【作者】 陆小兰；

【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】 溴甲烷和氯甲烷是大气中重要的痕量温室气体,对全球变暖和大气化学具有重要作用。海洋在溴甲烷和氯甲烷的生物地球化学循环中具有复杂的作用,海洋即是大气溴甲烷和氯甲烷的源,也是其汇,其中近岸海湾和陆架海域可能是大气中溴甲烷和氯甲烷的源区,虽然其面积只占到整个海洋面积的一小部分,但对温室气体释放的贡献较大。因此对这些海洋环境中溴甲烷和氯甲烷溶解的状态进行研究,对在全球尺度上准确地估算海洋对大气溴甲烷和氯甲烷的贡献和对未来气候的影响具有重要意义。本文以中国近海有代表性的陆架区—东海和黄海以及受人类活动影响较大的海湾—胶州湾为研究目标,对这些海域海水中溶解的溴甲烷和氯甲烷的浓度分布特征、饱和状态和海-气通量的时空变化进行了较为系统的研究,为估算中国海域对大气中溴甲烷和氯甲烷的区域性贡献提供了科学依据,同时为全球海洋溴甲烷和氯甲烷的数据库提供了大量的近海现场调查数据。本论文的主要研究成果如下:1.分别于2009年4-5月和2007年11月对东海、2008年8月对长江口附近海域海水中溶解的溴甲烷和氯甲烷进行了研究,结果表明：春季东海表层海水中溴甲烷和氯甲烷的平均浓度分别为4.75±0.83和85.7±18.8 pmol/L;秋季分别为2.74±1.49和83.5±11.8 pmol/L;夏季长江口附近海域分别为7.76±1.21和86.1±34.6 pmol/L,相应的春季和秋季长江口附近海域分别为5.24±0.59、90.6±12.8和2.82±1.13、87.3±8.7 pmol/L。因此东海水体中溶解的溴甲烷呈现明显的季节变化,总体上是夏季高于春季高于秋季；氯甲烷浓度尽管有季节差异,但变化幅度较小。春季和秋季表层海水中的溴甲烷和氯甲烷浓度自近岸向远海呈逐渐降低的趋势,在闽浙沿岸和长江口外呈现出明显的高浓度区,在陆架的东部出现了溴甲烷和氯甲烷浓度分别小于2.0-4.0和80.0 pmol/L的低值区,表明东、黄海海水中溴甲烷和氯甲烷的水平分布主要受到了近岸入海径流如长江冲淡水和闽浙沿岸流以及外海黑潮水的影响。春、秋季航次中对东海不同断面和黑潮水域不同站位水体中溴甲烷和氯甲烷浓度的垂直分布进行了研究,结果表明受长江冲淡水、台湾暖流和黑潮等水团以及光照和生物活动的共同影响,在不同断面和不同站位垂直分布存在一定的差异,但总体上垂向最大浓度均位于0-75m混合层内。春季东海表层海水中溴甲烷和氯甲烷的饱和异常值分别为248.3±56.6%和27.9±25.9%；夏季长江口附近海域分别为659.4±127.2%和91.2±62.4%；秋季东海分别为122.3±106.4%和42.6±16.3%。因此溴甲烷和氯甲烷的饱和异常值也有明显的季节性变化,且三个季节调查的东海海域溴甲烷和氯甲烷均处于过饱和状态,表明东、黄海在调查期间是大气溴甲烷和氯甲烷的源。根据现场风速和表层海水中溴甲烷和氯甲烷的浓度,利用Wanninkhof (1992)公式(W92)分别计算了上述调查海区中溴甲烷和氯甲烷的海-气通量,结果表明：春季溴甲烷和氯甲烷的平均海-气通量分别为59.4±50.5和286.0±324.2nmolm-2d-1;夏季分别为0.6±0.4和3.7±3.4 nmol m-2d-1；秋季分别为31.0±38.0和463.0±385.8nmolm-2d-1。因此可以看出二者的海-气通量也具有一定的季节变化,但由于受到风速的强烈影响,通量的变化趋势与浓度不完全一致,夏季由于受到低风速的影响通量最小2.分别于2008年7、8月、2009年3、5月和2007年11月对南黄海西部海水中溶解的溴甲烷和氯甲烷进行了研究,结果表明：南黄海西部上述5次调查(按顺序)溴甲烷的平均浓度分别为11.85±5.51、5.79±2.18、4.24±1.26、5.86±1.07和3.93±1.30 pmol/L;氯甲烷的平均浓度分别为240.9±104.1、135.0±50.1、81.6±31.8、86.1±22.1和104.5±23.2 pmol/L。因此南黄海西部表层海水中溴甲烷和氯甲烷的浓度呈现明显的季节变化,溴甲烷的浓度总体上呈现出夏季高于春季高于秋季；氯甲烷浓度夏季高于秋季高于春季。受到人类活动和生物及海洋物理状况的共同作用,黄海西部表层海水中溴甲烷和氯甲烷浓度的水平分布没有一致的规律性,但2008年夏季浒苔的生消明显影响了水体中溴甲烷和氯甲烷的浓度及其分布。秋季对35°N断面进行了溴甲烷和氯甲烷垂直分布的研究,结果表明由于受到各种人类活动、生物活动和南黄海冷水团的共同影响,二者的垂向最高浓度出现在0-30 m层。南黄海西部上述5次调查中溴甲烷的平均饱和异常值分别为940.4±496.0%、432.4±205.3%、98.6±52.1%、257.3±76.4%和163.4±75.6%；氯甲烷分别为352.4±189.8%、169.4±100.0%、-19.7±28.9%、7.2±25.8%和48.2±29.5%。因此二者的饱和异常值也表现出明显的季节变化,且溴甲烷在各次调查中均呈过饱和状态,表明在上述调查期间南黄海西部是大气溴甲烷的源；氯甲烷在2009年3月初春之际,总体上是处于不饱和状态,表明该次调查期间南黄海西部是大气氯甲烷的汇,其它调查期间是源。根据现场风速和表层海水中溴甲烷和氯甲烷的浓度,利用W92公式分别计算了上述调查中南黄海西部溴甲烷和氯甲烷的海-气通量,结果表明：南黄海西部上述5次调查中溴甲烷的平均海-气通量分别为108.9±82.1、0.4±0.4、35.1±29.2、77.1±109.7和29.2±31.2 nmolm-2d-1;氯甲烷的平均海-气通量分别为1738.1±1002.7、6.6±7.3、-272.5±506.2、104.0±311.1和307.9±245.3 nmolm-2d-1。可见在南黄海西部水域二者的平均海-气通量也有明显的季节变化,受到夏季现场调查较低风速的影响,2008年8月的通量值明显减小3.分别于2009年5月和2007年10月对山东半岛北部附近海域和北黄海海水中溶解的溴甲烷和氯甲烷进行了研究,结果表明：春季溴甲烷和氯甲烷的平均浓度分别为5.06±0.57和92.2±6.92 pmol/L;秋季分别为6.22±3.21和83.6±19.0 pmol/L,因此所调查的北黄海海域表层海水中溴甲烷和氯甲烷的浓度也呈现一定的季节变化,但其变化幅度不大。