Variations in ocean bottom pressure are important for understanding ocean circulation and climate. While most studies have focused on atmospherically driven variability, here we use eddy-permitting large ensemble simulation output from the OceaniC Chaos – ImPacts, strUcture, predicTability (OCCIPUT) project to isolate chaotic intrinsic variability generated by nonlinear oceanic processes. Analyzing separately the mean seasonal cycle and remainder variability in intra-annual (60–365 days) and subseasonal (2–60 days) bands, we find intrinsic variations larger than atmospherically driven ones over eddy-active regions across all timescales, particularly in the intra-annual range, where intrinsic variations dominate in almost 25% of the oceans. At scales larger than mesoscale, intrinsic variability is still considerable, supporting the process of energy inverse cascade towards lower frequency and larger scales. Results highlight the importance of intrinsic variability over a range of spatiotemporal scales and provide new insights on the interpretation of GRACE-like observations and their de-aliasing procedures.

Plain Language Summary

Variations in ocean bottom pressure reflect ocean mass redistribution and surface freshwater fluxes. The changes in ocean bottom pressure can be attributed to atmospherically driven signals and an oceanic intrinsic component, which is generated by the ocean itself and shows random and chaotic characteristics. While the former has been relatively well understood, the latter is less studied but important in interpreting bottom pressure measurements and model simulations. In this work, we use a large ensemble of global ocean/sea-ice model simulations from the OceaniC Chaos – ImPacts, strUcture, predicTability (OCCIPUT) project to isolate the intrinsic variations of ocean bottom pressure on subseasonal (periods <60 days) and intra-annual (period of 60 days–1 year) bands, as well as the mean seasonal cycle. Our results reveal substantial intrinsic variations over regions with active mesoscale eddies at all timescales, where intrinsic variations can be more important than atmospherically driven ones. Over intra-annual range, almost a quarter of the ocean shows stronger intrinsic variability. Considerable intrinsic variability is also found at scales larger than mesoscale, suggesting energy transfers from mesoscale to larger scales. Our work suggests the need for taking the intrinsic component into account when interpreting bottom pressure observations and model outputs.