Variability of neodymium isotopes associated with planktonic foraminifera in the Pacific Ocean during the Holocene and Last Glacial Maximum
Variability of neodymium isotopes associated with planktonic foraminifera in the Pacific Ocean during the Holocene and Last Glacial Maximum
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DOI：
10.1016/j.epsl.2016.05.011
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发表时间：
2016-08-01
影响因子：
5.3
通讯作者：
Rennie, Victoria
中科院分区：
文献类型：
--
作者：
Hu, Rong;Piotrowski, Alexander M.;Rennie, Victoria
太平洋深处蕴藏着最大的海洋碳库，这些碳库可能会在重要的气候时间尺度上与大气交换。然而，在最后一次冰川盛期(LGM)期间，深海太平洋的环流情况并没有得到很好的了解。浮游有孔虫上沉积的氧化铁-锰铁涂层中的钕(ND)同位素是古海洋学中深海水团重建的有价值的替代物。在这项研究中，我们提供了全新世浮游有孔虫的Nd同位素组成(epsilon(ND))和分布在太平洋上的55个新地点的LGM。全新世浮游有孔虫(ND)结果与近海海水资料一致，表明它们提供了太平洋深海现代底水ND同位素的可靠记录。有孔虫含量(ND)与海水磷酸盐浓度相关性较好(R2=0.80)，与硅酸盐相关性较差(R2=0.37)。我们的解释是，在深水质量平流和老化过程中，放射性成因的ND同位素通过从上层海洋释放的粒子添加到深海开阔的太平洋中。因此，这些数据还表明，太平洋中的钕同位素不太可能受到硅酸盐循环的控制。在北太平洋，冰期的Nd同位素组成与全新世的值相似，表明北太平洋深水(NPDW)的ND同位素组成保持不变(-3.5~4)。在LGM期间，贯穿整个水柱的西南太平洋岩心显示出较高的epsilon(ND)，这证实了先前关于北大西洋深水流入太平洋的减少的研究。然而，赤道西太平洋深水并没有记录到相应的辐射成因漂移，这意味着在末次盛冰期期间，放射性成因边界输入减少，这可能是因为在较强的冰川深边界流中，海水-粒子相互作用的持续时间较短。赤道东太平洋(EEP)中深处(1-2公里)存在明显的冰川负漂移(ND)，这可能表明NPDW返回核心区的影响更大，减少了EEP的局地输入。综上所述，我们的ND记录不支持动态缓慢的冰川太平洋翻转环流，并暗示太平洋深水碳储量的增加可能是由于冰川时代高纬度海气交换不良和生物泵效率提高所致。(C)2016爱思唯尔B.V.保留所有权利。
The deep Pacific Ocean holds the largest oceanic reservoir of carbon which may interchange with the atmosphere on climatologically important timescales. The circulation of the deep Pacific during the Last Glacial Maximum (LGM), however, is not well understood. Neodymium (Nd) isotopes of ferromanganese oxide coatings precipitated on planktonic foraminifera are a valuable proxy for deep ocean water mass reconstruction in paleoceanography. In this study, we present Nd isotope compositions (epsilon(Nd)) of planktonic foraminifera for the Holocene and the LGM obtained from 55 new sites widely distributed in the Pacific Ocean. The Holocene planktonic foraminiferal epsilon(Nd) results agree with the proximal seawater data, indicating that they provide a reliable record of modern bottom water Nd isotopes in the deep Pacific. There is a good correlation between foraminiferal epsilon(Nd) and seawater phosphate concentrations (R-2 = 0.80), but poorer correlation with silicate (R-2 = 0.37). Our interpretation is that the radiogenic Nd isotope is added to the deep open Pacific through particle release from the upper ocean during deep water mass advection and aging. The data thus also imply the Nd isotopes in the Pacific are not likely to be controlled by silicate cycling. In the North Pacific, the glacial Nd isotopic compositions are similar to the Holocene values, indicating that the Nd isotope composition of North Pacific Deep Water (NPDW) remained constant (-3.5 to 4). During the LGM, the southwest Pacific cores throughout the water column show higher epsilon(Nd) corroborating previous studies which suggested a reduced inflow of North Atlantic Deep Water to the Pacific. However, the western equatorial Pacific deep water does not record a corresponding radiogenic excursion, implying reduced radiogenic boundary inputs during the LGM probably due to a shorter duration of seawater-particle interaction in a stronger glacial deep boundary current. A significant negative glacial epsilon(Nd) excursion is evident in mid-depth (1-2 km) cores of the eastern equatorial Pacific (EEP) which may suggest a stronger influence of NPDW return flow to the core sites and decreased local input in the EEP. Taken together, our Nd records do not support a dynamically slower glacial Pacific overturning circulation, and imply that the increased carbon inventory of Pacific deep water might be due to poor high latitude air-sea exchange and increased biological pump efficiency in glacial times. (C) 2016 Elsevier B.V. All rights reserved.