Just out | Boron isotope-based seasonal paleo-pH reconstruction for the Southeast Atlantic – A multispecies approach using habitat preference of planktonic foraminifera @ Earth and Planetary Science Letters

Just out @ Earth and Planetary Science Letters

Boron isotope-based seasonal paleo-pH reconstruction for the Southeast Atlantic – A multispecies approach using habitat preference of planktonic foraminifera


Markus Raitzsch, Jelle Bijma, Albert Benthien, Klaus-Uwe Richter, Grit Steinhoefel, Michal Kučera


The boron isotopic composition of planktonic foraminiferal shell calcite (δ11BCc) provides valuable information on the pH of ambient water at the time of calcification. Hence, δ11BCc of fossil surface-dwelling planktonic foraminifera can be used to reconstruct ancient aqueous pCO2 if information on a second carbonate system parameter, temperature and salinity is available. However, pH and pCO2 of surface waters may vary seasonally, largely due to changes in temperature, DIC, and alkalinity. As also the shell fluxes of planktonic foraminifera show species-specific seasonal patterns that are linked to intra-annual changes in temperature, it is obvious that δ11BCcof a certain species reflects the pH and thus pCO2 biased towards a specific time period within a year. This is important to consider for the interpretation of fossil δ11BCc records that may mirror seasonal pH signals. Here we present new Multi-Collector Inductively Coupled Mass Spectrometry (MC-ICPMS) δ11BCc coretop data for the planktonic foraminifera species Globigerina bulloidesGlobigerinoides ruberTrilobatus sacculifer and Orbulina universa   and compare them with δ11Bborate derived from seasonally resolved carbonate system parameters. We show that the inferred season-adjusted δ11BCc11Bborate relationships are similar to existing calibrations and can be combined with published δ11BCc field and culture data to augment paleo-pH calibrations. To test the applicability of these calibrations, we used a core drilled on the Walvis Ridge in the Southeast Atlantic spanning the last 330,000 years to reconstruct changes in surface-water pCO2. The reconstruction based on G. bulloides, which reflects the austral spring season, was shown to yield values that closely resemble the Vostok ice-core data indicating that surface-water pCO2 was close to equilibrium with the atmosphere during the cooler spring season. In contrast, pCO2 estimated from δ11BCcof O. universaT. sacculifer and G. ruber that predominantly lived during the warmer seasons, exhibits up to ∼50 ppmv higher values than the Vostok ice-core data. This is probably due to the higher austral summer and fall temperatures, as shown by Mg/Ca to be on average ∼4 °C higher than during the cooler spring season, accounting for an increase in pCO2 of ∼4% per 1 °C. Our results demonstrate that paleo-pH estimates based on δ11BCc contain a significant seasonal signal reflecting the habitat preference of the recording foraminifera species.

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Keywords: boron isotopesplanktonic foraminiferaseasonality

DOI: 10.1016/j.epsl.2018.02.002

READ IT HERE: https://www.sciencedirect.com/science/article/pii/S0012821X1830058X

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Lurdes Fonseca

Assistant Professor and Researcher at University of Lisbon
Sociologist (PhD), Paleontologist (Researcher in Micropaleontology), Majors in Sociology and Biology, Minor in Geology. Main interests in Paleontology: Microfossils, Molecular fossils, Paleobiology and Paleoecology. (read more about me)

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