Great flood disrupted ocean currents, cooled climate, finds new research

Great flood disrupted ocean currents, cooled climate, finds new research

mongabay.com

June 29, 2006

Ocean circulation changes caused at the end of the past glacial period were more extensive than previously thought, according to new research scientists at the University of East Anglia and Cardiff University.

The findings, published in the June 30 issue of the journal Science, indicate that the catastrophic freshwater release from glacial lakes in North America slowed ocean circulation and cooled the climate some 8200 years ago.

According to a release from the University of East Anglia, the “research increases our understanding of the complex link between ocean circulation and climate change and highlights the sensitivity of the Atlantic overturning circulation to freshwater forcing.”

Christopher Ellison and Dr Mark Chapman, of the University of East Anglia’s School of Environmental Sciences, and Dr Ian Hall, of Cardiff University’s School of Earth, Ocean and Planetary Sciences used a sediment core drawn from the North Atlantic seabed to come to their conclusions.

The Great Flood had smaller impact than originally believed NASA climate modelers have simulated the climate changes caused by a massive deluge of freshwater into the North Atlantic that occurred near the end of the last Ice Age 8,000 years ago. At the time, retreating glaciers opened a route for two giant lakes known as Agassiz and Ojibway to rapidly and prodigiously drain into the North Atlantic ocean. Scientists believe that the tremendous influx of freshwater in the North Atlantic interfered with the ocean’s thermohaline circulation, which distributes heat around the globe, and may have caused average air temperatures to drop several degrees in some areas of the Northern Hemisphere.

Change in Atlantic circulation could plunge Europe into cold winters

The Atlantic Ocean circulation that carries warm waters north and returns cold waters south is slowing, putting Europe at risk of colder temperatures, according to research published in Nature. The Atlantic Heat Conveyor, the system of currents in the Atlantic Ocean that result in a net transport of warm water into the northern hemisphere, keeps western Europe warmer than regions at similar latitudes in other parts of the world. A weakening of the system, which includes the Gulf Stream, could cause a cooling in northwest Europe.

45% chance Gulf Stream current will collapse by 2100 finds research

New research indicates there is a 45 percent chance that the thermohaline circulation in the North Atlantic Ocean could shut down by the end of the century if nothing is done to slow greenhouse gas emissions. Even with immediate climate policy action, say scientists, there would still be a 25 percent probability of a collapse of the system of currents that keep western Europe warmer than regions at similar latitudes in other parts of the world. The Atlantic thermohaline circulation, better known as the Atlantic heat conveyor belt, is a system of currents in the Atlantic Ocean that result in a net transport of warm water into the northern hemisphere. A weakening of the system, which includes the Gulf Stream, could cause a cooling in northwest Europe and worsen droughts in equatorial Africa.

“The core contains sediments representing the warm interval since the last Ice Age,” said Dr. Ellison of the University of East Anglia. “The sediment includes a variety of small animals called foraminifera that record surface water conditions in their shells when living. We analysed changes in the abundance of different species of foraminifera and the chemistry of the shells to examine past patterns of climate change. We also analysed the sediment grain size to gauge the speed of deep ocean currents and therefore the strength of ocean circulation.”

The researchers said the findings provide the first direct evidence of both the freshwater forcing and the climate response to the event.

“The 8200-year-old event is the most recent abrupt climate change event and by far the most extreme cooling episode in the last 10,000 years, but up until now we knew comparatively little about its impact, if any, on the ocean circulation,” explained Dr. Chapman. “Our records show a sequenced pattern of freshening and cooling of the North Atlantic sea surface and an associated change in the deep ocean circulation, all key factors that are involved in controlling the state of northern hemisphere climate.”

“These findings have important implications for future research because they aid our understanding of the magnitude of forcing involved in rapid climate changes and the mechanisms involved,” Dr Hall added. “This provides a useful target for assessing the models that are used to predict future patterns of climate change”.”

This article is based on a release from the University of East Anglia.