Collaborative Research: BEST: Denitrification and global change in Bering Sea shelf sediments

观察到的白令海冰盖的季节性和年际变化模式似乎与全球气候变化有关。 这些模式表明，白令海的长期变暖将导致春季水华的时间发生变化，同时也会导致能量从底栖生物向中上层生物群落的流动。 该PI将测试的假设，即在春季水华的时间变化的变化，在白令海沉积物中的反硝化作用的速度，这将有重大影响，在这一地区的生产力。在东南白令海的陆架沉积物的反硝化作用估计将删除约三分之一的硝酸盐供应到白令海陆架。PI建议测试的具体假设是：（1）沉积物中的有机质输入和底栖动物洞穴密度与沉积物中的牙化作用相关，并在中等底栖动物密度时达到峰值;（2）大型底栖动物洞穴通风率与有机质输入相关;（3）氮返回上覆水体将是有机质输入的非线性递增函数;（4）到达沉积物的输出产物的比例将随着海冰融化的时间而变化。为了检验这些假设，他们将参加2007-2009年的海洋学考察，进行船上实验，并收集岩心样本，以测量氧、硝酸盐、铵、磷酸盐和硅酸盐的剖面和通量。 他们还将收集样品，用于测量222 Rn和210 Pb剖面，并据此分别计算沉积物生物灌溉率和整体沉积率。 这一测量组合将使他们能够估计沉积物的脱氮率、总的底栖碳氧化率、大型底栖生物的灌溉率和有机物埋藏率，并检验他们的假设。 此外，他们将使用这些数据来构建一个沉积氮循环的数学模型，该模型可用作更大的白令海生态系统模型的边界条件。据推测，目前，白令海大陆架上初级生产所需的氮来自大洋沃茨的跨大陆架运输和大陆架沉积物中的反硝化作用。 这两种氮源的相对重要性如何在改变的冰制度下发生变化以及对生态系统的影响仍然是重要的未解之谜。 这项研究工作应该在我们对现有条件的了解和对未来条件的预测方面提供相当大的改进。

Shull0612380Devol0612436Observed patterns of seasonal and inter-annual variation of ice cover in the Bering Sea appear to be linked to global climate change. These patterns suggest that long-term warming of the Bering Sea would cause a shift in timing of the spring bloom and, concomitantly, in energy flow from benthic to pelagic communities. The PIs will test the hypothesis that variation in the timing of the spring bloom changes the rate of denitrification in Bering Sea sediments, which will have substantial consequences for productivity in this region.Denitrification in shelf sediments of the southeastern Bering Sea is estimated to remove about one third of the total nitrate supply to the Bering Shelf. The specific hypotheses that the PIs propose to test are: (1) Dentirification covaries with organic matter input to the sediment and infaunal burrow densities, peaking at intermediate infaunal densities, (2) Macrofaunal burrow ventilation rates covary with organic matter input, (3) Return of nitrogen to the overlying water will be a non-linear increasing function of organic-matter input, and (4) The fraction of export production reaching the sediment will change with the timing of sea ice melt. To test these hypotheses, they will participate in oceanographic cruises in 2007-2009, conduct onboard experiments, and collect core samples for the measurement of profiles and fluxes of oxygen, nitrate, ammonium, phosphate and silicate. They will also collect samples for measurement of 222Rn and 210Pb profiles, from which they will calculate sediment bioirrigation rates and bulk sedimentation rates, respectively. This combination of measurements will allow them to estimate sedimentary denitrification rates, overall benthic carbon oxidation rates, macrobenthic irrigation rates and organic-matter burial rates, and to test their hypotheses. Additionally, they will use the data to construct a mathematical model of sedimentary nitrogen cycling that can be used as a boundary condition for larger Bering Sea Ecosystem models.It is assumed that, at present, the nitrogen needed to fuel the primary production on the Bering Sea shelf is derived from cross-shelf transport of oceanic waters and denitrification in shelf sediments. How the relative importance of these two sources of nitrogen would change under an altered ice regime and the consequences for the ecosystem remain important unanswered questions. This research effort should provide a considerable improvement in our knowledge of existing conditions and our projections of future conditions.