融冰期北极楚科奇海陆架中心区硅限制与来源补充

相对氮亏损(N:P约为7,小于16)的太平洋入流水携带的营养盐是支撑北冰洋上层生态系统的重要物质基础。海冰消退,光限制消失,楚科奇海陆架存在强烈的营养盐消耗与利用,广泛认为其表现为氮限制,因此该区域重点关注氮元素循环,对于硅元素的相关研究较少。本文基于2016年中国第七次北极科学考察和中国-俄罗斯首次联合北极科学考察两个同步进行的航次调查结果,全面展示了融冰期整个楚科奇海陆架区的营养盐分布格局。结果显示,硝酸盐和亚硝酸盐表层基本耗尽;硅酸盐表现为中心低,周围高,陆架中心区是强烈的硅限制区域,受到硅和氮的共同限制。沿着太平洋入流方向,S01、R01、LV77-01站位30 m以深硅酸盐浓度高于太平洋入流水端员,说明沉积物孔隙水向底层水释放硅酸盐,因此在浅水陆架区孔隙水可作为上层海洋硅酸盐的潜在来源。本研究结合文献数据计算得到楚科奇海陆架沉积物-水界面硅酸盐年通量为630.78 mmol·m^-2·a^-1,总量为3.75×10¹¹ mol·a^-1,是太平洋入流水所携带硅酸盐年通量的一半(6.59×10¹¹ mol·a^-1),表明沉积物孔隙水也是楚科奇海陆架硅酸盐的重要来源。

Silicon limitation and replenishment in central Arctic Chukchi Sea Shelf region during ice melting period

The relatively nitrogen-deprived (16>N:P≈7) nutrients carried by Pacific water inflow provide important support to the upper Arctic Ocean ecosystem. In the Chukchi Sea Shelf region nutrient consumption is strong as sea ice retreats and light becomes more accessible. It is generally believed that the primary production of this region is mainly limited by nitrogen, while little is known about other nutrients including silicate. In this study, based on the results of two simultaneous voyages—the 2016 Chinese Arctic Research Expedition and the 2016 Chinese-Russian “Arctic Silk Road” Expedition—we revealed the distribution pattern of nutrients in the entire shelf region during ice melting period. The nitrite and nitrate surface layers are nearly exhausted over a wide area, while silicate is low in the shelf center and high in the surrounding areas, indicating silicon and nitrogen are both limited at the shelf center. Along the path of Pacific water inflow, silicate concentrations are higher at depths above 30 m at stations S01, R01 and LV77-01 than at the end of water inflow, indicating silicate is released to the bottom water from sediment pore water. Therefore, sediment pore water can be potential source of silicate for the upper ocean in shallow shelf areas. In this study, combined with literature data, the calculated average silicate flux at the shelf sediment-water interface was 630.78 mmol·m^-2·a^-1, or 3.75×10¹¹ mol·a^-1 in total silicate, which equaled to half of silicate carried by Pacific water inflow (6.59×10¹¹ mol·a^-1). Thus sediment pore water is also an important source of silicate in the Chukchi Sea Shelf region.