Climate change across the Eocene/Oligocene and Oligocene/Miocene transitions: IODP Expedition 342, Newfoundland sediment drifts

二氧化碳是一种强大的温室气体，自工业革命开始（约250年）以来，其在地球大气中的浓度增加了约35%，以冰芯中获得的气泡测量，其浓度高于过去80万年中的任何时候。如果人造（人为）二氧化碳排放到大气中按照预计的速率，那么到2100年，二氧化碳浓度将达到自古近纪（约6500万至2300万年前）以来从未见过的水平，当时地球的气候比今天暖和得多，例如，真正的绿色格陵兰岛。这些惊人的观察结果有力地推动了我们对古近纪气候系统的理解。新生代的古气候记录大部分是通过对深海沉积物的分析拼凑而成的。它揭示了始新世早期（~55 Ma）以来的长期气候恶化，叠加了更高频率（10万年至10万年时间尺度）的变化，包括地球太阳轨道的变化和更极端的变化，包括短暂的漂移和更持久的气候状态变化。在每种情况下，古气候档案都表明观测到的气候信号与全球碳循环扰动之间存在密切关系。为了破译迫使这些气候变化和响应（反馈效应）的物理和生物地球化学机制，我们必须确定所涉及的变化的速率和全部幅度。到目前为止，这已经被证明是困难的，因为我们几乎所有关于上新世-更新世前气候变化的记录都来自沉积物积累非常缓慢（每千年约1厘米）的地点。综合海洋钻探计划远征队（IODP Exp., 342）直接解决了这个问题，他们在深海沉积物以异常快的速度（每千年高达10厘米）堆积的地点钻了一系列的洞，这些沉积物在J异常脊和东南纽芬兰脊的深西部边界流的影响下被扫过并堆积起来。该钻井地点因其是1912年4月从英国南安普敦前往美国纽约途中与冰山相撞沉没的皇家邮轮泰坦尼克号和1991年10月从马萨诸塞州格洛斯特出发的商业旗鱼船安德里亚·盖尔号的墓地而闻名，盖尔号在“完美风暴”中与所有船员一起在海上失踪。这些钻探的沉积物提供了北欧海和北冰洋流出的水的化学变化、流动历史和深度结构的档案，这些变化是在从一个以真正的绿色格陵兰岛和南极洲茂密森林为特征的无冰世界转变为两个半球都有主要冰盖的世界的过程中发生的。拟议的项目将生成新的高分辨率岩心扫描x射线荧光（XRF）记录，并在Exp. 342钻孔岩心中生成大量CaCO3的目标氧和碳同位素：(i)在考察地点之间生成高质量的年表和相关性，并与沉积速率较慢的其他地点的现有记录建立联系。（二）评价这些旋回地层记录的气候意义，并为对所涉及的海洋温度、冰量和二氧化碳水平的变化进行全面定量的地球化学分析奠定基础。

Carbon dioxide, CO2, is a powerful greenhouse gas and its concentration in Earth's atmosphere has increased by around 35% since the start of the Industrial Revolution (in ca. 250 yrs) to a level that is higher than at any time in the past 800 thousand years as measured in air bubbles obtained from ice cores. If man-made (anthropogenic) CO2 emissions to the atmosphere follow projected rates, then by 2100, concentrations will reach values not seen since the Palaeogene epoch (ca. 65-23 million years ago, Ma) when Earth's climate was much warmer than today, featuring, for example, a genuinely green Greenland. These startling observations provide a powerful incentive to improve our understanding of the workings of the Palaeogene climate system.The Cenozoic palaeoclimate record is largely pieced together from the analysis of deep-sea sediments. It reveals a long-term climatic deterioration since the early Eocene (~55 Ma) with superimposed higher-frequency (10 to 100 thousand year timescale) variations including those paced by changes in Earth's orbit of the Sun and more extreme changes, both transient excursions and more persistent shifts in climate-state. In each case, the palaeoclimate archive indicates a close relationship between the climate signal observed and perturbation to the global carbon cycle.To decipher the physical and biogeochemical mechanisms that forced these changes in climate and the responses (feedback effects) we must determine rates and full magnitude of the changes involved. Until now this has proved difficult because virtually all of our records of pre-Plio-Pleistocene climate change come from sites where sediments accumulate very slowly (~ 1 cm per thousand years). Integrated Ocean Drilling Program Expedition, IODP Exp., 342 addresses this problem directly by having drilled a series of holes at sites where deep-sea sediments have accumulated at unusually fast rates (up to 10 cm per thousand years) in sediment drifts that were swept and piled up under the influence flow path of the Deep Western Boundary Current on J Anomaly Ridge and Southeast Newfoundland Ridge. The drill site area is famous because it is the graveyard of RMS Titanic, which sank after colliding with an iceberg en route from Southampton, England, to New York City, USA, in April 1912 and of the Andrea Gail, the commercial swordfish vessel from Gloucester, Massachusetts, lost at sea with all hands during the "Perfect Storm" of October 1991. These sediments drilled provide an archive of changes in chemistry, flow history, and depth structure of waters exiting the Nordic seas and Arctic Ocean during the transition into a world with major ice caps in both hemispheres from an ice-free world featuring a genuinely green Greenland and lush forests on Antarctica.The proposed project will generate new high-resolution records of core-scanning X-ray fluorescence (XRF) and targeted oxygen and carbon isotopes of bulk CaCO3 in Exp. 342 drill cores: (i) To produce high quality chronologies and correlations among the expedition sites and ties to existing records from sites elsewhere where sedimentation rates are slower. (ii) To evaluate the climatic significance of these cyclostratigraphic records and lay the groundwork for a full quantitative geochemical analysis of the changes in ocean temperature, ice volume and CO2 levels involved.