Can sea levels diagnose the health of part of the world's ocean circulation?
5 March 2009, by Matthew Aylott
New research suggests subtle changes in sea level on the eastern coast of the United States may give clues to the strength of the most important ocean circulation in the North Atlantic.
The North Atlantic and Arctic Oceans are critical components of the ocean-climate system. Warm tropical waters flow northward, releasing hear to the North Atlantic region, and eventually flow into the depths of the Arctic Ocean.
This circulation, which includes the Gulf Stream, is under intense scrutiny from the international research community. Until recently, very little was known about its strength and variability. But we know in the past, large swings in its strength have been implicated in rapid changes in the climate of Northern Europe.
Previous research has raised the possibility that sea levels can diagnose the health of the ocean circulation known as the meridional overturning circulation, or MOC. Now new findings published in the journal Geophysical Research Letters confirm this by finding a close link between MOC variability and changes in sea level along the US Atlantic coast, indicating that sea level may be a useful indicator of MOC health.
Animation of the complex North Atlantic Ocean circulation. Warm surface waters (red) move northwards. Cool deep waters (blue) return to the tropics. Heat released to the atmosphere helps ensure Europe's temperate climate. Sea level changes off the coast of the US may indicate changes to part of this circulation
'Results [from previous studies] point to the difficulty of untangling the many ways a changing MOC may affect regional sea level variability,' explains Dr Rory Bingham, lead author of the research.
'We find a distinctive, topography-following pattern of sea level variability in the western North Atlantic that is closely linked with the changing strength of the MOC.'
The team based their results on a powerful computer of model of the global oceans. The resolution of the model, known as OCCAM, is so high it can replicate relatively small ocean processes like eddies.
They found slight drops in sea level were linked to a more rapid rate of overturning circulation. A drop in sea level along the US east coast of just two centimetres corresponded to an increase in the water volume flow rate of the MOC of one million cubic metres per second.
Satellite altimetry data and tide gauges along the North American east coast appear to back up the model results. The authors conclude that sea level along North America's east coast could indeed be a useful indicator of North Atlantic MOC health.
This research was carried out by scientists from the Proudman Oceanographic Laboratory in Liverpool, as part of the Natural Environment Research Council's Rapid climate Change programme.
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