Description: The Arctic cryosphere is changing and making significant contributions to 21st century sea level rise. The Pliocene epoch had similar CO2 levels to present and a warming comparable to model predictions for the end of this century, providing an opportunity to investigate the operation of Arctic climate in a warm world. The Late Pliocene has well documented climatic conditions. However, the state of the Arctic cryosphere remains partially constrained. Here, for the first time, we couple outputs from a Pliocene climate model with a thermodynamic iceberg model to simulate likely source regions for Ice Rafted Debris (IRD) found in the Nordic Seas from Marine Isotope Stage M2 to the mid Pliocene Warm Period (mPWP). We compare the fraction of melt given by the model scenarios with IRD data from four Ocean Drilling Program (ODP) sites within the Nordic Seas region. Marine sites 911A, 909C and 907A show a persistent occurrence of IRD that modeling results suggest is consistent with permanent ice on Svalbard. Our model results indicate that icebergs sourced from the east coast of Greenland do not reach the Nordic Seas sites during the warm late Pliocene, but instead travel south into the North Atlantic. Small amounts of IRD are found at Hole 642B in the Late Pliocene. Model results identify coastal Norway as the potential source, however this is inconsistent with current understanding of the Late Pliocene Scandinavian climate.

Description: There is an urgent requirement to understand how large fluctuations in tropical heat distribution associated with the El Niño-Southern Oscillation (ENSO) will respond to anthropogenic emissions of greenhouse gases. Intervals of global warmth in Earth history provide a unique natural laboratory to explore the behaviour of the ENSO in a warmer world. To investigate interannual climatic variability, specifically ENSO, in the mid-Piacenzian Warm Period (mPWP: 3.26 - 3.03 Ma), we integrate observations from the stable isotopes of multiple individual planktonic foraminifera from three different species from the eastern equatorial Pacific (EEP) with ENSO simulations from HadCM3, a fully coupled ocean-atmosphere climate model. Our proxy data and model outputs show persistent inter-annual variability during the mPWP caused by a fluctuating thermocline, despite a deeper thermocline and reduced upwelling. We show that the likely cause of the deeper thermocline is due to warmer equatorial undercurrents rather than reduced physical upwelling. We conclude that the mPWP was characterized by ENSO related variability around a mean state akin to a modern El Niño event. Furthermore, HadCM3 predicts that the warmer Pliocene world is characterized by a more periodic, regular amplitude ENSO fluctuation, suggestive that the larger and deeper west Pacific warm pool is more easily destabilized eastwards. These conclusions are comparable to the observed trend over the last forty years to more regular and intense ENSO events. Future research must resolve whether global warming alone, or in concert with tectonic factors, was sufficient to alter ENSO variability during warm intervals of the Pliocene.