Dany Dumont

Modeling the Dynamics of the North Water Polynya Ice Bridge

The North Water polynya, the largest polynya in the world, forms annually and recurrently in Smith Sound in northern Baffin Bay. Its formation is governed in part by the formation of an ice bridge in the narrow channel of Nares Strait below Kane Basin. Here, the widely used elastic‐viscous‐plastic elliptical rheology dynamic sea ice model is applied to the region. The idealized case is tested over a range of values for e 5 [1.2, 2.0] and initial ice thicknesses from 0.75 to 3.5 m, using constant northerly winds over a period of 30 days, to evaluate long-term stability of different rheological parameterizations. Idealized high-resolution simulations show that the formation of a stable ice bridge is possible for e # 1.8. The dependence of the solution in terms of grid discretization is studied with a domain rotated 458. A realistic domain with realistic forcing is also tested to compare time-variant solutions to actual observations. Cohesion has a remarkable impact on if and when the ice bridge will form and fail, assessing its importance for regional and global climate modeling, but the lack of observational thickness data during polynya events prevents the authors from identifying an optimal value for e.

Contribution of subsurface chlorophyll maxima to primary production in the coastal Beaufort Sea (Canadian Arctic): A model assessment

[1] Previous comprehensive investigations of the Canadian Arctic revealed that subsurface chlorophyll maxima (SCM) are widespread and long-lived structures that can contribute significantly to daily primary production in the water column. However, estimating the annual contribution of SCM to production with in situ or remote-sensing approaches is challenging in the high Arctic. For this reason and to estimate the impacts of fluctuating or changing environmental conditions on SCM, a numerical approach combining a turbulence model and an ecosystem model was implemented for the coastal Beaufort Sea. An ensemble analysis of simulations suggested that SCM contribute 65–90% of total annual primary production and that this proportion is weakly affected by ice regime, winter nitrogen (N) concentration, parameter values determining phytoplankton growth and decay or the physical forcing imposed, all varying within realistic values. Due to the persistent association between the SCM and the shallow nitracline, the pelagic ecosystem of the coastal Beaufort Sea is apparently characterized by a high ratio of new to total production, contrasting with the common assumption that oligotrophic systems are predominantly supported by recycled N and regenerated production. This study demonstrated that the use of a simple model in combination with in situ data leads to novel insights into biogeochemical processes that are otherwise very difficult to measure and track.

Turbulent nitrate fluxes in the Amundsen Gulf during ice‐covered conditions

3(2, 5) × 10 −3 m 2 s −1 and decreased exponentially to a depth of ∼50 m, below which it was roughly constant at the background value Kb =3 (2, 5) ×1 0 −6 m 2 s −1 .T he nitracline, centered around 62 m depth, was subject to an eddy diffusivity close to the background value Kb and the mean diffusive nitrate flux across the nitracline was Fnit = 0.5(0.3, 0.8) mmol m −2 d −1 . These observations are compared with other regions and the role of vertical mixing on primary production in the Amundsen Gulf is discussed. Citation: Bourgault, D., C. Hamel, F. Cyr, J.‐E. Tremblay, P. S. Galbraith, D. Dumont, and Y. Gratton (2011), Turbulent nitrate fluxes in the Amundsen Gulf during ice‐covered conditions, Geophys. Res. Lett., 38, L15602, doi:10.1029/2011GL047936.

