Mercury (Hg) is one of the primary contaminants of concern in the Arctic marine ecosystem. Methyl Hg (MeHg) is known to biomagnify in food webs. During the International Polar Year - Circumpolar Flaw Lead study, sea ice, seawater, bottom ice algae, phytoplankton and the herbivorous copepods were collected from the Amundsen Gulf to test whether ice algae and phytoplankton assimilate Hg from their habitat, and whether Hg bioaccumulates from the seawater to the primary consumers. Sea ice algae were found to accumulate Hg primarily from the bulk bottom ice, and the sea ice algae bloom depleted Hg stored within the bottom section of the ice. Furthermore, biodilution of Hg was observed to occur in sea ice algae. Higher concentrations of Hg were also found in phytoplankton and in grazing copepods. A positive correlation between MeHg and trophic level suggests the occurrence of MeHg biomagnification even at these low trophic positions.

Mercury (Hg) is one of the primary contaminants of concern in the Arctic marine ecosystem. Methyl Hg (MeHg) is known to biomagnify in food webs. During the International Polar Year - Circumpolar Flaw Lead study, sea ice, seawater, bottom ice algae, phytoplankton and the herbivorous copepods were collected from the Amundsen Gulf to test whether ice algae and phytoplankton assimilate Hg from their habitat, and whether Hg bioaccumulates from the seawater to the primary consumers. Sea ice algae were found to accumulate Hg primarily from the bulk bottom ice, and the sea ice algae bloom depleted Hg stored within the bottom section of the ice. Furthermore, biodilution of Hg was observed to occur in sea ice algae. Higher concentrations of Hg were also found in phytoplankton and in grazing copepods. A positive correlation between MeHg and trophic level suggests the occurrence of MeHg biomagnification even at these low trophic positions.

Sea-ice ecosystem modelling is a novel field of research. In this thesis, the main organism studied is sea-ice algae. A basic introduction to algae and its importance in the aquatic food web is given first. An introduction to modeling and its purposes is presented, and this is followed by a brief description of ice algae models in practice with some physical conditions which influence ecosystem modelling. In the following Chapter, a simple mathematical model to represent the algae population is derived, and analyzed using pseudo spectral numerical methods implemented with MATLAB. The behaviour of the algae population and the boundary layers are discussed by examining the numerical results. Perturbation and asymptotic analysis is used for further analysis of the system using Maple. In the following Chapter a Nutrient Phytoplankton Zooplankton Detritus (or NPZD) model, which is a commonly used type of model in marine ecosystem modelling, is developed based on the framework of Soetaert and Herman. The model is examined under five different experimental setups (herein we mean numerical experiments) and the results are discussed. The NPZD model implemented is compared with a well-studied model in the literature. Our model can be considered somewhat simpler than other models in the literature (though it still has a much larger parameter space than the idealized model discussed in the previous Chapter). Finally we discuss future directions for research.

Sea-ice ecosystem modelling is a novel field of research. In this thesis, the main organism studied is sea-ice algae. A basic introduction to algae and its importance in the aquatic food web is given first. An introduction to modeling and its purposes is presented, and this is followed by a brief description of ice algae models in practice with some physical conditions which influence ecosystem modelling. In the following Chapter, a simple mathematical model to represent the algae population is derived, and analyzed using pseudo spectral numerical methods implemented with MATLAB. The behaviour of the algae population and the boundary layers are discussed by examining the numerical results. Perturbation and asymptotic analysis is used for further analysis of the system using Maple. In the following Chapter a Nutrient Phytoplankton Zooplankton Detritus (or NPZD) model, which is a commonly used type of model in marine ecosystem modelling, is developed based on the framework of Soetaert and Herman. The model is examined under five different experimental setups (herein we mean numerical experiments) and the results are discussed. The NPZD model implemented is compared with a well-studied model in the literature. Our model can be considered somewhat simpler than other models in the literature (though it still has a much larger parameter space than the idealized model discussed in the previous Chapter). Finally we discuss future directions for research.

