Coupled change in global climate and the carbon cycle across the Eocene-Oligocene transition: New insight from the Pacific Ocean, IODP Exp 320

二氧化碳，CO2，是一种强大的温室气体，自工业革命开始以来，它在地球大气中的浓度增加了约35%。250年时间段）的水平高于过去80万年来的任何时候，如冰芯中的气泡所测量的。如果人为的CO2排放到大气中的速度符合预测的速度，那么到2100年，浓度将达到自古近纪以来地球上从未见过的值。65-23百万年前，马）。这些令人吃惊的观测结果意味着我们必须提高对古近纪气候的认识。可以说，关键的古近纪气候事件发生在34 Ma左右，当第一个大的南极冰盖迅速建立在始新世/渐新世过渡，EOT。冰盖气候模型实验的结果表明，这一事件可能代表了对大气中二氧化碳水平缓慢下降的“临界点”反应（比人为增加的速度慢许多数量级）。我们自己以前的研究结果表明，南极洲冰盖的增长跨越EOT与热带太平洋方解石补偿深度（CCD）的加深（超过一公里）同步发生。CCD是碳酸钙沉积物溶解在海洋中的深度，可以被认为是“海洋酸度指标”。整个EOT的海洋去酸化表明，从一个基本上没有冰川的“温室”世界到南极洲大冰原的转变与全球碳循环的大中断密切相关。南极洲冰盖的增长与热带太平洋深海的酸度有什么联系？此前，我们曾提出，南极大陆冰盖的增长导致海平面下降，杀死了以前在大陆架上蓬勃发展的大片碳酸钙（CaCO 3）分泌珊瑚礁。这将造成溶解的CaCO 3输入（来自河流）和输出（沉积物埋藏）到全球海洋之间的不平衡，需要加深《防治荒漠化公约》，直到通过增加深海中的CaCO 3沉积恢复平衡。在数值“箱模型”测试中，这种“货架到盆地的CaCO 3开关”机制比竞争机制，提出了解释EOT事件。然而，由于一些原因，陆架-海盆转换受到了质疑。例如，有人提出，整个EOT的碳循环变化是由表层海洋生产力的变化驱动的。2009年，综合大洋钻探计划第320远征队在太平洋上不同年龄的洋壳上钻了一系列孔。EOT在四个新的站点相继较浅的深度被捕获。我们的计划是比较化学EOT的“年龄-深度样带”的新网站与我们现有的记录从纬度样带的网站以前在该地区钻探（ODP腿199）。EOT的假设，调用CCD加深响应全球深海碳酸盐化学的变化（如。陆棚-盆地转换）应该产生一种沉积模式，它是深度的简单函数，而我们则根据表面生产力的变化预测纬度的印记。我们工作的一个关键是在我们的目标沉积物中进行前所未有的年龄控制。其他关键方面是两个新的网站，更丰富的CaCO 3和钙质微体化石在整个EOT（特别是最新的始新世）比最好的以前可用的太平洋网站（ODP 1218）和新的地球化学技术的可用性，以确定在碳酸盐化学变化的古代海洋。

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 a ca. 250 yr time period) to a level that is higher than at any time in the past 800 thousand years as measured in air bubbles from ice cores. If man-made (anthropogenic) CO2 emissions to the atmosphere follow projected rates, then by 2100, concentrations will reach values not seen on Earth since the Palaeogene epoch (ca. 65-23 million years ago, Ma). These startling observations mean that we must improve our understanding of Palaeogene climate. Arguably, the pivotal Palaeogene climate event occurred around 34 Ma when, the first large Antarctic ice sheets were rapidly established across the Eocene/Oligocene transition, EOT. Results of ice-sheet-climate model experiments indicate that this event might represent a 'tipping point' response to slow decline in atmospheric CO2 levels (many orders of magnitude slower than the rate of anthropogenic increase). The results of our own previous research show that the growth of ice sheets on Antarctica across the EOT occurred in lock-step with a deepening (by more than a kilometer) in the calcite compensation depth (CCD) in the tropical Pacific Ocean. The CCD is the depth at which calcium carbonate sediments are dissolved in the ocean and can be thought of as 'an ocean acidity indicator'. Ocean de-acidification across the EOT demonstrates that the switch from a largely non-glaciated 'greenhouse' world to one with large ice sheets on Antarctica was closely associated with a big disruption in the global carbon cycle. What linked ice sheet growth on Antarctica to the acidity of the tropical deep Pacific Ocean? Previously we have suggested that growth of ice sheets on the Antarctic continent causes sea level to fall, killing off the large expanse of calcium carbonate (CaCO3)-secreting reefs that previously flourished on the continental shelves. This would have caused an imbalance between the inputs (from rivers) and outputs (sediment burial) of dissolved CaCO3 to the global ocean requiring a deepening in the CCD until balance was restored through increased CaCO3 sedimentation in the deep ocean. In numerical 'box model' tests, this 'shelf-to-basin CaCO3 switching' mechanism performed better than competing mechanisms proposed to explain EOT events. Yet shelf-basin-switching has been called into question on a number of grounds. For example, it has been suggested that the carbon cycle changes across the EOT were driven by changes in surface ocean productivity. In 2009, Integrated Ocean Drilling Program Expedition 320 drilled a series of holes across the Pacific Ocean on ocean crust of different age. The EOT was captured in four new sites at successively shallower depths. Our plan is to compare the chemistry of this EOT 'age-depth transect' of new sites with our existing records from a latitudinal transect of sites drilled previously in the region (ODP Leg 199). Hypotheses for the EOT that invoke CCD deepening in response to changes in global deep ocean carbonate chemistry (eg. shelf-basin-switching) should produce a pattern of sedimentation that is a simple function of depth whereas we predict the imprint of latitude from changes in surface productivity. One key to our work is the potential for unprecedented age-control in our target sediments. Other key aspects are the availability of two new sites that are richer in CaCO3 and calcareous microfossils across the EOT (specifically the latest Eocene) than the best previously available Pacific site (ODP 1218) and new geochemical techniques for determining changes in carbonate chemistry of the ancient oceans.