Vertical Velocity 3D Estimates from the Linear Vorticity Balance in the North Atlantic Ocean

Large-scale three-dimensional vertical movements of the world's oceans play a fundamental role in their functioning, yet they are still overlooked. This study aims to enhance our understanding of the relationship between horizontal and vertical fl ows as a function of depth to derive some major characteristics of the w fi eld from a relatively well- constrained variable. For this purpose, we analyze an eddy-permitting ocean general circulation model simulation, focusing on the linear vorticity balance (LVB) over the North Atlantic basin. For spatial scales greater than 58, 8 , over more than 50-yr average, the LVB holds with less than 10% error over the whole depth range of most of the subtropical upper tachocline-upper ocean and part of the tropical one, away from western boundary currents and zonal tropical fl ows. The spatial extent of the balance diminishes in the intermediate ocean, particularly in the western half of the basin. Within the deep tachocline, the balance holds over large portions of the abyssal plains. Based on these results, the b-plane geostrophic vertical velocity is derived from the vertical indefinite fi nite integral of the geostrophic LVB from the surface. While its time mean aligns only qualitatively with the model reference w , it accurately captures the interannual variability over most of the basin, even close to eastern boundaries. However, it cannot reproduce the variability in the lower tropics, the western boundary, and the North Atlantic Current system. Our results emphasize the dominance of geostrophy in establishing most of the ocean model vertical fl ow variability.