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

Sambroto-0612427 Sigman-0612198该项目将在白令海东部陆架的冰影响和无冰地区直接测量新氮（硝酸盐）和再生氮的产量。新产量表示可供食物链更高层次使用的有机物质总量，新产量与总氮产量的比率（协比）表示生产与水体内放牧的联系程度。这一生态信息将被用来描述水柱和底栖消费者之间的初级生产的分区，以及这种变化如何与货架上的条件。PI假设再生生产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测试振荡控制假设的关键组成部分，该假设将气候变异性与通过食物网的营养流动联系起来。 由于在东白令海架上观察到浮游植物的显著演替和年与年的变化，因此将在评价氮生产力的同时评价群落组成。（15 N/14 N和18 O/16 O）和产生的氮形态（悬浮颗粒物和沉降颗粒物的15 N/14 N、溶解有机氮和铵态氮）。这些测量提供了一个被动同位素的方法，将反映硝酸盐同化的强度，并提供了一个新的限制货架上的新产品。 该项目将根据示踪剂孵化测量来校准这种新方法。被动同位素方法应特别有助于量化水动力复杂但生态上重要的地区的新生产，如陆架断裂，这些地区难以用标准预算和基于孵化的测量来描述。 最后，PI将检查的过程中，每年的变化，结合氮在货架上。该分析将用于检验以下假设：物理和生物过程的变化可能会通过控制货架上可用于生长的结合氮的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.