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International Ocean Discovery Program Site U1534 presents an opportunity to study the evolution of subantarctic surface waters in the Atlantic Ocean and investigate Subantarctic Front dynamics during glacial–interglacial transitions. Here we document stable carbon and oxygen isotopes (δ13C and δ18O) in the planktonic foraminifera Globigerina bulloides and Neogloboquadrina pachyderma (sinistral), as well as species abundances of all planktonic foraminifera present in the splice section of Site U1534 interpreted to represent Marine Isotope Stage 11 based on the shipboard stratigraphy. The planktonic assemblage is dominated by N. pachyderma (sinistral), with minor occurrences of other calcareous species; the lowest N. pachyderma (sinistral) abundances suggest the warmest upper ocean temperatures at ~43–44 m core composite depth below seafloor, Method A (CCSF-A). Results demonstrate that δ13C in N. pachyderma (sinistral) and G. bulloides varies from −0.12‰ to 1.01‰ and from 0.19‰ to 1.11‰, respectively. δ18O in N. pachyderma (sinistral) and G. bulloides varies from 1.68‰ to 2.92‰ and from 2.14‰ to 2.97‰, respectively. δ18O values oscillate through the section but are generally lowest near 43–44 m CCSF-A.
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A Sediment Trap Evaluation of B/Ca as a Carbonate System Proxy in Asymbiotic and Nondinoflagellate Hosting Planktonic Foraminifera
Abstract The ratio of boron to calcium (B/Ca) in a subset of foraminifera has been shown to covary with seawater carbonate chemistry, making this geochemical signature a promising proxy for carbon cycle science. Some studies suggest complications with the B/Ca proxy in photosymbiont‐bearing planktonic foraminifera, while relatively few studies have investigated B/Ca in species that lack large dinoflagellate symbionts. For the first time, we use a sediment trap time series to evaluate B/Ca of subtropical and subpolar planktonic foraminifera species that are asymbiotic (Globigerina bulloidesandNeogloboquadrina incompta) and a species that hosts small intrashell photosymbionts (Neogloboquadrina dutertrei). We find that B/Ca measurements across size fractions indicate overall little to no size‐dependent uptake of boron that has previously been reported in some symbiont‐bearing foraminifera.Neogloboquadrina incomptaandN.dutertreiB/Ca are strongly correlated with calcite saturation, pH, and carbonate ion concentration, which is in good agreement with the limited number of published core top results. WhileG.bulloidesB/Ca trends with seasonal fluctuations in carbonate chemistry, during discrete periods considerable B/Ca offsets occur when a crypticG.bulloidesspecies is known to be seasonally present within the region. We confirm presence and significant B/Ca offset between cryptic species by individual LA‐ICP‐MS analyses. This finding calls into question the use of traditional morphological classification to lump what might be genetically distinct species for geochemical analyses. Our overall results highlight the utility ofG.bulloides,N.incompta, andN.dutertreiB/Ca while bringing to light new considerations regarding divergent geochemistry of cryptic species.
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- Award ID(s):
- 1631977
- PAR ID:
- 10458518
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Paleoceanography and Paleoclimatology
- Volume:
- 35
- Issue:
- 2
- ISSN:
- 2572-4517
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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