Multidecadal decoupling between coral calcifying fluid and seawater saturation states

Ocean acidification poses a threat to coral skeleton formation via reductions in the saturation state of aragonite (ΩAr) in seawater. Given that corals precipitate their skeletons from a calcifying fluid supplied by seawater, reductions in seawater ΩAr should, in theory, confound calcification. Here, we reconstruct up to 200 years of coral calcifying fluid ΩAr, using Raman spectroscopy techniques, at approximately monthly resolution in two Porites sp. skeletal cores from the Coral Sea region to investigate (i) the regulation of coral calcifying fluid ΩAr and (ii) the skeletal calcification response to industrial-era ocean acidification. Our results reveal a significant increase in calcifying fluid ΩAr, suggesting that some corals may adjust to the pace of acidification in the wild more effectively than suggested by short-term laboratory studies.