Upper ocean nitrogen fluxes in the Polar Antarctic Zone: Constraints from the nitrogen and oxygen isotopes of nitrate
Upper ocean nitrogen fluxes in the Polar Antarctic Zone: Constraints from the nitrogen and oxygen isotopes of nitrate
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DOI：
10.1029/2009gc002468
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发表时间：
2009-11-26
影响因子：
3.5
通讯作者：
Dunbar, Robert B.
中科院分区：
文献类型：
--
作者：
DiFiore, Peter J.;Sigman, Daniel M.;Dunbar, Robert B.
本文报道了南极绕极锋以南季节性海冰覆盖的南极极区（PAZ）的硝酸盐氮（N）和氧（O）同位素测量结果。在夏季表层混合层中，硝酸盐的15 N/14 N和18 O/16 O比值均呈上升趋势，这与浮游植物吸收硝酸盐的预期结果--硝酸盐浓度的上升趋势有很强的相关性。培养的研究表明，藻类同化硝酸盐分馏硝酸盐N和O同位素相等，而以前的实地研究表明，硝酸盐N和O同位素的行为可以去耦真光区硝化作用。我们的PAZ的数据显示强耦合的硝酸盐的双同位素，南极夏季表层N循环的数值模型适合我们的观察（包括硝酸盐和悬浮颗粒N的同位素组成），如果硝化率不超过6%的硝酸盐同化率的浮游植物。该模型估计，硝酸盐同化的N同位素效应为5.0 +/-0.7%。这一估计缺乏一些与以前的研究在南极绕极流的不确定性，它是在低端的最新估计从南大洋，其中的范围，我们推测属性的混合层深度的影响同位素歧视的幅度。
We report nitrate nitrogen (N) and oxygen (O) isotope measurements from the seasonally sea ice covered Polar Antarctic Zone (PAZ) south of the Southern Antarctic Circumpolar Front. The 15 N/14 N and 18 O/16 O ratios of nitrate both increase into the summertime surface mixed layer, in strong correlation with the upward decrease in nitrate concentration, the expected result of nitrate assimilation by phytoplankton. Culture studies indicate that algal assimilation of nitrate fractionates the nitrate N and O isotopes equally, while previous field studies suggest that nitrate N and O isotope behavior can be decoupled by euphotic zone nitrification. Our data for the PAZ show strong coupling of the dual isotopes of nitrate, and a numerical model of Antarctic summertime surface layer N cycling fits our observations (including isotopic compositions of both nitrate and suspended particulate N) if the nitrification rate is no more than 6% of the nitrate assimilation rate by phytoplankton. The model estimates that the N isotope effect of nitrate assimilation is 5.0 +/- 0.7%. This estimate lacks some of the uncertainties associated with previous studies within the Antarctic Circumpolar Current, and it is at the low end of most recent estimates from the Southern Ocean, the range of which we speculatively attribute to an effect of mixed layer depth on the amplitude of isotope discrimination.