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Recent efforts using microstructure turbulence measurements have contributed to our understanding of the overall energy budget in lakes and linkages to vertical fluxes. A paucity of lake-wide turbulence measurements hinders our ability to assess how representative such budgets are at the basin scale. Using an autonomous underwater glider equipped with a microstructure payload, we explored the spatial variability of turbulence in pelagic and near-shore regions of Lake Geneva. Dissipation rates of kinetic energy and thermal variance were estimated by fitting temperature gradient fluctuations spectra to the Batchelor spectrum. In deep waters, turbulent dissipation rates in the surface and thermocline were mild (similar to 10(-8) W kg(-1)) and weakened toward the hypolimnion (similar to 10(-11) to 10(-10) W kg(-1)). The seasonal thermocline exhibited inhibited interior mixing, with extremely low values of mixing efficiency (Ri(f) << 0.1). In contrast, in the slope zone, a band of significantly enhanced energy dissipation (similar to 5 x 10(-8) W kg(-1)) extended well above the bottom boundary layer and was associated with strong, efficient mixing (Ri(f) > 0.17). The resulting contribution of the slope region to basin-scale mixing was large, with 90% of the basin-wide mixing-and only 30% energy dissipation-occurring within 4 km of the shoreline. This boundary mixing will modify overturning circulation and the transport pathways of dissolved compounds exchanged with the sediments. The dynamics responsible for the shift in the mixing regime, which appears crucial for the mixing budget of lakes, could not be fully unraveled with the collected observations. Additional model data analyses hint at the role of submesoscale instabilities.

Estuaries are among the world’s most productive ecosystems, but recent natural and anthropogenic changes have stressed these ecosystems. Tools to assess estuarine pelagic habitats are important to support and maintain healthy ecosystem function. In this work, we demonstrate that estuarine pelagic habitats can be identified by a simple ratio, termed the LE ratio, that takes into account the tidal excursion along a channel (a Lagrangian length scale) and the distance along that channel (an Eulerian length scale). To develop and assess this concept, numerical simulations of the 1D advection–dispersion equation of a conservative tracer and tidal excursion estimates based on data were used to formulize a conceptual model and to define exchange zones within a tidal channel. This conceptual model was then used to predict the extent of pelagic habitats in a terminal channel network in the Sacramento–San Joaquin Delta. Exchange zones mapped onto these channels were found to be in good agreement with independent estimates of residence time. Sensitivity analyses of the numerical model suggest that productive pelagic habitats can be expanded by a factor of 2 by either increasing dispersion or increasing spring–neap variability in mean tidal velocity. Such changes can also enhance flushing in upper channel reaches. These findings are relevant for tidal marsh restoration projects that aim to expand beneficial aquatic habitats by varying exchange or residence time over the spring–neap cycle, because this variability may interact synergistically with varying rates of phytoplankton growth due to spatiotemporal changes in environmental conditions.

Homing behavior for autonomous underwater vehicles (AUVs) is vital for autonomous docking and indispensable for recovery of vehicles in logistically difficult or hazardous conditions. Homing to a single acoustic beacon is a low-logistics solution to this engineering challenge. A homing application has been developed in C++ that applies a multilateration-based localization algorithm to estimate transponder location for homing. Mission oriented operating suite interval programming (MOOS-IvP) was implemented as a backseat driver on a Teledyne Gavia AUV to enhance the AUV with adaptive maneuvering capabilities; thus, enabling mission waypoints to be dynamically updated by the homing application ( pHomeToBeacon ) through the MOOS database and a developed iGavia crewmember. To demonstrate MOOS-IvP-GAVIA and homing capabilities using this first-principles approach to localization, field trials were undertaken in Kopavogur, Iceland, in June 2015 and proved consistent homing to a single beacon within 15 m accuracy. These trials were an industry-first of deploying a user-developed application on MOOS-IvP-GAVIA and of having a Gavia enhanced with adaptive maneuvering capabilities for homing. This new capability enables Gavia AUV to be used as a platform for future developer-led autonomy and applications. Ultimately, pHomeToBeacon will enable any AUV enhanced with MOOS-IvP to use acoustics to home to a surface vessel (stationary or underway) in preparation for autonomous subsea docking and recovery.

Milne Ice Shelf is located at the mouth of Milne Fiord (82.6$^\circ$N, 81.0$^\circ$W), on Ellesmere Island, Nunavut. This floating ice feature is attached to both sides of the fjord. During the mel...

Ice shelf dynamics and morphology play an important role in the stability of floating bodies of ice, in turn impacting their ability to buttress upstream grounded ice. We use a combination of satellite-derived data, airborne and ground-based radar data, and oceanographic data collected at the Nansen Ice Shelf in East Antarctica to examine the spatial variations in ice shelf draft, the cause and effects of ice shelf strain rates, and the role of a suture zone driving channelization of ocean water and resulting sub-ice shelf melt and freeze-on. We also use the datasets to assess limitations that may arise from examining only a sub-set of the data, in particular the reliance on hydrostatic balance equations applied to surface digital elevation models to determine ice draft morphology. We find that the Nansen Ice Shelf has highly variable basal morphology driven primarily by the formation of basal crevasses near the onset of floating ice convergence in the suture zone. This complex morphology is reflected in the ice shelf strain rates but not in the calculated hydrostatic balance thickness, which underestimates the scale of vertical and horizontal variability at the ice shelf base. The combination of thinner ice in the channelized suture zone, enhanced melt rates near the ice shelf edge, and complex strain rates driven by ice dynamics and morphology have led to the formation of fractures within the suture zone that have resulted in large-scale calving events. Other Antarctic ice shelves may also have complex morphology, which is not reflected in the satellite data, yet may influence their stability.

