A three component drag probe has been built, calibrated, and used to measure velocities beneath deep water ocean waves and turbulence in a tidal channel. Simple variable inductance devices which may be submerged in water were used as displacement transducers and the associated electronics provided voltage outputs which were proportional to the three components of force that were exerted on a small 5 cm diameter sphere. The force components were due to both the water drag force and the water inertial force in an accelerating flow field. Techniques are described for interpreting measurements made with the drag probe and for obtaining the three velocity components from the measured force components. From the drag probe calibration and its use in the field, it is concluded that the drag probe is a suitable instrument for the measurement of wave velocities and turbulence. Modifications are suggested to improve the performance of the drag probe. For the wave velocity measurements, the experimental results indicate that linear wave theory is adequate to describe the relations between the wave pressure and the wave velocity components. At frequencies higher than the predominant wave frequency the velocity spectra are roughly proportional to f⁻³ where f is the frequency in Hz. The wave velocity components were used to obtain an estimate of the directional energy spectrum. From the measurements in a tidal channel, it appears that the instrument is suitable to measure turbulent fluctuations with scale sizes larger than about 20 cm. If the turbulence were isotropic the velocity spectra would be proportional to f[⁻⁵/³]. Due to the influence of boundaries, the flow was not isotropic but the results appear to be consistent with other observations that turbulent velocity spectra usually show a f⁻¹ to f⁻² behavior and are quite different from wave velocity spectra. / Graduation date: 1971

A free-fall oceanographic instrument has been used to measure vertical microstructure scale gradients of horizontal velocity, temperature and electrical conductivity. The velocity gradients, or shears, were measured at scales between 3 and 40 cm by an airfoil shear probe whose specifications and calibration procedure are discussed. Data collected in the equatorial Atlantic in July 1974 indicated a consistent pattern of turbulence near the velocity core of the Atlantic Equatorial Undercurrent. (The velocity core is the region of maximum speed. ) The most intense turbulence was found above the velocity core of the undercurrent. Turbulence in the velocity core was weak and intermittently spaced. Below the core, near the base of the thermocline, moderately intense turbulence was found. The rate of viscous dissipation of turbulent energy has been estimated from the shear measurements, and typical values were 3x10 ⁻³ cm² sec ⁻³ above the velocity core. Spectra of the shears have been computed. At small wavelengths the measured spectral coefficients fall below the universal Kolmogoroff spectrum. This discrepancy between the two spectra is attributed to spatial averaging of velocity fluctuations by the shear probe. The estimates of viscous dissipation include a correction for this spatial averaging. An energy balance has been determined for the turbulent velocity fluctuations. Above and below the core the basic balance is local production of turbulent energy equals local dissipation, and this balance gives a vertical eddy viscosity of order 10 cm² sec ⁻¹ above the core. The equation of the energy balance of the average motion has been vertically integrated at the equator where meridional terms are assumed small. In the South Equatorial Current the rate of energy gain from the average zonal wind stress is balanced by the rate of energy loss to the zonal pressure gradient plus the rate of dissipation. In the undercurrent, above the core, the rate of energy gain from the zonal pressure gradient equals the rate of dissipation within the uncertainty of the measurements, and the advection term is small but not negligible. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

This thesis demonstrates that at low frequencies (periods longer than 2.5 days) local currents off the coast of Oregon are closely related to the wind. Wind and current observations made during August and September 1969 are described and compared to demonstrate that a relationship exists; the physics of the interaction is not understood. The data are described as functions of both time and frequency. Spectral analysis shows that wind and current were related at frequencies less than 0.017 cycles per hour and at the diurnal frequency; at other frequencies they are apparently not related. The wind and current were then filtered to suppress frequencies higher than 0.017 cycles per hour; they are shown as functions of time. Comparison of the time series reveals certain features of the relationship between wind and current. The current can be considered to be the sum of two parts: a "response" current, which is related directly to the wind, and a "residual" current which is also variable. The amplitude of the response depends on the amplitude of the wind and on the density profile of the water. The time lag between the wind and the response current was variable; on a few occasions the current led the wind. Both the response and the residual current were generally parallel to the bottom contours. The residual current seems to change during periods when the response current is interrupted, so that short current records are not indicative of the mean flow. / Graduation date: 1971

This study is performed in tandem with numerous experiments performed by the U.S. Navy to characterize the ocean environment in the South Florida region. The research performed in this study includes signal processing steps for isolating ocean phenomena, such as internal waves, in the magnetic field. Raw magnetometer signals, one on shore and one underwater, are processed and removed of common distortions. They are then run through a series of filtering techniques, including frequency domain cancellation (FDC). The results of the filtered magnetic residual are compared to similarly processed Acoustic Doppler Current Profiler (ADCP) data to correlate whether a magnetic signature is caused by ocean phenomena. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2017. / FAU Electronic Theses and Dissertations Collection

