【作者】 任春艳；

【导师】 杨桂朋；

【作者基本信息】 中国海洋大学 ， 海洋化学， 2010， 博士

【摘要】 一氧化碳(Carbon monoxide,CO)是大气中一种重要的痕量气体,对全球变暖和大气化学有重要作用。海洋是大气中CO的重要自然排放源,其中河口、海湾和陆架等近岸海域面积虽然只占整个海洋的一小部分,但对海洋排放CO的贡献较大。因此对典型的近岸海洋环境中溶解CO的生物地球化学进行研究,对在全球尺度上准确地估算海洋对大气CO的贡献和在全球范围内正确估计CO的光致生成对海洋中碳循环的影响具有重要意义。本文以中国近海有代表性的陆架海区—东海和黄海为研究目标,从海洋和大气两方面入手,率先对这一海域中溶解CO的浓度分布、时空变化、海-气通量、微生物消耗以及光化学生成进行了较为系统的研究,同时对受人类活动影响较大的半封闭的海湾—胶州湾中CO的光致生成进行了考察。本论文的主要研究结果如下：1.于2009年4-5月和2009年11-12月对东海和黄海海域不同深度的海水中的溶解CO的分布和海-气通量的时空变化进行了研究。春季和秋季东海表层海水中CO的平均浓度分别为2.42±1.86和0.88±0.52 nmol L-1;黄海表层海水中CO的平均浓度分别为2.23±1.46和0.80±0.56 nmol L-1。由此看出,东海和黄海表层海水中CO浓度呈现明显的季节变化,春季海水中溶解CO明显高于秋季,这主要是由于4、5月份的太阳光辐射明显高于12月所致。东海和黄海中CO的空间分布受到长江等陆源输入和贫营养的黑潮水系及其分支的影响。春季和秋季CO的水平分布大致相似,即从近岸向外海呈逐渐降低的趋势。春季和秋季不同断面不同站位CO浓度的垂直分布特征基本相同,CO浓度最大值一般出现在表层,随深度增加CO浓度逐渐减小。在没有太阳光透过的真光层以下检测到的CO浓度表明,海水中CO可能存在其他来源,如暗反应、垂直混合、上升流以及底层沉积物等。2.东海和黄海整个真光层水体中CO浓度均具有明显的周日变化,最大值是最小值的5～50倍。其中,各层CO浓度最小值均出现在凌晨前后,最大值出现时间各不相同。表层CO浓度最大值出现在下午14：00左右,滞后于最大太阳光辐射约2 h,表层以下其它各层CO最大值则出现在中午12：00左右,没有滞后效应。CO明显的周日变化特征进一步证明海水中CO主要是由光化学产生,表层海水中CO浓度主要由太阳光量子通量决定。3.春季和秋季CO在东海和黄海所有调查站位基本都是过饱和的,过饱和系数分别为16.05±13.54和3.88±2.95,表明调查期间东海和黄海是大气中CO的源。根据现场风速以及表层海水和大气中CO浓度,利用Wanninkhof公式(W92)计算了CO的海气交换通量。春季的海-气通量(6.67±4.61μmol m-2 d-1)明显大于秋季(0.84±0.82μmol m-2 d-1),这主要是由于春季有较大的过饱和系数(平均为16.05)和风速(平均为7.3 m s-1),而秋季尽管风速也较大(平均为6.3 m s-1),但由于过饱和系数(平均为3.88)明显低于春季,因而其海-气通量明显小于春季。根据春季和秋季计算的CO年平均通量以及东海和黄海的海洋面积,由此初步估算出东海和黄海中CO的年释放量为18.9±13.7 Gg CO-C yr-1。应用此数据进一步计算出全球陆架海域每年向大气释放的CO约为0.49±0.36 Tg CO-C yr-1,占全球释放量的约11%。由此证明尽管陆架海域的面积在全球海洋中所占比例很小(7～10%),但其对大气中CO的贡献较大。4.春季和秋季各站位表层海水中CO的微生物消耗大部分为一级反应,其消耗速率与Chl-a浓度呈正相关,而与盐度呈负相关。表层海水中CO的微生物消耗速率具有明显的季节变化,春季的kbio (0.22 h-1)明显大于秋季(0.16 h-1),这主要是由于春季海水中较大的Chl-a浓度和较高的海水温度所致。5.CO的光致生成受溶解有色物质(CDOM)来源和温度的影响。CO的表观量子产量(AQY)与254 nm处的比吸光系数(SUVA254)之间有良好的线性关系,表明陆源CDOM发生光化学降解生成CO的效率高于海源CDOM。同时,光脱色会对CO的量子产量产生影响。同一水样,光脱色程度越大,量子产率越小光脱色对陆源CDOM的影响大于海源CDOM。通过多元线性回归分析拟合出了东海和黄海中AQY与SUVA254和温度的关系方程,并计算出东海和黄海中CO的光致生成量为246.32 Gg CO-C yr-1。并进一步由此估算东海和黄海中DOC的总光矿化速率为7.1Tg C yr-1,占初级生产的3.9%。6.光脱色会显著降低胶州湾中含陆源CDOM较多的样品中CO的量子产量。同时,胶州湾中CO的表观量子产量与SUVA254和温度也均有线性相关。应用胶州湾秋季的平均太阳光量子通量,计算得到秋季胶州湾中CO的光致生成速率为36.16μmol m-2 d-1。由此进一步计算出胶州湾中DOC的总光矿化速率为12.58 mg C m-2 d-1,占初级生产的5.1%。更多还原

