Assessment of coral δ44/40Ca as a paleoclimate proxy in the Great Barrier Reef of Australia

• No correlation is found between skeletal δ44/40Ca and δ11B, δ18O and Sr/Ca ratios in a Porites coral.
• Coral skeletal δ44/40Ca shows a positive relationship with δ13C.
• Ca isotopic fractionation in corals is subjected to vital effects.

The Ca isotopic composition (δ44/40Ca) in a Porites spp. coral from the Great Barrier Reef was analyzed at monthly intervals for two consecutive years. It was found that variations in skeletal δ44/40Ca values over the 2-year period are slightly greater than the analytical precision of the measurements, although other coralline geochemical records (i.e., δ13C, δ18O, δ11B and Sr/Ca ratios) show remarkable variations. To evaluate the potential of δ44/40Ca as a paleoclimate proxy in corals, we compared δ44/40Ca with other well-established indicators, and found that δ44/40Ca values show little relationship to δ18O, Sr/Ca, Δδ18O, or δ11B values, thus suggesting that the influence of seawater temperature, seawater pH and river inputs on skeletal δ44/40Ca is limited or overwhelmed by other factors. However, skeletal δ44/40Ca values are significantly related to δ13C values (r = 0.46, p < 0.05; n = 27), thus indicating that Ca isotopic fractionation in corals is subjected to vital effect. The strong influence of biogenic factors on δ44/40Ca in corals, limit the applicability of coral δ44/40Ca to paleoclimate reconstruction.