The omnipresence of chromophoric dissolved organic matter (CDOM) in the open ocean enables its use as a tracer for biochemical processes throughout the global overturning circulation. We made an inventory of CDOM optical properties, ideal water age (τ) and apparent oxygen utilization (AOU) along the Atlantic, Indian and Pacific Ocean waters sampled during the Malaspina 2010 expedition. A water mass analysis was applied to obtain intrinsic, hereinafter archetypal, values of τ, AOU, oxygen utilisation rate (OUR), and CDOM absorption coefficients, spectral slopes and quantum yield for each one of the 22 water types intercepted during this circumnavigation. Archetypal values of AOU and OUR have been used to trace the differential influence of water mass ageing and ageing rates, respectively, on CDOM variables. Whereas the absorption coefficient at 325nm ( a 325 ) and the fluorescence quantum yield at 340 nm ( Φ 340 ) increased, the spectral slope over the wavelength range 275–295 nm ( S 275–295 ) and the ratio of spectral slopes over the ranges 275 –295 nm and 350–400 nm ( S R ) decreased significantly with water mass ageing (AOU). Combination of the slope of the linear regression between archetypal AOU and a 325 with the estimated global OUR allowed us to obtain a CDOM turnover time of 634 ± 120 years, which exceeds the flushing time of the dark ocean (〉200 m) by 46%. This positive relationship supports the assumption of in situ production and accumulation of CDOM as a by-product of microbial metabolism as water masses turn older. Furthermore, our data evidence that global-scale CDOM quantity ( a 325 ) is more dependant on ageing (AOU), whereas CDOM quality ( S 275–295 , S R , Φ 340 ) is more dependent on ageing rate (OUR).
Chemistry and Pharmacology