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Thwaites Eastern Ice Shelf is the remaining floating extension of Thwaites Glacier, anchored by an offshore pinning point at its northern terminus. Over the past two decades, TEIS has experienced progressive fracturing around a prominent shear zone upstream of its pinning point. Our study analyzes the shear zone fracture evolution from 2002 - 2022 and its control on the flow dynamics of the ice shelf, using remote sensing and in-situ GPS observations. We outlined three areas of interest within TEIS: the pinning-point shear zone, the mid-shelf region, and the region upstream of the pinning point. Then we compiled multi-year shear-zone fracture length and orientation statistics from Landsat and Sentinel-1 imagery and assessed their changes against evolving flow dynamics and shear strain rates. We found that the emergence of the shear zone fractures is dynamically linked with the shelf’s interaction with its neighbouring Thwaites Western Ice Tongue (TWIT) in different phases. These phases include the TWIT-driven acceleration phase (2002-2006), TEIS/TWIT shear-margin disintegration phase (2007-2012), TWIT disintegration phase (2012-2017) and TEIS mid-shelf acceleration phase (2017-2022). Post-2010, we observed the emergence of new rifts from the western part of the shear zone, which localized strain and expanded eastwards in the subsequent years. By 2016-17, the shearing-induced fractures rapidly grew, penetrating the entire shelf width. Subsequently, the mid-shelf ice accelerated eastward, while the ice upstream of the pinning point exhibited deceleration. In the austral winter of 2020, an upstream shift of the line of shearing caused an increase in the mid-shelf ice acceleration, as revealed by in-situ GPS observation. Our findings underscore two insights. First, the ongoing disintegration driven by shearing against the pinning point occurred in a two-stage process: growth of large shearing fractures, externally controlled by the flow of the neighboring TWIT earlier i

The pan-Arctic is disproportionately affected by global temperature increases due to climate change. Polar amplification and local climate feedback cycles, cause air temperature to rise around 2.4 times faster in the Arctic. The pan-Arctic covers approximately 26 million km2 of subbasins which contribute freshwater to the Arctic Ocean. Large-scale studies of climate warming impacts on terrestrial systems are rare because gathering observed data is expensive, difficult, and dangerous, and what is available is difficult to compile and lacks consistency. Modeled data are required for comprehensive long-term studies. This study analyses the pre-whitened annual trends of modeled soil temperature, water temperature, and river ice thickness for the historical period (1979-2019) and future projections (2020-2100) across the pan-Arctic domain using the AHYPEv4 model. These terrestrial hydrological components directly impact pan-Arctic ecology, and communities through permafrost thaw, increases in water temperature and decreases in river ice thickness. Analysis is done for the entire pan-Arctic domain, at the continental scale by comparing North America and Eurasia, and at the watershed scale for the 12 largest rivers (by historical volumes). Future climate projections come from the sixth phase of the Coupled Model Intercomparison Project, CMIP6. To capture uncertainty of future climate projections and socioeconomic response, an ensemble of climate models (CanESM5, MIROC6, and MRI-ESM2-0) and future warming scenarios (ssp1-2.6 and ssp5-8.5) capture the extreme ends of future change. This study shows increasing trends for future periods. Soil temperature increases from 0.032°C/year to 0.054°C/year, water temperature increases from 0.014°C/year to 0.031°C/year and losses in maximum ice thickness increase from 0.062 cm/year to 0.111 cm/year. Change point analysis shows that socio-economic pathways which result in lower future warming have mitigating effects on future trends mid

River flooding is the most common natural disaster in Canada, particularly in the prairie provinces. Floods occur when river discharge exceeds the volume a channel is capable of conveying. Extreme floods on meandering rivers can cause significant geomorphic change, however, the extent to which the sedimentary record of extreme floods differs from that of annual floods is unclear. In the past decade, the Assiniboine River in southwestern Manitoba has experienced three >200-year-recurrence interval floods. Recent studies of local and global climatic changes have suggested a potential for more extreme precipitation events that lead to increased flood risk. The objectives of this thesis are to: i) investigate the sediments deposited by these extreme floods, and ii) quantify the drivers of flood hazard on the Assiniboine River. The goal is to refine our understanding of the sedimentary record of multiple extreme floods and evaluate the relative contributions of in-channel sedimentation and climatic factors to recent flooding events. This thesis combines qualitative field-based investigations of point-bar deposits with quantitative stream-gauge data analysis to achieve these goals. Point bars in Spruce Woods Provincial Park have undergone extensive lateral migration over the past decade, with over 80% of migration occurring during three extreme flood events. The sedimentation associated with each flood event revealed that in some instances, extreme floods can generate an atypical coarsening upward profile of point-bar deposits. However, the deposits do not differ significantly from annual sedimentation, rather they are deposited more rapidly and in larger volumes. Data analysis of 60 years of stream-gauge data reveals that the greatest driver of flood hazard is an increase in flow frequency, however channel capacity changes have had a lesser but significant impact on decreasing the flood frequency. Climatic changes, specifically intense rainfall events, are a potential dr

