New research on the meridional overturning circulation


in Geek stuff, Science, The environment

Bird in a bush

Recent research undertaken by the Woods Hole Oceanographic Institution and Duke University suggests that ocean currents work differently from how they were previously considered to, with implications for climate change. Using a combination of two years worth of observations from underwater sensors and computer models, they determined that “much of the southward flow of cold water from the Labrador Sea moves not along the deep western boundary current, but along a previously unknown path in the interior of the North Atlantic.” If the results of this study are accurate, it could mean that previous attempts to model the climate system incorporated inappropriate behaviour for this current. As a result, they could have generated less accurate projections of how warming due to greenhouse gas concentrations will affect different parts of the climate system.

More information about the study is available in Nature: Interior pathways of the North Atlantic meridional overturning circulation. For those lacking time or access to Nature, here is the abstract:

To understand how our global climate will change in response to natural and anthropogenic forcing, it is essential to determine how quickly and by what pathways climate change signals are transported throughout the global ocean, a vast reservoir for heat and carbon dioxide. Labrador Sea Water (LSW), formed by open ocean convection in the subpolar North Atlantic, is a particularly sensitive indicator of climate change on interannual to decadal timescales. Hydrographic observations made anywhere along the western boundary of the North Atlantic reveal a core of LSW at intermediate depths advected southward within the Deep Western Boundary Current (DWBC). These observations have led to the widely held view that the DWBC is the dominant pathway for the export of LSW from its formation site in the northern North Atlantic towards the Equator. Here we show that most of the recently ventilated LSW entering the subtropics follows interior, not DWBC, pathways. The interior pathways are revealed by trajectories of subsurface RAFOS floats released during the period 2003–2005 that recorded once-daily temperature, pressure and acoustically determined position for two years, and by model-simulated ‘e-floats’ released in the subpolar DWBC. The evidence points to a few specific locations around the Grand Banks where LSW is most often injected into the interior. These results have implications for deep ocean ventilation and suggest that the interior subtropical gyre should not be ignored when considering the Atlantic meridional overturning circulation.

Improving our understanding of ocean currents should help to improve the accuracy of predictions from general circulation climate change models, and may be helpful in producing regionally specific projections of climate change impacts.

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{ 4 comments… read them below or add one }

Emily May 16, 2009 at 10:22 am


Eleanor Watson February 25, 2010 at 6:12 pm

Hi: Browsing your photos – this is a catbird. He displays a rusty patch under his tail which is hard to see. Has a very interesting song.
Enjoy these fellows in the Spring.

Milan February 28, 2010 at 1:36 pm

Thanks for the identification. I added it to my bird photo index page.

. November 4, 2010 at 2:26 pm

Earth’s climate change 20,000 years ago reversed the circulation of the Atlantic Ocean

The study shows that the ocean circulation was very different in the past and that there was a period when the flow of deep waters in the Atlantic was reversed. This happened when the climate of the North Atlantic region was substantially colder and deep convection was weakened. At that time the balance of seawater density between the North and South Atlantic was shifted in such a way that deep water convection was stronger in the South Polar Ocean. Recent computer models simulate a reversal of the deep Atlantic circulation under such conditions while it is only now with the new data generated by UAB scientists and their colleagues from Seville and the UK that the details of the circulation reversal become apparent. This situation occurred during the ice age 20,000 years ago. Although this was far back in time the results are relevant for our climate today and in the near future. The new study shows that the Atlantic MOC in the past was very sensitive to changes in the salt balance of Atlantic Ocean currents. Similar changes in seawater salt concentration are expected to occur in the North Atlantic in the course of climate warming over the next 100 years. Therefore the data to be published in Nature offer the climate modelling community the opportunity to calibrate their models and improve their capacity to predict reliably future ocean and climate changes.

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