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Marko J.R.,ASL Environmental Sciences Inc. | Jasek M.,BC Hydro
Cold Regions Science and Technology | Year: 2010

The basic concepts and operating principles of SWIPS (Shallow Water Ice Profiling Sonar) measurements in freezing rivers are outlined and described with reference to ongoing BC Hydro ice- and flow monitoring programs in the Peace River. Emphasis is given to identifying the nature of the measured quantities and their connections to the parameters conventionally used to describe and model rivers and their ice contents. Difficulties in deployment and data recovery, mostly associated with the growth of anchor ice, are described in terms of the evolution of successful approaches and the pitfalls encountered along the way. Distinctions are made among results obtained from targets at or inside floating surface ice and from particulate targets, suspended in the water column. Example results are presented in each case and put in the context of seasonal changes in the monitored quantities of interest. The usefulness of lower frequency measurements for ice cover studies is highlighted. Limited results from simultaneous multifrequency measurements on suspended particulate (frazil) targets are reviewed and analyzed to show the likely applicability of Rayleigh Law assumptions for observations made prior to ice cover stabilization and in, at least, the lower water column. This applicability is combined with estimates of absolute return strengths to make rough assessments of the ranges of particle sizes and concentration encountered in the Peace River studies. © 2010 Elsevier B.V.

Marko J.R.,ASL Environmental Sciences Inc. | Jasek M.,BC Hydro
Cold Regions Science and Technology | Year: 2010

Results from 2004-2008 BC Hydro SWIPS (Shallow Water Ice Profiling Sonar) monitoring programs on the Peace River are presented and analyzed with respect to their content of information on the properties and behaviour of frazil ice suspended in water column. Strong distinctions were made in analyses applied to data collected, respectively, prior to and following local stabilization of the seasonal ice cover. This choice is shown to reflect both the behaviour and origins of the frazil ice present in these two intervals. Pre-freeze-up frazil tends to coat submerged surfaces, grows rapidly while in suspension and is only rarely and episodically present. It shows time dependences quite different from those associated with frazil detected prior to freeze-up. Frazil under a stationary ice cover is ubiquitous, does not adhere to other materials and appears to closely associated with the ice cover undersurface. The return intensity profiles observed in pre-freeze-up frazil events increased roughly linearly with height in the water column. Profile comparisons with earlier simulation results allowed inferences on particle size distributions and their controlling processes. The bulk of data analysis efforts was devoted to clarifying the time dependences of the more abundant post-stabilization SWIPS intensity data and its underlying connections to changes in the major river, atmosphere and ice cover environmental parameters. The obtained results showed unlagged or weakly negatively-lagged, positive correlations between such intensities and both river water levels and air temperatures (or solar radiation input) on, at least, diurnal and shorter time scales. The water level parameter was the stronger of these two influences and was believed to be representative of a physical link to river flow speed. Lower frequency connections to the physical state of the ice cover were also apparent. Interpretations of these results were offered in terms of a local equilibrium between the suspended frazil population and a dynamic slush layer at the bottom of the ice cover. Initial steps were taken toward developing and testing analysis tools potentially capable of supporting combined analysis and modelling of this equilibrium. A simple interpretative approach was applied to data acquired at a single acoustic frequency based upon combined use of a Rouse Law-based Inverted sediment model of uniformly-sized spherical frazil particles and volume backscattering coefficients measured in post-freeze-up intervals. Results suggested consistency with the basic form of return intensity profiles at most but not all times. For suitable measurement periods, the approach yielded reasonable estimates of the major particle size and concentration parameters. The deficiencies of this approach are discussed and compared with expectations and results from recently successful simultaneous measurements at two acoustic frequencies. Priorities are identified for validation, and refinement of single and multifrequency approaches along with integrated study of the lower ice cover as part of a broader program to understand frazil ice growth in freezing rivers. © 2010 Elsevier B.V.