Marine phytoplankton are known to produce UV-absorbing compounds (UVACs) for protection against UV radiation. To assess whether the same strategy applies to sea ice-associated algal communities, MAAs were measured in algae associated with surface melt ponds, sea ice, sea ice−water interface, and underlying seawater in a coastal bay of the Canadian Arctic Archipelago during the 2011 spring melt transition. Six UVACs were detected as the spring melt progressed, namely shinorine, palythine, and porphyra-334 and three unknowns (U1, U2 and U3). U1 was most likely palythene, another MAA. The molecular identities of the other two UVACs, U2 and U3, which have an absorption maximum of 363 and 300 nm, respectively, remain to be structurally elucidated. The results confirm that Arctic sea ice-associated algal communities are capable of producing photoprotectants and that spatial and temporal variations in MAA and other UVAC synthesis are affected by snow cover and UV radiation exposure. / May 2016

The spring bloom of microalgae within the bottom of sea ice provides a significant contribution to primary production in the Arctic Ocean. The aim of this research was to improve observations of the ice algae bloom using a transmitted irradiance technique to remotely estimate biomass, and to examine the influence of physical processes on biomass throughout the sea ice melt season. Results indicate that bottom ice temperature is highly influential in controlling biomass variability and bloom termination. Snow depth is also significant as it buffers ice temperature from the atmosphere and largely controls transmission of photosynthetically active radiation (PAR). The relationship between snow depth and biomass can change over the spring however, limiting biomass accumulation early on while promoting it later. Brine drainage, under-ice current velocity, and surface PAR in the absence of snow cover are also important factors. Overall this research helps to characterize the spring ice algae bloom in the Arctic by improving in situ biomass estimates and identifying primary factors controlling it.

The spring bloom of microalgae within the bottom of sea ice provides a significant contribution to primary production in the Arctic Ocean. The aim of this research was to improve observations of the ice algae bloom using a transmitted irradiance technique to remotely estimate biomass, and to examine the influence of physical processes on biomass throughout the sea ice melt season. Results indicate that bottom ice temperature is highly influential in controlling biomass variability and bloom termination. Snow depth is also significant as it buffers ice temperature from the atmosphere and largely controls transmission of photosynthetically active radiation (PAR). The relationship between snow depth and biomass can change over the spring however, limiting biomass accumulation early on while promoting it later. Brine drainage, under-ice current velocity, and surface PAR in the absence of snow cover are also important factors. Overall this research helps to characterize the spring ice algae bloom in the Arctic by improving in situ biomass estimates and identifying primary factors controlling it.

abstract: Sea ice algae dominated by diatoms inhabit the brine channels of the Arctic sea ice and serve as the base of the Arctic marine food web in the spring. I studied sea ice diatoms in the bottom 10 cm of first year land-fast sea ice off the coast of Barrow, AK, in spring of 2011, 2012, and 2013. I investigated the variability in the biomass and the community composition of these sea-ice diatoms between bloom phases, as a function of overlying snow depth and over time. The dominant genera were the pennate diatoms Nitzschia, Navicula, Thalassiothrix, and Fragilariopsis with only a minor contribution by centric diatoms. While diatom biomass as estimated by organic carbon changed significantly between early, peak, and declining bloom phases (average of 1.6 mg C L-1, 5.7 mg C L-1, and 1.0 mg C L-1, respectively), the relative ratio of the dominant diatom groups did not change. However, after export, when the diatoms melt out of the ice into the underlying water, diatom biomass dropped by ~73% and the diatom community shifted to one dominated by centric diatoms. I also found that diatom biomass was ~77% lower under high snow cover (>20 cm) compared to low snow cover (<8 cm); however, the ratio of the diatom categories relative to particulate organic carbon (POC) was again unchanged. The diatom biomass was significantly different between the three sampling years (average of 2.4 mg C L-1 in 2011, 1.1 mg C L-1 in 2012, and 5.4 mg C L-1 in 2013, respectively) as was the contribution of all of the dominant genera to POC. I hypothesize the latter to be due to differences in the history of ice sheet formation each year. The temporal variability of these algal communities will influence their availability for pelagic or benthic consumers. Furthermore, in an Arctic that is changing rapidly with earlier sea ice and snowmelt, this time series study will constitute an important baseline for further studies on how the changing Arctic influences the algal community immured in sea ice. / Dissertation/Thesis / Masters Thesis Biology 2014

