Terrestrial and marine temperature evolution across 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's history with greenhouse conditions, which prevailed for nearly 2 million years. The optimum was associated with elevated atmospheric CO 2 (~400-600 ppm) and higher global temperatures, and therefore the optimum is considered one of the best analogues for future climate scenarios. However, existing temperature records, especially from northern high-mid latitudes, are relatively scarce. This limits our understanding of the global temperature evolution across the climatic optimum. Here, we present a multiproxy low-resolution temperature record from a ca. 250 m long sediment core which spans a shallow marine Miocene (ca. 20 to 8 Ma) succession, located at ~56°N (eastern North Sea). The water depth at the core location oscillated between 0 and 200 m during the Miocene. 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. Both records also 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. According to our preliminary results, bottom water temperature (derived from clumped isotopes measured on molluscs) in the Miocene oscillated between 6.8 (+/-1.8) °C and 9.5 (+/-2.3), with no apparent trend over time. Such low bottom water temperatures are difficult to reconcile with a rather shallow water depth and high sea surface temperatures. Therefore, to exclude either vital or contamination effects, we are planning to additionally obtain bottom water temperature from the calcareous benthic foraminifera, which are present in the core.