The aim of this meta-study is to provide an understanding of the events which slowly ended the Great Ice Age (GIA) and caused the formation of the Sahara Desert. During the GIA, a layer of floating ice 900 m thick in the Arctic Ocean and grounded ice in the North Sea prevented the flow of the Gulf Stream into the Arctic Ocean. An 8-km layer of salt at the bottom of the Gulf of Mexico suggests that the gulf has been an inland sea for a long period. It might have been separated from the Atlantic Ocean by an overflow via the Straits of Florida and a land bridge in the Yucatan Channel, which was reflected the North Equatorial Current (NEC) flow towards the coast of Northwest Africa as the GIA-Gulf Stream (GIA-GS). During the GIA, the return waters by the GIA-GS were warm, and the Sahara was "green." About 11,300 to 11,600 years ago, an earthquake might have cut the land bridge connecting the gulf to the Atlantic Ocean. This allowed the Gulf Stream Currents (GSC) to occupy their present flow route. Within 4,000 to 5,000 years, grounded and floating ice and continental glaciers had melted and the global sea level risen by 10 to 15 meters. By then, the return flow of water carried by the GSC into the Arctic Ocean was fully developed: first via undercurrents (mainly) into the Labrador Sea, and then from there to the coast of Northwest Africa as the North Atlantic Undercurrent (NAUC). Its upwelling waters desiccated the sea-air entering the Sahara. Paleobiological, paleohydrological, and paleontological observations confirm that the drying of the Sahara started in earnest about 6,000 years ago.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.