2019年冬季黄东海水体颗粒氮分布特征及其影响因素

The Distribution and Impacting Factors of Particulate Nitrogen in the Yellow Sea and East China Sea in Winter of 2019

中文关键词:  颗粒氮  氮同位素  黄、东海  氮循环  底边界应力

英文关键词:particulate nitrogen  nitrogen isotopes  the Yellow and East China Sea  nitrogen cycle  bottom boundary stresses

中文摘要:

      陆架边缘海是桥接陆地径流与开阔大洋的“缓冲带”，也是海洋氮循环最为活跃和复杂的场所。颗粒氮 （Particulate Nitrogen，PN） 是边缘海氮库中反应活性较高的组分，在氮循环中扮演重要角色。为研究边缘海颗粒氮的循环转化过程，本文通过测定2019年冬季黄、东海水体颗粒物的碳、氮含量及稳定同位素、硝酸盐氮氧同位素，分析黄、东海近岸和外海海域的表层、底层 PN含量及同位素的分布差异及其影响因素，探讨颗粒氮与水体溶解态氮耦合循环过程。冬季表、底层颗粒碳、氮浓度及颗粒氮同位素值 （δ15NPN） 都呈现近岸高、外海低的空间分布特征，颗粒碳同位素 （δ13CPOC） 则大致为北低南高的空间分布。表、底层硝酸盐氮同位素值（δ15NNO3） 分布均为北低南高、近岸低外海高，而硝酸盐氧同位素值 （δ18ONO3） 分布则是北黄海高、东海外海低。通过对多环境因子的主成分分析 （PCA），将调查海域划分为近岸表、底层和外海表、底层四个特征区域，分别探讨其PN循环转化过程。在黄海和东海近岸海域表、底层水体PN均主要受陆源输入和底层再悬浮影响，PN及δ15NPN因垂向混合而表、底差异较小。在外海表层水体，PN主要来源不完全是初级生产；外海底层水体NO??、PN及δ15NNO3、δ18ONO3、δ15NPN显示受黑潮水团跨陆架涌升影响较为明显。在外海底层海域，PN矿化过程和硝化过程扮演着重要角色，PN的降解驱动着DON和部分NO??的再生。通过综合分析海底边界剪切应力、环境因子并结合δ15NNO3、δ18ONO3、δ13CPOC和δ15NPN示踪，发现冬季近岸海域底边界过程强烈，再悬浮过程干扰了PN的δ15NPN源、汇信号，通过δ13CPOC和δ15NPN区分PN来源和示踪其转化过程存在一定局限性；远海由于其较弱的底边界动力过程，更加有利于PN的矿化、沉降和埋藏，PN的δ15NPN源、汇信号较为明显。

英文摘要:

      Continental marginal seas serve as "buffer zones" bridging terrestrial runoffs and the open ocean, and are among the most active and complex areas in the marine nitrogen cycle. Particulate nitrogen (PN) is a highly reactive component in the nitrogen pool in marginal seas, playing a crucial role in the nitrogen cycle. To investigate the cycling and transformation processes of particulate nitrogen in marginal seas, this study analyzed the carbon and nitrogen content and isotopic composition of particulate matter in the waters of the Yellow Sea and East China Sea during the winter of 2019, and explored the coupling cycling between PN and dissolved nitrogen by examining the spatial distribution and influencing factors of particulate nitrogen (PN) and its isotopes in the surface and bottom waters of coastal and offshore areas. Significant differences in particulate nitrogen cycling were found between coastal and offshore areas of the Yellow Sea and those of the East China Sea. Both surface and bottom layer particulate carbon, nitrogen, and particulate nitrogen isotopes (δ15NPN) presented a spatial distribution pattern of high concentrations near the coast and low concentrations offshore, whereas particulate carbon isotopes (δ13CPOC) displayed a noticeable north-low, south-high distribution. The nitrogen isotopes of nitrate (δ15NNO3) in both surface and bottom layers showed a north-low, south-high, coastal-low, and offshore-high distribution, while the oxygen isotopes of nitrate (δ18ONO3) were distributed with high values in the northern Yellow Sea and low values in the East China Sea. A principal component analysis (PCA) of multiple environmental factors was conducted to classify the research area into four distinct regions: nearshore surface, nearshore bottom, offshore surface, and offshore bottom. The transformation processes of particulate nitrogen (PN) cycling were examined in each region. In the nearshore region of the Yellow Sea and the East China Sea, both surface and bottom waters were primarily influenced by terrigenous inputs and bottom resuspension, resulting in minor differences in PN and δ1?NPN between surface and bottom layers due to vertical mixing. In the offshore surface regions, the primary source of PN was not solely from primary production. The offshore bottom region showed clear influences from Kuroshio water upwelling, as evidenced by NO??, PN, δ1?NNO?, δ1?ONO?, and δ1?NPN measurements. In these offshore bottom waters, PN mineralization and nitrification played significant roles, with PN degradation driving the regeneration of dissolved organic nitrogen (DON) and NO??. Comprehensive analysis of seabed boundary shear stress and environmental factors, combined with tracers such as δ1?NNO?, δ1?ONO?, δ13CPOC, and δ1?NPN, revealed intense bottom boundary processes in winter nearshore areas, where resuspension interfered with the δ1?NPN source and sink signals. This resulted in certain limitations of using δ13CPOC and δ1?NPN in the differentiation of PN sources and tracking of its transformation processes. In contrast, weaker bottom boundary dynamics in offshore areas favored PN mineralization, sedimentation, and burial, making the δ1?NPN source and sink signals more distinct.