Incorporation of boron isotopes into brachiopod shell calcite: implications for palaeo-pH reconstractions.

Jurikova, Hana, Liebetrau, Volker, Gutjahr, Marcus , Rollion-Bard, C., Hu, M. Y., Henkel, Daniela, Hiebenthal, Claas , Krause, Stefan, Schmidt, M., Laudien, J. and Eisenhauer, Anton (2018) Incorporation of boron isotopes into brachiopod shell calcite: implications for palaeo-pH reconstractions. [Talk] In: EGU General Assembly 2018. , 08.-13.04.2018, Vienna, Austria .

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Abstract

The boron isotope (δ11B) composition of marine calcifiers is considered to be one of the most reliable pH proxies, enabling us to reconstruct past ocean pH and infer on the associated changes in carbon budget involved (e.g. Gut-
jahr et al. 2017). The application of the commonly used δ 11 B archives such as foraminifera or corals is however mostly limited to the Cenozoic due to insufficient preservation or incomplete geological records. Brachiopods have a promising potential for extending our knowledge on seawater pH evolution throughout the entire Phanerozoic considering their high abundance in the fossil record and its origin dating back to the early Cambrian. Moreover,
their shell is composed of low-magnesium calcite, rendering brachiopods more resistant to post-depositional di-magenetic alteration of its primary chemical signal (e.g. Brand et al. 2012). Additionally, even today they present
an extant and widespread taxa, allowing for an assessment of the controls on boron isotope incorporation into brachiopod calcite and possible distortions of the signal due to vital effects or other processes.
We present a detailed exploration of boron isotope systematics in three different brachiopod species (Magellania venosa, Terebratella dorsata, Pajaudina atlantica) cultured under controlled laboratory settings for over a year. Our experimental setup includes a control (pH = 8.15) and two pH treatments (pH = 7.6 and 7.35), and we provide both bulk MC-ICP-MS as well as high spatial resolution SIMS data of the shell material. Our results indicate that boron incorporation is primarily driven by vital effects related to their ability to regulate calcifying fluid pH in
response to ambient changes, which we further validate by in vivo microelectrode measurements (e.g. Stumpp et al. 2012). Despite internal buffering, the local pH at calcification sites systematically decreases with seawater pH,
and hence is impacted by ocean acidification. This not only suggests that brachiopod shells serve as useful and conservative recorders of past ocean pH trends, but also provides new insights into mechanisms that may have
enabled brachiopod survival throughout several major environmental crises in the past.
Our findings have implications for past climate studies, as well as research on calcification processes and physio- logical adaptations to environmental change (e.g. the actual global ocean acidification).

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Document Type: Conference or Workshop Item (Talk)
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EOE-B Experimental Ecology - Benthic Ecology
Projects: BASE-LiNE Earth
Date Deposited: 04 Mar 2019 10:42
Last Modified: 04 Mar 2019 10:42
URI: http://oceanrep.geomar.de/id/eprint/45939

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