Distribution, Flux, Photoproduction And Biological Consumption Of Carbon Monoxide In Sea Water

Carbon monoxide (CO) acts an indirect atmospheric trace gas playing a role in the global warming and atmospheric chemistry. Although continental shelves, estuaries and bays only occupy a small part of the world ocean, they have significant contributions to the atmospheric CO. Therefore studies on the biogeochemistry of CO in coastal waters will be helpful to estimate the contributions of oceanic waters emissions to the atmospheric CO and the influence to the oceanic carbon cycling.In the present dissertation, we conducted CO studies in the Bohai Sea, the Yellow Sea and Jiaozhou Bay about variations of distributions of CO, sea-to-air fluxes, microbial consumption and photoproduction. Besides, the influence factors of photoproduction of CO in seawater are also studied in Jiaozhou Bay. The main conclusions are drawn as follows:(1) Concentration distribution, sea-to-air flux, photoproduction and biological consumption of carbon monoxide (CO) in the surface seawater and atmospheric CO mixing ratio were measured in the Yellow Sea and the Bohai Sea from April to may in 2010. A headspace analysis system was used for CO measurement. The concentrations of CO in the surface seawater was 1.24±0.79 nmol L^-1. Overall, the concentrations of CO displayed a decreasing trend from the coast to the offshore stations and followed diurnal variations after classifying and averaging the CO concentrations according to sampling and analyzing time in the unit of one hour, with maxima in midnoon 10 fold higher than predawn minima. The supersaturation factor is 3.61±2.99, indicating that the Yellow Sea and the Bohai Sea was a net source of atmospheric CO. The average sea-to-air fluxes of CO from the Yellow Sea and the Bohai Sea were estimated to be 2.13±2.91μmol m^-2 d^-1 by the W92 equation. Based on the the area of the Yellow Sea and the Bohai Sea, the CO emission was estimated to be 1.10 Gg CO-C in spring。Microbial consumption of CO in sea-surface in the Bohai Sea and the Yellow Sea typically followed first-order kinetics in most cases. The microbial CO consumption rate constant (kbio) was 0.29 h^-1and covaried with chlorophyll a concentrations.Using SMARTS2 spectral irradiance model to estimate CO production, the photoproduction rate of CO was 54.60μmol m^-2 d^-1 and the photoproduction of carbon in the Yellow Sea and the Bohai Sea was 26.95 Gg in spring.(2) Concentration distribution, sea-to-air flux and photoproduction of dissolved CO were investigated in the Jiaozhou Bay in January, March, May, June-December during 2009^-2011. Dissolved CO concentrations showed obvious seasonal variation, with the highest concentrations in summer (4.69 nmol L^-1) followed by spring (3.19 nmol L^-1); autumn (1.90 nmol L^-1),winter (0.98 nmol L^-1). Except for several stations in January 2011, CO supersaturation was ubiquitous at investigated sites, the average rspectively, in summer, spring, autumn and winter were 12.34, 8.02, 4.14 and 1.23, which suggested that the Jiaozhou Bay was a net source of atmospheric CO. The estimated atmospheric CO fluxes using the equation of W92 were 18.80, 15.08, 5.67 and 0.83 mol m^-2d^-1 in summer, spring, autumn, and winter, repectively. Overall, the concentrations of CO displayed a decreasing trend from the eastern to western coast and from the northern to southern part of the Bay.Based on the average annual atmospheric CO flux (10.10μmol m^-2 d^-1) and the area of the Jiaozhou Bay, the annual CO emission was estimated to be 0.02 Gg CO-C a ^-1.The annual CO photoproduction in the Jizoahou Bay was estimated to be 0.13 Gg CO-C a^-1 using SMARTS2 spectral irradiance model,, with an average photoproduction rate of the whole year was 71.01μmol m^-2 d^-1. Based on the average solar photon irradiance in the 4 seasons, the average photomineralization rate of DOC in Jiaozhou Bay of the whole year was estimated to be 23.8 mgC m^-2 d^-1, representing 6.5% of the primary production.(3) Concentration distribution, sea-to-air flux and photoproduction of CO were investigated during 4 seasons in the surface seawater of Jiaozhou Bay estuaries including Haibo, Licun, Baisha, Moshui Dagu, Caowen and Yang rivers during 2009^-2010. The average surface water concentrations of CO were 2.08±1.32, 2.40±0.95, 3.98±2.90 and 1.99±1.85 nmol L^-1 in spring, summerl, autumn and winter, respectively. Dissolved CO concentrations showed obvious seasonal variation. CO supersaturation was ubiquitous at all investigated sites in the estuaries of the Jiaozhou Bay in 4 seasons, the supersaturation factors were 35.71±13.79, 15.21±7.89, 7.59±3.08 and 6.09±3.35 in summer, spring, autumn and winter, respectively, which indicated that the Jiaozhou Bay estuaries were net sources of atmospheric CO. Then the average sea-to-air fluxes of CO from the Jiaozhou Bay estuaries were estimated to be 47.02±19.21, 54.00±16.73, 14.79±5.93 and 10.21±6.86μmol m^-2 d^-1 in summer, spring, autumn and winter, respectively, by the W92 equation. In connection with areas of the Haibo,Licun, Baisha, Moshui Dagu, Caowen river of the Jiaozhou Bay the preliminary CO emission from these estuaries is estimated to be 0.88 Gg CO-C a^-1,with an average sea-to-air flux of the whole year was 31.51μmol m^-2 d^-1. Annual CO photoproduction of the Jiaozhou Bay estuaries was 2.18 Gg CO-C a^-1, with the average photoproduction rate of the whole year was 118.90μmol m^-2 d^-1.The effects of the factors, including photo-intensity, water temperature, pH, salinity and photobleaching time of CDOM on the photoproduction of CO in seawater in several river mouthes of the Jiaozhou Bay were examined in this paper. The results indicate that the photoproduction rates of CO increase with higher light intensity, higher water temperature, higher pH and decrease with longer wavelength, more photobleaching time, higher salinity.