Evidence for middle Eocene Arctic sea ice from diatoms and ice-rafted debris
Evidence for middle Eocene Arctic sea ice from diatoms and ice-rafted debris
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DOI：
10.1038/nature08163
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发表时间：
2009-07
期刊：
影响因子：
64.8
通讯作者：
C. Stickley;K. S. John;N. Koç;R. Jordan;S. Passchier;R. B. Pearce;L. Kearns
中科院分区：
文献类型：
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作者：
C. Stickley;K. S. John;N. Koç;R. Jordan;S. Passchier;R. B. Pearce;L. Kearns
在北极中部Lomonosov海脊钻探的长岩芯中的海洋沉积物含有可追溯到始新世中期的冰筏碎片(IRD)，这促使人们最近提出，大约4600万年前(Myr)，北极出现了冰。然而，由于IRD可以通过冰山(源于陆上冰)和海冰运输，IRD的记录仅限于提供一般冰筏历史。区分海冰和冰川(陆基)冰至关重要，因为气候反馈机制不同，这些系统之间的全球影响也不同：海冰直接影响海洋-大气交换，而陆基冰影响海平面，从而影响海洋酸度。早些时候的一份报告根据IRD假设北极始新世中期存在海冰，尽管存在一些初步的支持证据，但这些数据既不全面，也不量化。在这里，我们展示了始新世中期北极海冰的存在，来自一组依赖海冰的硅藻化石(Synedropsis spp.)。对石英颗粒结构特征的分析进一步支持海冰是目前IRD的主要输运体。结合有关世界性硅藻的新信息和税务局现有记录，我们的数据有力地表明，海冰的形成分为两个阶段：最初在边缘大陆架地区形成∼47.5MYR，随后是∼0.5MYR，后来在北极中部近海地区开始形成季节性节奏的海冰。我们的数据建立了2-Myr的海冰记录，记录了在始新世中期气候降温阶段开始时，从温暖的无冰环境向以冬季海冰为主的环境的转变。
Oceanic sediments from long cores drilled on the Lomonosov ridge, in the central Arctic, contain ice-rafted debris (IRD) back to the middle Eocene epoch, prompting recent suggestions that ice appeared in the Arctic about 46 million years (Myr) ago,. However, because IRD can be transported by icebergs (derived from land-based ice) and also by sea ice, IRD records,are restricted to providing a history of general ice-rafting only. It is critical to differentiate sea ice from glacial (land-based) ice as climate feedback mechanisms vary and global impacts differ between these systems: sea ice directly affects ocean–atmosphere exchanges, whereas land-based ice affects sea level and consequently ocean acidity. An earlier report assumed that sea ice was prevalent in the middle Eocene Arctic on the basis of IRD, and although somewhat preliminary supportive evidence exists, these data are neither comprehensive nor quantified. Here we show the presence of middle Eocene Arctic sea ice from an extraordinary abundance of a group of sea-ice-dependent fossil diatoms (Synedropsisspp.). Analysis of quartz grain textural characteristics further supports sea ice as the dominant transporter of IRD at this time. Together with new information on cosmopolitan diatoms and existing IRD records, our data strongly suggest a two-phase establishment of sea ice: initial episodic formation in marginal shelf areas ∼47.5 Myr ago, followed ∼0.5 Myr later by the onset of seasonally paced sea-ice formation in offshore areas of the central Arctic. Our data establish a 2-Myr record of sea ice, documenting the transition from a warm, ice-free environment to one dominated by winter sea ice at the start of the middle Eocene climatic cooling phase.