Sub-orbital climate instability and its relation to Late Pliocence intensification of Northern Hemisphere Glaciation, IODP Sites 1308 and 1313

一亿年前，当恐龙在地球上行走时，大多数科学家认为极地没有我们今天看到的大冰盖。这些冰盖是什么时候形成的，为什么形成的？它们的增长速度有多快？一旦成立，它们的稳定性如何？这些都是我们试图通过从海底收集的沉积物岩芯生成过去气候变化的记录来回答的一些问题。我们的技术之一是计算冰川从大陆上剥离出来的小岩石碎片，并通过冰山的崩解和漂移将其输送到海底。另一种方法是测量捕获在被称为有孔虫的微小单细胞海洋动物的碳酸钙化石壳中的重氧同位素(18O/16O)和轻氧同位素(18O/16O)的比率(从实验室实验中得知，重氧同位素对冰量和温度敏感)。我们已经有了过去100 Ma气候变化的半连续、半定量的图像。这种模式是一种逐渐的长期降温，外加几次向更多冰川条件的大“转变”。叠加在这些变化上的是具有明显节奏的规则气候周期(例如，轨道周期约为100年、4万年)。在我们有足够高分辨率的记录(特别是过去500年)的地方，我们看到这些节奏上叠加着亚轨道尺度的振荡，涉及到好莱坞大片《后天》中流行的冰盖推进/崩溃和海洋环流变化。这些波动与我们对未来的担忧尤其相关。它们表明，即使在没有人类干预的情况下，整个气候系统，特别是北大西洋地区，即使在几十年内也能够以极快的速度进行大规模重组(特别是对欧洲西北部的情况造成极端后果)。一些人认为，亚轨道尺度的振荡是由地球外部的力驱动的(例如。太阳辐射的变化)。其他人认为内力很重要，因为我们可以看到，在过去的500年里，当冰盖很大时，亚轨道振荡被放大了。海洋沉积物中冰排碎片和氧同位素的记录表明，北半球从2.72 Ma开始就存在巨大的永久大陆冰盖。因此，出现的一个大问题是：随着被认为放大气候变异性的冰盖的形成，亚轨道尺度的气候变异性是如何演变的？在寻求回答这个问题时，我们过去一直受到缺乏连续、高分辨率的变化记录和出色的年龄控制的阻碍。然而，在快速堆积沉积物的地点谨慎地应用现代钻探方法有助于纠正这些问题。我们建议通过在2.84 Ma至2.4 Ma期间从北大西洋产生新的具有前所未有的连续性、分辨率和年龄控制的古气候记录来解决上述问题。通过测定亚轨道尺度气候不稳定对冰期-间冰期状态的敏感性，我们可以看到约2.8 Ma以来气候边界条件的变化。

One hundred million years ago (Ma), when dinosaurs walked Earth, most scientists think that the poles were free of the large icecaps that we see today. When and why did these icecaps form? How rapidly did they grow? Once established, how stable were they? These are some of the questions that we seek to answer by generating records of past climate change from sediment cores collected from the seafloor. One of our techniques is to count small rock fragments that have been scrapped off the continents by glaciers and delivered to the seafloor by calving and drifting of icebergs. Another is to measure the ratio of heavy and light oxygen isotopes (18O/16O) (known from laboratory experiments to be sensitive to ice-volume and temperature) trapped in the fossilised calcium carbonate shells of tiny single cellular marine animals called foraminifers. We already have a semi-continuous, semi-quantitative picture of climate change over the past 100 Ma. The pattern is one of gradual long-term cooling plus several big 'shifts' to more glaciated conditions. Superimposed on these changes are regular cycles in climate with distinct rhythms (eg. orbital cycles of ~100, 40 thousand years). Where we have high-enough resolution records (of the last 500 kyrs in particular) we see that superimposed on these rhythms are sub-orbital scale oscillations involving ice-sheet advance/collapse and ocean circulation change as popularised in the Hollywood blockbuster 'The Day After Tomorrow'. These oscillations are especially relevant to our concerns about the future. They demonstrate that, even without man's interference, the climate system in general and the North Atlantic region in particular is capable of undergoing massive re-organization extremely rapidly, within even a few decades (with extreme consequences for conditions in NW Europe in particular). Some suggest that sub-orbital scale oscillations are driven by forces external to Earth (eg. changes in solar insolation). Others think that internal forces are important because, we can see that in the last 500 kyrs sub-orbital oscillations were amplified when ice-sheets are large. Records of ice-rafted debris and oxygen isotopes from marine sediments suggest that large permanent continental ice-sheets were present in the northern hemisphere from ~2.72 Ma. One big question that arises, therefore, is: - how does sub-orbital scale climate variability evolve as the ice-sheets that are thought to amplify them form? In seeking to answer this question we have been hampered in the past by the lack of continuous, high-resolution records of change with excellent age control. However, careful application of modern drilling methods to sites of rapidly accumulating sediment is helping to remedy these problems. We propose to address the above problem by generating new palaeoclimate records of unprecedented continuity, resolution and age-control from the North Atlantic for the interval 2.84 Ma to 2.4 Ma. By determining the sensitivity of sub-orbital scale climate instability to glacial-interglacial state we can see how climate boundary conditions have changed since ~ 2.8 Ma.