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.

北极海域晚春季营养盐浓度的原位实测数据相对稀缺，原因在于广泛分布的海冰覆盖使得采样工作困难重重。2014年5—6月开展的SUBICE航次中，研究团队针对楚科奇海东北部海域实施了大范围综合调查，获取了水文要素、水华前无机大量营养盐、溶解氧、颗粒有机碳、颗粒氮及叶绿素a浓度的观测数据。整个研究区域内普遍分布着水温低于-1.5℃的冬季水团，水体垂向层结微弱。表层海水硝酸盐（NO3-）平均浓度为12.6±1.92 μM，近底层海水硝酸盐平均浓度为14.0±1.91 μM，且该浓度与盐度呈显著相关。最高硝酸盐浓度出现在中央水道流路内的冬季水团中；而加拿大海盆上层盐跃层水域内的北部陆架坡折周边，以及楚科奇海陆架东侧毗邻阿拉斯加海岸的海域，硝酸盐浓度则显著降低。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垂向积分硝酸盐含量差值估算得到，取值范围为28~38 g C·m⁻²·a⁻¹。这一结果远低于此前以白令海东南部硝酸盐浓度为基准得到的净群落生产力估算值。本研究结果表明，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获取硝酸盐剖面数据至关重要；同时还发现，春季海冰消融后，透过海冰的光照传输增强，可在远超此前认知的更大范围海域催生大规模浮游植物水华。