Photobleaching as a factor controlling spectral characteristics of chromophoric dissolved organic matter in open ocean

[摘要] Chromophoric dissolved organic matter (CDOM) ubiquitously occurs in marineenvironments and plays a significant role in the marine biogeochemicalcycles. Basin scale distributions of CDOM have recently been surveyed in theglobal ocean and indicate that quantity and quality of oceanic CDOM aremainly controlled by in situ production and photobleaching. However, factorscontrolling the spectral parameters of CDOM in the UV region, i.e., spectralslope of CDOM determined at 275–295 nm (S_275–295) and the ratio of twospectral slope parameters (S_R); the ratio of S_275–295 toS_350–400, have not been well documented. To evaluate the factorcontrolling the spectral characteristics of CDOM in the UV region in the openocean, we determined the quantitative and qualitative characteristics ofCDOM in the subarctic and subtropical surface waters (5–300 m) of thewestern North Pacific. Absorption coefficients at 320 nm in the subarcticregion were higher than those in the subtropical region throughout surfacewaters, suggesting that magnitudes of photobleaching were different betweenthe two regions. The values of S_275–295 and S_R were also higher inthe subtropical region than the subarctic region. The dark microbialincubation showed biodegradation of DOM little affected S_275–295, butslightly decreased S_R. On the other hand, increases in S_275–295 andrelative stableness of S_R were observed during photo-irradiationincubations respectively. These experimental results indicated thatphotobleaching of CDOM mainly induced qualitative differences in CDOM at UVregion between the subarctic and subtropical surface waters. The results ofthis study imply that S_275–295 can be used as a tracer ofphotochemical history of CDOM in the open ocean.

[学科分类] 地球化学与岩石