Coral carbon isotope sensitivity to growth rate and water depth with paleo sea level implications
Although reef coral skeletal carbon isotopes (d13C) are routinely measured, interpretation remains controversial. Here we show results of a consistent inverse relationship between coral d13C and skeletal extension rate over the last several centuries in Porites corals at Fiji, Tonga, Rarotonga and American Samoa in the southwest Pacific. Beginning in the 1950s, this relationship breaks down as the atmospheric 13C Suess effect shifts skeletal d13C 1.0%0 lower. We also compiled coral d13C from a global array of sites and find that mean coral d13C decreases by 1.4%0 for every 5 m increase in water depth (R 0.68, p 0.01) This highlights the fundamental sensitivity of coral d13C to endosymbiotic photosynthesis. Collectively, these results suggest that photosynthetic rate largely determines mean coral d13C while changes in extension rate and metabolic effects over time modulate skeletal d13C around this mean value. The newly quantified coral d13C water depth relationship may be an effective tool for improving the precision of paleo sea level reconstruction using corals.Rising anthropogenic CO2 levels in the atmosphere are resulting in ocean acidification which may impact coral growth rates. Here, the authors quantify the relationship between water depth and d13C compositions of South Pacific corals from the pre industrial era, and their results should lead to improvements in the precision of sea level reconstructions using fossil corals.
Nature Communications