【Abstract】 Carbon monoxide (CO) is an important atmospheric trace gas, which plays a significant role in the global warming and atmospheric chemistry. Global oceans are net natural sources of atmospheric CO. Although coastal regions such as continental shelves, estuaries and bays only occupy a small part of the world ocean, they appear to be responsible for a large part of the oceanic CO emission. Therefore studies on the biogeochemistry of CO in the coastal waters will be helpful to estimate the contribution of oceanic emissions to the atmospheric CO and the influence to the oceanic carbon cycling on a global scale.In the present dissertation, we choose the East China Sea (ECS) and the Yellow Sea (YS) as the study areas. The spatial and temporal variations of distributions of CO, sea-to-air fluxes, microbial consumption and photoproduction are systematically studied for the first time. The photoproduction of CO in Jiaozhou Bay that is affected seriously by human activities was also examined. The main conclusions are drawn as follows:1. The distributions and sea-to-air fluxes of CO are determined in the ECS and YS during April-May and Nov-Dec,2009. The surface water concentrations of CO in ECS in spring and autumn are 2.42±1.86 and 0.88±0.52 nmol L-1, respectively The surface concentrations of CO in YS in spring and autumn are 2.23±1.46 and 0.80±0.56 nmol L-1, respectively. CO concentrations show a notable seasonal variation, with those in spring higher than those in autumn, which corresponds with the solar photon irradiance higher in April-May than those in December. The spatial distributions of CO in the ECS and YS are obviously influenced by the Yangtze River import and the oligotrophic Kuroshio waters. When the distribution patterns are compared with each other in spring and autumn, they are nearly synoptic and decreased from inshore to offshore sites. Vertical profiles of concentration of CO along different transects and at different stations were similar. The highest concentrations of CO were generally found at the sea surface, concentrations of CO in the water column gradually decreased with depth. However, CO could be detected even at depths under euphotic zone, where the light intensity was under detection limit, indicating the existence of other sources of CO such as dark production, diffusion, deep water current, sediment, etc.2. CO concentrations exhibited obvious diurnal variations in almost the entire euphotic zone in the ECS and YS, with maximum values 5-50 folds higher than minimum values at two anchor stations. Minimal concentrations of CO all occurred before dawn. However, there were differences of the maximum concentrations of CO between the sea-surface and other depths. The peak of concentrations of CO was observed in the early afternoon (about 14:00), a time lag about 2 hours at the surface and at noon at other depths, respectively. Marked diurnal variation of concentrations of CO in seawater indicated that CO was produced primarily by photoreaction and the concentrations of CO in surface seawater were mainly related to the solar irradiance.3. CO supersaturation was ubiquitous at all investigated sites in the ECS and YS in spring and autumn, the supersaturation factors were 16.05±13.54 and 3.88±2.95, respectively, which indicated that the ECS and YS are net sources of atmospheric CO. A short-term estimate of near-instantaneous flux was based on the concentration of CO in surface water and in situ wind speed for each time point by the arithmetic of W92. The sea-to-air flux in spring (6.67±4.61μmol m-2 d-1) was much higher than that in autumn (0.84±0.82μmol m-2 d-1), mainly due to the higher supersaturation factors in spring (the average is 16.05μmol m-2 d-1) than those in autumn (the average is 3.88μmol m-2 d-1). In connection with the area of the ECS and YS, the preliminary CO emission from the ECS and YS is estimated to be 18.9±13.7 Gg CO-C yr-1. Extrapolation of the mean flux of the ECS and the YS to the global coastal surface area provides coastal emission of about 0.49±0.36 Tg CO-C yr-1, accounting for approximately 11% of the global oceanic CO emission, though it occupies a small part (7-10%) of the world ocean. Our results indicated that the coastal contribution to the global CO emissions should not be negligible.4. Microbial consumption of CO in sea-surface in the ECS and YS in spring and autumn typically followed first-order kinetics in most cases. The microbial CO consumption rate constants (kbio) covaried with chlorophyll a concentrations and diminished with salinity. CO consumption rates show obvious seasonal variations, with those in spring (0.22 h-1) higher than those in autumn (0.16 h-1), primarily due to relatively higher Chl-a concentrations and seawater temperatures.5. For CO photoproduction, effects of water temperature and the origin of CDOM on the apparent quantum yields of CO (AQYCO) were examined. AQYco showed a strong positive correlation with the dissolved organic carbon-normalized absorption coefficient at 254 nm (SUVA254), suggesting that terrestrial CDOM is more efficient at photochemically producing CO than marine origin CDOM. CDOM photobleaching dramatically decreased AQY on the most terrestrial CDOM, but had little effect on the most marine samples. An empirical equation was derived for predicting the CO photoproduction efficiency in the ECS and YS based on SUVA254 and water temperature. Annual CO photoproduction in the ECS and YS was estimated to be 246.32 Gg CO-C yr-1.6. CDOM photobleaching could dramatically decreased AQY on the most terrestrial CDOM samples in. AQYco in Jiaozhou Bay had a linear correlation with SUVA254 and water temperature. Based on the average solar photon irradiance in autumn, the photoproduction rate of CO in Jiaozhou Bay was estimated to be 36.16μmol m-2 d-1 in autumn. The total photomineralization of DOC in Jiaozhou Bay was estimated to be 12.58 mg C m-2 d-1, representing 5.1% of the primary production in autumn.更多还原