Posts Tagged ‘Last glacial period’

Since last ice age, warming and cooling have been caused by ocean currents

January 16, 2011

A new paper in Science giving ocean currents in the Atlantic their due (and without finding it necessary to appeal to tales of carbon dioxide). Perhaps the science is not so settled after all!

File:Oceanic gyres.png

The five major ocean-wide gyres — the North Atlantic, South Atlantic, North Pacific, South Pacific, and Indian Ocean gyres. Each is flanked by a strong and narrow “western boundary current,” and a weak and broad “eastern boundary current”: Wikimedia

The Deglacial Evolution of North Atlantic Deep Convection. by D. J. R. Thornalley, S. Barker, W. S. Broecker, H. Elderfield, I. N. McCave.  Science, 2011; 331 (6014): 202 DOI: 10.1126/science.1196812

Science Daily reports:

… 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.

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 January 14, 2011 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 North-East 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 North-East 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 degrees Celsius. ….. The new results suggest that the Atlantic ocean is capable of radical changes in how it circulates on time scales 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.”

Paper Abstract:

Deepwater formation in the North Atlantic by open-ocean convection is an essential component of the overturning circulation of the Atlantic Ocean, which helps regulate global climate. We use water-column radiocarbon reconstructions to examine changes in northeast Atlantic convection since the Last Glacial Maximum. During cold intervals, we infer a reduction in open-ocean convection and an associated incursion of an extremely radiocarbon (14C)–depleted water mass, interpreted to be Antarctic Intermediate Water. Comparing the timing of deep convection changes in the northeast and northwest Atlantic, we suggest that, despite a strong control on Greenland temperature by northeast Atlantic convection, reduced open-ocean convection in both the northwest and northeast Atlantic is necessary to account for contemporaneous perturbations in atmospheric circulation.

 


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