Seasonal and interannual variability in sources of nitrogen supporting export in the oligotrophic subtropical North Pacific Ocean
Seasonal and interannual variability in sources of nitrogen supporting export in the oligotrophic subtropical North Pacific Ocean
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DOI：
10.4319/lo.2002.47.6.1595
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发表时间：
2002-11-01
影响因子：
4.5
通讯作者：
Karl, DM
中科院分区：
文献类型：
--
作者：
Dore, JE;Brum, JR;Karl, DM
在数月至数年的时间尺度上，从海洋光带输出的有机氮（主要是下沉的颗粒氮，PN）被认为平衡了外源组合无机氮的输入（即出口产量平衡了新产量）。在北太平洋副热带少营养环流中，有两个重要的新氮来源：来自深水的硝酸盐向上通量和近地表水溶解N-2的生物固定。由于这些源具有明显的稳定同位素特征，我们能够使用沉降粒子的总PN和δ (15)N测量值和同位素质量平衡模型来解卷积硝酸盐通量和固氮对PN引力输出的相对和绝对贡献。1989 - 2001年，PN沉降通量及其同位素组成变化较大。季节上，N-2固定与混合层深度呈负相关，在6 ~ 8月达到最大值，而硝酸盐支撑出口与海温呈负相关，在2 ~ 3月达到最大值。这些模式与夏季重氮营养菌生物量和水柱N-2固定率的增加一致，这是由植氰菊酯色素浓度和N-15(2)示踪剂研究表明的。N-2固定对N输出的相对贡献率在36% ~ 69%之间（平均48%），且在观测期内呈显著上升趋势。尽管总PN输出与南方涛动指数相关，但基于硝酸盐和氮固定的组分似乎以不同的方式响应气候强迫，这使我们对气候引起的颗粒输出变化机制的解释变得复杂。
Over timescales of months to years, the export of organic nitrogen from the oceanic euphotic zone (principally as sinking particulate nitrogen, PN) is believed to balance the input of exogenous combined inorganic nitrogen (i.e., export production balances new production). In the oligotrophic North Pacific subtropical gyre, there are two significant sources of new nitrogen: the upward flux of nitrate from deep water and the biological fixation of dissolved N-2 in near-surface waters. Because these sources have distinct stable isotopic signatures, we were able to use the total PN and delta(15)N measurements of sinking particles and an isotopic mass balance model to deconvolute the relative and absolute contributions of the nitrate flux and nitrogen fixation to the gravitational export of PN. The sinking flux of PN and its isotopic composition both varied widely between 1989 and 2001. Seasonally, N-2 fixation correlated inversely with mixed-layer depth, reaching a maximum in June-August, whereas nitrate-supported export correlated inversely with sea surface temperature, reaching a maximum in February-March. These patterns were consistent with summertime increases in diazotroph biomass and water column N-2 fixation rates, as indicated by phycoerythrin pigment concentrations and N-15(2) tracer studies. Annually, the relative contribution of N-2 fixation to N export varied from 36 to 69% (mean = 48%) and showed a significant increasing trend over the period of observation. Although total PN export correlated with the Southern Oscillation Index, the nitrate- and nitrogen fixation-based components appeared to respond to climate forcing in distinct ways, complicating our interpretation of the mechanisms of climate-induced changes in particle export.