A basal stress parameterization for modeling landfast ice

Current large-scale sea ice models represent very crudely or are unable to simulate the formation, maintenance and decay of coastal landfast ice. We present a simple landfast ice parameterization representing the effect of grounded ice keels. This parameterization is based on bathymetry data and the mean ice thickness in a grid cell. It is easy to implement and can be used for two-thickness and multithickness category models. Two free parameters are used to determine the critical thickness required for large ice keels to reach the bottom and to calculate the basal stress associated with the weight of the ridge above hydrostatic balance. A sensitivity study was conducted and demonstrates that the parameter associated with the critical thickness has the largest influence on the simulated landfast ice area. A 6 year (2001–2007) simulation with a 20 km resolution sea ice model was performed. The simulated landfast ice areas for regions off the coast of Siberia and for the Beaufort Sea were calculated and compared with data from the National Ice Center. With optimal parameters, the basal stress parameterization leads to a slightly shorter landfast ice season but overall provides a realistic seasonal cycle of the landfast ice area in the East Siberian, Laptev and Beaufort Seas. However, in the Kara Sea, where ice arches between islands are key to the stability of the landfast ice, the parameterization consistently leads to an underestimation of the landfast area.

Numerical simulations of the spread of floating passive tracer released at the Old Harry prospect

The Gulf of St Lawrence is under immediate pressure for oil and gas exploration, particularly at the Old Harry prospect. A synthesis of the regulatory process that has taken place over the last few years indicates that important societal decisions soon to be made by various ministries and environmental groups are going to be based on numerous disagreements between the private sector and government agencies. The review also shows that the regulatory process has taken place with a complete lack of independent oceanographic research. Yet, the Gulf of St Lawrence is a complex environment that has never been specifically studied for oil and gas exploitation. Motivated by this knowledge gap, preliminary numerical experiments are carried out where the spreading of a passive floating tracer released at Old Harry is examined. Results indicate that the tracer released at Old Harry may follow preferentially two main paths. The first path is northward along the French Shore of Newfoundland, and the second path is along the main axis of the Laurentian Channel. The most probable coastlines to be touched by water flowing through Old Harry are Cape Breton and the southern portion of the French Shore, especially Cape Anguille and the Port au Port Peninsula. The Magdalen Islands are less susceptible to being affected than those regions but the probability is not negligible. These preliminary results provide guidance for future more in-depth and complete multidisciplinary studies from which informed decision-making scenarios could eventually be made regarding the exploration and development of oil and gas at the Old Harry prospect in particular and, more generally, in the Gulf of St Lawrence.

Liquid Crystal Photoalignment using New Photoisomerisable Langmuir-Blodgett Films

We present optical alignment studies of pure nematic liquid crystals using photoisomerisable Langmuir-Blodgett (LB) alignment layer. Monolayers of azobenzene-containing molecules exhibiting long lifetime for cis isomer are transferred on glass substrates using the Langmuir-Blodgett deposition technique. The anchoring produces homeotropic texture and the strength of this anchoring is increasing with increasing number of monolayers from 1 to 7. The exposition of the cells with UV light the spectrum of which corresponds to the absorption band of the dye in the trans conformation induces strong realignment of the LC molecules via the trans-cis photoisomerization process and the regulation of the film orientation by LCs. Such reorientation occurs mainly in the plane perpendicular to the polarization plane of the excitation.

Modeling Wind-Driven Circulation and Landfast Ice-Edge Processes during Polynya Events in Northern Baffin Bay

A high-resolution sea ice‐ocean numerical model of the North Water polynya has been developed to study the wind-driven circulation during polynya events. An idealized three-layer stratified ocean is used to initialize the model to characterize the baroclinic response to realistic wind and ice conditions. The model general circulation pattern is mainly forced by an along-channel sea level gradient between the Arctic Ocean and Baffin Bay, which determines the magnitude of the southward Baffin Current, and by an across-channel sea level gradient in Baffin Bay, which drives the northward West Greenland Current (WGC). These two currents are found to be anticorrelated to each other in the Smith Sound area. During strong northerly wind events, occurring quite frequently in the winter‐spring period in the polynya, nutrient-rich Baffin Bay waters transported by the WGC are forced toward the Greenland shelf, coinciding with upwelling events along the Greenland coast. Whenever an ice bridge is present (i.e., the polynya exists and is substantially open), upwelling also occurs at the landfast ice edge. In such cases, the total upwelling area is increased by an amount that depends on the form of the ice bridge but could easily double during certain years. The baroclinic circulation associated with the upwelling response includes the formation of a cyclonic eddy attached to the ice edge that is generated during strong northerly wind events. Primary production estimations reveal that upwelling during polynya events plays a significant role in the early spring phytoplankton bloom, suggesting that the disappearance of the polynya as a result of climate change may have profound implications for the entire ecosystem.

