Spectrally resolved efficiencies of carbon monoxide (CO) photoproduction in the western Canadian Arctic: particles versus solutes

[摘要] Spectrally resolved efficiency (i.e. apparent quantum yield, AQY) of carbonmonoxide (CO) photoproduction is a useful indicator of substratephotoreactivity and a crucial parameter for modeling CO photoproductionrates in the water column. Recent evidence has suggested that COphotoproduction from particles in marine waters is significant compared tothe well-known CO production from chromophoric dissolved organic matter(CDOM) photodegradation. Although CDOM-based CO AQY spectra have beenextensively determined, little is known of this information on theparticulate phase. Using water samples collected from the Mackenzie estuary,shelf, and Canada Basin in the southeastern Beaufort Sea, the present studyfor the first time quantified the AQY spectra of particle-based COphotoproduction and compared them with the concomitantly determinedCDOM-based CO AQY spectra. CO AQYs of both particles and CDOM decreased withwavelength but the spectral shape of the particulate AQY was flatter in thevisible regime. This feature resulted in a disproportionally higher visiblelight-driven CO production by particles, thereby increasing the ratio ofparticle- to CDOM-based CO photoproduction with depth in the euphotic zone.In terms of depth-integrated production in the euphotic zone, CO formationfrom CDOM was dominated by the ultraviolet (UV, 290–400 nm) radiationwhereas UV and visible light played roughly equal roles in CO productionfrom particles. Spatially, CO AQY of bulk particulate matter (i.e. the sumof organics and inorganics) augmented from the estuary and shelf to thebasin while CO AQY of CDOM trended inversely. Water from the deepchlorophyll maximum layer revealed higher CO AQYs than did surface water forboth particles and CDOM. CO AQY of bulk particulate matter exceeded that ofCDOM on the shelf and in the basin, but the sequence reversed in the estuary.Without consideration of the potential role of metal oxides (e.g. ironoxides) in particle photochemistry, mineral absorption-corrected CO AQY ofparticulate organic matter (POM) could, however, surpass its CDOMcounterpart in all three sub-regions and displayed magnitudes in the estuarythat overtook those in shelf and offshore waters. In terms of COphotoproduction, POM was thus more photoreactive than CDOM, irrespective ofthe organic matter's origins (i.e. terrigenous or marine). Riverine CDOMexhibited higher photoreactivity than marine CDOM and land-derived POMappeared more photoreactive than marine POM. AQY-based modeling indicatesthat CO photoproduction in the study area is underestimated by 12–32% ifthe particulate term is ignored.

[学科分类] 地球化学与岩石