L’océan Arctique est marqué par une forte saisonnalité qui se manifeste par la présence d’une banquise permanente dont l’extension varie entre 6 et 15 millions de kilomètres carré. Interface plus ou moins perméable, la banquise limite les échanges atmosphère - océan et affecte le budget énergétique global en réfléchissant une part importante du rayonnement incident. Le manteau neigeux qui se forme à sa surface est un élément essentiel notamment parce qu’il contribue fortement aux propriétés optiques de la banquise. D’une part par son albédo, proche de l’unité dans le visible, qui retarde sensiblement la fonte estivale de la glace. Et d’autre part, il est majoritairement responsable de l’extinction verticale de l’éclairement dans la banquise. Or, la faible intensité lumineuse transmise à la colonne d’eau constitue un facteur limitant important à l’accumulation de biomasse des producteurs primaires souvent des micro-algues, à la base des réseaux trophiques. Le manteau neigeux en surface, par ces propriétés physiques et leurs évolutions temporelles, joue donc un rôle essentiel en impactant directement l’initiation et l’amplitude de la floraison phytoplanctonique printanière. Dans le cadre du réchauffement climatique actuel, les mutations que subit la banquise : amincissement, réduction de son extension estivale et variations des épaisseurs du manteau neigeux bouleversent d’ores et déjà la production primaire arctique à l’échelle globale et régionale.Cette thèse vise à mieux comprendre la contribution du manteau neigeux au transfert radiatif global de la banquise, afin de mieux estimer son impact sur la production primaire arctique. Elle s’appuie sur un jeu de données collecté lors de deux campagnes de mesures sur la banquise en période de fonte. Les propriétés physiques de la neige, SSA et densité, permettent une modélisation précise du transfert radiatif de la neige qui est validée, ensuite, par les propriétés optiques comprenant : albédo, profils verticaux d’éclairement dans le manteau neigeux et transmittance à travers la banquise.Au printemps, la neige marine, marquée par une importante hétérogénéité spatiale, évolue suivant quatre phases distinctes. La fonte, d’abord surfacique puis étendue à toute l’épaisseur du manteau, se caractérise par une baisse de la SSA de 25-60 m2kg-1 à moins de 3 m2kg-1 provoquant une diminution de l’albédo dans le proche infrarouge puis à toute longueur d’onde ainsi qu'une augmentation de l’éclairement transmis à la colonne d’eau. Cette période est chaotique, et marquée par une forte variabilité temporelle des propriétés optiques causées par la succession d’épisodes de fonte et de chutes de neige. Les propriétés physiques de la neige sont utilisées par un modèle de transfert radiatif afin de simuler les profils verticaux d'éclairement, l’albédo et la transmittance de la banquise. La comparaison entre ces simulations et les profils d’éclairement mesurés met en évidence la présence d’impuretés dans la neige dont leurs natures et leurs concentrations sont estimées. En moyenne, la neige échantillonnée contenait 600 ngg-1 de poussières minérales et 10 nng-1 de suies qui réduisaient par deux l’éclairement transmis à la colonne d’eau. Enfin, la modélisation de l’éclairement à toute profondeur de la banquise, représentée de manière innovante par des isolumes, est mise en relation avec l’évolution temporelle de la biomasse dans la glace. Il apparaît que la croissance des algues de glace est systématiquement corrélée avec une augmentation de l’éclairement, et ce, jusqu’à des niveaux d’intensité de l’ordre de 0.4 uEm-2s-2. Ces variations d’éclairement sont causées par le métamorphisme et la fonte de la neige en surface. / The Arctic ocean shows a very strong seasonality trough the permanent presence of sea ice whose extent varies from 6 to 15 millions km2. As an interface, sea ice limits ocean - atmosphere interactions and impacts the global energy budget by reflecting most of the short-wave incoming radiations. The snow cover, at the surface, is a key element contributing to the optical properties of sea ice. Snow enhances further the surface albedo and thus delays the onset of the ice melt. In addition, snow is the main responsible for the vertical light extinction in sea ice. However, after the polar night, this low light transmitted to the water column is a limiting factor for primary production at the base of the oceanic food web. The snow cover, through the temporal evolution of its physical properties, plays a key role controlling the magnitude and the timing of the phytoplanktonic bloom. In the actual global warming context, sea ice undergoes radical changes including summer extent reduction, thinning and shifts in snow thickness, all of which already alter Arctic primary production on a regional and global scale.This PhD thesis aims to better constrain the snow cover contributions to the radiative transfer of sea ice and its impact on Arctic primary production. It is based on a dataset collected during two sampling campaigns on landfast sea ice. Physical properties of snow such as snow specific surface area (SSA) and density allow a precise modeling of the radiative transfer which is then validated by optical measurements including albedo, transmittance through sea ice and vertical profiles of irradiance in the snow.During the melt season, marine snow which shows strong spatial heterogeneity evolves fol- lowing four distinctive phases. The melting, which first appears at the surface and gradually propagates to the entire snowpack, is characterized by a decrease in SSA from 25-60 m2kg-1 to less than 3 m2kg-1 resulting in a decrease in albedo and an increase in sea ice transmittance. This is a chaotic period, where optical properties show a very strong temporal variability induced by alternative episodes of surface melting and snowfalls. The physical properties of snow are used in a radiative transfer model in order to calculate albedo, transmittance through sea ice and vertical profiles of irradiance at all depths. The comparison between these simulations and measured vertical profiles of irradiance in snow highlights the presence of snow absorbing impurities which were subsequently qualitatively and quantitatively studied. In average, impurities were composed of 660 ngg-1 of mineral dust and 10 ngg-1 of black carbon. They were responsible for a two-fold reduction in light transmitted through sea ice. The light extinction, calculated at all depths in sea ice, and represented by isolums, was compared to the temporal evolution of ice algae biomass. The results show that every significant growth in ice algae population is related to an increase of light in the ice. These growths were observed even at very low light intensities of 0.4 uEm-2s-2. Light variations in the ice were linked by snow metamorphism and snow melting at the surface.

