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

An 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.

Automated summary

This study used GO-SHIP's observational data to test the assumption of steady-state for deep ocean circulation, finding that, except for boundary currents, most regions in the deep ocean show quasi-steady-state planetary-scale potential density gradients during the modern observational period, with higher variability in some areas and shorter sections.