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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.

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. | 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.

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.

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.

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