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POGSON, L., B. TREMBLAY, D. LAVOIE, C. MICHEL, M. VANCOPPENOLLE, 2011. Development and validation of a one-dimensional snow-ice algae model against observations in Resolute Passage, Canadian Arctic Archipelago. J. Geophys. Res. (C Oceans), 116(4). Art. no C04010, 16 p .
Ice algae are an important component of the carbon cycle in the Arctic. We investigate the dynamics of an ice algae bloom by coupling an ice algae-nutrient model with a multilayer σ coordinate thermodynamic sea ice model. The model is tested with the simulation of an algal bloom at the base of first-year ice over the spring. Model output is compared with data from Barrow Strait in the Canadian Arctic Archipelago. Snow cover, through its influence on ice melt, is a dominant factor controlling the decline of the bloom in the model, a finding that supports past studies. The results show that under a higher snow cover (20 cm), biomass in the early stages of the algal bloom is less than expected from the observed data. This discrepancy is due to the severely light-limited algal growth, despite the close match between simulated and observed under-ice photosynthetically active radiation. This result raises issues of how photosynthetic parameters as well as radiative transfer is represented in one-dimensional ice models. This study also shows that for higher algal concentrations, when biomass is split over multiple layers rather than concentrated in one layer at the ice base, there is a reduction in algae accumulation, a result of self shading. In addition, experiments show a sensitivity of total biomass to the oceanic heat flux and ice layer thickness, both of which affect biomass loss at the ice base. Being able to accurately model physical conditions is essential before the seasonal dynamics of ice algae can be accurately modeled, and some recommendations for improvement are discussed.©2011 American Geophysical Union
LAVOIE, D., K.L. DENMAN, R.W. MACDONALD, 2010. Effects of future climate change on primary productivity and export fluxes in the Beaufort Sea. J. Geophys. Res. (C Oceans), 115(4): Art. no C04018, 15 p .
We present projections of future primary production for the Canadian Beaufort Shelf of the Arctic Ocean, using simulations of future climate change from the Canadian Global Climate Model (CGCM2) to force a coupled sea ice-ocean-biological one-dimensional model. We compare three 18 year simulations, 1975–1992, 2042–2059, and 2082–2099, to describe the impacts of a reduction in sea ice cover duration and thickness and an increase in surface freshwater fluxes. Our results show an increase in average annual primary production of 6 % between the period 1975–1992 and the period 2042–2059 and an increase of 9 % between 1975–1992 and 2082–2099. The relative contribution of the ice algal and spring phytoplankton blooms to the annual primary production is reduced in the future runs owing to a reduction in the length of the ice algal growth season (resulting from earlier snow and ice melt) and to a reduction in the replenishment of nutrient to the mixed layer in winter. The duration of the summer subsurface phytoplankton bloom increases, which favors the development of the main copepod species and leads to an increase in export production (16 % between 1975–1992 and 2082–2099) that is greater than the increase in primary production.©2010 American Geophysical Union
LAVOIE, D., R.W. MACDONALD, K.L. DENMAN, 2009. Primary productivity and export fluxes on the Canadian shelf of the Beaufort Sea: a modelling study. J. Mar. Syst., 88(3) 401-422 .
We present a coupled sea ice-ocean-biological (including ice algae) model in the Arctic Ocean. The 1D model was developed and implemented on the Canadian Beaufort Sea shelf to examine the importance of different physical processes in controlling the timing and magnitude of primary production and biogenic particle export over an annual cycle (1987). Our results show that the snow and sea ice cover melt and/or break-up controls the timing of the phytoplankton bloom but primary producers (ice algae and phytoplankton) on the outer shelf are essentially nutrient limited. The total annual primary production (22.7 to 27.7 g-C m-2) is thus controlled by nutrient "pre-conditioning" in the previous fall and winter and by the depth of wind mixing that is controlled in part by the supply of fresh water at the end of spring (ice melt or runoff). The spring bloom represents about 40 % of the total annual primary production and occurs in a period of the year when sampling is often lacking. Time interpolation of observed values to obtain total annual primary production, as done in many studies, was shown to lead to an underestimation of the actual production. Our simulated ratios of export to primary production vary between 0.42 and 0.44. ©2008 Elsevier B.V.
