Worldwide consequences of a mid-Holocene cooling in the Nordic Seas

Abstract

Apart from long-term changes, the Earth’s climate has been punctuated by numerous short-lived events that had a tremendous influence on terrestrial and marine ecosystems. The present interglacial is a relatively warm and stable period, especially compared to the preceding glacial time. However, several prominent cooling events have been identified within the Holocene, some of them of overregional importance. Based on previously published marine records from the Nordic Seas, we describe for the first time an event centered around 6.7 ka BP. Paleoceanographic proxies along the North Atlantic Drift reveal a distinct subsurface water cooling, preceded by a stepwise increase in sea-ice cover in the eastern Fram Strait. The results indicate that the onset of deep convection in the Greenland Sea and the westward shift of the main flow of Atlantic Water allowed sea-ice advection from the Barents Sea. The increased sea-ice cover weakened the Atlantic Water advection. The perturbation of the overturning circulation in the eastern Nordic Seas had far-reaching consequences, including changes in deep-water circulation in the North Atlantic, cooling over vast areas of both hemispheres, and weakening of the East Asian monsoon. The described events show that, during a relatively warm and stable interval, a fairly local cooling can occur, and the resulting sequence of environmental changes can spread globally. Understanding the mechanisms behind events that occur within generally stable intervals is invaluable for future climate predictions.