春季山东半岛北部附近海域溴甲烷和氯甲烷的饱和异常值分别为172.7±36.9%和4.4±10.1%；秋季北黄海分别为344.5±227.0%和27.7±28.8%,表明二者的饱和异常值也有季节变化,且在调查期间北黄海是大气溴甲烷和氯甲烷的源。根据现场风速和表层海水中溴甲烷和氯甲烷的浓度,利用W92公式分别计算了春、秋季所调查的北黄海海域溴甲烷和氯甲烷的海-气通量,结果表明：春季山东半岛北部附近海域溴甲烷和氯甲烷的平均海-气通量分别为56.4±24.5和35.0±207.6nmolm-2d-1;秋季北黄海分别为66.8±86.9和231.6±356.7nmolm-2d-1,总体上秋季通量大于春季。4.分别于2007年6、8月、2008年1月对胶州湾和2007年10月、2008年11月对胶州湾邻近海域海水中溶解的溴甲烷和氯甲烷进行了研究,结果表明：胶州湾上述3次调查(按顺序)溴甲烷的平均浓度分别为10.99±4.38、11.87±5.74和6.22±1.95pmol/L;氯甲烷的平均浓度分别为249.6±60.8、382.9±145.4和145.5±43.0pmol/L;其邻近海域2次秋季调查溴甲烷浓度分别为5.86±1.07、4.16±1.40pmol/L,氯甲烷浓度分别为151.6±24.8、144.4±48.6pmol/L。因此胶州湾及其邻近海域海水中溴甲烷和氯甲烷的浓度呈现出夏季高于春、秋季高于冬季的季节变化。受到人类活动、生物活动及海湾内外水交换的共同作用,胶州湾表层海水中溴甲烷和氯甲烷浓度的水平分布总体表现为东高西低,北高南低,湾内高湾外低的趋势。上述各次调查(按顺序)胶州湾及其邻近海域溴甲烷的饱和异常值分别为707.1±322.1%、949.7±460.0%、140.8±72.0%、449.1±107.2%和170.9±88.5%；氯甲烷饱和异常值分别为290.4±95.1%、668.3±296.9%、31.7±40.7%、169.7±42.6%和94.2±63.7%,因此胶州湾及邻近海域表层海水中溴甲烷和氯甲烷的饱和异常值具有明显的季节变化,其变化趋势与浓度一致,各次调查的饱和异常值数据表明胶州湾在各调查期间是大气溴甲烷和氯甲烷的源。根据胶州湾长期风速和表层海水中溴甲烷和氯甲烷的浓度,利用W92公式分别计算了上述调查中胶州湾及其邻近海域的溴甲烷和氯甲烷的海-气通量,结果表明：上述各次调查中胶州湾及其邻近海域溴甲烷的平均海-气通量分别为73.0±33.2、84.14±40.6、26.84±14.4、55.34±13.3和27.44±14.3nmol m-2 d-1；氯甲烷平均通量分别为1253.54±410.7、2312.84±1022.4、225.5±291.5、864.5±218.1和659.8±447.5 nmol-2d-1。由此可以看出,溴甲烷和氯甲烷的海-气通量具有一定的季节变化,且与二者浓度的季节变化趋势一致。其中胶州湾氯甲烷的海-气通量由于受其较高浓度的影响,通量普遍高于东、黄海。5.根据所调查海域的面积及其平均海-气通量,东、黄海面积约占全球海洋的0.3%,初步估算出东、黄海年释放溴甲烷和氯甲烷分别约为2.0和8.1 Gg,约占全球海洋释放量的3%和1%。当然由于各种不确定因素的存在,该释放量与实际释放量之间可能存在一定的误差。我们的研究表明,陆架海区,尤其是中低纬度陆架海域,虽然只占全球海洋的一小部分,但对全球海洋释放溴甲烷和氯甲烷的贡献不容忽视。更多还原

【Abstract】 Methyl bromide (CH3Br) and methyl chloride (CH3Cl) are important atmospheric trace gases, which play significant roles in the global warming and atmospheric chemistry. The ocean plays important and complex roles in the global biogeochemical cycles of these methyl halides. Coastal regions such as continental shelves, estuaries and bays appear to be the sources of atmospheric CH3Br and CH3Cl and responsible for a large part of the oceanic emission of CH3Br and CH3Cl, though their areas only occupy a small part of the world ocean. Therefore, studies on the occurrence of CH3Br and CH3Cl in coastal waters will be helpful to estimate the contribution of oceanic emission to the atmospheric CH3Br and CH3Cl on the global scale, and to predict the influence of oceanic to the global climate, especially in middle-low latitude.In the present dissertation, distributions, saturation anomalies, sea-air fluxes of CH3Br and CH3Cl in the coastal waters of China, i.e. the East China Sea (ECS) and the Yellow Sea (YS), and the Jiaozhou Bay, are studied systematically. The main research works are as