Persistence of the Large‐Scale Interior Deep Ocean Circulation in Global Repeat Hydrographic Sections

Abstract

AbstractAn assumption of steady‐state is a common basis for deep ocean circulation theory and observational strategies. We use GO‐SHIP's Easy Ocean uniformly gridded CTD data from repeat hydrographic sections to test this assumption. In particular, we ask: for what regions of the world ocean is there evidence that the planetary scale deep geostrophic shear and potential vorticity fields, related to potential density gradients, are in quasi‐steady‐state over the modern observational period? We find that away from boundary currents, planetary‐scale potential density gradients in most parts of the deep ocean are stable from occupation to occupation, with higher variability in a few expected regions and for shorter sections. Median standard errors from all sections are 12%–17% in the Pacific, 10%–23% in the Atlantic, and 11%–36% in the Indian Ocean, with the highest values at 2,000 dbar and lowest at 4,000 dbar.