100+ Years toward Understanding the Ocean Circulation

The central change in understanding of the ocean circulation during the past 100 years has been its emergence as an intensely time-dependent, turbulent, flow. What is known about the ocean is effectively what can be observed. Early technologies for making the difficult observations were adequate only to depict large-scale, quasi-steady flows. With the electronic revolution of the past 50+ years, the emergence of geophysical fluid dynamics for understanding, the strongly inhomogeneous turbulent nature of oceanic circulation physics finally emerged. Mesoscale (balanced) and submesoscale oceanic eddies at 100km horizontal scales and shorter, internal waves, and much smaller scales are now known to be central to much of the behavior of the system. Ocean circulation is now recognized to involve both eddies and larger-scale flows with dominant elements and their interactions varying amongst the classical gyres, the boundary current regions, the Southern Ocean, the tropics, and topographic interactions. With that understanding has come the emergence of numerical models of the global system, although major unresolved elements of ocean circulation physics remain missing.