Changes in Deep Ocean Contribute to a "See‐Sawing" Gulf Stream Path.

This study demonstrates that a decrease of the water‐mass density below 1,000 m has led to a pattern of see‐saw shift in the Gulf Stream (GS) position between 74 and 50°W in longitude during 1993–2017, with the New England Seamounts as the pivot point. The GS moved northward in the upstream region and shifted southward in the downstream. Our empirical orthogonal function analyses of satellite altimeter data demonstrate that the second mode (EOF2) represents changes in the GS strength and therefore can be used as an index for the Atlantic Meridional Overturning Circulation. Decreasing water density below 1,000 m is also the principal mechanism driving the weakening of the GS. Plain Language Summary: The Gulf Stream (GS) plays an important role in transporting heat from low to high latitudes, and its path becomes highly variable after passing the Cape Hatteras. Previous studies reported controversial behaviors of the path. Our study discovers that the changes in the path before and after the New England Seamounts are different, that the position of the upstream segment has a northward trend whereas the downstream segment has a southward trend. This study reveals that the second empirical orthogonal function mode of the altimeter data can represent the strength of the GS, and the changing strength is a controlling factor for the changing path. This study also finds that declining water density in the deep layer contributes to decreasing strength of the GS. Key Points: The Gulf Stream (GS) path has an oscillating spatial pattern, which is induced by declining water density at deep layerA new index for the strength of GS is proposed [ABSTRACT FROM AUTHOR]