Collaborative Research: BEST: Nitrogen supply for new production and its relation to climatic conditions on the eastern Bering Sea Shelf

Sambrotto-0612427Sigman-0612198该项目将通过示踪剂孵化测量，直接测量白令海东部陆架受冰影响和无冰地区的新(硝酸盐)和再生氮的产量。新生产量表明食物链较高级别可获得的有机物质总量，新生产量与总氮生产量的比率(共比率)表明生产量与水柱内放牧的联系程度。这些生态信息将被用来描述初级生产在水柱和底层消费者之间的分配，以及这种分配如何随着货架上的条件而变化。PI假设再生产量的季节性发展将与浮游动物种群的季节性发展密切相关，因此氮生产力数据将检验振荡控制假说的一个关键组成部分，该假说将气候变异性与通过食物网的营养流动联系起来。由于在白令东部陆架观察到浮游植物的显著演替和年际变化，将同时评估群落组成和氮生产力。该项目还将测量硝酸盐供应(15N/14N和18O/16O)和产生的氮的形式(悬浮和下沉颗粒、溶解有机氮和铵的15N/14N)的自然同位素比率。这些测量提供了一种被动同位素方法，将反映硝酸盐同化的强度，并对陆架新生产提供新的限制。该项目将对照示踪剂孵化测量来校准这一新方法。被动同位素方法在量化水动力复杂但具有生态重要性的区域的新产量方面应特别有用，例如搁架断裂，这些区域很难用标准预算和孵化测量来确定其特征。最后，PIS将检查货架上结合氮的年际变化过程。这一分析将被用来检验这样一个假设，即物理和生物过程的变化可能会通过控制货架上可供生长的结合氮量来影响较大生物体的生产力。

Sambrotto - 0612427Sigman - 0612198This project will measure new (nitrate) and regenerated nitrogen production directly with tracer incubation measurements in ice-impacted and ice-free regions of the eastern Bering Sea shelf. New production is indicative of the total amount of organic material available for higher levels of the food chain and the ratio of new to total nitrogen production (the co-ratio) indicates the degree to which production is linked to grazing within the water column. This ecological information will be used to characterize the partitioning of primary production between water column and bottom-dwelling consumers and how this changes with conditions on the shelf. The PIs hypothesize that the seasonal development of regenerated production will be closely associated with that of the zooplankton populations and thus the nitrogen productivity data will test a key component of the oscillating control hypothesis that links climate variability to the flow of nutrition through the food web. Community composition will be evaluated in parallel with nitrogen productivity because significant successional as well as year-to-year changes in phytoplankton have been observed on the eastern Bering shelf.This project also will measure the natural isotopic ratios of both the nitrate supply (both 15N/14N and 18O/16O) and the forms of nitrogen produced (the 15N/14N of suspended and sinking particles, dissolved organic N and ammonium). These measurements provide a passive isotope approach that will reflect the intensity of nitrate assimilation and provide a new constraint on shelf new production. The project will calibrate this new approach against tracer incubation measurements. The passive isotope approach should be particularly useful in quantifying new production in hydrodynamically complex, but ecologically important regions, such as the shelf break, that are difficult to characterize with standard budgets and incubation-based measurements. Finally, the PIs will examine the processes for year-to-year variations of combined nitrogen on the shelf. This analysis will be used to test the hypothesis that variations in physical and biological processes may influence productivity of larger organisms by controlling the amount of combined nitrogen available on the shelf for growth.