Eagle Robert A.

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Eagle
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Robert A.
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  • Article
    The influence of temperature and seawater carbonate saturation state on 13C–18O bond ordering in bivalve mollusks
    (Copernicus Publications on behalf of the European Geosciences Union, 2013-07-10) Eagle, Robert A. ; Eiler, John M. ; Tripati, Aradhna K. ; Ries, J. B. ; Freitas, P. S. ; Hiebenthal, C. ; Wanamaker, Alan D. ; Taviani, Marco ; Elliot, Mary ; Marenssi, S. ; Nakamura, K. ; Ramirez, P. ; Roy, K.
    The shells of marine mollusks are widely used archives of past climate and ocean chemistry. Whilst the measurement of mollusk δ18O to develop records of past climate change is a commonly used approach, it has proven challenging to develop reliable independent paleothermometers that can be used to deconvolve the contributions of temperature and fluid composition on molluscan oxygen isotope compositions. Here we investigate the temperature dependence of 13C–18O bond abundance, denoted by the measured parameter Δ47, in shell carbonates of bivalve mollusks and assess its potential to be a useful paleothermometer. We report measurements on cultured specimens spanning a range in water temperatures of 5 to 25 °C, and field collected specimens spanning a range of −1 to 29 °C. In addition we investigate the potential influence of carbonate saturation state on bivalve stable isotope compositions by making measurements on both calcitic and aragonitic specimens that have been cultured in seawater that is either supersaturated or undersaturated with respect to aragonite. We find a robust relationship between Δ47 and growth temperature. We also find that the slope of a linear regression through all the Δ47 data for bivalves plotted against seawater temperature is significantly shallower than previously published inorganic and biogenic carbonate calibration studies produced in our laboratory and go on to discuss the possible sources of this difference. We find that changing seawater saturation state does not have significant effect on the Δ47 of bivalve shell carbonate in two taxa that we examined, and we do not observe significant differences between Δ47-temperature relationships between calcitic and aragonitic taxa.
  • Article
    Thermal stress reduces pocilloporid coral resilience to ocean acidification by impairing control over calcifying fluid chemistry
    (American Association for the Advancement of Science, 2021-01-22) Guillermic, Maxence ; Cameron, Louise P. ; De Corte, Ilian ; Misra, Sambuddha ; Bijma, Jelle ; de Beer, Dirk ; Reymond, Claire E. ; Westphal, Hildegard ; Ries, Justin B. ; Eagle, Robert A.
    The combination of thermal stress and ocean acidification (OA) can more negatively affect coral calcification than an individual stressors, but the mechanism behind this interaction is unknown. We used two independent methods (microelectrode and boron geochemistry) to measure calcifying fluid pH (pHcf) and carbonate chemistry of the corals Pocillopora damicornis and Stylophora pistillata grown under various temperature and pCO2 conditions. Although these approaches demonstrate that they record pHcf over different time scales, they reveal that both species can cope with OA under optimal temperatures (28°C) by elevating pHcf and aragonite saturation state (Ωcf) in support of calcification. At 31°C, neither species elevated these parameters as they did at 28°C and, likewise, could not maintain substantially positive calcification rates under any pH treatment. These results reveal a previously uncharacterized influence of temperature on coral pHcf regulation—the apparent mechanism behind the negative interaction between thermal stress and OA on coral calcification.