High temperature seasonality as a signature of late-Quaternary AMOC weakening in Northern Europe

Late-Quaternary disruptions of the Atlantic Meridional Overturning Circulation (AMOC) have been linked to profound impacts on local and regional climate as well as vegetation. Temperature seasonality patterns during these AMOC events, most notably during the Younger Dryas, are not yet fully understood, as studies have shown two possible scenarios: overall cooling patterns in Younger Dryas, or warm summers with extreme winter cooling. Here we assess the seasonal temperature trends of late-Quaternary weak AMOC states in Northern Europe, based on new quantitative pollen- and plant macrofossil-based January and July temperature reconstructions using multi-method ensemble reconstruction approaches. For plant macrofossils, we implement a “dynamic” calibration approach, where a spatial extent of the modern calibration region varies based on an independent proxy for the past continentality regime. This allows the reconstruction to algorithmically select the most representative modern calibration region for each time slice. We find an indication that abrupt AMOC weakening is associated with winter-dominated cooling of up to 10 °C but relatively stable summers.