A mid‐Holocene transition in the nitrogen dynamics of the western equatorial Pacific: Evidence of a deepening thermocline?
A mid‐Holocene transition in the nitrogen dynamics of the western equatorial Pacific: Evidence of a deepening thermocline?
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DOI：
10.1029/2008gl035464
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发表时间：
2008-12
影响因子：
5.2
通讯作者：
M. Kienast;Moritz F. Lehmann;Axel Timmermann;Eric D. Galbraith;T. Bolliet;A. Holbourn;C. Normandeau;C. Laj
中科院分区：
文献类型：
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作者：
M. Kienast;Moritz F. Lehmann;Axel Timmermann;Eric D. Galbraith;T. Bolliet;A. Holbourn;C. Normandeau;C. Laj
棉兰老岛外海贫营养西赤道太平洋（WEP）沉积物δ 15 N记录表明，晚全新世沉积物δ 15 N显著低于早全新世沉积物δ 15 N，在7 ~ 3 kyr前，δ 15 N逐渐下降>3 ‰。对同一地区现代硝酸盐同位素剖面的分析表明，WEP N库对以下两种情况的敏感性：（1）北赤道海流（NEC）和棉兰老海流在地下沃茨从东赤道太平洋（EEP）平流输送富含15 N的硝酸盐;（2）在浅层，通过N2固定输入新的和15 N贫化的硝酸盐。我们认为，沉积δ 15 N的全新世减少反映了减少的相对输入的15 N富集硝酸盐的表面生物群，通过增加区域固氮，硝酸盐消耗的变化沿着平流路径的硝酸盐供应，或减少的垂直供应的15 N富集硝酸盐从NEC。后一种机制是一致的，全新世加深的WEP硝化/温跃层。
Sedimentary δ15N records from the oligotrophic western equatorial Pacific (WEP) off Mindanao show that late Holocene sedimentary δ15N is substantially lower than that of the early Holocene, following a gradual >3 ‰ decrease that occurred between 7 and 3 kyrs ago. Analyses of modern day nitrate isotope profiles from the same region indicate the sensitivity of the WEP N pools towards (1) the advection of 15N‐enriched nitrate from the Eastern Equatorial Pacific (EEP) by the North Equatorial Current (NEC) and the Mindanao Current in subsurface waters and, (2) at shallow depths, the input of new and 15N‐depleted nitrate through N2 fixation. We suggest that the Holocene decrease in sedimentary δ15N reflects a diminished relative input of 15N‐enriched nitrate to the surface biota, either through an increase of regional nitrogen fixation, a change in nitrate consumption along the advective path of nitrate supply, or a decrease in the vertical supply of 15N‐enriched nitrate from the NEC. The latter mechanism is consistent with a Holocene deepening of the WEP nitracline/thermocline.