<scp>CDOM</scp> spectral slope (<scp><i>S</i></scp><sub>275–295</sub>) as tracers of water masses, <scp>CDOM</scp> heterogeneity, and <scp>Δ<sup>14</sup>C‐DOC</scp> in an oligotrophic marginal sea
Guisheng Song, Fangming Yang, Philippe Massicotte, Hao Wei, Huixiang Xie
Abstract
Abstract The absorption spectral slope, S 275–295 , is an optical metric frequently employed for characterizing chromophoric dissolved organic matter (CDOM). We collected CDOM absorption ( a CDOM ) and fluorescence spectra from the oligotrophic offshore South China Sea to identify the major determinant of S 275–295 and to explore the potential of S 275–295 as physical and biogeochemical tracers. S 275–295 linearly decreased with increasing humic‐like fluorescent DOM, revealing the latter as the primary control on S 275–295 . The variability of S 275–295 consistently declined from the surface to deep water, making S 275–295 a potential indicator of CDOM molecular heterogeneity. The S 275–295 vs. a CDOM plot was found to be a useful tool for characterizing water masses. The 14 C content of dissolved organic carbon (Δ 14 C‐DOC) shows a strong correlation to S 275–295 , demonstrating S 275–295 to be a proxy of the 14 C‐age of DOM. A provisional equation, ln(−Δ 14 C‐DOC) = (−0.85 ± 0.06) × ln( S 275–295 ) + (8.78 ± 0.19), was proposed to estimate Δ 14 C‐DOC from S 275–295 for global oligotrophic oceans.