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

白令海冰盖的季节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，并随之而来的是能量流动从海底群落转向远洋群落。PIS将检验这样一种假设，即春季水华的时间变化会改变白令海沉积物中的反硝化速率，这将对该地区的生产力产生重大影响。据估计，白令海东南部陆架沉积物中的反硝化作用会减少白令海大陆架总硝酸盐供应的三分之一。PIs建议检验的具体假设是：(1)牙化作用与输入到沉积物中的有机质和底栖动物洞穴密度有关，在中等底栖动物密度时达到峰值；(2)大型动物洞穴通气率与有机质输入有关；(3)氮向上覆水的返还将是有机物质输入的非线性增加函数；(4)到达沉积物的出口产品的比例将随着海冰融化的时间而变化。为了验证这些假设，他们将参加2007-2009年的海洋巡航，进行船上实验，并收集岩心样本，用于测量氧、硝酸盐、铵、磷酸盐和硅酸盐的分布和通量。他们还将收集样本以测量222Rn和210Pb剖面，他们将根据这些剖面分别计算沉积物生物灌溉率和整体沉降率。这种测量组合将使他们能够估计沉积反硝化速率、整体底栖生物碳氧化率、大型底栖动物灌溉率和有机质埋藏率，并检验他们的假设。此外，他们将利用这些数据建立一个沉积氮循环的数学模型，作为更大的白令海生态系统模型的边界条件。目前，假设目前白令海陆架初级生产所需的氮来自海洋水域的跨陆架运输和陆架沉积物中的反硝化作用。在冰川变化的情况下，这两种氮源的相对重要性将如何变化，以及对生态系统的影响仍然是重要的悬而未决的问题。这项研究工作应该会为我们对现有条件的了解和对未来条件的预测提供相当大的改进。

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.