Distribution, Sources And Sinks Of Carbon Monoxide In The Bohai And Yellow Seas

Carbon monoxide (CO), one of the most important prevalent trace gases in the troposphere, can react with hydroxyl radicals in the troposphere. CO indirectly affects the concentrations of many chemically active gases in atmosphere and thus is regarded as an indirect greenhouse gas. The ocean has long been recognized as an important natural souce of atmospheric CO. Therefore, the study of CO biogeochemical cycle in the ocean plays a significant role in the global carbon cycle.In the dissertation, the Bohai Sea (BS) and Yellow Sea (YS), the typical China shelf seas, were selected as study areas. The spatial and temporal distributions as well as the sources and sinks of CO were systematically investigated during 4 seasons (Spring,1-22 May,2012; Summer,13-30 June,2011; Fall,8-22 September,2010; Winter,1-21 November). Additionally, the budget of the sources and sinks of CO in the surface water of the BS and YS was estimated. The main conclusions are drawn as follows:(1) There were obvious spatial and temporal variations in the distributions of the atmospheric CO over the BS and YS. The seasonal average atmospheric mixing ratios ([CO]atm) were higher in the BS (572 ppbv) than in the YS (497 ppbv). In seasonal variations, the [CO]atm in the BS decreased with the order:Fall> Winter> Summer> Spring, while those in the YS displayed the following order:Fall> Spring> Summer> Winter. The [CO]atm were highest in the fall both in the BS and YS. In regional variations, the [CO]atm in the BS were lower than those in the YS in spring, while the [CO]atm in the BS were higher than those in the YS in the other seasons.(2) There were obvious spatial and temporal variations in the distributions of CO in the surface water in the BS and YS. The seasonal average concentration in the surface water ([CO]surf) in the BS (1.59 nmol L-1) was approximately equal to that in the YS (1.82 nmol L-1). In seasonal variations, the [CO]surf in the BS decreased with the order:Summer> Spring> Fall> Winter, while those in the YS displayed the following order:Spring> Summer> Fall> Winter. In the BS and YS, the [CO]surf were higher in spring and summer while those were lower in the fall and winter. The [CO]surf were lowest in winter in the BS and YS. In regional variations, the [CO]surf in the BS were higher than those in the YS in summer and the fall, while the [CO]surf in the BS were lower than those in the YS in spring and winter.(3) The diurnal variations of CO were observed in the BS and YS. Minimal concentration of CO occurred before dawn and rose to a maximum after noon. Vertical profiles of CO concentrations were investigated during the cruises. The CO concentrations peaked in the surface water and rapidly declined with the depth, from a certain depth to the bottom the CO concentrations varied little and remained almost constant, the CO concentrations might slightly increase in the bottom in some stations.(4) Compared with the atmospheric CO, CO concentrations in the surface of the BS and YS were supersaturated in all seasons. In general, the BS and YS were a net source of atmospheric CO. Specifically, the BS was a sink of atmospheric CO in winter while it was a source in the other seasons; the YS was a source of atmospheric CO in all seasons. Sea-to-air flux of CO varied spatially and temporally in the BS and YS. In seasonal variations, the sea-to-air flux of CO in the BS decreased with the order:Summer> Spring> Fall> Winter, while that in the YS displayed the following order:Spring> Summer> Fall> Winter. In the BS and YS, the sea-to-air flux of CO was higher in spring and summer while that was lower in the fall and winter. The sea-to-air flux of CO was lowest in winter in the BS and YS. In regional variations, the sea-to-air flux of CO in the BS was higher than that in the YS in summer, while the sea-to-air flux of CO in the BS was lower than that in the YS in the other seasons.(5) CO sources in the surface water of the BS and YS are photoproduction, thermal or dark production and emissions by phytoplankton. The photochemical degradation of chromophoric dissolved organic matter is the major source. Additionally, the CO photoproduction rate varied seasonally and displayed the following order:Summer> Spring> Fall> Winter. CO sinks in the surface water of the BS and YS are the sea-to-air flux and microbial consumption. The microbial consumption is the major sink. Similarly, the microbial consumption rate varied seasonally and decreased with the order:Summer> Spring> Fall> Winter. The CO source (56.9-74.6 Gg CO-C yr-1) and sink (66.1 Gg CO-C yr-1) strengths are approximately in balance for the surface water in the BS and YS on the whole. The result accords with the marine steady-state theory.