Intensive phytoplankton blooms, which mainly consist of diatoms, take place in the northern Bering and Chukchi Seas from spring to summer. Little is known, however, about the diatoms contributing to new production in these waters during summer when the water column is often stratified. In this study, using a ¹³C, ¹⁵N dual isotope tracer technique plus scanning electron microscopy, we assessed the diatom genera or species contributing to new production in surface waters of the northern Bering and Chukchi Seas in July 2013. Relatively high concentrations of nitrate, nitrite, phosphate, and silicate were observed at Bering Strait and Chukchi Shelf stations, whereas at the other stations surface nitrate was generally depleted. Surface ammonium levels were relatively high (0.05–1.52 µM), suggesting the high activity of heterotrophic organisms. In surface waters, hourly nitrate uptake rates ranged from 0.03 to 3.73 mg N m⁻³h⁻¹, while the ammonium uptake rates varied between 0.04 and 0.43 mg N m⁻³h⁻¹. As a result, the mean f-ratio was computed as 0.62 ± 0.23 during observation. We found that the nitrate uptake rates were positively correlated with ambient nitrate levels, indicating that the activity was mainly regulated with the physical process of nitrate supply. The diatom Chaetoceros (mainly C. socialis/gelidus) numerically dominated the surface diatom assemblages. Contributions of C. socialis/gelidus (9 ± 4 µm in size) to the total armored phytoplankton abundance increased with an increase in the water column stratification, whereas Thalassiosila spp. (26 ± 8 µm) showed the opposite trend. These results were consistent with the survival strategy of small diatoms for nutrient uptake in oligotrophic waters through their higher cell surface area to volume ratios. On the other hand, the carbon biomass of Thalassiosira became relatively high in surface waters, and significantly correlated with f-ratio. We conclude that the centric diatom Thalassiosira plays a key role in determining new production in surface waters of the study area during summer.

从春季到夏季，主要由硅藻组成的密集浮游植物大量繁殖发生在白令海北部和楚科奇海。然而，人们对在夏季水柱经常分层时在这些水域中促进新产量的硅藻知之甚少。在本研究中，使用¹³ C、¹⁵N 双同位素示踪技术加上扫描电子显微镜，我们评估了 2013 年 7 月白令海和楚科奇海北部地表水中有助于新生产的硅藻属或种。白令海峡和楚科奇陆架台站，而其他台站地表硝酸盐普遍枯竭。表面铵水平相对较高 (0.05–1.52 µM)，表明异养生物的高活性。在地表水中，每小时硝酸盐吸收率在 0.03 到 3.73 mg N m ^-3 h ^-1之间变化，而铵吸收率在 0.04 到 0.43 mg N m ^-3 h ^-1之间变化。因此，平均f-ratio 在观察期间计算为 0.62 ± 0.23。我们发现硝酸盐吸收率与环境硝酸盐水平呈正相关，表明活性主要受硝酸盐供应的物理过程的调节。硅藻Chaetoceros（主要是C. socialis/gelidus）在数量上在表面硅藻组合中占主导地位。C. socialis/gelidus（大小为 9 ± 4 µm）对总装甲浮游植物丰度的贡献随着水柱分层的增加而增加，而Thalassiosila属 (26 ± 8 µm) 显示出相反的趋势。这些结果与小硅藻在贫营养水域中通过其较高的细胞表面积与体积比吸收养分的生存策略一致。在另一方面，对生物质碳海链成为在地表水中相对较高，和显著相关与˚F -ratio。我们得出的结论是，中心硅藻Thalassiosira在决定夏季研究区地表水中的新产量方面起着关键作用。