Marko J.R.,ASL Environmental Sciences Inc. | Topham D.R.,ASL Environmental Sciences Inc.
Cold Regions Science and Technology | Year: 2015

Measurements of volume backscattering coefficients in brine suspensions of neutrally buoyant, uniformly-sized, polystyrene spheres and disks were used to quantify size, shape and concentration dependences expected in equivalent measurements on freshwater suspensions of frazil ice. The results confirmed expectations of qualified compatibility with existing scattering theory. Specifically, the measured logarithmic backscattering coefficients were expressible, to within 1-2. dB, as products of particle concentration and individual cross sections as calculated from the modal expansion of Faran (1951) applied to spheres with radii equal to either their actual values or (for hexagonal disks) to "effective" spherical radii. The limitations on the applicability of the theory were closely linked to: acoustic frequency, target-volume-determined effective radii; the linear dimensions of the faces of the individual target disks; and to particle concentrations. For combinations of particle dimensions, acoustic frequencies and concentrations outside of a well-defined Rayleigh Linear (RL) concentration dependence range, the relationships between measured volume backscattering coefficients and particle properties were complex and not amenable to a simple interpretation: reflecting, it is believed, polystyrene-specific scattering features. The features of the observed extensive Anomalous Linear (AL) and Non-Linear (NL) concentration dependence regimes were documented in terms of both their parameter dependences and the forms and parameters associated with their deviations from RL regime dependences. Analyses focused on identifying the boundaries of the latter regimes which currently provide the only measurement environments compatible with accurate extraction of particle concentration and size parameters. These identifications, made on the basis of polystyrene in brine data, were used, after insertion of frazil and freshwater material parameters, to identify equivalent RL boundaries for ABS (Acoustic Backscattering Sonar) frazil measurements. In practical terms, this framework led to estimates of upper and lower limits for usable ABS acoustic frequencies and established upper limits on the concentrations of larger frazil particles contributing significantly to backscattering signal returns. These results formed the basis for a measurement framework for obtaining validated frazil characterizations. This framework was tested on mixtures of differently-sized pseudo-frazil species to show compatibility between mixture data and equivalent backscattering coefficients calculated for each mixture on the basis of its composition and measured single species coefficients. Applications of this framework to actual frazil field data are essential for both further testing of effectiveness and to allow refinements of imposed, intentionally conservative, restrictions. Results of such applications are described and interpreted in a second publication. © 2015 Elsevier B.V.

Asplin M.G.,University of Manitoba | Asplin M.G.,ASL Environmental Sciences Inc. | Scharien R.,University of Manitoba | Else B.,University of Manitoba | And 4 more authors.
Journal of Geophysical Research: Oceans | Year: 2014

Decline of the Arctic summer minimum sea ice extent is characterized by large expanses of open water in the Siberian, Laptev, Chukchi, and Beaufort Seas, and introduces large fetch distances in the Arctic Ocean. Long waves can propagate deep into the pack ice, thereby causing flexural swell and failure of the sea ice. This process shifts the floe size diameter distribution smaller, increases floe surface area, and thereby affects sea ice dynamic and thermodynamic processes. The results of Radarsat-2 imagery analysis show that a flexural fracture event which occurred in the Beaufort Sea region on 6 September 2009 affected ∼40,000 km2. Open water fractional area in the area affected initially decreased from 3.7% to 2.7%, but later increased to ∼20% following wind-forced divergence of the ice pack. Energy available for lateral melting was assessed by estimating the change in energy entrainment from longwave and shortwave radiation in the mixed-layer of the ocean following flexural fracture. 11.54 MJ m-2 of additional energy for lateral melting of ice floes was identified in affected areas. The impact of this process in future Arctic sea ice melt seasons was assessed using estimations of earlier occurrences of fracture during the melt season, and is discussed in context with ocean heat fluxes, atmospheric mixing of the ocean mixed layer, and declining sea ice cover. We conclude that this process is an important positive feedback to Arctic sea ice loss, and timing of initiation is critical in how it affects sea ice thermodynamic and dynamic processes. Key Points Fractured sea ice is more vulnerable to lateral melting Timing of flexural swell is key to surface albedo Mixing of open water in fractured ice may enhance melting © 2014. American Geophysical Union and Crown copyright.