The ice-covered period in lakes is increasingly recognized for its unique hydrodynamic and biogeochemical phenomena and ecological relevance yet it remains poorly studied compared to the ice-free season. Knowledge gaps exist where research areas – hydrodynamics, biogeochemistry and biology – intersect. For example, density-driven circulation under ice coincides with an expansion of the anoxic zone, but abiotic and biotic controls on oxygen depletion have not been disentangled. While heterotrophic microorganisms and migrating phytoplankton often thrive at the oxycline, the extent to which physical processes induce fluxes of heat and substrates that further support under-ice food webs is uncertain. Similarly, radiatively-driven convection under ice in spring can promote growth of motile phytoplankton or diatoms depending on flow velocity, water clarity and mixing depth, but links between functional trait selection, trophic transfer to zooplankton and fish and the prevalence of microbial versus classical food webs in seasonally ice-covered lakes remain unclear. Under-ice processes cascade into and from the ice-free season, and are relevant to annual cycling of energy and carbon through aquatic food webs. Understanding the coupling between state transitions and the reorganization of trophic hierarchies is essential for predicting complex ecosystem responses to climate change. In this presentation, we briefly review existing knowledge regarding physical processes in lakes in winter and the parallel developments in under-ice biogeochemistry and ecology. We then illustrate interactions between these processes, identify extant knowledge gaps whose solution requires interdisciplinary approaches, and present (novel) methods to address outstanding questions.

When a subsea pipeline is laid on an uneven seabed, certain sections may have an initial elevation with respect to the far-field seabed, eo, and thus potentially affecting the on-bottom stability of the pipeline. This paper focuses on quantifying the effects of the upstream dimensionless seabed shear stress, θ∞, and Reynolds number, Re, on: (1) the maximum dimensionless seabed shear stress beneath the pipe, θmax, to be compared to the critical shear stress in order to determine whether scour would occur and progress towards an equilibrium state; and, (2) the dimensionless equilibrium scour depth beneath the pipe, Seq/D. Using a 2-D Reynolds averaged Navier-Stokes (RANS) approach along with the k-ω Shear Stress Transport (SST) turbulence model, a parametric study involving 243 computational fluid dynamics (CFD) simulations was conducted. The simulation results were used to develop a closed-form equation for the prediction of θmax. Subsequently, experimental measurements of Seq/D have been compiled from published literature, to develop a new closed-form equation for the prediction of Seq/D with a high correlation to the experimental data. In summary, we present two closed-form equations for the prediction of θmax and Seq/D for pipelines with an initial eo/D, which are applicable for both clear-water and live-bed conditions. The effects of θ∞ and Re have been included, albeit Re having a small influence as compared to the other parameters.

When scour occurs beneath a subsea pipeline and develops to a certain extent, the pipeline may experience vortex-induced vibrations, through which there can be a potential accumulation of fatigue damage. However, when a pipeline is laid on an uneven seabed, certain sections may have an elevation with respect to the far-field seabed, eo, at which the development of scour would vary. This work focused on predicting the development of the scour depth beneath subsea pipelines with an elevation under steady flow conditions. A range of pipe elevation-to-diameter ratios (i.e. 0 ≤ eo/D ≤ 0.5) have been considered for laboratory experiments conducted in a sediment flume. The corresponding equilibrium scour depths and scour time scales were obtained; experimental data from published literature have been collected and added to the present study to produce a more complete analysis database. The correlation between existing empirical equations for predicting the time scale and the experimental data was assessed, resulting in a new set of constants. A new manner of converting the scour time scale into a non-dimensional form was found to aid the empirical equations in attaining a better correlation to the experimental data. Subsequently, a new empirical equation has also been proposed in this work, which accounts for the influence of eo/D on the non-dimensional scour time scale. It was found to have the best overall correlation with the experimental data. Finally, full-scale predictions of the seabed gaps and time scales were made for the Tasmanian Gas Pipeline (TGP). Keywords: Scour time scale, Equilibrium scour depth, Subsea pipelines, Pipe elevation, Steady currents

This article presents the open water propeller characteristics and the four-quadrant propeller models as applied to a torpedo-shaped underwater vehicle. A series of experiments with a Gavia autonomous underwater vehicle propeller were conducted in the towing tank using a rotor testing apparatus. The purpose of these tests was to measure the propeller thrust and torque under varying flow conditions and then to be used as the basis of the developed propeller models. These mathematical models were constructed using two regression models, a polynomial and a Fourier series. Model coefficients were derived using the method of least squares and a comparison analysis was also conducted to test the robustness of the methodology. Results show that the Fourier series models were able to produce a reasonable and accurate approximation of thrust and torque coefficients with a small number of parameters in the examined condition of this study. The obtained four-quadrant open water characteristics of the autonomous underwater vehicle propeller model would be utilised to improve the system mathematical model for more accurate simulation and controller design, to compare the autonomous underwater vehicle performance equipped with different propulsion units, and to validate computational fluid dynamic results.

