The Atlantic Meridional Overturning Circulation (AMOC) plays a vital role in transporting climate change signals across the global ocean. A team of international researchers collaborated on a study of the less-explored AMOC pathways, specifically focusing on a substantial mid-depth Eastern Pathway (EP) of the North Atlantic Deep Water (NADW).  Byrd Center Principal Investigator Zhengyu Liu, Atmospheric Sciences Program Director and Max Thomas Professor of Climate Dynamics in the Department of Geography at The Ohio State University, was the lead author of the study published last month in Nature Geoscience. 

The study integrated hydrographic observations, model simulations, and reanalysis to highlight the significance of the mid-depth EP, located east of the Mid-Atlantic Ridge, in transporting half of the NADW across the intergyre boundary—the crucial zone between the subtropical and subpolar gyres around 45 degrees North where different ocean currents meet and interact. In oceanic terms, a "gyre" denotes a major circular ocean current system, driven by global wind patterns and Earth's rotation, pivotal in distributing thermal energy and materials throughout the oceans.

This pathway is primarily influenced by wind-induced ocean circulation dynamics rather than bottom topography. The study underscores that contrary to traditional views, which emphasize the Deep Western Boundary Current and an eddy-driven interior pathway west of the Mid-Atlantic Ridge, the EP is essential for the southward transport of NADW from the subpolar to the subtropical gyre. The term "eddy-driven" refers to the process influenced by mesoscale swirls or eddies in the ocean, which play a crucial role in the movement and mixing of water masses.

The findings reveal that surface winds are paramount as they drive the eastward currents at the intergyre boundary, facilitating the EP. This wind-driven mechanism is consistent across various model resolutions and scenarios, even those that discount the influence of bottom topography. 

The implications of this research extend beyond mere mapping of AMOC pathways. It calls for further investigations into the AMOC’s influence on climate variability and response, particularly considering that current climate models often do not fully account for eddy-driven pathways. Moreover, the study proposes that the AMOC's adjustment processes in the ocean are likely more intricate than previously believed, shaped by different pathways and their interactions with wind patterns and ocean currents. This international effort adds a significant chapter to understanding global ocean circulation dynamics.

Read more about "Wind-steered Eastern Pathway of the Atlantic Meridional Overturning Circulation" or download the PDF.