【作者】 张永；

【导师】 陈国华； 谢惠祥；

【作者基本信息】 中国海洋大学 ， 海洋化学， 2008， 博士

【摘要】 一氧化碳(CO)在海洋有机碳循环过程中起着非常重要的作用。表层海水中的CO主要是通过有色溶解有机物(CDOM)的光降解产生的,其中大部分被微生物所消耗,一小部分通过海气界面扩散进入大气。另外,溶解有机物(DOM)在无光环境中也会分解产生一部分CO。CO的光致生成量在大洋水中已经有了比较合理的界定,但是在河口和近岸水中的产量还不清楚。与光化学反应相比,CO微生物消耗的研究迄今为止开展较少,暗反应的研究则几乎没有。本文系统研究了加拿大圣劳伦斯河口水中CO的光化学反应、暗反应和微生物消耗,在此基础上对其生物地球化学循环做了平衡预算。进而把暗反应速率方程推广应用到全球海域,计算了全球海洋中CO的暗反应产量和深海稳态浓度,并对CO的微生物消耗量进行了估算。CO的光致生成受水温和CDOM的起源(陆源vs.海源)及光照时间的影响。为了便于比较,CO量子产率(Φco(λ))经太阳光量子通量(Q(λ))加权平均后简化为一个数值Φco。Φco随着盐度的增加(0-33)而降低,并与254 nm处的比吸光系数(SUVA254)有良好的线性正相关;这表明陆源CDOM光降解产生CO的效率高于海源CDOM。光照会引起CDOM的吸光系数降低,即光脱色。光脱色能显著降低低盐度水样的Φco,在光脱色的初始阶段降幅最大;但是对高盐度水样几乎没有影响。温度每升高20oC,低盐度水样的Φco升高~ 70%而高盐度水样仅仅升高30 - 40%。上述结果表明:水温和CDOM的起源及光照时间都对CO的光致生成有显著影响。在构建各种时空尺度的光化学模型时,都应充分考虑到上述因素的影响。通过多元线性回归分析拟合出了Φco与各变量的关系方程,据此计算出圣劳伦斯河口水中CO的光致生成量为26.2 Gg CO-C a-1。CO的暗反应速率(Qco)在水平方向自上游至下游依次递减,垂直方向自上至下递减。Qco与CDOM的含量呈线性正相关。陆源DOM产生CO的效率高于海源DOM。Qco与温度的关系服从线性阿伦尼乌斯行为,低盐度水样的反应活化能高于高盐度水样。Qco在pH 4-6时保持相对稳定,pH 6-8时缓慢增长,随着pH的进一步增加迅速升高。离子强度和铁对Qco几乎没有影响。通过多元线性回归分析拟合出了Qco与各变量的关系方程,据此计算出圣劳伦斯河口水中CO的暗反应产量为4.06 Gg CO-C a-1。CO的微生物消耗实验在船上现场测定。当水样中CO含量较低(通常[CO] < 12 nmol L-1)时,CO微生物消耗呈一级反应的特征,一级反应速率常数(Kco)随盐度的增加而降低,即Kco在低盐度的上游区段和Saguenay河高于圣劳伦斯湾。表层水中的Kco的变化范围:五月0.053 -1.01 (中间值: 0.14) h-1、七月0.081- 0.60 (中间值: 0.27) h-1、十月0.035 - 0.71 (中间值: 0.13) h-1、十二月0.024 - 0.38 (中间值: 0.032) h-1。Kco的变化主要受水温和细菌浓度的影响。温度每升高10oC, Kco升高40 - 80% (平均值: 53%)。反应活化能22-38 (平均值: 28) kJ mol-1。在[CO] 0-15 nmol L-1的范围内,CO的微生物消耗服从Wright-Hobbie动力学;随着[CO]的进一步升高,反应出现抑制现象。Wright-Hobbie动力学参数:最大消耗速率(Vmax)为0.15- 4.3 (平均值: 0.72) nmol L-1 h-1,并与盐度大致呈负相关;半饱和浓度(Km)为1.7- 6.5 (平均值: 4.1) nmol L-1,与其它参数没有关联。通过多元线性回归分析拟合出了Kco与各相关变量的关系方程,计算出圣劳伦斯河口表层水中CO的微生物消耗量为24.7 Gg CO-C a-1。圣劳伦斯河口水中CO的总产量为30.3 Gg CO-C a-1,其中光化学反应贡献了87%,是主要的来源,暗反应贡献了13%,是次要来源。表层水中CO的微生物消耗量占总产量的～81%,是主要的汇。考虑进海气扩散的影响,表层水中CO的总消耗量占总产量的～91%,源和汇基本持平。全球海洋中的CO暗反应产量为17.10 Tg CO-C a-1,其中91%产自大洋,9%产自近岸,或者54%产自表面混合层,46%产自次表层。与最新的全球海洋CO光致生成量(50 Tg CO-C a-1)相比,CO的暗反应产量是显著的。表层海水中的暗反应对海气通量的贡献约为15.7%。根据深海CO的稳态理论计算出大洋深处[CO](0.05-0.1 nmol L-1)接近当今测量技术的方法空白。全球海洋中CO的微生物消耗量估计为63.58 Tg CO-C a-1。更多还原

