Isotopic constraints on glacial/interglacial changes in the oceanic nitrogen budget
Isotopic constraints on glacial/interglacial changes in the oceanic nitrogen budget
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DOI：
10.1029/2003gb002189
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发表时间：
2004-10-28
影响因子：
5.2
通讯作者：
Haug, GH
中科院分区：
文献类型：
--
作者：
Deutsch, C;Sigman, DM;Haug, GH
我们使用海洋氮循环的地球化学盒模型（包括沉积物和低氧水体中的 N-2 固定和反硝化）研究了海洋硝酸盐的 N-15/N-14 对冰川/间冰期氮收支变化的响应。考虑到硝酸盐浓度和 N-2 固定/反硝化之间的一系列可能的反馈，该模型使我们能够量化不同海洋硝酸盐池对水柱冰消增加和沉积反硝化的同位素响应。将这一响应与现有的古海洋学数据进行比较，这些数据表明低氧区域硝酸盐 N-15/N-14 的早期冰消期最大值，并且全球海洋硝酸盐 N-15/N-14 没有显着的冰期至全新世晚期变化。与 Brandes 和 Devol [2002] 的工作一致，我们发现海洋硝酸盐的稳态 N-15/N-14 主要由水体中发生的总反硝化部分控制。因此，由于水柱反硝化和氮库之间的强烈反馈或由于海平面上升导致沉积物反硝化增加引起的水柱与沉积物反硝化比率的冰消峰，可以解释在水柱反硝化区下方的沉积物中观察到的冰消N-15/N-14最大值。总反硝化率和平均海洋硝酸盐浓度也是稳态硝酸盐 N-15/N-14 的重要决定因素。因此，模拟真实的冰川消融 N-15/N-14 最大值进一步要求 N-2 固定和反硝化作用的综合负反馈相对较强，并且 N 损失相对较小。我们的结果表明，冰川海洋的氮库存最多比现在多 30%，可能多不到 10%。
We investigate the response of the N-15/N-14 of oceanic nitrate to glacial/interglacial changes in the N budget, using a geochemical box model of the oceanic N cycle that includes N-2 fixation and denitrification in the sediments and suboxic water column. This model allows us to quantify the isotopic response of different oceanic nitrate pools to deglacial increases in water column and sedimentary denitrification, given a range of possible feedbacks between nitrate concentration and N-2 fixation/denitrification. This response is compared to the available paleoceanographic data, which suggest an early deglacial maximum in nitrate N-15/N-14 in suboxic zones and no significant glacial-to-late Holocene change in global ocean nitrate N-15/N-14. Consistent with the work of Brandes and Devol [2002], we find that the steady state N-15/N-14 of oceanic nitrate is controlled primarily by the fraction of total denitrification that occurs in the water column. Therefore a deglacial peak in the ratio of water column-to-sediment denitrification, caused by either a strong feedback between water column denitrification and the N reservoir or by an increase in sediment denitrification due to sea level rise, can explain the observed deglacial N-15/N-14 maximum in sediments underlying water column denitrification zones. The total denitrification rate and the mean ocean nitrate concentration are also important determinants of steady state nitrate N-15/N-14. For this reason, modeling a realistic deglacial N-15/N-14 maximum further requires that the combined negative feedbacks from N-2 fixation and denitrification are relatively strong, and N losses are relatively small. Our results suggest that the glacial oceanic N inventory was at most 30% greater than today's and probably less than 10% greater.