Characterising the middle Miocene Mi-events in the Eastern North Atlantic realm: A first high-resolution marine palynological record from the Porcupine Basin

•The Miocene Mi-3a, Mi-3b and Mi-4 events can be observed in our high-resolution record.•These events correlate to cooling of surface waters and a possible drop in sea-level.•An acme of the dinocyst species Palaeocystodinium occurs during Mi-3b.•Palaeoenvironmental preferences of 5 dinocyst species were determined.

The warm climate of the Miocene peaked during the middle Miocene Climatic Optimum (MMCO; 17–14.5 Ma). After the MMCO, global climate went through several short-lived cooling events: the Mi-events (Miocene isotope events). One of the more severe Mi-events is Mi-3, associated with East Antarctic Ice Sheet growth, species turnover in terrestrial and marine realms, Northern Hemisphere and mid-latitude aridification and Antarctic sea-surface temperature cooling. CO2 reconstructions, as well as the aforementioned observations, suggest that a drawdown of CO2 and/or changes in ocean circulation led to the changes surrounding Mi-3. A combination of eccentricity and obliquity amplitude modulation minima, favourable conditions for ice growth, has also been suggested as a possible triggering mechanism. However, an exact cause cannot be pinpointed yet. High-resolution records necessary to investigate the exact order of events surrounding Mi-3 and the possible role of orbital forcing, a very likely trigger, are sparse.Integrated Ocean Drilling Program (IODP) Leg 307 recovered such a high resolution record from the middle Miocene at the Porcupine Basin (offshore south-western Ireland). Well-preserved palynomorphs, mainly organic-walled dinoflagellate cysts, acritarchs and some pollen were extracted from Site U1318, and relative and absolute abundance changes were determined. Using dinocysts and calcareous nannoplankton the age model for the record was improved. Based on the palynology, the Mi-3a, Mi-3b and Mi-4 events were successfully identified and concomitant palaeoenvironmental change was observed. These events, although different in magnitude, can be associated with a decrease in sea-surface temperature, as well as with a likely fall in sea-level. Furthermore, possible palaeoenvironmental preferences of 5 dinocyst taxa were determined, based on observations from the record and multivariate statistics.