LAVOIE, D., M. STARR, B. ZAKARDJIAN, P. LAROUCHE, 2007. Identification of ecologically and biologically significant areas (EBSA) in the Estuary and Gulf of St. Lawrence: primary production ; Identification de zones dimportance écologique et biologique (ZIEB) pour lestuaire et le golfe du Saint-Laurent: production primaire. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2007/079, 33 p .
In this report, we analyse of a large set of chlorophyll a, nitrate, and primary production observations gathered from the early 70's as well as results from a 3D coupled physical-biological model to identify ecologically and biologically significant areas (EBSAs) for primary production in the Gulf and Estuary of St. Lawrence. High phytoplankton production and Chl a concentration are found successively in all regions of the Gulf and Estuary of St. Lawrence, and thus all regions are important for phytoplankton production at one time or another during the year. However, only a few regions stand out as EBSAs if we consider their importance on an annual basis, based on uniqueness and aggregation criteria as defined in CSAS Ecosystem Status Report 2004/006. The most important zones are the Lower Estuary, the Gaspé Current, and the Northwestern Gulf.
LAVOIE, D., K. DENMAN, C. MICHEL, 2005. Modeling ice algal growth and decline in a seasonally ice-covered region of the Arctic (Resolute Passage, Canadian Archipelago). J. Geophys. Res. (C Oceans), 110. art. no C11009, 17 p .
We have developed a coupled snow-ice-ice algae model to investigate the importance of different ice algal growth limitation terms, as well as different loss terms, in regulating the ice algal biomass accumulation at the bottom of landfast ice in the Canadian Archipelago. The model results are compared with data collected from May to July 2002 at a station near Resolute in Barrow Strait. Our results show that ice algae are light limited at the beginning of the bloom, then fluctuate between light and nutrient limitation, finally remaining nutrient limited toward the end of the bloom. The fortnightly tide modulates the ice algal biomass through the supply of nutrient to the ice algal layer but mainly through modulation of the bottom ice melt rate. We also demonstrate that the bottom ice melt rate regulates the maximum biomass attained in the region and that a rapid increase in ice temperature can lead to a significant decline in ice algal biomass. The eventual termination of the bloom is triggered by melting of the snow cover and results from (1) increased ice algal losses due to high bottom ice melt rate and (2) decreased ice algal growth due to nutrient limitation caused by the formation of a meltwater lens below the ice. Finally, our results show that the snow cover controls the length of the bloom, such that earlier snowmelt that is expected to accompany climate warming may lead to a reduction in ice algal production.©2005 The American Geophysical Union
SIMARD, Y., D. LAVOIE, F.J. SAUCIER, 2002. Channel head dynamics : capelin (Mallotus villosus) aggregation in the tidally driven upwelling system of the Saguenay - St. Lawrence Marine Park's whale feeding ground. Can. J. Fish. Aquat. Sci., 59: 197-210 .
Capelin (Mallotus villosus) tridimensional distribution at the head of the Laurentian Channel in the St. Lawrence estuary was investigated using 38- and 120-kHz acoustic surveys in the summers of 1994, 1995, 1997, and 1998. The results are interpreted with the help of a high-resolution tridimensional tidal circulation model. Total biomasses were small (93-4583 t) and showed rapid fluctuations, whereas mesoscale distribution was more constant. Capelin tended to occupy the very end of the channel head, especially the slopes and shallows surrounding the basins. This pattern did not coincide with the krill distribution, but the two total biomass series were significantly correlated. Capelin tidal dynamics is characterized by herding of capelin against the channel head slopes by the starting flooding currents, followed by an upwelling over the sills and shallows during maximum flood currents, and a return to the channel by the surface outflow during ebb. Each side of the channel head has a distinct capelin retention tidal cycle involving passive advection, swimming, and the two-layer estuarine circulation. This capelin distribution and tidal dynamics closely match the local fin whale (Balaenoptera physalus) and minke whale (Balaenoptera acutorostrata) distributions observed from the whale-watching fleet and typical tidal feeding strategies at the channel head.