Porri F.,Rhodes University | Porri F.,South African Institute For Aquatic Biodiversity | Jackson J.M.,University of Cape Town | Jackson J.M.,ASL Environmental Sciences Inc. | And 4 more authors.
Journal of Marine Systems | Year: 2014

The coupling of benthic and pelagic life stages of marine invertebrates is central to understanding their population dynamics and is influenced by hydrodynamic processes at multiple spatial scales. Here we provide a regional scale study that identifies mesoscale oceanographic features linked to the distribution of mussel larvae. We surveyed the distribution of mussel larvae along 12 shelf to slope transects within an alongshore distance of about 700. km along the Agulhas Bank off South Africa. Oceanographic and larval abundance data were collected simultaneously to determine how larval distribution is related to physical factors. Larval abundances were most closely correlated with temperature, salinity, beam attenuation (which indicates particle concentrations), and zonal (east-west) water velocity. In most regions, the highest larval concentrations were observed within an average distance of 3.7. km from the coastline. Three mesoscale oceanographic mechanisms were identified that could explain larval distribution on separate parts of the coast. These were: a solitary meander whose leading end advects the Agulhas Current onto the continental shelf as an Agulhas Current Meander and whose lagging end advects the Agulhas Current offshore as a Natal Pulse, and the accumulation of larvae in a region with known internal wave activity. The Agulhas Current Meander swept large numbers of recently "spawned" larvae up to 30. km offshore, acting as a corridor for larval loss, or a population sink. Onshore retention seems, however, to be generally characteristic of this region, when the Agulhas Current is not on the continental shelf. This study highlights how mesoscale features are associated with larval density, transport, and coupling between the pelagic and benthic systems of the Agulhas Bank. © 2014 Elsevier B.V.

Borstad G.,ASL Environmental Sciences Inc. | Crawford W.,Canadian Department of Fisheries and Oceans | Hipfner J.M.,Environment Canada | Thomson R.,Canadian Department of Fisheries and Oceans | Hyatt K.,Canadian Department of Fisheries and Oceans
Marine Ecology Progress Series | Year: 2011

There are few studies of the mechanistic links between physical environmental processes and biotic responses in marine ecosystems that have strong predictive power. At Triangle Island, the largest seabird colony along Canada's Pacific coast, annual breeding success of rhinoceros auklets Cerorhinca monocerata varies dramatically. Previous studies have correlated this variability with ocean temperature, but this relationship occasionally fails, suggesting that it is not causal. We used historical satellite data time series of sea surface temperature, chlorophyll, and winds to study the oceanography of this remote colony. We found that rhinoceros auklets bred more successfully when the spring transition in regional winds and the resulting spring phytoplankton bloom occurred early in April. These factors appear to control the annual recruitment of Pacific sandlance Ammodytes hexapterus, as measured by the percent by biomass of young-of-the-year sandlance in the nestling diet. These linkages imply bottom-up control in this system. Suggesting broader implications of our work, we also found that marine survival of economically and culturally important sockeye salmon Oncorhynchus nerka from nearby Smith Inlet was strongly correlated with the fledgling mass of the rhinoceros auklets, sandlance in the chicks' diets, and regional chlorophyll in April. The timing of the spring wind transition and phytoplankton bloom appear to be important for other predators in this system. We think that these relationships with wind and chlorophyll derived from satellite data are potentially valuable explanatory tools that will be widely applicable to studies of early marine survival of many marine species. © Inter-Research 2011.

Myers P.G.,University of Alberta | Kulan N.,ASL Environmental Sciences Inc.
Journal of Physical Oceanography | Year: 2012

Southward transports in the deep western boundary current across 538°N, over 1949-99, are determined from a historical reconstruction. Long-term mean transports, for given water masses, for net southward transport (the southward component of the transport not including recirculation given in parentheses) are 4.7 ± 2.3 Sv (5.1 ± 2.4 Sv) (Sv=10 6 m 3 s 1) for the Denmark Strait Overflow Water, 6.1 ± 2.7 Sv (6.8 ± 1.7 Sv) for the Iceland-Scotland Overflow Water, 6.5 ± 2.6 Sv (7.1 ± 1.8 Sv) for classical Labrador Sea Water, and 2.3 ± 1.9 Sv (2.7 ± 3.4 Sv) for upper Labrador Sea Water. The estimates take into account seasonal and interannual variability of the isopycnal positions and suggest the importance of including this factor. A strong correlation, 0.91, is found between variability of the total and baroclinic transports (with the barotropic velocity removed) at the annual time scale. This correlation drops to 0.32 if the baroclinic transports are, instead, computed based upon the use of a fixed level of no motion at 1400 m. The Labrador Sea Water layer shows significant variability and enhanced transport during the 1990s but no trend. The deeper layers do show a declining (but nonstatistically significant) trend over the period analyzed, largest in the ISOW layer. The Iceland-Scotland OverflowWater presents a 0.029 Sv yr -1 decline or 1.5 Sv over the 50-yr period, an 18%-22% decrease in its mean transport. © 2012 American Meteorological Society.

