Nitrogen isotopic evidence for a poleward decrease in surface nitrate within the ice age Antarctic
Nitrogen isotopic evidence for a poleward decrease in surface nitrate within the ice age Antarctic
复制标题
氮同位素证据表明冰河时代南极洲表面硝酸盐向极地减少
DOI：
10.1016/j.quascirev.2008.02.005
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发表时间：
2008
影响因子：
4
通讯作者：
D. Sigman
中科院分区：
文献类型：
--
作者：
R. Robinson;D. Sigman
沿西纬 170° 横断面的表面沉积物硅藻结合 δ15N 显示，在南极极锋南部，先前未观察到的增加。向南的 δ15N 增加最好是由向南的两个变化的组合来解释，即硝酸盐同位素效应的减少 (ε) 和硝酸盐消耗程度的增加，两者都与混合层浅入季节性冰区 (SIZ) 相关。新的岩心记录显示，在最后一个冰河时期，硅藻结合的 δ15N 发生了大幅变化，δ15N 较高的区间包括末次盛冰期、海洋同位素第 5 阶段和第 4 阶段以及海洋同位素第 6 阶段之间的过渡，而其他区间的 δ15N 与间冰期沉积物相似。正如之前发表的记录中所见，0–3‰范围内的变化可能完全是由于 ε 的变化造成的。然而，在三个新记录中观察到的 4-10‰ 的变化幅度以及这些记录相对于混合层深度的现代经向梯度的位置似乎需要增加硝酸盐消耗来解释高 δ15N 区间。这些新地点位于现代南极洲绕极流锋（SACCF）附近，其中一个地点已被证明与末次盛冰期期间零星的夏季海冰有关。与其他南极地点一样，可用的代理数据表明它们的特点是出口产量较低。基于这些和其他观察结果，我们提出，现代南极表面向南微弱的硝酸盐减少是冰期南极完全发育的“营养锋”，与 SACCF 相关。需要现代海洋和古海洋学工作来检验这一假设，这将对大气中的二氧化碳产生重大影响。
Surface sediment diatom-bound δ15N along a latitudinal transect of 170°W shows a previously unobserved increase to the South of the Antarctic Polar Front. The southward δ15N increase is best explained by the combination of two changes toward the South, a decrease in the isotope effect of nitrate assimilation (ε) and an increase in the degree of nitrate consumption, both associated with shoaling of the mixed layer into the seasonal ice zone (SIZ). New downcore records show high amplitude changes in diatom-bound δ15N during the last ice age, with intervals of higher δ15N, including the last glacial maximum, the transition between marine isotope stages 5 and 4, and marine isotope stage 6, while other intervals are similar in δ15N to interglacial sediments. Variation in the range of 0–3‰, as seen in previously published records, may be entirely due to changes in ε. However, the observed magnitude of the change of 4–10‰ in the three new records and the locations of these records relative to the modern meridional gradient in mixed layer depth appear to require increased nitrate consumption to explain the high-δ15N intervals. The new sites are near the modern Southern Antarctic Circumpolar Current Front (SACCF), and one of the sites has been shown to be associated with sporadic summer sea ice during the LGM. As with other Antarctic sites, the available proxy data suggest that they were characterized by lower export production. Based on these and other observations, we propose that the weak southward nitrate decrease in the modern Antarctic surface was a fully developed “nutrient front” in the glacial Antarctic, associated with the SACCF. Both modern ocean and paleoceanographic work is needed to test this hypothesis, which would have major implications for atmospheric CO2.
影响因子：
4
作者：
Gersonde, R;Crosta, X;Armand, L
通讯作者：
Armand, L
影响因子：
--
作者：
de Boer, A. M.;Sigman, D. M.;Russell, J. L.
通讯作者：
Russell, J. L.