Vocal Classification of Vocalizations of a Pair of Asian Small-Clawed Otters to Determine Stress

Asian Small-Clawed Otters (Aonyx cinerea) are a small, protected but threatened species living in freshwater. They are gregarious and live in monogamous pairs for their lifetimes, communicating via scent and acoustic vocalizations. This study utilized a hidden Markov model (HMM) to classify stress versus non-stress calls from a sibling pair under professional care. Vocalizations were expertly annotated by keepers into seven contextual categories. Four of these—aggression, separation anxiety, pain, and prefeeding—were identified as stressful contexts, and three of them—feeding, training, and play—were identified as non-stressful contexts. The vocalizations were segmented, manually categorized into broad vocal type call types, and analyzed to determine signal to noise ratios. From this information, vocalizations from the most common contextual categories were used to implement HMM-based automatic classification experiments, which included individual identification, stress vs non-stress, and individual context classification. Results indicate that both individual identity and stress vs non-stress were distinguishable, with accuracies above 90%, but that individual contexts within the stress category were not easily separable

Observations of turbulence and mixing in the southeastern Beaufort Sea

In this thesis, I use a novel set of hydrography and turbulence measurements from the southeastern Beaufort Sea to i. compare estimates of the turbulent kinetic energy dissipation rate, ε, obtained independently from shear and temperature microstructure measurements; ii. characterize turbulence and mixing in the Amundsen Gulf region of the southeastern Beaufort Sea; and iii. describe the characteristics of tracer diffusion in an oceanic flow as it transitions between fully turbulent and nearly-laminar. I collected the measurements over 10 days in 2015 using an ocean glider measuring temperature, conductivity, and pressure on O(10)-cm scales and shear and temperature on O(1)-mm turbulent scales. The two independent ε estimates agree within a factor of 2 when ε exceeds 3 × 10⁻¹¹ W kg⁻¹, but diverge by up to two orders of magnitude at smaller values. I identify the noise floor of the shear measurements as the primary reason for this divergence and, therefore, suggest that microstructure temperature measurements are preferable for estimating ε in low energy environments like the Beaufort Sea. I find that turbulence is typically weak in Amundsen Gulf: ε has a geometric mean value of 2.8 × 10⁻¹¹ W kg⁻¹ and is less than 1 × 10⁻¹⁰ W kg⁻¹ in 68% of observations. Turbulent dissipation varies over five orders of magnitude, is bottom enhanced, and is primarily modulated by the M2 tide. Stratification is strong and frequently damps turbulence, inhibiting diapycnal mixing in up to 93% of observations. However, a small number of strongly turbulent mixing events disproportionately drive net buoyancy fluxes. Heat fluxes are modest and nearly always below 1 W m⁻². Finally, I use the turbulence measurements to demonstrate how tracer diffusion in the ocean transitions continuously between turbulent diffusion and near-molecular diffusion as turbulence weakens and stratification strengthens. I use the buoyancy Reynolds number, ReB, to quantify the relative energetic contributions of potential and kinetic energy to the flow dynamics and find that present models for tracer diffusion are accurate to within a factor of 3 when ReB > 10. However, contrary to expectations, I find that significant enhanced tracer diffusivity at turbulent scales remains present when ReB is below unity.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat

Double diffusion in Powell Lake : new insights from a unique case study

High resolution measurements of temperature and electrical conductivity in Powell Lake, British Columbia provide an extensive set of layer and interface observations of a double diffusive staircase found between 325–350 m depth. Powell Lake is an ex-fjord with a quiescent salt layer at thermal steady state in which double diffusion is naturally isolated from turbulent and advective processes. Layers are coherent on the basin scale and their characteristics have a well defined vertical structure. The steady state heat flux is estimated from the large-scale temperature profile and agrees with an earlier estimate of the flux in the sediments. These estimates are compared to a 4/3 flux parameterization which agrees with the steady state flux to within a factor of 2. The discrepancy is explained by testing the scaling underlying the parameterization directly, and it is found that the assumed power law deviates systematically from the observations. Consequently, a different scaling which better describes the observations is presented. The assumption that interfacial fluxes are dominated by molecular diffusion is tested by comparing the interfacial gradient to that expected from the steady state heat flux; at low density ratios, the average interfacial gradient is not sufficiently large to account for transport by molecular diffusion alone, indicating that double diffusive fluxes cannot generally be estimated from bulk interface properties. Salinity interfaces are only marginally (9%) smaller than temperature interfaces, and a simple model to describe the observed difference is presented and shown to be consistent with the observations.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat

Double diffusion in saline Powell Lake, British Columbia

Powell Lake contains a deep layer of relic seawater separated from the ocean since the last ice age. Permanently stratified and geothermally heated from below, this deep layer is an isolated geophysical domain suitable for studying double-diffusive convection. High-resolution CTD and microstructure measurements show several double-diffusive staircases (R-rho = 1.6 to 6) in the deep water, separated vertically by smooth high-gradient regions with much larger density ratios. The lowest staircase contains steps that are laterally coherent on the basin scale and have a well-defined vertical structure. On average, temperature steps in this staircase are 4 mK, salinity steps are 2 mg kg(-1), and mixed layer heights are 70 cm. The CTD is capable of measuring bulk characteristics of the staircase in both temperature and salinity. Microstructure measurements are limited to temperature alone, but resolve the maximum temperature gradients in the center of selected laminar interfaces. Two different algorithms for characterizing the staircase are compared. Consistent estimates of the steady-state heat flux (27 mW m(-2)) are obtained from measurements above and below the staircase, as well as from microstructure measurements in the center of smooth interfaces. Estimates obtained from bulk interface gradients underestimate the steady-state flux by nearly a factor of 2. The mean flux calculated using a standard 4/3 flux law parameterization agrees well with the independent estimates, but inconsistencies between the parameterization and the observations remain. These inconsistencies are examined by comparing the underlying scaling relationship to the measurements

Measuring the Dissipation Rate of Turbulent Kinetic Energy in Strongly Stratified, Low-Energy Environments : A Case Study From the Arctic Ocean

We compare estimates of the turbulent dissipation rate, , obtained independently from coincident measurements of shear and temperature microstructure in the southeastern Beaufort Sea, a strongly stratified, low-energy environment. The measurements were collected over 10 days in 2015 by an ocean glider equipped with microstructure instrumentation; they yield 28,575 shear-derived and 21,577 temperature-derived estimates. We find agreement within a factor of 2 from the two types of estimates when exceeds 3 × 10−¹¹ W/kg, a threshold we identify as the noise floor of the shear-derived estimates. However, the temperature-derived estimates suggest that the dissipation rate is lower than this threshold in 58% of our observations. Further, the noise floor of the shear measurements artificially skews the statistical distribution of below 10−¹⁰ W/kg, that is, in 70% of our observations. The shear measurements overestimate portions of the geometric mean vertical profile of by more than an order of magnitude and underestimate the overall variability of by at least 2 orders of magnitude. We further discuss uncertainties that arise in both temperature- and shear-derived estimates in strongly stratified, weakly turbulent conditions, and we demonstrate how turbulence spectra are systematically modified by stratification under these conditions. Using evidence from the temperature-gradient spectral shapes and from the observed distributions, we suggest that the temperature-derived dissipation rates are reliable to values as small as 2 × 10−¹² W/kg, making them preferable for characterizing the turbulent dissipation rates in the weakly turbulent environment of this study. The data may be downloaded at doi:10.14288/1.0368671.Science, Faculty ofNon UBCEarth, Ocean and Atmospheric Sciences, Department ofReviewedFacultyResearcherGraduat