A micropalaeontological perspective on export productivity, oxygenation and temperature in NE Atlantic deep-waters across Terminations I and II
A micropalaeontological perspective on export productivity, oxygenation and temperature in NE Atlantic deep-waters across Terminations I and II
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DOI：
10.1016/j.gloplacha.2015.06.002
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发表时间：
2015-08
影响因子：
3.9
通讯作者：
P. Grunert;L. Skinner;D. Hodell;W. Piller
中科院分区：
文献类型：
--
作者：
P. Grunert;L. Skinner;D. Hodell;W. Piller
研究了伊比利亚西南边缘底栖有孔虫的普查计数，以重建I和II两端深水水文的过去变化。详细的底栖动物区系数据（> 125 μm尺寸分数）使我们能够评估地压学过程和限制尺寸分数所施加的局限性。U1385遗址近代（泥线）与化石组合的比较表明，星虫类（约占现今动物群的80%）的壳在死后迅速解体，导致化石组合贫乏。虽然在这种情况下，定量替代方法的应用存在问题，但化石组合仍然可以提供定性的古环境信号，尽管这些信号在125-212 μm粒度层中最充分地表达，但在> 212 μm粒度层中也有一定程度的表达。底栖有孔虫组合的变化揭示了有机质供应、深水氧合和温度变化的信息。MIS 2通常以高营养状态和可变氧条件为特征，氧合最低在新仙女木期（YD）和海因里希森林期（HS） 1、2和3达到顶峰。低氧条件与水温下降和底栖生物δ13C降低相吻合，表明在这些时期南方源水团的强烈影响。HS 1是这些层段中最极端的，进一步证明AMOC暂时严重减少甚至关闭。随着MIS 1的启动，有机质供应量减少，并建立了NEADW沐浴的较好通风的深水环境。对于终止方案II，南方水源的明确迹象仅限于HS 11的早期阶段。在HS 11后期，深水环境似乎是由有机质供应的强烈增加决定的，这可能解释了早期研究中底栖生物δ13C和Mg/Ca记录的解耦是植物碎屑对碳同位素信号的影响。然而，不能排除存在温暖的、营养丰富的、缺氧的水体。随着间冰期MIS的开始，5e的营养条件减少，NEADW的通气量增加。
Census counts of benthic foraminifera were studied from the SW Iberian Margin to reconstruct past changes in deep-water hydrography across Terminations I and II. Detailed benthic faunal data (> 125 μm size-fraction) allow us to evaluate the limitations imposed by taphonomic processes and restricted size-fractions. The comparison of recent (mudline) and fossil assemblages at IODP Site U1385 indicates the quick post-mortem disintegration of shells of astrorhizoid taxa (~ 80% of the present-day fauna), resulting in impoverished fossil assemblages. While the application of quantitative proxy methods is problematic under these circumstances, the fossil assemblages can still provide a qualitative palaeoenvironmental signal that, while most fully expressed in the 125–212 μm size-fraction, is nonetheless also expressed to some degree in the > 212 μm size-fraction.Variations in the benthic foraminiferal assemblages reveal information about changing organic matter supply, deep-water oxygenation and temperature. MIS 2 is generally characterized by an elevated trophic state and variable oxic conditions, with oxygenation minima culminating in the Younger Dryas (YD) and Heinrich Stadials (HS) 1, 2 and 3. Low oxic conditions coincide with decreased water-temperature and lower benthic δ13C, pointing to the strong influence of a southern sourced water-mass during these periods. HS 1 is the most extreme of these intervals, providing further evidence for a severe temporary reduction or even shutdown of AMOC. With the inception of MIS 1, organic matter supply reduced and a better ventilated deep-water environment bathed by NEADW is established.For Termination II, clear indications of southern-sourced water are limited to the early phase of HS 11. During the latter part of HS 11, the deep-water environment seems to be determined by strongly increased supply of organic matter, potentially explaining the decoupling of benthic δ13C and Mg/Ca records of earlier studies as a phytodetritus effect on the carbon isotope signal. However, the presence of a warm, nutrient-rich and poorly oxygenated water-mass cannot be ruled out. With the inception of interglacial MIS 5e trophic conditions are reduced and ventilation by NEADW increases.