极区海冰冻融过程中N2O行为研究

Nitrous oxide (N2O) is an important atomospheric trace gas: in the troposphere it acts as a strong greenhouse gas and in the stratosphere it is the major precursor of ozone depleting nitric oxide radical. Ocean contributes a quarter of overall sources of N2O, so biogeochemical cycal of N2O in ocean drawed widely attention. However, N2O in polar ocean has not well-known because of sea ice cover in most of time and the difficult of field investage in rigorous climate. The couple models simulations showed polar amplification of climate change. Polar warming is faster than other region and sea ice is quickly reducing in the Arctic. These changes will affect on the cycly of greenhouse gas in polar region. Sea ice formation and thawing is only environmental processes in the polar ocean. Several recent researches in polar ocean showed a rare phenomenon in non-polar ocean which is undersaturated N2O in the surface water resulting from dilution of thawing water of sea ice. It is probable that sea ice can affect N2O in polar ocean, but effect of sea ice on N2O in polar ocean has never been studied so far. In this project, based on difficult of field work, we are going to set up a sea ice formation-thawing experimental simulator and analyze the concentration of N2O in atomosphere, sea water and ice by using of very well-developed analytic techeniques in our laboratory. The behaviour of N2O during forming and thawing of sea ice and the effect of sea ice on the cycle of N2O in polar ocean will be disscuted from the results of simulation experiments. This study is vitally important first step to understanding the role that sea ice plays in cycle of N2O in polar ocean.

N2O是具有臭氧破坏作用的温室气体，对全球气候变化有重要影响。海洋来源N2O对全球收支的重要贡献使其在近几十年备受关注。尽管目前对极区海洋N2O循环的研究尚十分有限。申请人所在团队近年调查结果表明极区海洋存在其他海区鲜见的N2O不饱和现象。现有证据表明夏季融冰水的稀释作用可能是造成此现象的重要机制。据此，申请人提出以下假设：海冰融化过程将使极区海洋成为大气N2O的汇区。本项目拟搭建海冰模拟系统，及实验室最先进的N2O分析技术监测海冰形成和融解过程中N2O在气-液-固三相中的含量变化。结合现场调查获得的数据，论证上述假设，并评估海冰冻融过程对N2O源汇特性强度，以及海洋N2O收支的影响。

大气N2O既具有温室效应，又能破坏臭氧层，海洋是大气N2O的重要来源，表层海洋通常呈N2O饱和或过饱和现象。然而，在极区海洋调查研究中发现罕见的N2O不饱和现象，由于现场调查大部分都在融冰期，融冰水稀释可是是重要原因。然而，至今尚无极区海冰冻融过程中N2O行为的研究。为解决该科学问题，本项目通过室内海冰形成模拟实验与极区海洋现场调查相结合的方法研究了极区海冰冻融过程N2O行为。.具体研究内容包括： 1）对北极和亚北极海洋N2O调查结果分析，探讨极区海洋N2O分布格局和主控因子；2）设计制作室内小型海冰模拟实验装置，并进行模拟实验，研究海冰形成过程中N2O去向；3）调查极区海冰N2O浓度，并观测夏季海冰消融期表层海水N2O含量变化趋势。4）依据上述模拟实验和现场观测结果阐述海冰冻融过程N2O行为极其对极区海洋N2O循环的贡献。.通过上述研究得到以下结果：1）在北极73°N以北楚科奇深海平原上层水体，N2O相对大气明显不饱和，是大气N2O的汇，海气通量为-10.2 ± 1.4 μmol m-2 d-1，融冰水稀释很可能是表层不饱和的主要原因。2）自主设计制作的小型室内海冰模拟系统，能成功模拟海冰形成过程，获国家发明专利授权。3）室内模拟试验结果表明，海冰形成时57.6% N2O会进入盐卤水中并向下层水体输送，而30.8%仍会存留于海冰中，剩余的11.7%可能释放到大气中。4）南极现场海冰中N2O含量仅为1.9 nmol/L，夏季海冰消融期南极表层水N2O确实受融冰水影响而与盐度同步降低。5）极区海冰冻融过程中N2O行为如下：海冰冻结过程中少量释放入大气，大部分随盐卤水向下层水体输送，剩余约30.8%仍留在海冰中，而海冰消融过程中表层水从大气吸收N2O。初步估算表明，海冰冻融可导致极区海洋从大气中吸收N2O的量为0.00493 Tg N yr-1。.本研究首次阐明极区海冰冻融过程中N2O的行为，并初步量化评估了海冰冻融过程对极区海洋N2O循环的贡献。这将推动对极区海洋N2O循环的进一步认识，并有助于评估全球变暖导致的海冰退缩变迁的气候效应。