6.5 ka BP cold spell in the Nordic Seas: a potential trigger for a global cooling event?

The present interglacial is a relatively warm and stable interval, especially compared to the preceding glacial period. However, several prominent cooling events have been identified within the Holocene epoch. Most of them occurred in its early or late part, while the middle Holocene was generally considered the warmest and most stable phase. Some of the cooling events (e.g., the well-known 8.2 ka BP event) have been proven to be of overregional importance. Here we focus on an event centred around 6.5 ka BP observed in marine records from the Norwegian Sea and the Fram Strait that has not been described previously. Planktic foraminiferal records from cores along the North Atlantic Drift reveal a subsurface water cooling that in the Fram Strait was more prominent than the well-known 8.2 ka BP event. The increase in the abundance of cold water foraminiferal species is preceded by a stepwise expansion of sea ice in the eastern Fram Strait and is accompanied by a decrease in the abundance of planktic foraminiferal species, an increase in shell fragmentation and IRD deposition. At the same time, alkenone-derived surface water temperatures in the north-eastern Norwegian Sea remain high, suggesting that the cooling was related to a drop in Atlantic Water advection rather than an external forcing. We discuss the possible causes of this event and its potential consequences, including the triggering of a global climatic deterioration that occurred shortly thereafter. Understanding the mechanisms behind such cold spells occurring within a generally warm interval is invaluable for future climate predictions. This study was supported by grant no. 2020/39/B/ST10/01698 funded by the National Science Centre, Poland.