Data from: Late spring nitrate distributions beneath the ice-covered northeastern Chukchi Shelf

Measurements of late springtime nutrient concentrations in Arctic waters are relatively rare due to the extensive sea ice cover that makes sampling difficult. During the SUBICE cruise in May-June 2014, an extensive survey of hydrography and pre-bloom concentrations of inorganic macronutrients, oxygen, particulate organic carbon and nitrogen, and chlorophyll a was conducted in the northeastern Chukchi Sea. Cold (< -1.5°C) winter water was prevalent throughout the study area, and the water column was weakly stratified. Nitrate (NO3-) concentration averaged 12.6±1.92 μM in surface waters and 14.0±1.91 μM near the bottom and was significantly correlated with salinity. The highest NO3- concentrations were associated with winter water within the Central Channel flow path. NO3- concentrations were much reduced near the northern shelfbreak within the upper halocline waters of the Canada Basin and along the eastern side of the shelf near the Alaskan coast. Net community production (NCP), estimated as the difference in depth-integrated NO3- content between spring (this study) and summer (historical), varied from 28-38 g C m-2 a-1. This is much lower than previous NCP estimates that used NO3- concentrations from the southeastern Bering Sea as a baseline. These results demonstrate the importance of using profiles of NO3- measured as close to the beginning of the spring bloom as possible when estimating local NCP. They also show that once the snow melts in spring, increased light transmission through the sea ice to the waters below the ice could fuel large phytoplankton blooms over a much wider area than previously known.

由于北极海域海冰覆盖范围广、采样难度极大，晚春季北极水体营养盐浓度的原位实测数据相对稀缺。2014年5-6月的SUBICE科考航次中，研究团队于楚科奇海东北部海域开展了大范围水文调查，并测定了春季水华发生前的无机大量营养盐、溶解氧、颗粒有机碳、颗粒氮以及叶绿素a的浓度。研究区域内普遍分布温度低于-1.5℃的冬季水团，水体垂向层结较弱。表层海水硝酸盐（NO3-）平均浓度为12.6±1.92 μM，近底层海水浓度为14.0±1.91 μM，且浓度与盐度呈显著相关关系。中央水道流路内的冬季水团中硝酸盐浓度最高。加拿大海盆上层盐跃层水域的北部陆坡坡折带附近，以及阿拉斯加沿岸陆架东侧区域，硝酸盐浓度显著降低。净群落生产力（Net Community Production, NCP）通过本次春季观测与历史夏季观测的水柱积分硝酸盐含量差值计算得到，其范围为28-38 g C m⁻² a⁻¹。该结果远低于此前以白令海东南部海域硝酸盐浓度作为基线得到的净群落生产力估算值。本研究结果证实，在估算局地净群落生产力时，尽可能在春季水华起始阶段附近采集硝酸盐剖面数据的重要性。研究同时表明，春季积雪融化后，透过海冰的光照传输增强，可在远超此前认知范围的广阔区域内催生大规模浮游植物水华。