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 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="" green-to-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="" green-to-blue="" ratios="" (=""> 0.6) and large downcore variability (range of ≥ 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.