白令海和西北冰洋海水DMSP时空变化格局和生产周转研究

Oceanic dimethylsulfoniopropionate (DMSP) is rapidly cycled and is thought to be a major source of carbon and sulfur for phytoplankton and microbial communities and a major precursor of the climate active gas DMS. DMSP cycling is therefore of considerable interest to the international scientists from broad range of disciplines including biogeochemistry, ecology and atmospheric science. In this project, we will study the spatio-temporal dynamics, production and turnover of DMSP in the Bering Sea and western Arctic Ocean which play a critical role in both past and present global climate change. We will use a novel isotope tracer method to quantify the in-situ turnover rates of DMSP and its related compounds (DMS) in the Bering Sea, Chukchi Sea and Canada Basin, and to investigate temporal evolution of cycling rates and the biochemical factors which control the fate of sulfur from DMSP in the Bering Sea and western Arctic Ocean. Results from this study will provide unique data to determine how the branching ratios between the lyase and demethylation pathways vary in different currents of the investigation areas, to identify the main production and degradation contributors of DMSP, and to quantify the contribution of DMSP to bacterial/phytoplankton carbon and sulfur demands in the Bering Sea and western Arctic Ocean. The resulting data will greatly advance our knowledge of how DMSP is processed in the study area, how it impacts the chemistry of surface waters through the production of important reduced sulfur compounds DMS, and how global warming and rapid sea ice retreat affects the Arctic DMSP sink and source, with a focus on biological and physical processes in the Arctic Ocean.

作为海洋具有重要气候意义的生源活性气体二甲基硫（DMS）的主要前体物质、海洋浮游植物和微生物生长重要的硫源和碳源，DMSP研究是目前国际海洋科学研究的前沿领域。本项目将聚焦于全球气候变化响应和反馈最敏感的白令海和西北冰洋，以海水DMSP时空格局和生物周转为研究核心，具体测定白令海、楚科奇海、加拿大海盆海水DMSP浓度、生产和降解速率，重点研究白令海、楚科奇海、加拿大海盆海水DMSP浓度的时空变化特征及关键生产降解过程，认清DMSP分布、生产和周转的区域差异性和特殊性，识别DMSP主要生产者和降解者，定量确定DMSP对浮游植物和细菌碳硫源的贡献，筛选影响DMSP浓度时空变化格局和生产降解的调控因素，揭示北极海域在海洋生源硫的生物地球化学循环中的独特性和敏感性，对全球DMSP生产周转过程提供创新性认识，为深入研究北极海域对区域和全球生态效应、气候变化的响应提供科学依据。

本项目研究了白令海和西北冰洋海水DMSP的时空变化格局和生产周转，（1）认清了DMSP等生源硫化合物的分布、生产和周转的区域差异性。白令海表层DMSP浓度及其生产消费速率从中央盆地到大陆架率呈下降趋势。从白令海到楚科奇海，DMS水体积分浓度显著增长两倍。71°N冰缘线浮游植物藻华区出现DMSP浓度高值。垂直混合加剧造成67.7°N水团交汇区出现了DMSP等生源硫化合物浓度高值。（2）厘清了DMSP等生源硫化合物时空变化和生产降解的重要调控因素。浮游植物和浮游动物生物量和种类、太平洋入流水强度和营养盐浓度是DMSP等生源硫化合物浓度空间变化的重要调控因素。Chl a与DMSPp和DMS正相关，DMS和营养盐间显著负相关。太平洋入流水增强导致了DMS高值区在白令海峡东部垂直扩张和西部表层的水平扩张。白令海海表温度升高2.8°C，浮游植物生物量和甲藻比重提升，大型桡足类的优势地位逐步被小型桡足类所取代，DMSP等生源硫化化合物高浓度区域水平范围明显扩大，垂向延伸至深水区，DMS海气释放量显著提高3-5倍。DMS微生物消耗比DMS海空交换快约6倍，表明表层DMS微生物降解速率是比海气释放更重要的消耗途径。（3）查清亚北极和北极海域对DMSP等生源硫化合物生物地球化学循环的区域性贡献和敏感性。白令海和楚科奇海DMS海气通量从2012年4.89μmol/(m2·d-1)明显升高到2016年14.42μmol/(m2·d-1)，明显高于全球平均水平。太平洋入流水扩展，楚科奇海表层DMS及其海气通量显著增加了三倍，造成凝云结核和辐射强度提高了2.5倍。（4）深化极区海洋生源活性气体气候效应。扩展研究了南大洋生源活性气体挥发性卤代烃（VHCs）的空间变化特征和来源。双温层是夏季上层水体中重要的VHCs储层。发现人为CCl4（平均浓度为44.9pmol/L）存在于南极海域。夏季CCl4、C2Cl4、CHBrCl2和CH2Br2海气通量估算值平均分别为478.7、93.7、33.7和61.8nmol/(m2·d)，表明南极半岛北部海域是大气中VHCs的重要来源，对上空臭氧空洞的形成具有潜在的不利影响。本项目深化了生源活性气体释放对气候和环境变化贡献的认识，为研究极地海域对全球生态效应和气候变化的响应提供科学依据。