This study presents a system identification algorithm to determine the linear and nonlinear parameters of an autonomous underwater vehicle (AUV) motion response prediction mathematical model, utilising the recursive least squares optimisation method. The key objective of the model, which relies solely on propeller thrust, gyro measurements and parameters representing the vehicle hydrodynamic, hydrostatic and mass properties, is to calculate the linear velocities of the AUV in the x, y and z directions. Initially, a baseline mathematical model that represents the dynamics of a Gavia class AUV in a calm water environment was developed. Using a novel technique developed in this study, the parameters within the baseline model were calibrated to provide the motion response in different environmental conditions by conducting a calibration mission in the new environment. The accuracy of the velocity measurements from the calibrated model was substantially greater than those from the baseline model for the tested scenarios with a minimum velocity prediction improvement of 50%. The determined velocities will be used to aid the inertial navigation system (INS) position estimate using a Kalman filter data fusion algorithm when external aiding is unavailable. When an INS is not externally aided or constrained by a mathematical model such as that presented here, the positioning uncertainty can be more than 4% of the distance travelled (assuming a forward speed of 1.6 m s $$^{-1})$$ . The calibrated model is able to compute the position of the AUV within an uncertainty range of around 1.5% of the distance travelled, significantly improving the localisation accuracy.

Internal waves are ubiquitous features of lakes and oceans, significantly contributing to vertical mixing across large areas, driving gas, nutrient, sediment, and heat exchange between deep and surface waters. Traditionally moorings have been used to sample internal wave fields; providing good temporal data but limited spatial information. More recently, buoyancy-driven autonomous underwater vehicles (aka gliders) have enabled additional characterization of internal waves. Gliders are capable of travelling large distances over periods ranging from days to months, some yo-yoing to depths in excess of 1000 m, making them a promising tool for internal wave observation that better resolve spatial variability of these phenomena. They have been used to characterize mixing from internal waves in multiple ocean locations (e.g. the South China Sea, the Pacific Ocean off the California Coast, the Tasman Sea, and the Faroe Bank Channel) and several deep lakes (e.g. Lake Tahoe, Lake Geneva and Lake Superior). To date no optimal method to implement gliders to measure internal wave characteristics has been determined, although different research groups have experimented with several approaches. Previously employed approaches include using a glider as a virtual mooring, along-shore transects, across-shore transects, and flying a zig-zag pattern across the path of wavefronts. In the work presented here, data were collected in Lake Tahoe (USA), where local bathymetry (down to a maximum depth of 501 m) is known to produce trapped internal waves across a wide range of depths. At various locations, internal waves were concurrently measured using a G2 Slocum glider, moored thermistors and a moored Acoustic Doppler Current Profiler (ADCP). Using these complementary datasets, we can compare the effectiveness of existing and new sampling approaches by flying multiple missions where the vehicle's path varies in orientation and length relative to the wavelength and return period of known internal waves. Internal waves can be identified using spectral analysis of temperature time-series measurements, producing a power spectrum similar to the Garrett-Munk spectrum. Peaks in the power spectrum are expected at known (from previous observational and modelling work) and calculated frequencies corresponding to specific internal wave modes. The success of the sampling method can be assessed by the extent to which the expected spectral peaks are evident in the power spectrum. Additionally, through the application of a dynamic flight model, the vertical water velocities experienced by the glider can be estimated and compared to those expected from internal waves and measured by a nearby moored ADCP. Other criteria to be considered are the width of the confidence interval, the possibility of double counting waves in closed basins, and minimization of spatio-temporal smearing. Identifying the best way to employ a glider to measure an internal wave will lead to improved data collection from future glider deployments.

Autonomous underwater vehicles (AUVs) use secondary velocity over ground measurements to aid the Inertial Navigation System (INS) to avoid unbounded drift in the point-to-point navigation solution. When operating in deep open ocean (i.e., in blue water—beyond the frequency-specific instrument range), the velocity measurements are either based on water column velocities or completely unavailable. In such scenarios, the velocity-relative-to-water measurements from an acoustic Doppler current profiler (ADCP) are often used for INS aiding. ADCPs have a blanking distance (typically ranging between 0.5 and 5 m) in proximity to the device in which the flow velocity data are undetectable. Hence, water velocities used to aid the INS solution can be significantly different from that near the vehicle and are subjected to significant noise. Previously, the authors introduced a nonacoustic method to calculate the water velocity components of a turbulent water column within the ADCP dead zone using the AUV motion response (referred to as the WVAM method). The current study analyzes the feasibility of incorporating the WVAM method within the INS by investigating the accuracy of it at different turbulence levels of the water column. Findings of this work demonstrate that the threshold limits of the method can be improved in the nonlinear ranges (i.e., at low and high levels of energy); however, by estimating a more accurate representation of vehicle hydrodynamic coefficients, this method has proven robust in a range of tidally induced flow conditions. The WVAM method, in its current state, offers significant potential to make a key contribution to blue water navigation when integrated within the vehicle's INS.

