中国北方海域近海酸化的时空变异及调控- - 典型海域比较

Eutrophication-induced coastal hypoxic waters often have quite low pH values. This coastal acidification is in general a regional and seasonal phenomenon. It is very different from ocean acidification induced by the long-term increase of atmospheric CO2. The latter effect occurs on a global scale and shows a clear tendency. Compared with the typical decline of 0.06 pH units in the upper open ocean in the past 15 years, however, coastal acidification is characterized by a short-term but very sharp pH drop of 0.3 or more pH units on a seasonal timescale, and is usually accompanied by a short supply of dissolved oxygen (DO). Therefore, the eutrophication/hypoxia induced coastal acidification may cause much more stress to marine organisms. We have observed significant coastal acidification associated with different levels of oxygen depletion in Bohai Sea, Yellow Sea and East China Sea. We have found different seasonal variation of coastal acidification and thereby different controlling mechanisms in different sea area. We are planning to examine seasonal distributions of DO, pH, carbonate system and nutrients in the Bohai Sea, the Yellow Sea and the Changjiang plume influenced northern East China Sea. This study will provides, for the first time, a fully evaluation of coastal acidification in this world's major shelf system. Considering the fact that Changjiang River is the only large river in these contrasting coastal systems, we can study different maintaining mechanism of the coastal acidification in RiOMar (River-dominated Ocean Margins) and non-RiOMar systems. We will also examine seasonal variation of CaCO3 saturation in these marine-aquaculture-involved key coastal waters.

近海酸化通常是由于生源颗粒大量耗氧释放CO2而发生。与开阔大洋响应全球大气CO2升高而表现出比较缓慢的酸化进程截然不同的是，近海酸化可在短时间内迅速发展，并且常与贫氧相伴，因而对水生生物造成较大的环境胁迫，易酿成突发性的灾害事件。观测结果表明，季节性的底层耗氧和酸化现象在中国北方各个浅水海域都可以发生，酸化区域的强酸浓度在数月内升高60%-200%，这相当于大洋表层未来50-150年的酸化进程。近海酸化现象在中国北方各个海区的空间分布各有特点，季节变化也不尽相同，本研究拟在渤、黄、东海开展系统的调查研究，通过对比分析不同海区春、夏、秋三季底层溶解氧、pH、碳酸钙饱和度的分布格局及其在重点海区的月际变化，基本阐明中国北方近海海域季节性酸化的时空变异及调控。研究成果对于准确评估我国北方海域的海洋环境状况，以及正确理解高CO2对这些海域的环境效应，都将提供重要依据。

近海富营养化海域易发生季节性的底层快速耗氧和酸化现象，可在短时间内迅速发展，酸化区域的氢离子浓度在数月内升高60%~200%，这相当于大洋表层未来50~150年的酸化进程，因而对水生生物造成较大的环境胁迫，易酿成突发性的灾害事件。项目组在渤、黄、东海开展系统的调查研究，通过对比分析不同海区水柱溶解氧、pH、碳酸钙饱和度的季节分布格局及其在重点海区的月际变化，基本阐明了中国北方近海海域季节性酸化的时空变异及其调控。通过整理北黄海春、夏、秋、冬四季的水体碳酸盐体系数据，首次在中国近海开阔海域报道极低的文石饱和度（1.13~1.40），其范围在10月和11月覆盖了北黄海大部分海区的底层，并在有些站位通过水柱混合作用上升到表层。调查资料的分析和在实验室内开展的养殖贝类CO2酸化模拟实验都表明，在这样的低文石饱和度的海水环境中，已经发生一定程度的碳酸钙溶解。进而利用2013年夏季在北黄海获取的海水碳酸盐体系调查资料，分析了河流冲淡水和呼吸作用的联合作用对海水碳酸钙饱和度的影响，指出这是2013年8月在河流冲淡水影响区域出现海水文石型碳酸钙不饱和现象的主要原因。数据还表明酸化海水对养殖贝类的呼吸活动造成抑制。在北黄海观测到的秋季底层海水文石饱和度数据比之前在南海北部粤东上升流区和东海北部长江口底层缺氧区报道的相关数据都低，说明北黄海可能是中国近海最容易受海洋酸化影响的海区，对水产养殖和海洋经济构成现实的危胁。