南大洋N2O源汇格局：驱动机制及其对海洋N2O收支的影响

N2O is one of the most important green house gases and ozone deplector which is more and more concerned by researchers recently. Ocean is regarded as one of the most important N2O sources. However, little is known so far about the role Sothern Ocean plays in global N2O budget, thought it was considered as the most significant oceanic N2O source area. Three hypothesis were put forward according to the results of field work:1) N2O in ice shelf waters and circumpolar deep waters are formed by different mechanism and affected by different physical processes; mixing of these two water masses enhence production of N2O in subsurface water near the Continental Water Boundary, 2) undersaturation of N2O in surface Southern Ocean is maintained by gracier melt water, wet deposition and strong stratification during summer 3) above processes make Southern Ocean a sink for N2O during summer time. To prove these hypothesis,several cruises is planned to take N2O, H2O and N2O stable isotopic sample. using these and nutrient, CTD data,forming mechanism of N2O will be discussed. Model will be set up to stimulate the processes that sustain the undersaturation of N2O in Southern Ocean surface water and analysis its driving mechanism. Finaly, air-sea fluxes model combine with remote sensing will be used to estimate the sink strength of Southern Ocean and its impact on global N2O budget.

N2O在全球变化扮演重要角色，海洋是N2O的主要来源之一。然而，南大洋N2O的研究至今仍十分有限。本研究针对调查发现的南大洋表层海水N2O不饱和现象，提出科学假说：1）普里兹湾陆缘水边界两侧水体N2O分布特征受不同物理控制过程和生物形成机制影响，陆缘水边界混合过程促进锋面区域次表层水体中N2O生产；2）南大洋表层海水应存在融冰水和降水输入等机制，在夏季强烈的层化作用下维持N2O不饱和状态；3）上述过程作用共同促使夏季南大洋成为大气N2O的汇。为证实上述假说，本项目拟展开若干航次，采集N2O, H2O、N2O稳定同位素，以及化学物理参数，探讨南大洋不同海区N2O形成机制，建立模型模拟表层海水N2O不饱和状态的驱动机制；最终通过遥感和海气通量等方法，评估夏季南大洋汇强度，及其对全球N2O收支的贡献。

N2O是三大温室气体之一，在全球变暖中扮演着重要角色，同时N2O也是臭氧耗散的主要反应气体。海洋是N2O的主要来源之一，南极海冰季节变化影响对南大洋N2O的海气源汇格局评估，加上至今仍十分有限现场观测数据，因此开展南大洋N2O源汇格局：驱动机制及其对海洋N2O收支的影响具有重要意义。本项目研究针对现场调查中发现的南大洋表层海水N2O不饱和现象，开展了三方面主要内容的研究工作：（1）南大洋分布特征并剖析南极普里兹湾站区N2O形成机制；（2） 南大洋表层海水N2O不饱和状态的调控机制；（3）南大洋N2O海气通量，分析南大洋在全球N2O收支中的作用。该研究工作运用传统气相色谱分析方法、化学计量学，遥感与海气交换通量评估模型联用等方法对关键参数和过程开展调查和研究。研究结果显示：除上升流的贡献以外，南大洋次表层可能存在N2O形成的过程，并贡献区域N2O海气通量；高纬度表层海水存在N2O不饱和现象和融冰过程的贡献有关，由于海冰中N2O的含量极低，其溶解过程必然引起混合的表层水体N2O浓度的下降；南大洋整体上是全球N2O的重要来源，然而其源强比之前模型模拟研究结果降低，约为1.2TgN/a；并且，绕极深层流涌升导致的普里兹湾表层过饱和现象主要存在于65S左右的区域；类似现象发生于南极半岛周边的斯科舍海。此外通过执行该项目，研究团队还建立了当前国际领先的温室气体走航观测技术，获得了4项国家发明专利。成果提高我国科学家在国际上的显示度，促进了与美国、德国、比利时和韩国的合作。通过该项目研究工作，研究团队发表论文24篇，其中4篇与N2O研究密切相关论文发表在国际顶级杂志Journal of Geophysical Research.