Photochemical Mineralization of Terrigenous DOC to Dissolved Inorganic Carbon in Ocean

Abstract

When terrigenous dissolved organic carbon (tDOC) rich in chromophoric dissolved organic matter (tCDOM) enters the ocean, solar radiation mineralizes it partially into dissolved inorganic carbon (DIC). This study addresses the amount and the rates of DIC photoproduction from tDOC and the area of ocean required to photomineralize tDOC. We collected water samples from 10 major rivers, mixed them with artificial seawater, and irradiated them with simulated solar radiation to measure DIC photoproduction and the photobleaching of tCDOM. The linear relationship between DIC photoproduction and tCDOM photobleaching was used to estimate the amount of photoproduced DIC from the tCDOM fluxes of the study rivers. Solar radiation was estimated to mineralize 12.5 ± 3.7 Tg C yr−1 (10 rivers)−1 or 18 ± 8% of tDOC flux. The irradiation experiments also approximated typical apparent spectral quantum yields for DIC photoproduction (ϕλ) over the entire lifetime of the tCDOM. Based on ϕλs and the local solar irradiances in river plumes, the annual areal DIC photoproduction rates from tDOC were calculated to range from 52 ± 4 (Lena River) to 157 ± 2 mmol C m−2 yr−1 (Mississippi River). When the amount of photoproduced DIC was divided by the areal rate, 9.6 ± 2.5 × 106 km2 of ocean was required for the photomineralization of tDOC from the study rivers. Extrapolation to the global tDOC flux yields 45 (31–58) Tg of photoproduced DIC per year in the river plumes that cover 34 (25–43) × 106 km2 of the ocean.

Biological transformation of Arctic dissolved organic matter in a NE Greenland fjord

“…) indicating that the marine end‐member is the important FDOM source rather than the local runoff. The reduced intensity of visible wavelength FDOM in the freshwater influenced surface layer could potentially also have been caused by photochemical degradation (Ward et al ; Aarnos et al ). However, as the ice in the Young Sound fjord system disappears after the summer solstice, the sun angle is also decreasing rapidly and as a result, the inner fjord system is shaded by surrounding mountains preventing direct exposure.…”

Composition and cycling of dissolved organic matter from tropical peatlands of coastal Sarawak, Borneo, revealed by fluorescence spectroscopy and parallel factor analysis

“…However, our knowledge of the biogeochemical cycling of peat-derived DOM in Southeast Asia is still limited. Although several studies have shown that peatland-draining blackwater rivers in Sumatra and Borneo carry extremely high DOC concentrations (3000-5500 µmol L −1 , or 36-66 mg L −1 ) with a predominantly terrestrial origin (Alkhatib et al, 2007;Baum et al, 2007;Rixen et al, 2008;Harun et al, 2015Harun et al, , 2016Müller et al, 2015Müller et al, , 2016Cook et al, 2017), more detailed analysis of the chemical composition of peat-derived DOM, and determination of its lability to different degradation processes, are mostly lacking. Moreover, most of these studies did not sample beyond the upper estuaries.…”

DOC Transport and Export in a Dynamic Tropical Catchment

“…Hereby, wetlands play a remarkable role in controlling carbon sequestration (Aiken & Cotsaris, 1995;Cook et al, 2017;Dittmar et al, 2006;Moyer et al, 2015) from inland sources. Overall, half of the carbon exported from inland waters reaches the oceans as organic molecules (Aarnos et al, 2018;Battin et al, 2009). Therefore, quantification of riverine carbon fluxes from dynamic tropical forests may contribute to (a) validate global predictions and (b) reduce uncertainties of carbon sequestration estimates under different climate change scenarios (Shih et al, 2018;Tranvik et al, 2018).…”