Polyakov I.V.,University of Alaska Fairbanks | Pnyushkov A.V.,University of Alaska Fairbanks | Rember R.,University of Alaska Fairbanks | Padman L.,Earth and Space Research | And 3 more authors.
Journal of Physical Oceanography | Year: 2013

A 1-yr (2009/10) record of temperature and salinity profiles from Ice-Tethered Profiler (ITP) buoys in the Eurasian Basin (EB) of the Arctic Ocean is used to quantify the flux of heat from the upper pycnocline to the surface mixed layer. The upper pycnocline in the central EB is fed by the upward flux of heat from the intermediate-depth (̃150-900 m) Atlantic Water (AW) layer; this flux is estimated to bẽ1Wm-2 averaged over one year. Release of heat from the upper pycnocline, through the cold halocline layer to the surface mixed layer is, however, seasonally intensified, occurring more strongly in winter. This seasonal heat loss averages ̃3-4Wm-2 between January and April, reducing the rate of winter sea ice formation. This study hypothesizes that the winter heat loss is driven by mixing caused by a combination of brine-driven convection associated with sea ice formation and larger vertical velocity shear below the base of the surface mixed layer (SML), enhanced by atmospheric storms and the seasonal reduction in density difference between the SML and underlying pycnocline. © 2013 American Meteorological Society.

Schweigert J.F.,Canadian Department of Fisheries and Oceans | Thompson M.,Canadian Department of Fisheries and Oceans | Fort C.,Canadian Department of Fisheries and Oceans | Hay D.E.,Nearshore Research | And 2 more authors.
Progress in Oceanography | Year: 2013

The Pacific herring (Clupea pallasi) resource has supported one of the most important commercial fisheries on Canada's west coast for more than a century. Like many pelagic species, herring productivity has fluctuated throughout this period, especially for the largest population, which spawns in the Strait of Georgia. To provide long term sustainability and cogent management advice it is critical to understand the factors determining herring productivity. Since productivity can be influenced by survival of early life history stages, especially for pelagic species such as herring, we assessed the contribution of bottom-up forcing factors on young of the year (YOY) herring abundance and growth. Herring spawning is closely linked to the annual plankton production cycle and the match (or mismatch) between egg deposition and the initiation of the spring plankton bloom has a substantial impact on survival and production of YOY herring. Enhanced long-term monitoring of the production cycle could provide a better understanding and ultimately a prediction of Pacific herring production within the Strait of Georgia. © 2013.

Marko J.R.,ASL Environmental Sciences Inc. | Jasek M.,BC Hydro
Cold Regions Science and Technology | Year: 2015

A four-frequency SWIPS (Shallow Water Ice Profiling Sonar) instrument was deployed in the Peace River during the November 2011-May 2012 period near the Town of Peace River. The deployment site was previously used for deployments of one- and two-frequency SWIPS instruments. Acoustic volume backscattering coefficient and ice thickness data were collected at frequencies 125kHz, 235kHz, 455kHz and 774kHz. The data, acquired as a function of height in the water column, were processed to test particle size, concentration and acoustic frequency restrictions identified in a closely-related laboratory study of backscattering in pseudo-frazil suspensions (Marko & Topham, 2015) prior to applying optimal processing strategies on the 2011-2012 frazil data. Although one of the transducers (235kHz) displayed anomalous returns under certain environmental conditions, simultaneous measurements at 125kHz, 455kHz and 774kHz were found to yield consistent measures of particle concentration, size distribution and fractional volume with accuracies limited, primarily, only by the 1dB transducer calibration uncertainties. Fractional volumes were found to vary by less than an order of magnitude from interval to interval, with maximum values being approximately 10-4 (0.01%) except within, roughly, 0.75m of the river surface where interpretations were complicated by the frequent presence of surface ice. These results confirmed the effectiveness of multifrequency acoustic backscattering sonar (ABS) technology in applications to frazil monitoring problems and expanded its range of applicability beyond that conservatively estimated in the laboratory. The obtained data also provided an unprecedented basis for evaluating current river ice modeling assumptions. Comparisons with corresponding results from CRISSP model runs appear to be indicative of massive over-prediction of suspended frazil despite good model performance for simulating surface ice quantities. The origins of the possible discrepancies are discussed and accompanied by suggested options for improving model performance. © 2014.

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