Doppler Velocity Logs (DVL) can provide a simple under water navigation aid for Autonomous Underwater Vehicles (AUV) by measuring relative velocities with respect to the speed over ground. A valid reference velocity is difficult to calculate when this approach is applied under a moving frame of reference such as drifting ice. The primary challenge of under-ice localization is to accurately estimate the AUV location and its trajectory in the global coordinate system when DVL measurements are being made relative to a constantly drifting ice surface. In this paper, the author introduces and compares two types of error sources, scale factor error of DVL and navigation error due to ice drift. An error reduction model using a Bayesian filter algorithm is developed for improved estimations, in conjunction with a novel correction method for accurate AUV navigation under ice. The concept of shift factor is introduced in this paper as the key to solve both error sources. Having the knowledge of the true beacon location, shift factors in vector quantity are extracted based on the collected relative velocity profiles by DVL. The shift factors are directly applied to update the final AUV location. The result presents approximately 70.8% of maximum error reduction. The impact of survey pattern, bearing angle to the beacon, pinging frequency on the accuracy of the vehicle localisation are discussed.

When a subsea pipeline is laid on an uneven seabed, the pipeline can have an initial elevation, potentially compromising its on-bottom stability; scouring due to flow conditions around the pipe can further exacerbate the problem. We assess the capability of the two-phase Eulerian-Eulerian OpenFOAM solver, twoPhaseEulerFoam, in terms of predicting the equilibrium scour depth beneath a pipe at different initial elevations under a steady current for the live bed condition. The predictions were found to be in good agreement with published experimental and numerical results; however, similar to a recent study involving another two-phase Eulerian-Eulerian model, the scour time scale was under-predicted. The predicted equilibrium scour depth was seen to decrease with an increase in the initial pipe elevation. The numerical results were also compared to predictions that were made using previous empirical equations. The most comprehensive equation to date showed a good agreement with the present numerical results. We conclude that this open-source solver, twoPhaseEulerFoam, can be used to predict the equilibrium scour depth beneath subsea pipelines, with short computation times and negligible mesh dependency.

Author(s): Roberts, DC; Forrest, AL; Sahoo, GB; Hook, SJ; Schladow, SG | Abstract: Snowmelt is a significant source of carbon, nutrient, and sediment loads to many mountain lakes. The mixing conditions of snowmelt inflows, which are heavily dependent on the interplay between snowmelt and lake thermal regime, dictate the fate of these loads within lakes and their ultimate impact on lake ecosystems. We use five decades of data from Lake Tahoe, a 600 year residence-time lake where snowmelt has little influence on lake temperature, to characterize the snowmelt mixing response to a range of climate conditions. Using stream discharge and lake profile data (1968–2017), we find that the proportion of annual snowmelt entering the lake prior to the onset of stratification increases as annual snowpack decreases, ranging from about 50% in heavy-snow years to close to 90% in warm, dry years. Accordingly, in 8 recent years (2010–2017) where hourly inflow buoyancy and discharge could be quantified, we find that decreased snowpack similarly increases the proportion of annual snowmelt entering the lake at weak to positive buoyancy. These responses are due to the stronger effect of winter precipitation conditions on streamflow timing and temperature than on lake stratification, and point toward increased nearshore and near-surface mixing of inflows in low-snowpack years. The response of inflow mixing conditions to snowpack is apparent when isolating temperature effects on snowpack. Snowpack levels are decreasing due to warming temperatures during winter precipitation. Thus, our findings suggest that climate change may lead to increased deposition of inflow loads in the ecologically dynamic littoral zone of high-residence time, snowmelt-fed lakes.

This paper presents the development of a heading angle observer for Underwater Remotely Operated Vehicles (ROVs) during dynamic conditions in the presence of roll/pitch oscillation and acceleration disturbances. Unlike previous algorithms, which focused on deep water working environments where the external accelerations and oscillation were rather small, this paper proposes a heading observer that deals with the effects of near surface working conditions on ROVs, such as waves or unexpected water currents. These effects cause significant roll and pitch disturbances as well as high-acceleration drift motions, which affect the measurements from the incorporated sensor system. To overcome this situation, a novel heading observer is proposed, consisting of two Kalman filter (KF) steps: one for acceleration elimination and one for roll and pitch oscillation compensation. The data from the inertial measurement unit and the magnetometer are combined to estimate and compensate for external accelerations and roll/pitch disturbances by adjusting the covariance values. Free running tests, based on a physical ROV model, were conducted under various working environments to verify the performance of the proposed observer. The comparison with previous algorithms was also made to verify the effectiveness of the proposed algorithm.

The hydrodynamic interaction between an Autonomous Underwater Vehicle (AUV) manoeuvring in close proximity to a larger underwater vehicle can cause rapid changes in the motion of the AUV. This interaction can lead to mission failure and possible vehicle collision. Being self-piloted and comparatively small, an AUV is more susceptible to these interaction effects than the larger body. In an aim to predict the manoeuvring performance of an AUV under the effects of the interaction, the Australian Maritime College (AMC) has conducted a series of computer simulations and captive model experiments. A numerical model was developed to simulate pure sway motion of an AUV at different lateral and longitudinal positions relative to a larger underwater vehicle using Computational Fluid Dynamics (CFDs). The variables investigated include the surge force, sway force and the yaw moment coefficients acting on the AUV due to interaction effects, which were in turn validated against experimental results. A simplified method is presented to obtain the hydrodynamic coefficients of an AUV when operating close to a larger underwater body by transforming the single body hydrodynamic coefficients of the AUV using the steady-state interaction forces. This method is considerably less time consuming than traditional methods. Furthermore, the inverse of this method (i.e. to obtain the steady state interaction force) is also presented to obtain the steady-state interaction force at multiple lateral separations efficiently. Both the CFD model and the simplified methods have been validated against the experimental data and are capable of providing adequate interaction predictions. Such methods are critical for accurate prediction of vehicle performance under varying conditions present in real life.

