Sub-annual fluorescence measurements of coral skeleton: relationship between skeletal luminescence and terrestrial humic
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Sub-annual fluorescence measurements of coral skeleton: relationship between skeletal luminescence and terrestrial humiclike substances Nikita Kaushal1 • Liudongqing Yang1,2 • Jani T. I. Tanzil2,3,4 • Jen Nie Lee5 Nathalie F. Goodkin1,2,6 • Patrick Martin1
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Received: 13 April 2020 / Accepted: 19 May 2020 Ó The Author(s) 2020
Abstract Some massive coral core slices reveal luminescent bands under ultraviolet light, which have been attributed to terrestrial humic acids in the skeleton. Coral luminescence has therefore been used to reconstruct past climate and hydrological variability. However, it has remained unresolved how closely coral luminescence at sub-annual resolution is related to terrestrial humic acid concentrations. This study presents a solution-based fluorescence method to quantify terrestrial humic substances in less than 4 mg of coral powder. The results show that in Topic Editor Anastazia Banaszak Nikita Kaushal and Liudongqing Yang have contributed equally to the work.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00338-020-01959-x) contains supplementary material, which is available to authorized users. & Nikita Kaushal [email protected] & Patrick Martin [email protected] 1
Asian School of the Environment, Nanyang Technological University, Singapore, Singapore
2
Earth Observatory of Singapore, Nanyang Technological University, Singapore, Singapore
3
St. John’s Island National Marine Laboratory, National University of Singapore, Singapore, Singapore
4
Tropical Marine Science Institute, National University of Singapore, Singapore, Singapore
5
Faculty of Science and Marine Environment, Universiti Malaysia Terengganu, Kuala Nerus, Malaysia
6
Department of Earth and Planetary Sciences, American Museum of Natural History, New York, USA
corals from Malaysia and Singapore, the luminescence green-to-blue ratio is correlated with skeletal concentrations of terrestrial humic substances (R2 [ 0.40, p \ 0.001) at two sites that are exposed to terrestrial dissolved organic matter from peatlands on Sumatra. In contrast, coral cores from two other sites located far from major terrestrial organic matter sources show lower greento-blue values and no convincing correlation with fluorescence intensity of terrestrial humic substances in the skeleton. Abiogenic aragonite precipitation experiments with both terrestrial and marine organic matter sources confirmed that terrestrial humic substances are readily incorporated into aragonite, but not fluorescent organic matter from marine sources. The results of this study suggest that in coral cores with high luminescence greento-blue ratios ([ 0.6) and large downcore variability (range of C 0.05), the green-to-blue ratio is strongly linked to variation in terrestrial humic substances. Coral cores therefore have the potential to reconstruct past variation in terrigenous dissolved organic carbon fluxes. Keywords Fluorescent dissolved organic matter Coral luminescence Humic-like substances EEM Ter
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