N2 fixation variability in the oligotrophic Sulu Sea, western equatorial Pacific region over the past 83 kyr
N2 fixation variability in the oligotrophic Sulu Sea, western equatorial Pacific region over the past 83 kyr
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DOI：
10.1007/s10872-006-0066-2
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发表时间：
2006-08
影响因子：
2.3
通讯作者：
K. Horikawa;M. Minagawa;Y. Kato;M. Murayama;S. Nagao
中科院分区：
文献类型：
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作者：
K. Horikawa;M. Minagawa;Y. Kato;M. Murayama;S. Nagao
氮固定是向海洋补充新氮的重要生物过程，在调节海洋硝酸盐库存量中起着关键作用。然而，由于过去的气候变化，固氮率是如何、何时以及在何处发生变化的，目前尚不清楚。本文报道了赤道西太平洋苏禄海沉积岩心（KH02-4 SUP8）近83 kyr来氮同位素组成（δ15N）的新记录。数据允许重建海洋中的氮固定变率。与北太平洋中水沉积物、沉降物和悬浮颗粒有机质（POM）的δ15N值（平均值为5.8‰）相比，沉积物、下沉物和悬浮颗粒有机质（POM）的同位素值都较轻。这些较轻的δ15N值反映了苏禄海表层水对n2的固定作用。δ15N质量平衡模型显示，在54 ~ 34 kyr期间，MIS-3和MIS-2的n2固定率显著提高。据推测，阿拉伯海和热带东太平洋较高的间冰期反硝化速率可能会显著降低全球海洋氮储量，并导致少营养区氮固定增加，但我们的研究并未揭示这样的模型。苏禄海固氮速率的变化可能是区域响应，而由于季风驱动的混合增强，表层水中磷酸盐的积累被认为在MIS-3和MIS-2期间刺激了n2固氮的增强。
N2fixation is an important biological process that adds new nitrogen to oceans and plays a key role in modulating the oceanic nitrate inventory. However, it is not known how, when, and where N2fixation rates have varied in response to past climate changes. This study presents a new record of nitrogen isotopic composition (δ15N) over the last 83 kyr from a sediment core (KH02-4 SUP8) taken in the Sulu Sea in the western equatorial Pacific region; data allow the N2fixation variability in the sea to be reconstructed. Sediments, sinking, and suspended particulate organic matter (POM) all have lighter isotopic values compared to the δ15N values of substrate nitrate (av. 5.8‰) in North Pacific Intermediate Water. These lighter δ15N values are regarded as reflecting N2fixation in the Sulu Sea surface water. A δ15N mass balance model shows that N2fixation rates were significantly enhanced during 54–34 kyr in MIS-3 and MIS-2. It has been speculated that higher interglacial denitrification rates in the Arabian Sea and the eastern tropical Pacific would have markedly decreased the global oceanic N inventory and contributed to the increase in N2fixation in oligotrophic regions, but such a model was not revealed by our study. It is possible that changes in N2fixation rates in the Sulu Sea were regional response, and accumulation of phosphate in the surface waters due to enhanced monsoon-driven mixing is thought to have stimulated enhancements of N2fixation during MIS-3 and MIS-2.