Below the temperature of maximum density (TMD) in freshwater lakes, heating at the lateral margins produces gravity currents along the bottom slope, akin to katabatic winds in the atmosphere and currents on continental shelves. We describe axisymmetric basin-scale circulation driven by heat flux at the shorelines in polar Lake Kilpisjarvi. A dense underflow originating near the shore converges toward the lake center, where it produces warm upwelling and return flow across the bulk of lake water column. The return flow, being subject to Coriolis force, creates a lake-wide anticyclonic gyre with velocities of 2–4 cm s-1. While warm underflows are common on ice-covered lakes, the key finding is the basin-scale anticyclonic gyre with warm upwelling in the core. This circulation mechanism provides a key to understanding transport processes in (semi) enclosed basins subject to negative buoyancy flux due to heating (or cooling at temperatures above TMD) at their lateral boundaries.

This paper aims to develop an optimal state feedback controller using the Linear Quadratic Regulator for an autonomous underwater vehicle equipped with an innovative collective and cyclic pitch propeller. This new type of propulsion system offers advantages such as good manoeuvrability for the torpedo shaped underwater vehicle at low speed operations. To develop the linear controller, the underwater vehicle general equations of motion are decoupled into non-interacting longitudinal and lateral subsystems in the form of linear state space models. The vehicle hydrodynamic coefficients and the propulsor dynamic model are derived using the system identification method and experiments in the towing tank. The control objectives are to maintain the autonomous underwater vehicle at desired depth and heading with the newly developed propulsor. The performance of the controller is demonstrated by simulation using MATLAB/SimulinkTM. The results show that the designed controller gives good performance and effectiveness in which the vehicle is able to follow the reference input signals.

Ice shelves control sea-level rise through frictional resistance, which slows the seaward flow of grounded glacial ice. Evidence from around Antarctica indicates that ice shelves are thinning and weakening, primarily driven by warm ocean water entering into the shelf cavities. We have identified a mechanism for ice shelf destabilization where basal channels underneath the shelves cause ice thinning that drives fracture perpendicular to flow. These channels also result in ice surface deformation, which diverts supraglacial rivers into the transverse fractures. We report direct evidence that a major 2016 calving event at Nansen Ice Shelf in the Ross Sea was the result of fracture driven by such channelized thinning and demonstrate that similar basal channel-driven transverse fractures occur elsewhere in Greenland and Antarctica. In the event of increased basal and surface melt resulting from rising ocean and air temperatures, ice shelves will become increasingly vulnerable to these tandem effects of basal channel destabilization.

Laminated sediments in Lake Ohau, Mackenzie Basin, New Zealand, offer a potential high-resolution climate record for the past 17 kyr. Such records are particularly important due to the relative paucity of detailed palaeoclimate data from the Southern Hemisphere mid-latitudes. This paper presents outcomes of a study of the sedimentation processes of this temperate lake setting. Hydrometeorological, limnological and sedimentological data were collected over a 14 month period between 2011 and 2013. These data indicate that seasonality in the hydrometeorological system in combination with internal lake dynamics drives a distinct seasonal pattern of sediment dispersal and deposition on a basin-wide scale. Sedimentary layers that accumulate proximal to the lake inflow at the northern end of the lake form in response to discrete inflow events throughout the year and display an event stratigraphy. In contrast, seasonal change in the lake system controls accumulation of light (winter) and dark (summer) laminations at the distal end of the lake, resulting in the preservation of varves. This study documents the key processes influencing sediment deposition throughout Lake Ohau and provides fundamental data for generating a high-resolution palaeoclimate record from this temperate lake.

Observations of a cyclonic gyre in an ice-covered, midsize (, 5 km2), temperate lake are presented. Horizontal and vertical measurements of temperature and electrical conductivity measurements were collected using a conductivity–temperature–depth logger mounted on an autonomous underwater vehicle and additional instrumentation. These measurements revealed a cylindrical density anomaly with a radius of , 110 m extending from the surface to , 14 m depth. The observed radius is smaller than the internal Rossby radius of deformation (, 200 m), which suggests a cyclogeostrophic balance between centripetal, Coriolis, and pressure forces. The maximum azimuthal velocity, calculated assuming this balance, was , 2.1 cm s21 at 6–8 m depth. The Rossby number associated with this velocity was 1.7; this is consistent with the cyclogeostrophic assumption (i.e., Rossby number . 1) and nearly twice that of similar under-ice eddies in the Arctic Ocean. The estimated Ekman spindown timescale is 1.5–15 d, but despite this, the gyre appeared to be relatively unchanged over 6 d of field observations. This persistence implies the gyre was forced over the course of the field study; however, the source of the forcing is unknown. Horizontal temperature transects at and below the bottom of the gyre revealed coherent temperature fluctuations suggestive of vertical transport associated with the gyre.

