Middle Miocene environmental change in the eastern Atlantic Ocean at the Porcupine Basin (IODP Leg 307) : results from an integrated palynological and biogeochemical study

The relatively warm climate of the Miocene reached peak values during the middle Miocene Climatic Optimum (MMCO; 17-14.5 Ma). After the MMCO, the global climate started cooling. This happened through several short-lived cooling events, represented by positive oxygen isotope excursions: the Mi-events. These disturbances can be associated with growth of the East Antarctic Ice Sheet and potentially Northern Hemisphere ice expansion. The causes and consequences of the Mi-events are not well constrained. For this reason we want to examine the role of the Gulf Stream in the cooling and subsequent warming of the Mi-events, since it is a possible mechanism to amplify regional changes in northwestern Europe. Integrated Ocean Drilling Program (IODP) Leg 307 recovered a high resolution record from the middle Miocene of the Porcupine Basin, offshore southwestern Ireland and therefore under the influence of the Gulf Stream. We have extracted well-preserved palynomorphs (mainly organic-walled dinoflagellate cysts, acritarchs, some pollen) and organic molecules for paleothermometry (e.g. TEX86 and UK'37) from core 1318B. With these proxies the development of the Mi-3 and Mi-4 events are reconstructed on high resolution, by assessing e.g. temperature, sea level, thermocline depth and productivity. First results indicate a pronounced cooling as recorded simultaneously in TEX86, Uk'37 and dinoflagellate cyst assemblages during Mi-4. The presented results will focus in detail on the phasing and rates of change in the reconstructed Mi-events