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Dramatic ocean circulation changes revealed

14 January 2011

New research shows that as the last Ice Age came to an end, the formation of deep water in the Northeast Atlantic repeatedly switched on and off, causing centuries of climate warming and cooling.

The unusually cold weather this winter has been caused by a change in the winds. Instead of the typical westerly winds warmed by Atlantic surface ocean currents, cold northerly Arctic winds are influencing much of Europe.

However, scientists have long suspected that far more severe and longer-lasting cold intervals have been caused by changes to the circulation of the warm Atlantic Ocean currents themselves.

Shells of a type of foraminifers. Copyright Cardiff University.

Now new research, led by Cardiff University with scientists in the UK and US, reveals that these ocean circulation changes may have been more dramatic than previously thought.

The findings, published today (14 January) in the journal Science, show that as the last Ice Age came to an end (10,000 - 20,000 years ago) the formation of deep water in the Northeast Atlantic repeatedly switched on and off. This caused the climate to warm and cool for centuries at a time.

The circulation of the world's ocean helps to regulate the global climate. One way it does this is through the transport of heat carried by vast ocean currents, which together form the 'great ocean conveyor'.

Key to this conveyor is the sinking of water in the Northeast Atlantic, a process that causes warm tropical waters to flow northwards in order to replace the sinking water. Europe is kept warmer by this circulation, so that a strong reduction in the rate at which deep water forms can cause widespread cooling of up to 10°C.

Lead author Dr David Thornalley, from the Cardiff School of Earth & Ocean Sciences, explains how the scientists studied changes in ocean circulation: "We retrieved ocean sediment cores from the seafloor of the Northeast Atlantic which contained the shells of small organisms. We used these shells to examine the past distribution of radiocarbon in the ocean.

"Radiocarbon is a radioactive form of carbon that acts like a natural stopwatch, timing how long it has been since water was last at the sea surface. This allows us to determine how quickly deep water was forming in the Northeast Atlantic at different times in the past."

The team of scientists found that each time deep water formation switched off, the Northeast Atlantic did not fill with water that sank locally. Instead it became inundated with water that had originally formed near Antarctica and then spread rapidly northwards. The new results suggest that the Atlantic Ocean is capable of radical changes in how it circulates on timescales as short as a few decades.

Dr Thornalley said, "These insights highlight just how dynamic and sensitive ocean circulation can be. Whilst the circulation of the modern ocean is probably much more stable than it was at the end of the last Ice Age, and therefore much less likely to undergo such dramatic changes, it is important that we keep developing our understanding of the climate system and how it responds when given a push."

The research is funded through the Natural Environment Research Council's Rapid Climate Change programme and the National Science Foundation (USA). The Science paper 'The Deglacial Evolution of North Atlantic Deep Convection' can be read on the Science website.

Further information

Emma Darling
Public Relations
Cardiff University
Tel: 029 2087 4499

Dr David Thornalley
Cardiff School of Earth & Ocean Sciences
Cardiff University
Tel: 029 2087 4573

NERC Press Office
Natural Environment Research Council
Polaris House, North Star Avenue
Swindon, SN2 1EU
Tel: 01793 411561
Mob: 07917 557215

Notes

1. Cardiff University is recognised in independent government assessments as one of Britain's leading teaching and research universities and is a member of the Russell Group of the UK's most research intensive universities. Among its academic staff are two Nobel Laureates, including the winner of the 2007 Nobel Prize for Medicine, University President Professor Sir Martin Evans.

Founded by Royal Charter in 1883, today the University combines impressive modern facilities and a dynamic approach to teaching and research. The University's breadth of expertise in research and research-led teaching encompasses: the humanities; the natural, physical, health, life & social sciences; engineering & technology; preparation for a wide range of professions; and a longstanding commitment to lifelong learning. Three major new research institutes, offering radical new approaches to neurosciences and mental health, cancer stem cells and sustainable places were announced by the University in 2010.

2. The Natural Environment Research Council is the UK's main body for funding and managing world-class research, training and knowledge exchange in the environmental sciences. It coordinates some of the world's most exciting research projects, tackling major issues such as climate change, environmental influences on human health, the genetic make-up of life on Earth, and much more. NERC receives around £400m a year from the government's science budget, which it uses to fund independent research and training in universities and its own research centres.

3. The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering. In fiscal year 2010, its budget is about $6·9 billion. NSF funds reach all 50 US states through grants to nearly 2,000 universities and institutions. Each year, NSF receives over 45,000 competitive requests for funding, and makes over 11,500 new funding awards. NSF also awards over $400m in professional and service contracts yearly.

Press release: 01/11

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