Sea surface and terrestrial temperature evolution across the transition towards the Miocene Climatic Optimum in the eastern North Sea Basin

The Miocene Climatic Optimum (∼16.9-14.7 Ma) was the most recent interval in Earth history with atmospheric CO 2 concentrations above ∼400 ppm. The climatic optimum is associated with elevated temperatures, especially in the middle and higher latitudes. However, existing temperature records, especially from northern high-mid latitudes, are relatively scarce. This limits our understanding of the global temperature evolution across the optimum. Here, we present a multiproxy low-resolution temperature record from a ca. 250 m long sediment core which spans a shallow marine (0-200 m water depth) Miocene (ca. 20 to 8 Ma) succession, located at ~56°N (eastern North Sea). The core is the most northerly located site with a long term (Early to Late Miocene) temperature record derived from both terrestrial palynomorphs (pollen and spores for the air temperature reconstruction) and marine alkenones (organic compounds for the sea surface temperature reconstruction). The updated pollen record shows mean annual temperatures between 16 and 18 °C prior to the optimum, and 18-20 °C during the optimum. Alkenone-based sea surface temperatures reached a maximum value of ~29°C at the climatic optimum and are in the range of the warmest month temperatures shown by the pollen record. Both terrestrial and sea surface temperatures show, in accordance with global records, a gradual cooling following the Miocene Climatic Optimum. Further, the elevated sea surface temperature during the climatic optimum corresponds with a higher relative abundance of warm-water dinoflagellate cyst taxa. However, the sea surface temperature shows a short-lasting temperature drop of more than 2°C at the local maximum regressive surface which is considered to be related with the global sea level rise associated with the MCO.