Investigating controls on barium incorporation in non-spinose foraminifera
NanoSIMS images of two cultured specimens of N. dutertrei. Mg/Ca data for these shells was published in Fehrenbacher et al., 2017. Ocean grown calcite (marked with an 'o') has elevated Ba compared to the cultured calcite (marked with a 'c'). Ratios are as high as 200 micromol/mol in the cultured calcite and far exceed expected Ba/Ca values for foraminifera. The cultured calcite has low Ba/Ca ratios, as expected given the Ba/Ca ratios of the culture seawater (see Fehrenbacher et al., 2018).
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Forty years ago, researchers exploring foraminifera geochemistry were perplexed that species that lacked spines had elevated barium (Ba) within their shell calcite. They speculated various mechanisms were responsible, from contamination, to prey preference, to a greater affinity for Ba incorporation into their shell during growth.
In Fehrenbacher et al. (2018), we conducted the first ever barium partition coefficient experiment for a non-spinose species, demonstrating that they incorporate Ba solely as a function of the seawater they grow in. Yet specimens that grow in the open ocean have highly elevated and variable Ba that cannot be explained by seawater Ba composition alone. We hypothesize these species live in particulates, where Ba is elevated, during their lifecycle. This hypothesis is supported by microbiome analyses of living specimens that found cercozoa, a bacterium associated with particulates (Bird et al., 2018), and recent experiments demonstrating their affinity for attaching to particulates (MS in prep). Our findings suggest non-spinose foraminifera occupy a profoundly different ecological niche compared to spinose-species and this fundamentally changes how they can be used in paleoclimate research.
This research led to a successfully funded proposal that supports OSU graduate student Theresa Fritz-enders and several undergraduate students. Theresa is working to establish a new proxy using Ba/Ca ratios (MS in prep). For her research, she also demonstrated that Ba/Ca ratios can be heavily altered using standard foraminifera cleaning protocols (paper in review).
This page was last updated October 2020.
In Fehrenbacher et al. (2018), we conducted the first ever barium partition coefficient experiment for a non-spinose species, demonstrating that they incorporate Ba solely as a function of the seawater they grow in. Yet specimens that grow in the open ocean have highly elevated and variable Ba that cannot be explained by seawater Ba composition alone. We hypothesize these species live in particulates, where Ba is elevated, during their lifecycle. This hypothesis is supported by microbiome analyses of living specimens that found cercozoa, a bacterium associated with particulates (Bird et al., 2018), and recent experiments demonstrating their affinity for attaching to particulates (MS in prep). Our findings suggest non-spinose foraminifera occupy a profoundly different ecological niche compared to spinose-species and this fundamentally changes how they can be used in paleoclimate research.
This research led to a successfully funded proposal that supports OSU graduate student Theresa Fritz-enders and several undergraduate students. Theresa is working to establish a new proxy using Ba/Ca ratios (MS in prep). For her research, she also demonstrated that Ba/Ca ratios can be heavily altered using standard foraminifera cleaning protocols (paper in review).
This page was last updated October 2020.