Effects of sea ice cover on satellite-detected primary production in the Arctic Ocean Biology Letters

The influence of decreasing Arctic sea ice on net primary production (NPP) in the Arctic Ocean has been considered in multiple publications but is not well constrained owing to the potentially large errors in satellite algorithms. In particular, the Arctic Ocean is rich in coloured dissolved organic matter (CDOM) that interferes in the detection of chlorophyll a concentration of the standard algorithm, which is the primary input to NPP models. We used the quasi-analytic algorithm (Lee et al. 2002 Appl. Opti.41, 5755−5772. (doi:10.1364/AO.41.005755)) that separates absorption by phytoplankton from absorption by CDOM and detrital matter. We merged satellite data from multiple satellite sensors and created a 19 year time series (1997–2015) of NPP. During this period, both the estimated annual total and the summer monthly maximum pan-Arctic NPP increased by about 47%. Positive monthly anomalies in NPP are highly correlated with positive anomalies in open water area during the summer months. Following the earlier ice retreat, the start of the high-productivity season has become earlier, e.g. at a mean rate of −3.0 d yr−1 in the northern Barents Sea, and the length of the high-productivity period has increased from 15 days in 1998 to 62 days in 2015. While in some areas, the termination of the productive season has been extended, owing to delayed ice formation, the termination has also become earlier in other areas, likely owing to limited nutrients. Grant no. NNX14AL80G Grant no. NNX14AM15G

北极海冰减少对北冰洋净初级生产力（Net Primary Production, NPP）的影响已在多项学术出版物中被探讨，但由于卫星反演算法存在潜在的较大误差，该效应尚未得到精准约束。尤为关键的是，北冰洋富含有色溶解有机物（Coloured Dissolved Organic Matter, CDOM），会干扰标准算法对叶绿素a浓度的反演，而叶绿素a浓度正是NPP模型的核心输入参数。本研究采用了可将浮游植物吸收与CDOM、碎屑物质吸收相分离的准解析算法（Lee等，2002，《应用光学》，41卷，5755−5772页，DOI:10.1364/AO.41.005755）。我们整合了多颗卫星传感器的观测数据，构建了1997–2015年共计19年的NPP时间序列数据集。在此期间，环北极区域的年总NPP与夏季月最大NPP均提升了约47%。夏季NPP的月度正异常与同期无冰水域面积的正异常呈现高度相关性。随着海冰消融提前，高生产力季节的起始时间不断前移——例如北巴伦支海的平均速率达−3.0天/年——高生产力时段的持续时长也从1998年的15天延长至2015年的62天。尽管部分区域因海冰形成延迟，使得生产力季节的结束时间有所延后，但在其他区域，由于营养盐供给受限，生产力季节的结束时间反而提前了。本研究受资助项目号NNX14AL80G与NNX14AM15G支持。