Approximately 12% of the world's oceans are covered by ice. Understanding the physical processes, ecosystem structure, mixing dynamics and the role of these inaccessible environments in the context of global climate change is extremely important. Autonomous Underwater Vehicles (AUVs) play a major role in the potential exploration of these water systems due to the challenges of human access and relatively high associated risk. That said, AUV navigation and localization is challenging in these environments due to the unavoidable growth of navigational drift associated with inertial navigation systems, especially in long range missions under ice where surfacing in open water is not possible. While acoustic transponders have been used, they are time consuming and difficult to deploy. Terrain Relative Navigation (TRN) and Simultaneous Localization and Mapping (SLAM) based technologies are emerging in recent years as promising navigation solutions as they neither require deploying navigational aids or calculating the distance travelled from a reference point to determine location. One of the key challenges of underwater or under-ice image based localization results from the unstructured nature and lack of significant features in underwater environments. This issue has motivated the review presented in this paper, which outlines a potential area of under-ice AUV navigation and localization by combining TRN and SLAM with image matching methods for navigation in featureless environments.

Bottom seated subsea pipelines resting on an erodible bed are subjected to scour and transport processes. These processes potentially undermine pipeline integrity by increasing free-span lengths and resulting in bending stresses. Making predictions of scour is fraught with challenges including: (1) determining when pipeline burial or lowering will occur; (2) unexpected obstacles to scour propagation (e.g. rocks); and, (3) varying incidence angles of fluid flow. Due to these challenges, pipeline surveys remain a key part of ongoing asset management. Field observations of phenomena such as self-burial and the impact of flow incidence angles and localized water velocities also help us characterize the subsea pipeline environment. The validation of empirical formulas through comparison to field data is essential for high-risk regions. For this investigation scour beneath a relatively deep and relatively shallow section of the Tasmanian Gas Pipeline in south-eastern Australia was examined. Our data were collected by an Autonomous Underwater Vehicle (AUV), a Remotely Operated Vehicle (ROV) and Acoustic Doppler Current Profiler (ADCP). tour findings suggest to refine empirical formulas to better explain the coupled effects of waves and currents. An improvement on these formulas may reduce the frequency of monitoring surveys required. AUV and ROV surveys are powerful resources to better inform decision making of these assets and better understand scour at individual sites.

Since the beginning of space exploration, methods and protocols of exploration have been developed using space analogs on Earth to reduce research costs, develop safe deployment/retrieval protocols, and ready astronauts for hostile environments in less threatening settings. Space analogs are required as much as ever today as astronauts and scientists develop new tools and techniques for exploration, while working to address evolving mission objectives from low-earth orbit to deep-space exploration. This study examines coordinated human and robotic exploration at the Aquarius Underwater Habitat off of the coast of Key Largo, Florida, in support of the NEEMO 15 (NASA Extreme Environment Mission Operations) program. The exploration scheme presented in this work fuses (1) robotic precursor missions as a means of remote sensing data collection; (2) crowdsourcing to process immense amounts of data to identify key targets of interest that might be missed in the tight cycle of mission operations; and (3) human exploration to examine locations directly up close and collect physical samples that require involved sampling techniques. Autonomous underwater vehicles (AUVs) and single-person submersibles, called DeepWorkers™, were used as underwater analogs of robotic systems currently being used and human-operated vehicles (HOVs) proposed for use on a Near Earth Asteroid (NEA), the Moon, or Mars. In addition to operational lessons learned for space exploration that are directly applicable to ocean exploration, ocean floor mapping provides new levels of detail of benthic habitat critical for coral reef monitoring and management. Opportunistic (onsite adaptive) data sampling also took place by placing self-recording instrumentation onto each of the DeepWorkers, increasing the collection of scientific information during the submersible missions and contributing to mission planning for optimal and efficient use of expensive assets.

The establishment, spread, and impact of the invasive bivalve Corbicula fluminea (C. fluminea), in Lake Tahoe threatens native species distribution in the lake and, potentially, has long-term implications for water clarity. In 2009, UBC-Gavia, an Autonomous Underwater Vehicle (AUV), was used as a platform to collect georeferenced imagery of the benthic regions of Lake Tahoe to determine the lake-wide distribution of C. fluminea. Images were collected in water depths less than 10 m at an approximately constant height above the bottom of 2 m. Images were processed using a semi-automated procedure to determine the ratio of the lakebed covered by exposed C. fluminea shells. A visual review was conducted on a subset of the images to determine presence of filamentous algae that has been observed in association with C. fluminea. Nearly 100km of shoreline was covered over a 7-d period, and C. fluminea presence was reconfirmed in 4 regions and additional 10 regions identified. In regions where the presence of C. fluminea was confirmed, C. fluminea depth distribution was validated by comparing image detection counts and results from a benthic sediment grab sample survey. Three regions around the lake were identified to have filamentous green algae or charophyte species. It was impossible to identify species of the known filamentous algal taxa (Cladophora glomerata, Spirogyra spp., and Zygnema spp.). The collected imagery provides a synoptic view on species distribution within the lake that can be used for efficient monitoring of invasive species in freshwater and saltwater bodies. © 2012, by the American Society of Limnology and Oceanography, Inc.