follows:1. Distributions, saturation anomalies, sea-air fluxes of CH3Br and CH3Cl are determined in the ECS during Apr-May,2009 and Oct-Nov,2007 and in the waters adjacent to the Yangtze Estuary during Aug,2008. The results show that the average concentrations of CH3Br and CH3Cl in the surface waters of the ECS are 4.75±0.83 and 85.7±18.8 pmol/L in spring; those are 2.74±1.49 and 83.5±11.8 pmol/L in autumn, respectively. In the waters off the Yangtze River Estuary, those are 5.24±0.59 and 90.6±12.8 pmol/L in spring,7.76±1.21 and 86.1±34.6 pmol/L in summer,2.82±1.13 and 87.3±8.7 pmol/L in autumn, respectively. In general, average concentrations of CH3Br in the surface waters in the ECS show obvious seasonal variations, with those in summer higher than those in spring and higher than those in autumn, while seasonal variations of CH3Cl are not distinct. The horizontal distributions of CH3Br and CH3Cl in the ECS are obviously influenced by the Yangtze River and the Kuroshio waters in spring and autumn, illustrating a decreasing trend from inshore to offshore sites, without being strongly biased by temporal change. The vertical distributions along different transects and at different stations of CH3Br and CH3Cl in the ECS are studied. The results show that the distributions are influenced by the coastal currents, the Taiwan Warm Current and the Kuroshio. The vertical profiles of the two gases differed among stations, with maxima generally appearing in the mixed layer (0-75 m). The surface waters of the ECS in spring, summer and autumn are generally supersaturated for CH3Br and CH3Cl and the saturation anomalies (SA) of CH3Br are 248.3±56.6%,659.4±127.2% and 122.3±106.4%; those of CH3Cl are 27.9±25.9%,91.2±62.4% and 42.6±16.3%, respectively, indicating that the ECS is a net source for the atmospheric CH3Br and CH3Cl in the investigated time. Based on in situ wind speeds and the surface concentrations, Wanninkhof relationship (W92) is employed to estimate the sea-to-air fluxes of CH3Br and CH3Cl. The results show that average CH3Br fluxes in spring, summer and autumn are 59.4±50.5,0.6±0.4 and 31.0±38.0 nmol m-2 d-1; those of CH3Cl are 286.0±324.2,3.7±3.4 and 463.0±385.8 nmol m-2 d-1, respectively. Therefore, the and CH3Cl fluxes display obvious seasonal variations, which are not agreement with the concentration variations, with the lowest in summer due to lower wind speeds.2. Distributions and fluxes of CH3Br and CH3Cl are determined during 5 surveys on the western part of the Southern Yellow Sea (WPSYS) in Jul, Aug,2008, Mar, May,2009 and Nov,2007. The surface CH3Br and CH3Cl concentrations show apparently seasonal variations, with