Dimethylsulphide (DMS) is an important marine biogenic gas and can be released into atmosphere through seaair gas exchange. The oxidants of DMS in atmosphere are the main compounds of pristine marine sulphate aerosols and would affect the global climate change finally. Almost all the atmospheric DMS, about 90%, comes from the ocean. The southern ocean, which consists about 20% of the whole ocean area, is one of the largest atmospheric DMS sources. In contrast  with the other oceans, the Southern Ocean appears great spatial and temporal variability of surface seawater DMS. In addition, there are the complex hydrography system, variable sea ice condition and various biologic activities in the Southern Ocean as to make survey and understand DMS as well as its controlling factors most difficult. Moreover, it is significant to integrate the DMS seaice exchange processes and its controlling factors studies. In order to develop survey and research on the seaair DMS exchange and biogeochemistry processes, estimate methods of the seaair DMS fluxes will be reviewed, characteristics of the spatial and temporal distribution of surface seawater DMS will be discussed and the seaair DMS flux in the Southern Ocean will be assessed. Finally, major controlling factors of DMS seaair DMS processes will also be analyzed.

二甲基硫(DMS)是一种重要的海洋生源硫化物，通过海—气交换进入大气后生成生物源硫酸盐气溶胶从而对气候产生影响。海洋是大气DMS的主要源地，海洋大气中约90%的DMS来自海洋。南大洋占世界大洋面积的20%，是全球DMS重要的源之一。相较其他海域，南大洋表层海水DMS存在显著的时空变化。由于南大洋复杂的水文环境、多变的海冰情况和受多种生物活动作用的影响，完全了解这一区域DMS海—气交换过程及其控制因素变得更加复杂、困难。此外，开展DMS的冰—气交换过程及其控制因素的研究也很有意义。为了便于今后在极区开展DMS海—气交换过程的研究，深入探究极区DMS的生物地球化学过程。因此，对南大洋DMS海—气通量的估算方法进行讨论，分析南大洋表层海水DMS的分布特征及南大洋DMS海—气输送通量，对南大洋DMS海—气交换过程的控制因素进行探讨。

The vertical distribution of marine phytoplankton is complicated. However, a bell-shape vertical profile of phytoplankton in mass concentration is frequently observed in coastal seas and open oceans. The corresponding Subsurface Chlorophyll Maximum Layers (SCML) have caused a very high scientific interest and have been studied well. SCM can be characterized by three parameters, i.e., depth, thickness and intensity of the SCML. However, challenges still exist on how to best characterize the three parameters. They are determined by marine hydrology, nutrient concentrations and phytoplankton species, etc. A few studies have been conducted to explore variability of three parameters among different oceans. In general, compared with coastal seas，seasonal variation of the three parameters in open oceans is insignificant. It is also indicated that the three parameters are deeper，thicker and smaller in open oceans than coastal seas. In oligotrophic ocean, the depth of SCML was mainly a function of light and turbulent diffusion. Its intensity was determined by light, turbulent diffusion and biogenic processes associated with zooplankton grazing. However, the quantitative relationship between these biogenic processes and the three parameters are not well established. For example, how the sinking rate of phytoplankton, physiological adaptation capabilities, motility, trophic interactions affect them are poorly understood, and further investigations are needed. This review also finds  that the SCML study in coastal seas is rare, which could be due to the lack of a long-term and high-timeresolution observation in those areas. By use of satallite data, in situ data and physical-biological models, it might be useful for further  understanding SCM furtherly. 

在多数情况下，海水中叶绿素垂直分布是不均匀的。次表层叶绿素最大值是其中较为常见的一种形式，普遍存在于大洋及沿岸海域。次表层叶绿素最大值层（SCML）的深度、厚度与强度是表征海洋次表层叶绿素最大值（SCM）现象的主要特征因子，受海洋水文环境、营养盐分布以及浮游植物种类等因素共同影响，在不同季节不同海区的分布有较大差异。总体上，相对近海，大洋中SCML特征因子的季节变化较小，SCML深度较大，厚度较大，强度较小。寡营养盐海区SCML深度及强度的影响因素研究已有较明确结论，SCML深度主要受物理因素（光照条件及水体混合程度）影响，而强度则受物理、生物因素（光照条件、水体混合程度或浮游动物摄食等）共同影响。近海富营养盐海区，SCML特征因子的影响因素研究较为薄弱。长时间序列、高分辨率观测站在相应海区的建立，对推进海洋SCM，尤其是近海SCM的研究有重要意义。卫星观测、现场观测和数学模型相结合，定量研究SCML特征因子与各物理、生物、化学因子的普适性关系，是进一步研究SCML特征因子的重要方向之一。

Abstract

Temporal and spatial distributions of dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) were determined in the East China Sea and the Yellow Sea during June–July, 2006 and January–February, 2007. The concentrations of DMS and total DMSP in surface water in the study area were 5.64 (1.79–12.24) and 28.25 (13.98–44.93) nmol L⁻¹ in summer, and were 1.79 (1.02–3.51) and 11.01 (6.90–17.98) nmol L⁻¹ in winter, respectively. The distributions of DMS and DMSP in the study area were obviously influenced by the Yangtze River effluent and the Kuroshio water. Even under highly variable hydrographic conditions, a significant relationship was observed between DMS and chlorophyll a concentrations in summer as well as in winter, suggesting that phytoplankton biomass might play an important role in controlling DMS distribution in the study area. The summer ratios of DMS/chlorophyll a and DMSP/chlorophyll a were approximately twofold higher than winter values, corresponding with the temporal variation in phytoplankton community structure between summer and winter. The sea-to-air fluxes of DMS were estimated to be 5.32 and 11.92 μmol m⁻² d⁻¹ using the equations of Liss and Merlivat (1986) and Wanninkhof (1992), respectively.

Highlights

? The distributions of DMS and DMSP in the ECS and the YS are obviously influenced by the Yangtze River effluent and the Kuroshio water, exhibiting large seasonal and spatial variability. ? A good relationship between DMS and chlorophyll a concentrations is found in the study area. ? Temporal variations in the ratios of DMS/chlorophyll a and DMSP/chlorophyll a are significantly related to the difference of the phytoplankton composition and abundance between summer and winter. ? The emission of DMS from the ECS and YS is estimated.