Nitrogen Cycling in Marine Sediments: Isotope Fraction- ation Effects

提出了一项初步研究，以评估15/N/14N比值对研究沉积氮循环的有用性。海洋沉积物中的反硝化作用，特别是大陆架上的反硝化作用，是海洋中组合氮的主要汇，除硝化作用外，已知还会使氮同位素产生强烈的分馏作用。对于沉积物，耦合的硝化-反硝化和通量的输运控制可能会强烈地改变这些分馏效应。最初的目标将是确定氮同位素信号是否足够大，使它们既连贯又可解释。模型分析表明，情况将是这样。位于缅因州湾和百慕大之间的横断面上的巴兹湾将被研究。孔隙水NO3-、NH4+和沉积物PN的15N值将在岩心下部测定，通量室实验将确定相对于水柱的净同位素效应。对岩心切片进行培养实验，确定微生物分馏因素。

A pilot study is propoosed to evaluate the usefulness of 15/N/14N ratios for studying the sedimentary nitrogen cycle. Denitrification in marine sediments, particularly on continental shelves, is a principal sink for combined nitrogen from the ocean and in addition to nitrification is known to strongly fractionate nitrogen isotopes. For sediments, coupled nitrification-denitrification and transport control of fluxes are likely to strongly modify these fractionation effects. Initial objectives will be to determine whether nitrogen isotopic signals are sufficiently large such that they are both coherent and interpretable. Model analysis suggests that this will be the case. Sites in Buzzards Bay-MA, along a transect between the Gulf of Maine and Bermuda will be studied. 15N values for pore-water NO3-, NH4+, and sediment PN will be determined downcore and flux chamber experiments will be carried out to determine the net isotopic effect with respect to the water column. Incubation experiments of core slices will be carried out to determine microbial fractionation factors.