TRACE ELEMENTS IN CALCIFYING MARINE INVERTEBRATES INDICATE DIVERSE SENSITIVITIES TO THE SEAWATER CARBONATE SYSTEM

Abstract:

Surface ocean absorption of anthropogenic CO₂ emissions resulting in ocean acidification may interfere with the ability of calcifying marine organisms to biomineralize, since the drop in pH is accompanied by reductions in CaCO₃ saturation state. However, recent experiments show that net calcification rates of cultured benthic invertebrate taxa exhibit diverse responses to pCO₂-induced changes in saturation state (Ries et al., 2009). Advancement of geochemical tools as biomineralization indicators will enable us to better understand these results and therefore help predict the impacts of ongoing and future decrease in seawater pH on marine organisms. Here we build upon previous work on these specimens by measuring the elemental composition of biogenic calcite and aragonite precipitated in four pCO₂ treatments (400; 600; 900; and 2850 ppm). Element ratios (including Sr/Ca, Mg/Ca, Li/Ca, B/Ca, U/Ca, Ba/Ca, Cd/Ca, and Zn/Ca) were analyzed in 18 macro-invertebrate species representing seven phyla (crustacea, cnidaria, echinoidea, rhodophyta, chlorophyta, gastropoda, bivalvia, annelida), then compared to growth rate data and experimental seawater carbonate system parameters: [CO₃^2-], [HCO₃^-], pH, saturation state, and DIC. Correlations between calcite or aragonite composition and seawater carbonate chemistry are highly taxa-specific, but do not resemble trends observed in growth rate for all species. Apparent carbonate system sensitivities vary widely by element, ranging from strongly correlated to no significant response. Interpretation of these results is guided by mounting evidence for the capacity of individual species to modulate pH and/or saturation state at the site of calcification in response to ambient seawater chemistry. Such biomineralization pathways and strategies in turn likely influence elemental fractionation during CaCO₃ precipitation.

Ries, J.B., A.L. Cohen, A.L., and D.C. McCorkle (2009), Marine calcifiers exhibit mixed responses to CO₂-induced ocean acidification, Geology, 37(12), 1131-1134.