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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >External N inputs and internal N cycling traced by isotope ratios of nitrate, dissolved reduced nitrogen, and particulate nitrogen in the eastern Mediterranean Sea
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External N inputs and internal N cycling traced by isotope ratios of nitrate, dissolved reduced nitrogen, and particulate nitrogen in the eastern Mediterranean Sea

机译：地中海南部的外部氮输入和内部氮循环，其硝酸盐，溶解的还原氮和颗粒态氮的同位素比示踪

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摘要

The eastern Mediterranean Sea is an unusually nutrient-poor ocean basin where the ~(15)N/~(14)N isotope ratios in many compartments of reactive nitrogen are lower than in comparable oceanic settings. To elucidate possible reasons, we determined stable isotope ratios in nitrate, suspended particulate nitrogen (PN), and total dissolved reduced nitrogen for stations across the eastern Mediterranean Sea occupied in January and February 2007; sinking PN was collected at one of the stations in the period from February to September 2007. The δ~(15)N levels of all reactive N compartments in waters of the basin are very low (grand average 2.6‰) compared to other oceanic environments. Deep water nitrate below 500 m water depth (δ~(15)N = 2.2 ± 0.3‰) was more depleted in ~(15)N than nitrate generally found in deep water nitrate pools of other oceans (δ~(15)N ranges from 4.7 to 5.4‰), whereas ~(15)N was enriched in suspended particulate N (δ~(15)N = 7.3 ± 0.8‰) and reduced dissolved N (δ~(15)N = 5.7 3.8‰) compared to nitrate and sinking particulate N intercepted in sediment traps (δ~(15)N = 0.9 ± 0.8‰). We infer that extensive mineralization is the cause of the isotopic makeup of reactive N in deep water, in concert with the lack of water column denitrification. Nitrogen and oxygen isotope ratios in nitrate of the mixed layer suggest an external source of nitrate depleted in ~(15)N, probably anthropogenic NO _x rather than fixed nitrogen. To explain the observed isotope anomaly in the mixed layer, either the ammonium formed by the breakdown of organic matter must be predominantly nitrified, or atmospheric NO_x characteristically enriched in ~(18)O was present.
机译：地中海东部是一个异常贫瘠的海盆，在该海盆中，许多活性氮区的〜（15）N /〜（14）N同位素比均低于同类海洋环境。为了阐明可能的原因，我们确定了2007年1月和2007年2月在地中海沿岸各站点的硝酸盐，悬浮颗粒氮（PN）和总溶解还原氮的稳定同位素比; 2007年2月至2007年9月期间，在一个站点收集了下沉PN。与其他海洋环境相比，流域水域中所有反应性N隔室的δ〜（15）N水平非常低（平均为2.6‰）。 。低于500 m水深的深水硝酸盐（δ〜（15）N = 2.2±0.3‰）比其他海洋深水硝酸盐池中常见的硝酸盐（δ〜（15）N范围）中的〜（15）N消耗更多。从4.7到5.4‰），而〜（15）N富含悬浮颗粒氮（δ〜（15）N = 7.3±0.8‰），溶解氮含量降低（δ〜（15）N = 5.7 3.8‰）沉积物中截留的硝酸盐和下沉的颗粒氮（δ〜（15）N = 0.9±0.8‰）。我们推断，广泛的矿化作用是深水中反应性N同位素组成的原因，这与缺乏水柱反硝化作用有关。混合层硝酸盐中氮和氧的同位素比值表明，〜（15）N贫化的硝酸盐的外部来源可能是人为的NO_x，而不是固定的氮。为了解释在混合层中观察到的同位素异常，要么必须将有机物分解形成的铵主要进行硝化，要么存在特征性地富含〜（18）O的大气NO_x。

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