| dc.description.abstract | This dissertation has combined observations from four Slocum glider missions in the deep Gulf of Mexico to quantify the turbulent kinetic energy (TKE) dissipation rates (ϵ) and diffusive mixing processes in the basin. The Thorpe scale (TM) method is used to estimate ϵ and then used to construct depth ϵ profiles (surface to 1000 m) using the Large Eddy Method (LEM). The accuracy of the TM-LEM estimates are compared and quantified against direct estimates from a simultaneous /co-located MicroRider deployment in the Gulf of Mexico (i.e., a glider equipped with MicroRider). Survey-averaged profiles of the three methods are compared and found to be within the range of expected error, i.e., within a factor of 2. Profile to profile comparison of ϵ reveals that LEM overestimates when the magnitude of ϵ is small. The overestimation is attributed to the stratification-dependent detection limits of the LEM and is mostly observed in deep water, where ϵ falls close to the noise level of LEM. Spectral comparison of dissipation rates from the three methods (using histograms of occurrence) confirms that the LEM and TM are able to capture dissipation rate variability greater than 1 × 10−9 Wkg−1; however, less than this limit, only the direct measurement of TKE dissipation rate (in regions of weak vertical density gradients) are robust. Despite this limitation, the TM -LEM-derived dissipation rate estimates are able to provide structures that are interpretable as associated with the underlying physical processes of the deep ocean. Maps showing the temporal and spatial variability of ϵ are able to reveal the well-defined turbu-lence structure of LCE and LC. Eddy-induced elevated ϵ are observed around the core of LC and LCE, but the interior of the eddy core is relatively quiescent when compared to the oceanic frontal regions of the eddy. Diapycnal mixing around the eddy cores is suppressed due to the presence of stronger stratification. Away from the eddy cores, where stratification is less, diapycnal mixing is enhanced. The analysis quantifying the relative strength of the diffusion processes, using Turner Angle and density ratio, concluded that salt-fingering is the dominant double-diffusive process in the GoM and is related to proximity to the LC and to depth of observation influence the strength of the salt-fingering in the water column. The potential for fine-structure thermohaline staircases is quantified and observations of irregular shape staircases in the deep GoM are reported for the first time. The glider-based measurements provide an economical option to estimate ocean turbulence and has the potential to fill the gaps between the direct microstructure measurements provides opportunity to obtain mixing parameters of the world ocean in the absence of direct microstructure observations. | |