The circular wave basin provides a means of physically modeling the nearshore without the typical problems associated with end walls. Three different coastal processes were examined to demonstrate the use of a spiral wavemaker in a circular wave basin. These were longshore currents, shear waves, and groin circulation. A beach was designed and constructed to concentrate breaking in a narrow region and minimize wave reflection. Currents in the longshore direction were generated by both the motion of the wavemaker and oblique wave approach. Two methods for measuring nearshore currents were employed. First, a 3-D acoustic current meter was positioned at various locations in the cross shore and the local radial and tangential velocities were recorded. Second, a video camera was placed approximately 8 meters above the wave basin to record the motion of a ball in the nearshore. The video tape was digitized by an image processor and the motion of the ball was determined. Measurements of nearshore circulation in the circular wave basin were used to investigate longshore currents, shear waves, and groin circulation. Average measured longshore current profiles in the cross shore were compared with numerical model predictions. An analysis of the existence of shear waves in the circular wave basin was performed by calculating longshore and cross shore current spectra. Particular attention was focused on the low frequency end of the spectra where shear waves are most energetic. Model groins were placed in the circular wave basin and measured currents were compared to predicted circulation patterns. All three applications indicated that the circular wave basin is a useful device for simulating coastal processes in a laboratory environment. / Graduation date: 1992

The Arctic is a hotspot of global change. For example, changes caused by global warming are both amplified and are seen more rapidly in the Arctic (e.g., Serreze & Francis, 2006; Bekryaev et al., 2010; Serreze & Barry, 2011; Overland et al. 2015; Macdonald et al., 2015). Thus, the Arctic is an indicator of the state of the planet. Among the strongest changes that have been observed in the Arctic Ocean are changes in circulation regimes, hydrographic properties and freshwater content and composition. These changes have the potential of global impact through interaction with the deep-water formation regions of the North Atlantic Ocean, a major source of deep and bottom water in the global ocean. Although significant progress in understanding the signals of change in the Arctic Ocean and their causes has been made during the past decades there are still some fundamental questions unanswered. They include the stability of the circulation of the upper waters and changes in the freshwater budget and how these changes are connected to changes in the composition of the freshwater lens that covers the Arctic Ocean. In this thesis, we address these two topics using measurements of isotopes obtained during over three decades of Arctic Ocean section work.This dissertation is composed by three parts and its structure mimics the layered vertical structure of the Arctic Ocean water column. Chapter 1 is dedicated to the Atlantic waters, Chapter 2 to the halocline waters, and Chapter 3 to the freshwater sources and their distribution and variability in the surface layer. In the first two chapters, we present transient tracer (³H/³He) and hydrographic data from over 25 years of Arctic oceanographic campaign ranging from 1987 to 2013 to evaluate flow rates and circulation pathways in the Upper Halocline Water (UHW), Lower Halocline Water (LHW), and Atlantic Layer on a pan-Arctic scale. In agreement with previously established circulation schemes, tracer data show that the flow paths in the LHW and the Atlantic layer are typically topographically steered with the presence of a cyclonic boundary current along the continental shelf and separate circulation branches tracking major bathymetric features, such as the Lomonosov Ridge. Tracer data suggest that the general circulation of UHW is decoupled from the cyclonic regime observed in the deeper layer, and strongly influenced by surface stress forcing, such as the anticyclonic Beaufort Gyre. Within the limits of our method, tracer data show that the mean flow paths and spreading velocities have been more or less constant over the past three decades despite dramatic shifts in the Arctic system heat and freshwater balances from anthropogenic climate change over imposed to a high natural variability. The third and final chapter discusses the water-mass composition and the distribution of freshwater sources in Canadian Basin, the western section of the Arctic Ocean. Results are produced by performing a water-mass decomposition on the water samples collected during the 2015 Arctic GEOTRACES (GN01) oceanographic expedition. Stable isotope measurements (H₂¹⁸O/H₂¹⁶O and DHO/H₂O ratios) are used in combination with salinity and nutrients data to calculate the water-mass components for the upper 500 m Arctic Ocean (mixed layer through Atlantic Water layer). The sources of liquid freshwater into the Arctic Ocean include Pacific water, sea ice meltwater, river discharge and net precipitation. The topmost 50 meters of Canadian Basin contain the large fraction of freshwater from sea ice meltwater and meteoric water. Pacific water dominated the freshwater budget along the 2015 GN01 transects from 100 to 250 m. These depths are also characterized by a strong brine rejection signal, reflecting an enhanced annual sea ice cycle with more ice refreezing and melting each year, and an overall loss of multiyear ice. The 2015 results are compared with the overlapping 1994 and 2005 Arctic Ocean Sections (AOS94 and AOS05) and discussed in the context of regional and temporal variability of liquid freshwater and its components distribution. Our findings show significant increases in the Canadian Basin total liquid freshwater reservoir both compared to the 1994 and 2005 transects confirming a freshwater accumulation in the Canadian Basin already established by numerous observations and modeling studies (Gilles et al., 2012; Carmack et al., 2016; Proshutinsky et al. 2019; Solomon et al., 2021). The total freshwater reservoir increased by ca. 12,500 km³ from 1994 to 2015, of which ca. 5,000 km3 are within the Beaufort Gyre. Meteoric and Pacific freshwater components were the largest sources of the observed freshwater accumulation in the upper 500m of the western Arctic Ocean. An intensified Ekman transport in the Beaufort Gyre and increased availability of freshwater for accumulation are the two primary drivers for freshwater accumulation in the Canadian Basin. Within the limits of our analysis, it is not possible to quantitatively estimate the relative importance of the each forcing nor to resolve the seasonal to year‐to‐year variability. Our tracer-based analysis suggests that there is a significant variability in the freshwater components and UHL distribution while the major features of the circulation patterns and spreading velocities of the AW and the LHW have remained largely stable over the past decades. Future research should address whether in a fast changing Arctic, the dynamics of the surface layer will expand to the halocline and Atlantic layer substantially destabilizing the current Arctic Ocean water column with potentially dramatic consequences.