L’océan Arctique, particulièrement sensible au changement climatique, a vu lors des dernières décennies une augmentation de sa température deux fois supérieure à la moyenne mondiale. Certains scientifiques prévoient la disparition complète de la banquise pour 2050. Du fait de la future disparition des algues de glace et de l’augmentation de la fonte du pergélisol, une réévaluation de leurs contributions respectives au stockage de CO2 est nécessaire. Dans cette étude, nous avons ainsi montré que les algues de glace possèdent une forte capacité de préservation dans les sédiments (et donc de stockage du CO2) due à l’incapacité de leurs bactéries à les reminéraliser. A l’inverse, les quantités grandissantes de pergélisol rejetées en mer sont fortement reminéralisables. L’effet conjoint de l’augmentation du rejet de CO2 lors de la dégradation du pergélisol et de la diminution de son stockage par les algues de glace devrait donc contribuer à une amplification du réchauffement climatique. / With a rise in Arctic temperatures almost twice as large as the global average in recent decades, it is at high latitude that the effects of global warming are the most evident. Thus, some scientists have already predicted the complete disappearance of sea ice for 2050. Due to the future disappearance of ice algae and the increase of permafrost thawing, a reassessment of their respective contributions to CO2 storage was required. We have shown that unlike permafrost, ice algae are highly preserved in sediments (allowing CO2 storage) due to the inability of their bacteria to remineralize them. The combined effect of increasing discharge of permafrost by Arctic rivers and decreasing storage of ice algae due to the disappearance of sea ice should thus contribute to increase the global warming.