Orbital Scale alkenone based CO2 records across the Pliocene intensification of Northern hemisphere glaciation

The most informative analogues for future anthropgenic climate change are likely to be those with boundary conditions similar to today. The late Pliocene is the most recent time in earth history with elevated global temperatures and CO2 estimated to be similar to that anticipated by the end of this century. Furthermore, Pliocene continental positions and vegetation distributions are thought to be broadly similar to today. Consequently the IPCC fourth assessment report highlighted the Pliocene as an important time period for further study. Recently our understanding of Pliocene CO2 and temperature has improved, with publication of multiple records from alkenone and boron isotope reconstructions for CO2, and Mg/Ca, UK’ 37 and TEX86 reconstructions for sea surface temperature. However, none of the published CO2 records have sufficient temporal resolution to resolve orbital scale variations in CO2, or to determine the relationship between the apparent reduction in atmospheric CO2 and the intensification of northern hemisphere glaciation. Here we present new high resolution records of CO2 and temperature from ODP Site 999 over the critical interval from 3.3 to 2.6 Ma using alkenone palaeobarometry and the UK’37 and TEX86 palaeothermometers. By combining these with a full analysis of the biotic response to changing conditions and reconstructing haptophyte cell sizes, critical for the alkenone palaeobarometer, we present well constrained, coupled records of the response of the climate system to changing CO2