the highest observed in summer and the lowest in autumn (CH3Br) or early spring (CH3Cl). The average concentrations of CH3Br in the surface waters of 5 surveys above are 11.85±5.51,5.79±2.18, 4.24±1.26,5.86±1.07 and 3.93±1.30 pmol/L; those of CH3C1 are 243.9±104.1, 135.0±50.1,81.6±31.8,86.1±22.1 and 104.5±23.2 pmol/L, respectively. The two gases show different distributions in the WPSYS of 5 surveys, and the bloom of Enteromorpha Prolifera affects strongly the distributions of CH3Br and CH3Cl in Jul,2008. Results of the vertical profiles of CH3Br and CH3Cl at 35°N transect in the Southern Yellow Sea (SYS) show that the distribution are influenced by SYS Cool Water and anthropogenic activity, with maxima generally appearing in the mixed layer (0-30 m). The CH3Br SA of 5 surveys are 940.4±496.0,432.4±205.3, 98.6±52.1,257.3±76.4 and 163.4±75.6%; those of CH3Cl are 352.4±189.8, 169.4±100.0,-19.7±28.9,7.2±25.8 and 48.2±29.5%, respectively. Therefore, the SA of CH3Br and CH3Cl show obvious seasonal variations, which are similar to the concentrations. The SYS are supersaturated for CH3Br in 5 surveys and also for CH3Cl except for the survey on Mar,2009, indicating that the WPSYS is a net source of atmospheric CH3Br during the studied time and of CH3Cl except for Mar,2009. Study on the flux in the WPSYS demonstrates that there exists the seasonal cycle of the fluxes of CH3Br and CH3Cl. The fluxes of CH3Br of 5 surveys in the WPSYS are 108.9±82.1,0.4±0.4,35.1±29.2,77.1±109.7 and 29.2±31.2 nmol m-2 d-1; those of CH3Cl are 1738.1±1002,6.6±7.3,-272.5±506.2, 104.0±311.1 and 307.9±245.3 nmol m-2 d-1, respectively. The fluxes in summer are lowest due to lower wind speeds, similar to the ECS.3. Distributions and fluxes of CH3Br and CH3Cl are determined in the Northern Yellow Sea (NYS) in May,2009 and Oct,2007. The results show that the average concentrations of CH3Br and CH3Cl in the surface waters are 5.06±0.57 and 92.2±6.92 pmol/L in spring; those are 6.22±3.21 and 83.6±19.0 pmol/L in autumn, respectively. Therefore, the CH3Br and CH3Cl concentrations in the NYS also varied with the season, but the range of variation are not large. The saturation anomalies of CH3Br and CH3Cl are 172.7±36.9% and 4.4±10.1% in spring; those are 344.5±227.0% and 27.7±28.8% in autumn, respectively. Therefore, the seasonal variations of the SA are observed in the NYS for the two gases, with the SA in autumn higher than those in spring. The NYS are supersaturated for the two gases, indicating that the NYS is a net source of atmospheric CH3Br and CH3Cl during the investigated time. The fluxes of CH3Br and CH3Cl in the NYS are 56.4±24.5,35.0±207.6 nmol