夏季南海北部典型中尺度物理过程对营养盐及溶解氧分布特征的影响

依据2011年8月24日—9月5日对南海北部海域的现场调查,分析了涡旋这一典型中尺度物理过程对营养盐(NO-3-N,PO3-4-P,SiO2-3-Si)及溶解氧分布特征的影响.结果表明,夏季南海北部营养盐及溶解氧的分布受中尺度海洋过程的影响显著.在水平分布上,各项营养盐基本呈现近海高远海低的分布特征.东沙群岛附近海域由于受反气旋型涡旋的影响,反气旋型涡旋将珠江口水推至外海,使得东沙群岛附近海域呈现明显的高N、Si,低P的珠江口水特征.在断面分布上,位于珠江口附近海域的B、C断面营养盐浓度水平较低,表层低浓度营养盐向下扩张明显,营养盐浓度等深线也明显下移,其可能受到反气旋型涡旋中心区域的影响;而位于海南岛附近海域的D、F断面,底层低温高盐海水不断向上涌升,可能受到反气旋型涡旋边缘的影响,使得表层海水受到富含高浓度营养盐的底层海水的补充,为表层浮游植物的生长提供了丰富的物质基础.位于广东沿岸附近海域的A断面及东沙群岛附近海域的E断面则受季节性上升流的影响大于反气旋型涡旋的影响,表现出明显的低温、高盐、高P、低溶解氧的上升流特征.

Influence of typical mesoscale oceanographical process on the distribution of nutrients and dissolved oxygen in the Northern part of South China Sea in summer

Field investigation was carried out from 24^th August to 5^th September, 2011 to study the effects of eddy, one of the most typical mesoscale oceanographical processes, on nutrients and dissolved oxygen in northern South China Sea. The results showed that the distribution of nutrients and DO was significantly influenced by eddy. As for horizontal distribution, nutrient concentrations decreased from inshore to offshore in the study area. Seawater of Dongsha archipelago presented high concentrations of N and Si and a low concentration of P, similar to that in Zhujiang River, indicating that anti-cyclonic eddies may push the Zhujiang river water to offshore. Results of vertical distribution pattern of nutrients and dissolved oxygen also indicated the importance of mesoscale oceanographical process in the study area. The nutrient concentrations at section B and C, located at the adjacent area of Zhujiang River, were relatively low. Surface water with low nutrient concentrations was observed to outspread to the bottom, and the nutrient isoline also moved downward, which may be influenced by the center of anti-cyclonic eddies. Bottom seawater with low temperature and high salinity was observed to move upward at section D and F, located around Hainan Island. These results imply that nutrients in surface water could be supplemented by bottom water with high nutrient concentrations, subsequently enhancing the growth of phytoplankton. Thus, section D and F may be influenced by the brink of anti-cyclonic eddies. Furthermore, low temperature, high salinity, high P and low DO were observed at section A close to Guangdong coastal areas and section E nearby the Dongsha archipelago, which may reflect the influence of upwelling in these areas.