New research on the meridional overturning circulation

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.

Author: Milan

In the spring of 2005, I graduated from the University of British Columbia with a degree in International Relations and a general focus in the area of environmental politics. In the fall of 2005, I began reading for an M.Phil in IR at Wadham College, Oxford. Outside school, I am very interested in photography, writing, and the outdoors. I am writing this blog to keep in touch with friends and family around the world, provide a more personal view of graduate student life in Oxford, and pass on some lessons I've learned here. View all posts by Milan