This study was motivated by an interest in understanding the potential effects of climate change and glacier retreat on late summer water temperatures in alpine areas. Fieldwork was carried out between July and September 2007 at Place Lake, located below Place Glacier in the southern Coast Mountains of British Columbia. Place Lake has an area of 72 000m2, a single inlet and outlet channel, and an approximate residence time of 4 days. Warming between the inlet and outlet of the lake ranged up to 3 C and averaged 1.8 C, which exceeds the amount of warming that occurred over the 1 km reach of Place Creek between the lake outlet and tree line. Over a 23-day period, net radiation totalled about 210 MJ m–2, with sensible heat flux adding another 56 MJm-2. The latent heat flux consumed about 8% of the surface heat input. The dominant heat sink was the net horizontal advection associated with lake inflow and outflow. Early in the study period, temperatures between the surface and 6-m depth were dominantly at or above 4 C and were generally neutral to thermally stable, whereas temperatures decreased with depth below 6m and exhibited irregular sub-diurnal variations. The maximum outflow temperature of almost 7 C occurred in this period. We hypothesize that turbidity currents associated with cold, sediment-laden glacier discharge formed an underflow and influenced temperatures in the deeper portion of the lake but did not mix with the upper layers. Later in the study period, the lake was dominantly well mixed with some near-surface stability associated with nocturnal cooling. Further research is required to examine the combined effects of sediment concentrations and thermal processes on mixing in small proglacial lakes to make projections of the consequences of glacier retreat on alpine lake and stream temperatures.

The fate of inflows into lakes has been extensively studied during summer stratification but has seen relatively little focus during the weak winter stratification, with or without ice-cover. Field observations are presented of groundwater inflow into a shallow bay of a subarctic lake. Atmospheric forcing of the bay during the study period was extremely variable and coincided with spring ice-cover break-up. Two dominant wind regimes were identified; (1) weak wind-forcing (wind speed 5 m s−1 and open water). At a relatively constant temperature of ~3.3°C, the groundwater inflow was closer to the temperature of maximum density than the water in the main body of the lake, which during the observed winter stratification is ~1.2°C. During weak wind-forcing, the stratification within Silfra Bay approximated two-layers as this denser groundwater formed a negatively buoyant underflow. A calculated underflow entrainment rate of 2.8 × 10−3 agrees well with other underflow studies. During strong wind-forcing, the water column out to the mouth of the bay became weakly stratified as the underflow was entrained vertically by wind-stirring. Observed periods of mixing can be predicted to occur when turbulent kinetic energy (TKE) production by wind stirring integrated over the underflow hydraulic residence time in the bay exceeds the potential energy associated with the stratification. A decrease of ice cover, as observed in the studied subarctic lake over the last decade, will result in the underflow being more frequently exposed to the strong wind-forcing regime during winter, thereby altering the winter distribution of groundwater inflow within the lake.

Detailed sea ice draft mapping was recently accomplished in the Beaufort Sea, north of Alaska, in 2007 and in the Lincoln Sea, north of Canada's Ellesmere Island, in 2008 using a small (3 m long, 20 cm diameter), man-handleable Gavia AUV incorporating an inertial navigation system and a 500 kHz phase-measuring swath sonar. The topography of specific ice features was mapped across 80 m-wide swaths by performing repeated runs in the vicinity of access holes drilled in the sea ice. The paper discusses the technical and operational developments undertaken to successfully accomplish the missions, including test deployments in a frozen Canadian lake prior to each Arctic deployment. Example data are shown and accuracy issues discussed. (C) 2008 Elsevier B.V. All rights reserved.

The objectives of this study are two-fold: (1) to describe and quantify the seasonal physical and chemical limnological properties of Pavilion Lake, a microbialite-rich lake in British Columbia, Canada, and (2) to gain a broader limnological context of Pavilion Lake by examining the limnology and hydrology of the lakes and groundwater systems in the area (∼30 km radius). Pavilion Lake is a dimictic lake with annual ice-cover. It is a hard water (mean CaCO 3 = 181.8 mg L -1), ultra-oligotrophic (mean Total Phosphorus [TP] = 3.3 μg L -1) lake, that is groundwater fed most likely through diffuse, low velocity local and regional sources. Principal Components Analysis (PCA) separated Pavilion Lake from the other groundwater, stream and lake samples along a conductivity and pH gradient on Axis 1 (λ 1 =0.392), and a nutrient (Total Nitrogen [TN], TP) and K +, Mg 2+, Si gradient on the second axis (λ 2 = 0.160). Pavilion Lake has the lowest Ca 2+ and TP concentrations, and the highest Na + concentrations and optical transmissivity amongst all sampled sites. Furthermore, the lake is characterized by low sedimentation rates. These characteristics are potentially important factors in supporting the past and on-going development of microbialites within the lake. Our study provides a limnochemical reference to consider in the conceptualization of ideal environments supporting large-scale microbialites. © E. Schweizerbart'sche Verlagsbuchhandlung 2009.

Penetrative convection in the surface layer of a midsize temperate lake (5 km2) was investigated in both summer and winter using a conductivity–temperature–depth (CTD) logger mounted on an autonomous underwater vehicle (AUV) flown repeatedly along horizontal transects at selected depths. In summer, the epilimnion cooled differentially during a calm evening (240 and 297 W m22 on the east and west sides of the lake, respectively). These cooling rates agree well with the average net heat flux of 270 W m22 estimated from meteorological data. Density currents were driven by this differential cooling. In winter, CTD profiles during a sunny day showed four distinct thermal layers beneath the ice (,50 cm thick), consistent with radiative penetrative convection: a stratified diffusive layer just beneath the ice (top 1.6 m); a well-mixed convective layer (that deepens at 1.14 m d21 and warms at 0.015u Cd 21 during the observation period); an entrainment layer (1.5 m thick); and a weakly stratified quiescent layer (to bottom). AUV transects, flown at constant depths in each layer, revealed a 150-m wide region displaying evidence of penetrative convection, surrounded by regions with negligible heat changes. These high-resolution, horizontal CTD measurements provided insight into previously unresolved physical dynamics of the well-mixed layer of a temperate lake in quasi–shear-free conditions that would have been difficult to quantify during summer months and impossible under winter ice cover without the use of an AUV platform. In temperate lakes, during periods of little or no wind exposure, penetrative convection driven by a destabilizing buoyancy flux will be the dominant source of vertical mixing in the upper layers of the water column. Above the temperature of maximum density, penetrative convection

