MEASUREMENTS OF TURBULENCE AND FOSSIL TURBULENCE NEAR AMPERE SEAMOUNT

Measurements of temperature and velocity microstructure near and downs tream of a shallow seamount are used to compare fossil turbulence vers us non-fossil turbulence models for the evolution of turbulence micros tructure patches in the stratified ocean. According to non-fossil ocea nic turbulence models, all overturn length scales L(T) of the microstr ucture grow and collapse in constant proportion to each other and to t he turbulence energy (Oboukov) scale L(O) and the inertial buoyancy (O zmidov) scale L(R) drop(is an element of/N-3)(1/2) of the patches; tha t is, with L(Tms) approximate to,1.2L(R), and viscous dissipation rate is an element of approximate to is an element of(0). According to th e Gibson fossil turbulence model, all microstructure originates from c ompletely active turbulence with is an element of greater than or equa l to is an element of(0) approximate to 3L(T)(2)N(3)( 28 is an element of(0)) and L(T)/ root 6 approximate to L(Tms), but this rapidly deca ys into a more persistent active-fossil state with is an element of(0) greater than or equal to is an element of greater than or equal to(F) approximate to 30vN(2), where N is the buoyancy frequency and v is th e kinematic viscosity and, without further energy supply, finally reac hes a completely fossil turbulence hydrodynamic state of internal wave motions, with is an element of less than or equal to is an element of (F). The last turbulence eddies, with is an element of approximate to is an element of(F), vanish at a buoyant-inertial-viscous (fossil Kolm ogorov) scale L(KF) that is much smaller than the remnant overturn sca les L(T), for large is an element of(O)/is an element of(F) ratios. Th ese density, temperature, and salinity overturns with L(T) approximate to 0.6L(R0) >> 0.6L(R) persist as turbulence fossils (by retaining th e memory of E,) and collapse very slowly. In the near wake below the s ummit depth of Ampere seamount, a much larger proportion of completely active turbulence patches was found than is usually found in the ocea n interior away from sources. Dissipation rates is an element of and t urbulence activity coefficients A(T) drop(is an element of/is an eleme nt of(0))(1/2) of microstructure patches were found to decrease downst ream, suggesting that the active turbulence indicated by the patches w ith A(T) greater than or equal to l was caused by the presence of the seamount as a turbulence source. Therefore, the turbulence and mixing processes of ocean layers far away from turbulence sources probably ha ve been undersampled by microstructure data sets lacking any A(T) grea ter than or equal to 1 patches. This is because large fractions of the mixing and viscous dissipation of the patches occur in short-lived ac tive turbulence regimes that are too brief to be detected. Consequentl y, large underestimates of the true space-time average turbulence flux es and turbulence and scalar dissipation rates may result if non-fossi l turbulence models are assumed in ocean microstructure data interpret ation.