| Polycyclic aromatic hydrocarbons(PAHs),widely distributed in the marine environment,are a class of semi-volatile pollutants.They are regarded as a category of persistent organic pollutants(POPs)with certain toxicity,bioaccumulation and the potential of long-range transport.Oceans are important reservoirs and sinks for most POPs,and several interface processes,such as air-sea exchange,phase partitioning and particle sinking,are especially taking place at their upper layer.Oceanic processes could lead to pollutants transporting in different spatial and dimensional scales,and pose direct and indirect impacts on their sourcesink patterns in the marine environments.Based on field works carried out in the open oceans(Pacific Ocean,Atlantic Ocean,Arctic Ocean,Indian Ocean and Southern Ocean),typical marginal seas(South China Sea,Bering Sea)and bay(Prydz Bay),oceanic transport of PAHs and its machenisms(physical pump,biological pump and microbilogical pump)are discussed in this thesis,and the major conclusions are as below.In the north-hemispheric oceans,concentrations of dissolved PAHs showed a decreasing trend in the surface waters from the North Pacific via the Arctic Ocean to the North Atlantic,and their inventories were 10091,39988 and 5333 tons in the Bering Sea,Arctic Ocean and Norwegian Sea respectively.The lateral transport fluxes of PAHs flowing into the Arctic Ocean through the Fram Strait,the Barents Sea and the Bering Strait are 720±620,370±130 and 180±60 tons/year,and the flux of the outflow from Arctic Ocean through the Greenland Sea is 930±710 tons/year,leading a net inflow(340±97 tons/year)to Arctic Ocean.Based on the disequilibrium of 210Po/210Pb,the sinking flux of particulate PAHs is estimated as 1883-3663 ng/m2/d on the Bering Shelf,and their residence time is 64-112 d in the mixed layer.Regarding the intense transport and removal processes in the shelf area,the broad Bering Shelf is suggested playing a role in "purifying" PAHs from the Pacific to the Arctic Ocean.Dissolved PAHs in the Southern Ocean showed a similar level to that in the northhemispheric oceans,but different in the variation extent and compositions.According to the results of the field observation during the Chinese 27th Antarctic Expedition,PAH concentrations showed a relatively low level in the open waters of the Southern Ocean(2.4±1.4 ng/L).The distribution of PAHs was characteristic with oceanic fronts,and the role of ocean fronts on PAHs needs to be further explored.Results of principal component analysis indicated that PAHs were more likely from the leakage of petroleum products along the equatorial Indian Ocean and Australian coast,while they were more likely from the combustion process in the Southeast Asia and Southern Oceans.In the marginal sea,such as the South China Sea,PAHs on the continental shelf were of higher levels than those in the open basin areas.PAH isomeric ratios and principal component analysis illustrated their mixed sources,and full-depth profiles of dissolved PAHs showed an"enrichment in surface and exhaustion in the deep" pattern.In the cross-shelf area,upwelling could enhance the scavenging efficiency of PAHs on the upper layer.While in the open-basin area,PAHs were more likely influenced by the halocline stratification and eddy diffusion,and their vertical flux due to eddy diffusion was estimated to be 39±12 ng/m2/d.The interaction between the marginal sea and open ocean would have an impact on the fate of PAHs.PAH concentrations in the Pacific Ocean and South China Sea showed spatial distinctions,and a common depletion for 3-ring PAHs was found in the northern South China Sea compared to the modelling results of conservative mixing by Kuroshio intrusion.The biodegradation process was enhanced by Kuroshio intrusion,which improved the temperature,oxygen and PAH bioavailability.In the water column,3-ring PAHs’ depletion was most significant at the surface but for 4-ring PAHs,that was at deep chlorophyll maximum layer.This study highlighted that the oceanic transport of PAHs not only influences their physical processes such as dilution and migration,but also influences their biological pump and microbial pump.Among the water masses of Prydz Bay and its adjacent waters,dissolved PAHs showed highest concentration in winter water and the lowest level in Circumpolar Deep Water.The inventory of PAHs in Prydz Bay was estimated as 180 tons,and seawater is the largest storage compartment.The variance of Phe/Ant values with depths reflected the influence of stratification on the vertical transport of pollutants.PAH levels from the Ice Shelf Water were of a high level,indicating ice is a potential "secondary source" of PAHs in the Antarctica.In summary,the transport of PAHs was moderated by the combined effects of physical pump,biological pump and microbiological pump in seawater.Oceanic fronts and thermohalocline had blocking effects on PAHs’ lateral and vertical transport respectively,while mesoscale eddies had less influence on their vertical diffusion.On the continental shelf with relatively high primary production,the vertical particulate export would "purify" PAHs driven by biological pump.Besides the dilution effect,the exchange of water mass could influence the biodegradation extent for low-molecular weight PAHs. |
