Chromium isotope fractionation between modern seawater and biogenic carbonates from the Great Barrier Reef, Australia: Implications for the paleo-seawater δ53Cr reconstruction

0496023 - GLÚ 2019 RIV NL eng J - Journal Article
Farkaš, J. - Frýda, J. - Paulukat, C. - Hathorne, E. C. - Matoušková, Šárka - Rohovec, Jan - Frýdová, B. - Francová, M. - Frei, R.
Chromium isotope fractionation between modern seawater and biogenic carbonates from the Great Barrier Reef, Australia: Implications for the paleo-seawater δ53Cr reconstruction.
Earth and Planetary Science Letters. roč. 498, 15 September (2018), s. 140-151. ISSN 0012-821X. E-ISSN 1385-013X
Institutional support: RVO:67985831
Keywords : chromium * isotopes * REE * carbonates * seawater * Great Barrier Reef
OECD category: Volcanology
Impact factor: 4.637, year: 2018

This study investigates chromium isotope variations (delta53Cr) and REE patterns in present-day biogenic carbonates and ocean waters from Lady Elliot Island (LEI) located in the southern Great Barrier Reef (GBR), Australia, which is one of the world's largest carbonate-producing shelf ecosystems. Our results from carbonates collected at LEI revealed a systematic and statistically significant correlation (r2 = 0.83, p < 0.05) between delta53Cr and cerium anomaly (Ce/Ce*) data in molluscan shells (i.e., gastropods). This implies a redox-controlled incorporation of Cr from seawater into a shell during mineralization mediated by the organism. In particular, shells with higher delta53Cr values, which approach the Cr isotope composition of local seawater, tend to be associated with more negative Ce/Ce*. Importantly, the intercept of the above delta53Cr vs. Ce/Ce* correlation points to the Cr isotope composition of local ocean water, which has an average delta53Cr of + 0.82 ± 0.13. Interestingly, the only calcifying organism from LEI that yielded identical delta53Cr vs. Ce/Ce* values as those in ambient ocean water was a microbial calcitic carbonate produced by red coralline algae (Lithothamnion sp.). This organism thus seems to incorporate Cr isotopes and REE from seawater without additional biological discrimination and/or isotope fractionation effects. Our compilation of delta53Cr data from recent marine biogenic carbonates originating from the main oceanic confirms that marine carbonates tend to be systematically enriched in light Cr isotopes relative to local ocean waters. Trace element constraints, however, indicate that some of these shifts to lower delta53Cr values (i.e., approaching -0.1 per mil) are related to a presence of lithogenic Cr in the shells, causing a diagenetic overprint of the primary marine delta53Cr signal.
Permanent Link: http://hdl.handle.net/11104/0289532