Ocean Boundary Pressures as an efficient means to measure the global ocean circulation.

Most ocean observables are dominated by local variability, leading to the requirement of a dense observing array to calculate the integrated effects which are of broader scale relevance. Ocean bottom pressure (OBP), recently adopted as an Essential Ocean Variable, is an exception which shows coherent variations over extremely large length scales. In particular, we show that a model with realistic mesoscale variability demonstrates coherent OBP variability along the global continental slope with characteristic length scales of tens of thousands of kilometres. We show how these signals permit monitoring of the Meridional Overturning Circulation, and provide insights into the sources of that variability. We also show how boundary pressure measurements allow the global circulation of a realistic model to be understood in terms of classical idealised models, how they measure the integrated flow in boundary currents, and how they relate to global-scale dynamical sea level differences. Furthermore, we demonstrate an observational method that permits the clear separation of dynamical OBP changes from seismic changes and vertical land movement. We make the case that a small number of Eulerian observations could provide a disproportionately large amount of information about the global ocean circulation.