Alexander L. Forrest

Limnology of Pavilion Lake, B. C., Canada - characterization of a microbialite forming environment.

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.

UNCLOS under ice survey - An historic AUV deployment in the Canadian high arctic

In March and April 2010, an ISE Explorer Autonomous Underwater Vehicle (AUV), built for Natural Resources Canada (NRCan), was deployed to Canadas high Arctic. Its mission was to undertake under-ice bathymetric surveys in support of Canadas submission to establish the outer limits of its continental shelf under the United Nations Convention on the Law of the Sea (UNCLOS). During this deployment several under-ice records were broken and several new technologies were demonstrated.

Axisymmetric circulation driven by marginal heating in ice‐covered lakes

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.

Experiences from two-years' through-ice AUV deployments in the high Arctic

We present operational experiences from two deployments of a small Gavia AUV in the high Arctic. Deployments took place from the U.S.-led APLIS camp, in the Beaufort Sea during May 2007 and from a small independent ice camp, on the fast ice just north of Canadas Ellesmere Island, in May 2008. Both deployments took place through a 3 times 1 m access hole in first-year (FY) sea ice made with hot water drilling equipment. A heated tent was placed over the hole and repeated runs made to characterise the sea ice in the area. The second deployment demonstrated the minimum logistics required to run a small AUV in this manner, only requiring a working tent, one sleeping tent and two or three people. It was staged from shore using skidoos. Study areas included all typical types and ages of ice - level and ridged FY ice, rubble fields (FY and multi-year (MY)), and MY floes and ridges. Both deployments were coordinated with simultaneous overflights by aircraft- and helicopter-borne instruments, allowing co-registration of snow+ice freeboard (from a scanning laser profilometer) and ice+snow thickness, from an electromagnetic induction device (HEM), operated by the University of Alberta. In situ measurements of ice thickness (grids and transects of drilled holes) validated results from all instruments.

The influence of an Antarctic glacier tongue on near-field ocean circulation and mixing

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 (<50 m) to the sidewall of the glacier in order to capture near-field flow distortion. Scalar (temperature and conductivity) and shear microstructure profiling captured small-scale vertical variability. Flow magnitudes exceeded 0.3 m s−1 through a combination of tidal flow (∼8 cm s−1) and a background/residual flow (∼4–10 cm s−1) flowing to the NW. Turbulence was dominated by deeper mixing during spring tide, likely indicative of the role of bathymetric variation which locally forms an obstacle as great as the glacier. During the neap tide, near-surface mixing was as energetic as that seen in the spring tide, suggesting the presence of buoyancy-driven near-surface flows. Estimates of integrated dissipation rate suggest that these floating extensions of the Antarctic ice sheet alter energy budgets through enhanced dissipation, and thus influence coastal near-surface circulation.

AUV measurements of under-ice thermal structure

Underwater technologies have advanced to the point where the development of autonomous underwater vehicles, or AUVs, is driven by the scientific end user rather than the AUV developer. This results from AUV platforms becoming increasingly commercially available and finding application in a wide range of fields including physical, chemical, biological and geological sciences. Scientific payloads carried by these vehicles in ice-covered waters dramatically increase the quality of data being collected while concurrently increasing the range of observation (e.g. the Beaufort Sea, the Weddell Sea). They also present a unique opportunity to access under-ice regions where it is operationally difficult or logistically impossible to operate with surface vehicles. This reduces deployment infrastructure, associated expenses and facilitates the collection of water property measurements beneath ice-cover, a difficult and potentially dangerous endeavour using conventional techniques, especially when ice-cover is thin, frazil, candled or partially open. This latter capability is extremely important for making observations and conducting scientific research in ocean, coastal, and inland waters in the Canadian Arctic. Since initial deployments in 2006, dasiaUBC-Gaviapsila, an AUV operated by the University of British Columbia Environmental Fluid Mechanics (UBC-EFM) group, has been deployed in several under ice experiments. In February 2008, measurements were made under ice cover by UBC-Gavia in Pavilion Lake, BC. These were a follow up to the successful AUV deployments conducted at the same site in 2007 as well as deployments in the Beaufort Sea. In addition to resolving horizontal variability in the previously measured thermal structure, the primary scientific objective was to examine the thermal structure correlation with the physical properties of the overlying ice cover. In May 2008, the same vehicle was deployed through sea-ice off the north coast of Ellesmere Island, NU, in the Canadian High Arctic, with the objective of measuring the draft of deformed ice using multibeam swath bathymetry. Initial measurements of near shore horizontal temperature variability was quantified by a CTD onboard the AUV while concurrent measurements were being made from a thermistor chain moored on the ice surface. This paper will review the initial scientific results of these two experiments examining the thermal structure in the context of scientific questions driving AUV under-ice experimentation. In addition, novel techniques of AUV deployment, navigation and recovery, developed for this project, are described in the context of operational problems forecasted for Polar Regions.

Seasonal variability in turbidity currents in Lake Ohau, New Zealand, and their influence on sedimentation

Layers of sediment that are deposited on the floor of Lake Ohau, New Zealand, offer a means to reconstruct past climate conditions in the Southern Hemisphere at subdecadal and annual resolution. A robust understanding of the modern physical processes that control the influx and dispersal of sediment in the lake is required to reconstruct climate from these sedimentary archives. In this study, water temperature and velocity measurements collected during 2012–13 were analysed to determine the primary physical processes that influence sediment transport in the lake. Sediment input from river inflow occurs throughout the year but exhibits strong seasonal variation. Large inflow events (Q>500m3s–1) that follow strong summer rainstorms trigger high-concentration turbidity currents, which are the main agents for sediment delivery and deposition. During winter, smaller turbidity currents also occur after rain events and contribute to annual sediment accumulation. In addition, large internal waves were observed during the summer and may influence sedimentation. In conclusion, several processes including river inflow, internal waves and convectively driven flows control sediment deposition and accumulation in the Lake Ohau system. We utilise these observations to establish a conceptual model to explain the observed infill stratigraphy in Lake Ohau and guide interpretation of the longer sedimentary record.

Mesophotic Coral Ecosystems: A Geoacoustically Derived Proxy for Habitat and Relative Diversity for the Leeward Shelf of Bonaire, Dutch Caribbean

Current trends demonstrate coral reef health in serious decline worldwide. Some of the most well preserved coral reefs in the Caribbean basin are located in the waters surrounding Bonaire, in the Dutch Caribbean. In many places on the leeward side on islands dominated by trade winds, the shallow reef systems extend into deeper water where they are known as Mesophotic Coral Ecosystems (MCE). Autonomous Underwater Vehicles (AUVs) were used to collect geoacoustic data of these leeward reefs at multiple sites as part of an ocean exploration project. AUV swath bathymetry and side-scan sonar data were analyzed for depth, acoustic backscatter intensity, seafloor slope and rugosity. These geomorphic metrics were then used as inputs to generate a composite synthetic index of bottom-type to delineate MCE features. A confusion matrix statistical analysis of the acoustic class map showed an overall accuracy of the acoustic classes at 66%, with accuracy of the hard coral class the highest at 83% and the sandy-bottom class the lowest at 55. The hard coral class was also the statistically most reliable, at over 80%, with the noise class coming in as the least reliable. This morphologic habitat index is a potentially useful new tool in quantifying the extent of MCE located in proximity to Marine Protected Areas (MPAs).

Autonomous underwater vehicle motion response: a nonacoustic tool for blue water navigation

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 mea- surements 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 blank- ing 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 cal- culate 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 con- ditions. 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.

Multiplatform ocean exploration: Insights from the NEEMO space analog mission

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 deepspace 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 precursormissions 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.