Experimental Assessment of the Performance of High-Frequency CODAR and WERA Radars to Measure Ocean Currents in Partially Ice-Covered Waters

AbstractHigh-frequency radars (HFRs) measure ocean surface currents remotely through the Bragg scattering of radio waves by surface gravity waves with wavelengths shorter than 50 m. HFR range is affected by sea ice, which dampens surface gravity waves and limits wind fetch for adjacent open waters. HFR range sensitivity to sea ice concentration was empirically determined for two types of HFR—Coastal Ocean Dynamics Applications Radar (CODAR) and Wellen Radar (WERA)—installed on the shores of the lower St. Lawrence estuary, Canada, during winter 2013. One CODAR was operating at 13.5 MHz on the southern shore, and one WERA was operating at 16.15 MHz on the northern shore. Ranges were determined using a signal-to-noise ratio threshold of 6 dB for first-order Bragg scattering measured by the receive antenna elements. Ranges were normalized for expected ranges in ice-free conditions, using empirical relationships determined during summer 2013 between the range and surface gravity wave energy at the Bragg freque...

In-fiber variable optical attenuation with ultra-low electrical power consumption

The variable optical attenuator (VOA) is an important part of agile optical telecommunication systems. VOAs built on so called free space technologies carry important drawbacks in terms of mechanical reliability, size and optical loss. Evanescent field approach have been used to design VOAs with very low insertion loss. Thermo-optic modulation mechanism was mainly used to control the attenuation level, which unfortunately requires from 10 to 100 times more electrical power compared to above mentioned free space architectures. This power consumption issue may be very challenging in high count arrays of VOAs. At the same time, liquid crystals (LC) have been proved to require very low electrical power for operation. In the present work, we report the creation of evanescent field modulation based VOA with extremely low insertion loss (below 0.1dB) and low electrical power consumption by removing a portion of the original fibers cladding and replacing it by a specifically synthesized composite LC material, which have an ordinary refractive index lower than the glass one. The initial orientation of LC molecules provides an effective refractive index of the electro-optic cladding that is equal to the refractive index of the original silica cladding. We then create a LC molecule reorientation by the so-called Fredericksz effect by applying to the LC material an electrical voltage. This reorientation changes the refractive index around the depressed cladding area and brings to the partial leakage of the guided radiation into the cladding area, achieving thus attenuation levels above 50dB. Measured maximum electrical power consumption of the VOA is in the microwatt range.

Low loss and low polarization dependent fiber variable optical attenuators

We present the optical performance of a compact variable optical attenuator (VOA) developed at Photintech. The presented VOA’s operation principle is based on the guided wave evanescent field manipulation. Access to the evanescent portion of the guided radiation is achieved by replacing the original waveguide’s cladding with a thermo-optic composite polymer (TOP) material. By changing the temperature of the thermo-optic (TO) material we create guided radiation partial leakage attenuating thus the light. Nevertheless, using polymer materials usually creates significant birefringence due to shrinkage during polymerization or thermal stresses during operation and the polarization dependence of such devices is relatively high. We apply a specific cladding geometry and heating electrode (pending patent of Photintech Inc.), which ensures axial compensation of the birefringence, providing thus very small polarization dependence. In-fiber design provides also low insertion loss (IL) and high dynamic range operation. Control electronics allow the VOA to operate with a precision better than 0.1dB. The developed VOA can be used in agile optical networks, for applications such as dynamic gain equalisation, dynamic channel equalisation, optical transmitter power control and receivers protection in telecommunication systems.