Struvite, a crystalline structure comprised of ions of magnesium (Mg2+), ammonium (NH4-N) and phosphate (PO4-P), is commonly encountered in wastewater treatmentplants (WWTPs) through struvite encrustation. The gradual growth of this crystal can lead to h igh maintenance costs, due to downtime and replacement parts. Several struvite recovery unit processes have been developed in an effort to reduce this problem, through the preferential removal of the constituent ions (Mg2+, NH4-N, and PO4-P) upstream of problem areas (e.g. anaerobic digester supernatants). One of the key elements of process control for these systems is accurately determining the constituent concentrations. Although a wide variety of measurement techniques exist for both NH4-N and PO4-P, the presence of PO4-P interferes with the measurement of Mg2+. Ion selective electrodes (ISEs) were tested on wastewater samples to determine Mg2+ concentrations. It was found that the two ISE tested produced unreliable results, as they both proved non-specific t o Mg2+. A modification, using polyaluminum chloride (PAC), was developed to remove the interference of phosphates from the colorimetric technique. It was found to produce reliable results within 10% of those results predicted by atomic absorption. The resulting technique averaged about 10 minutes per sample and could be conducted inexpensively at a laboratory facility at WWTPs.

Struvite, a crystalline structure comprised of ions of magnesium Mg +2 , ammonium NH4 -N , and phosphate PO4 -P ,i s commonly encountered in wastewater treatment plants WWTPs through struvite encrustation. The gradual accumulation of this crystal in pipes and fittings leads to high costs due to downtime and replacement of parts. Technologies that are used to reduce this problem are ideally located in biological nutrient removal plants downstream of anaerobic digesters, as high levels of NH4 - N and PO4 - P typically characterize anaerobic digester supernatants. In 2003-2004, two technical-scale, struvite recovery studies were conducted on-site at the City of Penticton, B.C., Canada and the City of Richmond, B.C., Canada using a novel technology developed by the environmental engineering group at the University of British Columbia. The results of these studies showed an average reduction of 80% in phosphate and a dense, spherical product, 5-10 times larger than any commercially available struvite to date. Overall, the recovery of struvite has enormous commercial potential, which results in WWTP becoming more sustainable, concurrently reducing problems typically associated with their operation.

Seafloor environments at ever increasing depths on the continental shelf are being resolved at ever higher resolutions as a result of changing sensor technologies and, in part, with the emergence of Autonomous Underwater Vehicles (AUVs) as stable survey platforms. The new age of underwater robots to act as platforms which we can use to deploy sensors to gather information in the ocean is only limited by our imagination. This chapter provides an overview of this technology for applications on the continental shelf. It explores the basic fundamentals of AUV operation and the types of associated instrumentation, the current state of commercial and academic activity and the broad disciplines across which AUVs are currently been employed. AUVs are highly effective tools for sampling in continental shelf marine environments because: (1) they are untethered and can conduct non-destructive sampling in remote habitats (e.g. under ice shelves and over complex terrain) and in depths > 1000 m; (2) they can repeat spatial surveys with a high degree of precision over time; and (3) they can be equipped with a wide range of tools and sensors to sample both physical, chemical and biological data. Unfortunately by the time this chapter is in print, it realistically will already be out of date, as a result of the speed of the technological advancement in this discipline of underwater engineering.

In advanced wastewater treatment plants (AWWTP), the recovery of phosphorus (P) has become a recent focus of the wastewater engineering industry. The potential economic savings behind improved sludge management and the control of struvite encrustation in AWWTP are two of the primary driving forces behind this. Process control of phosphorus (struvite) recovery systems has only been partially successful because: (1) key control variables have yet to be identified and (2) there is no adequate performance evaluation model that is applicable to struvite recovery technologies. In process control, two different types of modeling are most commonly seen: mechanistic and “black-box” style models. In recent years, varying models have been developed to try to predict the formation of struvite in both sludge digestion process lines and P-recovery technologies designed for struvite removal. All of these are strictly mechanistic models, based on either the chemical equilibrium of the system or the associated kinetic parameters, with varying degrees of complexity. Artificial neural networks (ANN), as a type of black-box modeling, have seen limited application in wastewater treatment with regards to phosphate recovery. The analysis of several historical daily operational databases evaluated the predictive ability of two mechanistic and one ANN models. It was determined that the newly developed ANN model was not site specific and had the highest predictive ability of the three. This would be beneficial for the development of an automated control system for struvite removal package treatment processes.

The article of record as published may be located at http://dx.doi.org/10.1002/2013JC009070 In situ measurements of flow and stratification in the vicinity of the Erebus Glacier Tongue, a 12 km long floating Antarctic glacier, show the significant influence of the glacier. Three ADCPs (75, 300, and 600 kHz) were deployed close (