【Abstract】 Carbon monoxide (CO) plays an important role in the marine organic carbon cycling. CO in the surface ocean is produced primarily from photolysis of chromophoric dissolved organic matter (CDOM) and is lost by microbial consumption and air-sea outgassing. CO photoproduction fluxes are reasonably constrained in open-ocean waters, but remain obscure in estuary and coastal areas. Compared to photoproduction, CO microbial consumption is less studied; thermal (dark) production of CO, another potentially important source of marine CO, has drawn little attention. This study systematically investigated the photoproduction, dark production, and microbial consumption of CO in the St. Lawrence estuarine system (Canada). A budget of CO biogeochemical cycling in the estuarine system was made. Based on the empirical equation developed from the estuary, annual CO dark production in global oceans and steady- state [CO] in deep open ocean were estimated. Furthermore, annual CO microbial consumption in global oceans was derived.For CO photoproduction, effects of water temperature and the origin and light history of CDOM on the apparent quantum yields of CO (Φco) was examined. The solar insolation-weighted mean apparent quantum yield of CO (Φco) decreased as much as fourfold with increasing salinity and showed a strong positive correlation with the dissolved organic carbon-normalized absorption coefficient at 254 nm. This suggests that terrestrial CDOM is more efficient at photochemically producing CO than is CDOM of marine origin. CDOM photobleaching, mainly at the very early stage, dramatically decreasedΦco (by up to 6.4 times) for low salinity samples, but had little effect on the most marine sample. For a 20oC increase in temperature,Φco increased by ~70% for low-salinity samples and 30-40% for saline samples. This study demonstrates that water temperature, as well as the CDOM’s origin and light history, strongly affect the efficiency of CO photoproduction. These factors should be taken into account in modeling the photochemical fluxes of CO and other related CDOM photoproducts on varying spatiotemporal scales. An empirical equation was derived for predictiong the CO photoproduction efficiency in the St. Lawrence estuarine system. Annual CO photoproduction in the St. Lawrence estuarine system was estimated as 26.2 Gg CO-C a-1.The dark production rate of CO, Qco, in the water column of the St. Lawrence estuarine system decreased seaward horizontally and downward vertically. Qco exhibited a positive, linear correlation with the abundance of CDOM. As for photoproduction, Terrestrial DOM was also more efficient in the CO dark production than marine DOM. The temperature dependence of Qco can be characterized by the Arrhenius equation with the activation energies of freshwater samples being higher than those of salty samples. Qco remained relatively constant between pH 4-6, ascended slowly between pH 6-8 and then rapidly with further increasing pH. Ionic strength and iron chemistry had little influence on Qco. An empirical equation, describing Qco as a function of CDOM abundance, temperature, pH and salinity, was established. Dark production in the St. Lawrence estuarine system was estimated as 4.06 Gg CO-C a-1.The investigations of CO microbial consumption in the St. Lawrence estuarine system were conducted aboardship during the cruises of July 2004, October and December 2005, and May 2007. Kco showed an increasing trend along a salinity- gradient transect from the Gulf of St. Lawrence to Quebec City and to the organic-rich Saguenay River. Kco for surface waters ranged from 0.053 to 1.01 (median: 0.14) h-1 in spring, 0.081 to 0.60 (median: 0.27) h-1 in July, 0.035 to 0.71 (median: 0.13) h-1 in October, and 0.024 to 0.38 (mean: 0.032) h-1 in December. The major intra- and inter-seasonal variances of Kco can be accounted for by variations in water temperature and bacterial abundance. Kco displayed a moderate temperature dependence, increasing by ca. 40 to 80% (mean: 53%) per 10oC of increase in temperature. The activation energy was estimated to be 22-38 (mean: 28) kJ mol-1. Microbial organisms in freshwater zones showed less temperature-dependence in relation to CO consumption than organisms in saltwater zones. CO consumption approximately followed Wright-Hobbie kinetics up to 15 nmol L-1 [CO] and transformed to inhibition kinetics at higher [CO]. The maximum CO consumption rate (Vmax) in the Wright-Hobbie kinetic equation ranged from 0.15 to 4.3 (mean: 0.72) nmol L-1 h-1 and roughly anti-correlated with salinity. The half-saturation concentration (Km) was in the range 1.7 to 6.5 (mean: 4.1) nmol L-1 but exhibited no consistent relationships with other measured parameters. An empirical equation describing Kco as a function of water temperature, salinity, and total bacterial density was established. Microbial consumption of CO in the surface mixed layer of St. Lawrence estuarine system was estimated as 24.7 Gg CO-C a-1.Total CO production in the St. Lawrence estuarine system was 30.3 Gg CO-C a-1, 87% of which came from photoproduction, hence being a major source and leaving dark production a minor source. In the surface mixed layer, microbial CO consumption was ~81% of total production, acting as the major CO sink. Taking into account of air-sea flux, the total CO sink is ~ 91% of the total CO source, a reasonable match. The empirical equation of CO dark production was extrapolated to global scales. The total CO dark production in global oceans was estimated to be 17.10 Tg CO-C a-1 with 91% from blue waters and 9% from coastal waters, or 54% from the surface mixed layer and 46% from the sub-surface. The total dark source is significant compared to the best available estimate of the total marine CO photoproduction (50 Tg CO-C a-1) while the mixed-layer dark source contributes 15.7% to the oceanic CO flux to the atmosphere. Steady-state deep-water CO concentrations inferred from Qco and microbial CO uptake rates (0.05-0.1 nmol L-1)is comparable to the modern analytical method’s blank. The global microbial CO consumption rate is estimated to be ~63.58 Tg CO-C a-1, based on the calculated dark production in this study and photoproduction and air-sea flux in the published papers.更多还原