m-2 d-1 in spring and 66.8±86.9,231.6±356.7 nmol m-2 d-1 in autumn, respectively.4. Distributions and fluxes of CH3Br and CH3Cl are determined during 3 surveys on the Jiaozhou Bay in Jun, Aug,2007, Jan,2008 and its adjacent areas in Oct,2007 and Nov,2008. The surface CH3Br and CH3Cl concentrations in the Jiaozhou Bay show apparently seasonal variations, with the concentrations in summer higher than those in spring and the lowest in winter. The average concentrations of CH3Br in the surface waters of 3 surveys above are 10.99±4.38,11.87±5.74 and 6.22±1.95 pmol/L; those of CH3Cl are 249.6±60.8,382.9±145.4 and 145.5±43.0 pmol/L, respectively. The average concentrations of CH3Br in the waters adjacent to the Bay are 5.86±1.07 pmol/L in Oct,2007 and 4.16±1.40 pmol/L in Nov,2008; those of CH3Cl are 151.6±24.8 and 144.4±48.6 pmol/L, respectively. The two gases show similar distributions in the Jiaozhou Bay and display a decrease from the eastern to western coast, from the northern to southern part of the Bay, influenced strongly by the input of the polluted river waters and the sewage waters along the eastern coast. The CH3Br SA of 5 surveys in the Bay and its adjacent areas are 707.1±322.1%,949.7±460.0%,140.8±72.0%,449.1±107.2% and 170.9±88.5%; those of CH3C1 are 290.4±95.1%,668.3±296.9%,31.7±40.7%, 169.7±42.6% and 94.2±63.7%, respectively. Therefore, the Jiaozhou Bay is supersaturated and is a net source for atmospheric CH3Br and CH3Cl. Based on long-term wind speeds and the surface concentrations, Wanninkhof relationship (W92) is employed to calculate the sea-to-air fluxes of CH3Br and CH3Cl in the Jiaozhou Bay. The results show that average CH3Br fluxes of 5 surveys are 73.0±33.2,84.1±40.6,26.8±14.4,55.3±13.3 and 27.4±14.3 nmol m-2 d-1; those of CH3Cl are 1253.5±410.7,2312.8±1022.4,225.5±291.5,864.5±218.1 and 659.8±447.5 nmol m-2 d-1, respectively. Therefore, sea-to-air fluxes of CH3Br and CH3Cl in the Jiaozhou Bay show obvious seasonal variations, with the highest occurring in summer and the lowest in winter, which are agreement with the concentration variations.5. Based on the investigated area and the average fluxes of CH3Br and CH3Cl, the annual CH3Br and CH3C1 emission from the ECS and the Yellow Sea (YS) are estimated to be 2.0 and 8.1 Gg/a. Although the ECS and YS occupies only 0.3% of the total ocean in area, the contributions of the ECS and YS to the net global sea-to-air CH3Br and CH3Cl fluxes are estimated to be about 3% and 1%, which means that shelf waters contribute significant amount to the total oceanic CH3Br and CH3Cl fluxes compared with open waters, especially in middle-low latitude shelf waters.更多还原