor et al, 2017;Hoogakker et al, 2018). Our NanoSIMS results show that this cleaning procedure is not sufficient, at least if it is applied FIGURE 8 | A comparison of quantitative I/Ca ratios (µmol/mol) measured on the same six specimens of U. striata from the Peruvian OMZ with NanoSIMS (this study) and SIMS (Glock et al, 2016).…”

“…Due to the ongoing ocean deoxygenation (Schmidtko et al, 2017), several redox-sensitive element-tocalcium ratios in foraminiferal calcite have been brought to attention as possible paleoproxies for past redox conditions. The most prominent ones are the Mn/Ca (Munsel et al, 2010;Ní Fhlaithearta et al, 2010Glock et al, 2012;Groeneveld and Filipsson, 2013;McKay et al, 2015;Barras et al, 2018;Petersen et al, 2018;Guo et al, 2019) and the I/Ca ratios (Lu et al, 2010(Lu et al, , 2016Glock et al, 2014Glock et al, , 2016Taylor et al, 2017;Hoogakker et al, 2018).…”

A New biological proxy for deep-sea paleo-oxygen: Pores of epifaunal benthic foraminifera

“…Relatively new redox proxies, including I/Ca 6 – 8 and δ 13 C 9 have been applied mainly to planktonic foraminifera or infaunal benthic foraminifera, which may not reflect bottom water conditions. Multiple species analyses using I/Ca and/or δ 13 C show promise, but may be complicated by subsurface pore water chemistry 10 . Well established redox proxies based on concentrations of S, Fe, Mo, and U in bulk sediment can trace the more extreme changes in oxygen concentration in remote Earth history, such as during the Archean 11 , 12 .…”

Reconstructing Paleo‐oxygenation for the Last 54,000 Years in the Gulf of Alaska Using Cross‐validated Benthic Foraminiferal and Geochemical Records

“…This suggests that this upper OMZ site experienced lower oxygen conditions in the past than anywhere in the modern GoA. While benthic foraminiferal proxies primarily reflect pore water oxygenation, previous studies have related low (<5%) abundances of oxic taxa to I/Ca values from epifaunal benthic foraminifera that suggest dysoxic bottom waters (Taylor et al, 2017). In our record, species assigned to the weakly-hypoxic to oxic category make up fewer than 5% of individuals in samples with the lowest BDO values.…”

“…Thus, better ventilation and decreased biological productivity during colder periods in the OSIW had broad effects on oxygenation in the GoA and California margin (K. Ohkushi et al, 2016;Shibahara et al, 2007). However, a decrease in primary productivity locally may also contribute to the increase in oxygenation on the California margin (Taylor et al, 2017).…”