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

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.