沉积物对北极楚科奇海近底层海水氮营养盐高值区的贡献

Nitrogen deficiency which has already greatly limited the primary production process is the most distinctive feature of nutrients cycles in the Arctic Ocean. Besides, the marine food chain and biological pump are also influenced by the N deficiency. Based on these reasons, it is meaningful to study the N complementary mechanism in this area. It was observed many times by Previous Chinese Arctic Research Expedition that the nitrate concentrations in some areas are obviously higher than the rest in Chukchi sea shelf and slope area. Besides, the nitrate concentration increased with water depth and the highest value appeared very near to the sediment surface. The reason for this high concentration is unclear due to the deficiency of further study. This study would focus on these abnormal areas. Multidisciplinary measurements including the high-resolution observations of nitrate, sediment-water N fluxes, N2 fluxes and also the sediment oxygen consumption rate would be included in this research to reveal the N production, consumption and release processes on the sediment-water interface. The key environmental factors including TOC, TON, δ13C, δ15N and benthic biomass etc. would also be measured to comprehensively analyze the main influence factors on sediment-water N release. The research results is expected to reveal the N complementary mechanisms in Chukchi shelf and slope areas and also the concomitant ecological efficiency caused by sediment N release.

氮（N）亏损是北冰洋营养盐循环最为显著的水化学特征之一，N不足限制了楚科奇海陆架区的初级生产过程，是影响食物链和生物泵的关键控制因子。因此，了解该海区水体N的补充机制有重要意义。尽管楚科奇海陆架区N营养盐浓度总体较低，但在局部海域常年存在N营养盐的高值区，且越接近沉积物底界面其浓度越高。由于受限于进一步的针对性观测和研究，无法回答沉积物底界面过程对此究竟有无重要贡献。本研究拟聚焦N营养盐异常区，在水柱剖面N营养盐高分辨率观测以及沉积物间隙水无机N分析的基础上，采用原状柱样连续流动培养法对沉积物底界面无机N、N2交换通量以及表层沉积物耗氧速率进行测定，再结合沉积物有机碳氮及其稳定同位素以及底栖生物量等重要环境参数，对沉积物底界面N营养盐交换通量及关键影响因子进行研究，评估沉积物对底层海水高浓度N营养盐的贡献。成果将为深入解析快速变化下的北极N营养盐补充机制及其生态和碳汇效应具有重要意义。

项目围绕原定目标开展了为期三年的研究工作。在第一年度主要进行了历史资料搜集和整理工作，制定了详细的项目执行计划，搭建了现场观测、采样装置和设备，并在近岸短期航次进行了验证。随后主要通过搭载中国第十次北极考察进行现场观测，采集样品，通过在实验室内的进一步分析测试，获取了项目所需的全部数据。该研究紧密围绕西北冰洋陆架区上覆水营养盐异常这一科学目标开展系列研究，首先对上覆水中各营养盐浓度进行系统观测，观测结果表明五项营养盐均在陆架区出现分布热点，其浓度明显高于周围海区。此外，项目组还对重要生源气体分布特征进行了拓展研究，发现其浓度与营养盐分布类似，同样出现了异常高值，尤其是在楚科奇海R04和R10站位底层水中发现了二氧化碳浓度极大值，这表明强烈的有机质降解导致了剧烈的营养盐再生过程，从而通过扩散、底栖生物扰动等过程向上覆水体释放，支撑上层海洋的初级生产过程。通过采用经典的15N稳定同位素示踪技术对沉积物中脱氮速率的测定表明，在营养盐热点区域的反硝化速率同样较高。而楚科奇海表层沉积物反硝化速率普遍高于白令海，这是因为楚科奇海更高的初级生产力导致了更为剧烈的有机碳积累和降解过程，充分的厌氧环境和充足的有机质为脱氮过程发生提供了良好条件，最终导致西北冰洋陆架区成为显著的脱氮热点。