The first incident happened around 9,000 years ago and the second around 8,000 years ago: both were attributed to shifts in the Gulf Stream, which helps moderate the U.K. climate by keeping it warm and wet. Each episode was characterized by an average summertime 1.6 degree Celsius cooling in the Northwest. Also, they determined that the cold periods lasted up to 50 years and 150 years for the first and second episodes, respectively.
"At Hawes Water mud has been deposited continuously without any gaps, which allows us to measure an accurate timeline of events. We have monitored the modern environment of the lake for the past eight years and this has shown us how to read the past climate record from the ancient mud in the lake. Isotope analysis helped us identify the episodes of climate change.
We then used fossilized heads of non-biting midges, which are preserved in every spoonful of mud. They tell us the temperature at the time the mud was deposited. We compare the population of midge heads in each sediment sample with the population of midges in Scandinavian lakes, which span a wide range of modern day temperatures," said Jim Marshall, a professor in the Department of Earth and Ocean Sciences.
Interestingly, these two abrupt episodes of climate change correlated directly with two recorded incidents of climate deterioration in regions such as Greenland. This is significant because it shows that changes in the Gulf Stream likely affected the "Atlantic Conveyor" (also known as the ocean conveyor belt), a global density-driven circulation of ocean water that results in cold water sinking near the poles being replaced by warmer water from the tropics, which plays a crucial role in maintaining the planet's climate. The slow-moving process, if made unstable or shut down completely, can cause the Earth's climate to suddenly become much colder. "Our study provides evidence that the two climate shifts we detected were directly linked to a slow-down in the conveyer," explained Marshall.
Image courtesy of the University of Liverpool
Via ::ScienceDaily: Fossilized Midges Provide Clues To Future Climate Change (news website)