Calcium isotopes in scleractinian fossil corals since the Mesozoic; implications for vital effects and biomineralization through time

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doi: 10.1016/j.epsl.2016.03.012
Author(s): Gothmann, Anne M.; Bender, Michael L.; Blättler, Clara L.; Swart, Peter K.; Giri, Sharmila J.; Adkins, Jess F.; Stolarski, Jaroslaw; Higgins, John A.
Author Affiliation(s): Primary:
Princeton University, Department of Geosciences, Princeton, NJ, United States
Other:
University of Miami, United States
California Institute of Technology, United States
Polish Academy of Sciences, Institute of Paleobiology, Poland
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, Vol.444, p.205-214. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. Includes appendix. 49 refs.; illus., incl. 3 tables
Summary: We present a Cenozoic record of δ44/40Ca from well preserved scleractinian fossil corals, as well as fossil coral δ44/40Ca data from two time periods during the Mesozoic (84 and 160 Ma). To complement the coral data, we also extend existing bulk pelagic carbonate records back to ∼80 Ma. The same fossil corals used for this study were previously shown to be excellently preserved, and to be faithful archives of past seawater Mg/Ca and Sr/Ca since ∼200 Ma (Gothmann et al., 2015). We find that the δ44/40Ca compositions of bulk pelagic carbonates from ODP Site 807 (Ontong Java Plateau) and DSDP Site 516 (Rio Grande Rise) have not varied by more than ∼±0.20 ppm over the last ∼80 Myr. In contrast, the δ44/40Ca compositions of Mesozoic and Early Cenozoic fossil corals are ∼1 ppm lighter than those of modern corals. The observed change in coral δ44/40Ca does not likely reflect secular variations in seawater δ44/40Ca. Instead, we propose that it reflects a vital effect of calcification - specifically, a sensitivity of coral Ca isotope discrimination to changing seawater [Ca] and/or pH. Support for this hypothesis comes from the presence of an empirical correlation between our coral δ44/40Ca record and records of seawater [Ca] and pH since the Mesozoic (Lowenstein et al., 2003; Honisch et al., 2012). We explore various mechanisms that could give rise to such a vital effect, including: (1) changes in calcification rate, (2) changes in proton pumping in exchange for Ca2+, (3) variable Rayleigh distillation from an isolated calcifying fluid, and (4) changes in the calcium mass balance of the extracellular calcifying fluid (termed here the "leaky Ca model"). We test for the dependence of seawater δ44/40Ca on external seawater [Ca] by measuring the δ44/40Ca of cultured corals grown in seawater solutions with [Ca] ranging from 10 to 15 mmol/kg. Corals grown under elevated [Ca] conditions show a slight, ∼0.15 ppm depletion of δ44/40Ca at higher seawater [Ca] - a supportive but not definitive result. Abstract Copyright (2016) Elsevier, B.V.
Year of Publication: 2016
Research Program: DSDP Deep Sea Drilling Project
IODP Integrated Ocean Drilling Program
IPOD International Phase of Ocean Drilling
ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Alkaline earth metals; Anthozoa; Atlantic Ocean; Biomineralization; Ca-44/Ca-40; Calcification; Calcium; Carbonates; Cnidaria; DSDP Site 516; Deep Sea Drilling Project; Equatorial Pacific; Experimental studies; IPOD; Integrated Ocean Drilling Program; Invertebrata; Isotope ratios; Isotopes; Leg 130; Leg 72; Mesozoic; Metals; North Pacific; Northwest Pacific; ODP Site 807; Ocean Drilling Program; Ontong Java Plateau; PH; Pacific Ocean; Pelagic environment; Reconstruction; Rio Grande Rise; Scleractinia; Sea water; Secular variations; South Atlantic; Stable isotopes; West Pacific; Zoantharia
Coordinates: N033622 N033626 E1563730 E1563728
S301636 S301635 W0351706 W0351707
Record ID: 2016056441
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands