Seasonal and regional characterization of horizontal stirring in the global ocean (original) (raw)

Horizontal mixing and the distribution of coherent structures in the global ocean 1 are analyzed using Finite-Size Lyapunov Exponents (FSLE), computed for the sur-2 face velocity field derived from the Ocean general circulation model For the Earth 3 Simulator (OFES). FSLEs measure horizontal stirring and dispersion; additionally, 4 the transport barriers which organize the oceanic flow can roughly be identified 5 with the ridges of the FSLE field. We have performed a detailed statistical study, 6 particularizing for the behaviour of the two hemispheres and different ocean basins. 7 The computed Probability Distributions Functions (PDFs) of FSLE are broad and 8 asymmetric. Horizontal mixing is generally more active in the northern hemisphere 9 than in the southern one. Nevertheless the Southern Ocean is the most active 10 ocean, and the Pacific the less active one. A striking result is that the main cur-11 rents can be classified in two "activity classes": Western Boundary Currents, which 12 have broad PDFs with large FSLE values, and Eastern Boundary Currents with 13 narrower ranges and lower FSLE values. Both classes are also found when we corre-14 late FSLE fields with Eddy Kinetic Energy (EKE) and vorticity (ω), with particular 15 dispersion relations. These relations characterize the dynamics of different ocean ar-16 eas, which would influence the presence and evolution of biological markers, among 17 other variables.