Coral carbon isotope sensitivity to growth rate and water depth with paleo-sea level implications

Abstract

Although reef coral skeletal carbon isotopes (δ 13 C) are routinely measured, interpretation remains controversial. Here we show results of a consistent inverse relationship between coral δ 13 C 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 13 C Suess effect shifts skeletal δ 13 C > 1.0‰ lower. We also compiled coral δ 13 C from a global array of sites and find that mean coral δ 13 C decreases by −1.4‰ for every 5 m increase in water depth ( R = 0.68, p < 0.01). This highlights the fundamental sensitivity of coral δ 13 C to endosymbiotic photosynthesis. Collectively, these results suggest that photosynthetic rate largely determines mean coral δ 13 C while changes in extension rate and metabolic effects over time modulate skeletal δ 13 C around this mean value. The newly quantified coral δ 13 C-water depth relationship may be an effective tool for improving the precision of paleo-sea level reconstruction using corals.

Traces of the 1997 Indonesian Wildfires in the Marine Environment From a Network of Coral δ13C Records

“…The seasonal pattern of the coral δ 13 C values is consist with metabolic fractionation, whereby light‐enhanced photosynthesis preferentially takes up 12 C and leads to 13 C enrichment of the internal DIC pool and thus an enrichment in the skeletal δ 13 C value. There are some differences in seasonal variations of δ 13 C between the corals, which may reflect the differences in local marine environment, such as nutrients, seawater isotopic composition, coral growth depth, and coral photosynthetic rate (Dassié et al, 2013; Deng et al, 2013; Linsley et al, 2019), and/or the chronological uncertainty (Delong et al, 2013).…”

“…Coral forms its aragonite skeleton by utilizing dissolved inorganic carbon (DIC) from the extracytoplasmic calcifying fluid, which is derived mainly from metabolic CO 2 and seawater DIC (Gattuso et al, 1999). Consequently, coral skeletal δ 13 C reflects changes in coral physiological processes as well as seawater DIC δ 13 C (Linsley et al, 2019). Carbon dioxide released through forest and peat fires is lower in δ 13 C relative to the atmosphere (Finkelstein et al, 2006; Schuur et al, 2003), resulting in a decrease in δ 13 C in atmospheric CO 2 and, consequently, surface seawater DIC via atmosphere‐ocean exchange (Quay, Richey, et al, 1992; Quay et al, 2003).…”

Functional diversity of microboringOstreobiumalgae isolated from corals

“…Here, we show that non‐decalcified endolithic Ostreobium filaments (δ 13 C −11.2 ± 0.8‰) were depleted in 13 C compared to reference seawater DIC (in the range of −5 to 2‰; see Patterson and Walter, 1994 for δ 13 C values of tropical seawater in carbonate reefs), and more enriched compared to their coral carbonate substrates. Indeed, the mean δ 13 C value of bleached Pocillopora acuta coral skeletons was −13.9 ± 0.03‰, which corresponds to the low range of values recorded for hermatypic, symbiotic coral skeletons (Linsley et al ., 2019), likely due to aquarium coral growth restrictions and maybe reduced photosynthesis, increased respiration and oxidation of organic matter. This result, combined with the 13 C‐bicarbonate uptake experiment, strongly supports the hypothesis that endolithic Ostreobium used mainly DIC from seawater.…”

Late Pleistocene Carbon Cycle Revisited by Considering Solid Earth Processes

“…with on average a 13 C of −3.8‰ (de Leeuw et al, 2007;Huybers & Langmuir, 2009;Sano & Williams, 1996;Shaw et al, 2003). Furthermore, carbonate lost to the ocean due to coral reef growth leaves the ocean with a 13 C of −1.36‰ which is the mean from 41 pre-Suess effect samples in the review of Linsley et al (2019). With the chosen Redfield ratio in organic matter of C:P = 123:1 (Körtzinger et al, 2001) the sedimentary loss of PO 3− 4 is balanced by a constant riverine input of 24 ⋅ 10 9 mol P/yr.…”