New insights on the ubiquity of chromophoric products of microbial degradation in the dark global ocean

Careful examination of the absorption coefficient scans of chromophoric dissolved organic matter (CDOM) from the dark ocean samples collected during the Malaspina 2010 circumnavigation allowed us to identify two repeated protuberances, hereafter ‘shoulders’, at 280-320 nm (shoulder I) and 415 nm (shoulder II). A matlab toolbox was developed to deconvolve the absorption coefficient signal exclusively attributed to those shoulders from the standard decreasing exponential curve proper of humic materials. Shoulder I distribution was omnipresent and it sources may be linked partly to nitrate and likely to the antioxidant deoxygadusol too. However, the occurrence of shoulder II was more restricted to certain areas and its source has been recently associated to the enzyme cytochrome c. Application of a water mass analysis to the apparent oxygen utilization (AOU, a proxy to water mass ‘ageing’), ideal age, and absorption coefficients of shoulder I and II unveiled that ideal age was the factor that best explains the distribution of shoulder I whereas ‘ageing’ was the factor that best explains the distribution of shoulder II