LAVOIE, D., Y. SIMARD, F.J. SAUCIER, 2000. Aggregation and dispersion of krill at channel heads and shelf edges : the dynamics in the Saguenay - St. Lawrence Marine Park. Can. J. Fish. Aquat. Sci., 57: 1853-1869 .
The spatial organization of the euphausiid (Thyanoessa raschi and Meganyctiphanes norvegica) aggregation at the head of the Laurentian Channel is examined using 120-kHz echointegration data from eight surveys in the summers of 1994 and 1995 and currents obtained from a high-resolution three-dimensional circulation model. Circulation is the main factor controlling the abundance and distribution of krill. The main aggregation pattern is U-shaped and includes an entrance corridor along the northern edge of the channel, a major accumulation zone off Les Escoumins, and an exit corridor along the southern edge. However, this mesoscale aggregation exhibits rapid fluctuations in spatial pattern and global abundance, due to the redistribution of krill within and out of the study area. The local accumulations are controlled by the interactions between the semidiurnal tidal currents, the topography, and the negative phototactism of krill. The strong vertical currents found along the channel slopes upstream of Les Escoumins and at the sills act to concentrate and pile up krill. The aggregation and dispersion mechanisms are strongly influenced by the deepwater blocking process taking place at the sills. The fortnightly tidal cycle and freshwater runoff modulate the blocking intensity. This krill aggregation dynamic is of primary importance for the trophic link with the baleen whales and fish in the Saguenay - St. Lawrence Marine Park.
SIMARD, Y., D. LAVOIE, 1999. The rich krill aggregation of the Saguenay - St. Lawrence Marine Park : hydroacoustic and geostatistical biomass estimates, structure, variability, and significance for whales. Can. J. Fish. Aquat. Sci., 56: 1182-1197 .
The euphausiid aggregation at the head of the main channel of the estuary and Gulf of St. Lawrence was surveyed using 120- and 38-kHz hydroaccoustics in the summers of 1994 and 1995. A systematic sampling grid covering an area of 1319 km2 was visited eight times. Fish echoes were separated from kill echoes using the difference in backscattering strength at the two frequencies. Global estimates were obtained from geostatistical methods for both total biomass and the fraction exceeding 5 g wet•m-3. The euphausiids were always exclusively composed of individuals of the oldest cohorts (2+) of the two species Thysanoessa raschi and Meganyctiphanes norvegica. Total biomass varied from 8 ± 96 ± 8 kt and cutoff biomass from 0 to 56 ± 6 kt. The two types of estimates were linearly related. Biomass was autocorrelated up to distances of 10-15 km. An anisotropic structure with radii of similar 2 x 5 km, stretched along the channel axis, was discernible at a small scale. The particular size distribution of euphausiids and the large variations in the global estimates appear to be controlled by horizontal transport. The study area appears to be the richest krill aggregation site yet documented in the northwest Atlantic, with densities similar to the rich krill aggregation areas of the Antarctic. The krill aggregation is at the heart of this traditional whale feeding ground.
LAVOIE, D., Y. SIMARD, J. BENOÎT, P. LAROUCHE, B. THIBEAULT, 1996. Distribution des masses d'eau à la tête du chenal laurentien dans l'estuaire du Saint-Laurent aux étés 1994 et 1995. Rapp. tech. can. hydrogr. sci. océan., 176, 126 p .
Satellite thermal images and temperature and salinity profiles, taken during the summers of 1994 and 1995, are used to describe the water masses at the head of the Laurentian channel. The three typical water masses of this system; the surface, the intermediate and the bottom layers showed : 1) a thinning and an elevation of the cold intermediate layer at the end of the summer, associated with a thickening of the bottom layer, 2) a colder intermediate layer in 1995, 3) a recurrent spatial structure, characterized by a convergence of the cold intermediate layer off Les Escoumins. Upwelling of intermediate cold waters at the head of the Laurentian channel was observed most of the time, as well as many fronts associated with its contact with adjacent waters from the Saguenay and the upper estuary. Our results suggest that the intensity and occurrence of these phenomena were modulated by the fortnightly tidal cycle and by the wind which regularly generated cold water upwelling along the north shore.
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