Atlantic Ocean Circulation as the Driving Force for the Holocene Thermal Maximum and Millennial Scale Climatic Variability

Abstract

The aim of this meta-study is to provide an understanding of the Atlantic Ocean Circulation as the driving force for the Holocene Thermal Maximum (HTM) and Millennial Scale Climatic Variability. In addition to continental ice sheets, during the Great Ice Age (GIA) there was also a 900-m thick floating ice shelf (FIS) in the Arctic Ocean. Below the FIS, it was likely freshwater. It is plausible that around 11,700 BP the Gulf Stream established the present flow route. Until around 10,800 BP the Grand Banks of Newfoundland (GBN) diverted part of the Gulf Stream flow west towards the north-eastern American coast, where the HTM existed between ca. 11,600 and 10,800 BP. Soon after the Gulf Stream was able to flow over the GBN, the HTM started in Ireland ca. 10,700 BP. By ca. 10,000 BP, the Gulf Stream arrived on the coast of Norway, which diverted the outflow south through the English Channel for approximately 2,000 years. In Northern and Central Europe, the HTM existed between ca. 9,500 and 7,000 BP. Due to the melting of ice, the outflow turned brackish, and was mainly surface currents, having a temperature of around 0°C. The formation of descending salty water (DSW), which creates the suction of the Gulf Stream, was low. Between ca. 6,000 and 4,500 BP, there was Mid-Holocene cooling. Then the Arctic Ocean water was salinated by double diffusive convection (DDC). When DSW formation increased to its present-day volume, the Neoglacial period started ca. 4,500 BP. Since then, outflow has taken place mainly through cold (approximately -2°C) undercurrents. At this time, the intensive millennial scale cycling of warmer and colder periods also started. When increasingly larger areas in Arctic Ocean are covered by insulating multi-year ice (MYI), DSW formation and the suction of the Gulf Stream decrease, and vice versa. The amplitude of the cycle is approximately 750 to 800 years.