Under-ice export flux measurements by short-term drifting sediment traps at 27 stations in the Arctic Ocean during summer 1995, 1997, and 2012

A critical question regarding the organic carbon cycle in the Arctic Ocean is whether the decline in ice extent and thickness and the associated increase in solar irradiance in the upper ocean will result in increased primary production and particulate organic carbon (POC) export. To assess spatial and temporal variability in POC export, under-ice export fluxes were measured with short-term sediment traps in the northern Laptev Sea in July-August-September 1995, north of the Fram Strait in July 1997, and in the Central Arctic in August-September 2012. Sediment traps were deployed at 2-5 m and 20-25 m under ice for periods ranging from 8.5 to 71 h. In addition to POC fluxes, total particulate matter, chlorophyll a, biogenic particulate silica, phytoplankton, and zooplankton fecal pellet fluxes were measured to evaluate the amount and composition of the material exported in the upper Arctic Ocean. Whereas elevated export fluxes observed on and near the Laptev Sea shelf were likely the combined result of high primary production, resuspension, and release of particulate matter from melting ice, low export fluxes above the central basins despite increased light availability during the record minimum ice extent of 2012 suggest that POC export was limited by nutrient supply during summer. These results suggest that the ongoing decline in ice cover affects export fluxes differently on Arctic shelves and over the deep Arctic Ocean and that POC export is likely to remain low above the central basins unless additional nutrients are supplied to surface waters.北冰洋有机碳循环领域的核心科学问题之一在于：海冰范围与厚度的缩减，以及由此引发的上层海洋太阳辐射增强，是否会导致初级生产提升与颗粒有机碳（Particulate Organic Carbon, POC）输出增加。为评估POC输出的时空变异特征，研究团队于1995年7-9月、1997年7月以及2012年8-9月，分别在拉普捷夫海北部、弗拉姆海峡北侧以及北冰洋中部，利用短期沉积物捕集器对冰下输出通量进行了测定。沉积物捕集器布设于冰下2-5米与20-25米水深处，部署时长介于8.5至71小时之间。除POC通量外，研究团队还同步测定了总颗粒物、叶绿素a、生源颗粒硅、浮游植物以及浮游动物粪球通量，以解析北冰洋上层海洋输出物质的总量与组成特征。值得注意的是，在拉普捷夫海陆架及其邻近海域观测到的高输出通量，可能是高初级生产、沉积物再悬浮以及海冰融化释放颗粒物共同作用的结果；而2012年海冰范围达到有记录以来最小值时，尽管中央海盆区光照条件显著增强，其输出通量仍处于低位，这表明夏季POC输出受营养盐供给限制。上述研究结果表明，海冰的持续缩减对北极陆架与深海大洋的输出通量影响存在显著差异；且除非向表层水体补充额外营养盐，否则中央海盆区的POC输出量大概率将持续维持低位。