Snow plays a vital role in near-shore landfast sea ice physical and biological processes. It needs to be monitored to understand sea ice processes and also to estimate sea ice thickness. However, snow depth remains difficult to estimate directly from space which forces the sea ice thickness products to use snow depth from model outputs or out-of-date climatology. Satellite altimetry based dual-radar and coincident laser/radar have been considered for providing regular estimates of snow depth on sea ice. In addition to the limitations associated with the functioning of individual altimeters, snow on landfast sea ice presents its challenges especially due to the lack of leads. While past studies have mostly focused on approaches suited to pack ice in the Central Arctic, this study aims to provide critical observations from landfast first-year sea ice in the Canadian Arctic. Surface-base altimeter retrievals from snow on sea ice at Churchill, Manitoba are compared to snow on lake ice demonstrating that the position of the Ku-band main scattering horizon is impacted by the presence of brine in the snowpack. The satellite-level study conducted at Dease Strait near Cambridge Bay is the first to assess the possibility of using coincident laser/radar altimeters (Cryo2Ice) for estimating snow depth on land-fast and lead-less sea ice at the Canadian Arctic Archipelago. The retrieved Cryo2Ice snow depths were underestimated by an average of 20.7 % which is slightly higher than the tidal adjustment applied. However, snow geophysical properties and surface roughness are seen to significantly bias Cryo2Ice retrievals. Both surface and satellite-based studies point towards the position of the Ku-band main scattering horizon being closer to the air-snow interface as opposed to the generally assumed snow-ice interface. Therefore, findings from this study may be useful for monitoring snow depth on land-fast sea ice using currently available and future satellite altimeters whereby sno

Climate change impacts have brought up the need for a better understanding of the rapidly changing ecosystem of the Arctic. Arctic marine ecosystems, such as around Southampton Island in Hudson Bay, are supported by phytoplankton production. In turn, phytoplankton production, which is influenced by environmental conditions and processes, can impact pelagic and benthic food webs. The goal of this thesis was to determine the physical processes driving phytoplankton production around Southampton Island, Nunavut during summer. Three subgroups of differing physical characteristics of the water column were distinguished: the Northwest Narrows group (well-mixed water connecting Roes Welcome Sound and Frozen Strait), the Hudson Bay group (warmer stratified waters to the south of Southampton Island), and the Foxe group (colder stratified northeastern waters in Foxe Basin and Foxe Channel). The different physical characteristics resulted in contrasting phytoplankton production and phytoplankton bloom stages around the island. In particular, a highly productive phytoplankton bloom supported by mixing and high nutrient availability, was observed in the Northwest Narrows group. Phytoplankton production estimates in the Northwest Narrows group were higher than estimates for Hudson Bay and Foxe Basin, and comparable to those in Hudson Strait. The substantial variability phytoplankton production around Southampton Island highlights the importance of local processes for primary production in the Arctic. This also calls to the necessity for future work to identify similar regions that have the potential to support high phytoplankton production in the Arctic.

Hudson Bay is a large Arctic/sub-Arctic shelf sea that covers an area of approximately 841,000 km2, and is estuarine in character, with a large watershed and more than 40 rivers discharging into the bay. Sediment core data for 18 new cores in Hudson Bay was used to understand the processes effecting sedimentation in the bay. This data was interpreted together with sedimentation rates and inventories of 210Pb and 137Cs from previously published articles, archived cores, and geophysical data from the past four decades. Geophysical data shows that the bulk of sedimentation occurs offshore, between 100 and 150 m depth, on the east and northwest coasts of the bay, localized depressions along the southern coast between 50 and 100 m depth, and basins in the center of the bay. Inventories of 210Pb and 137Cs are variable but overall show a trend of lower inventories in the northwest to higher inventories in the southeast. Both geophysical and geochemical data show that sedimentation in the bay is largely transient with sediment deposits at the base of slopes, in localized depressions, and near the mouths of rivers.

In Arctic marine environments, the renewal of surface nutrient stocks through physical and biogeochemical processes during winter is critical to support primary production later in the season when solar irradiance is sufficient. Landfast sea-ice and river discharge in the riverine coastal domain influence not only the structure of the coastal water column, but also impact the movement and distribution of nutrients within the system. Over the last several decades, both climate change and anthropogenic activities have caused shifts in both sea-ice and riverine cycles. Winter freshwater tracer and nutrient data from Canadian Arctic coastal areas, such as in Hudson Bay are extremely scarce. In this thesis I begin to fill this gap, focusing on three coastal regions: northeast James Bay (NEJB), northwest Hudson Bay (NWHB), and southeast Hudson Bay (SEHB). The objective is to evaluate the relationships between freshwater sources and nutrient distributions, during ice-covered and ice-free seasons, across the selected coastal domains. I present new nutrient (nitrate, phosphate, and silicate) and freshwater tracer (oxygen isotope ratio, salinity) data for water samples collected during ice-covered conditions, and additionally, data from open-water conditions in NEJB. Samples were collected with the help of numerous community members and guides between 2016-2019. Each region was distinct in terms of freshwater composition and influence, with NEJB strongly influenced by La Grande River, as its large under-ice plume (because of regulation) drove surface nutrient concentrations in winter (high nitrate, low phosphate). The sea-ice cycle (withdrawal of freshwater and release of brine during formation) was the dominant influence on NWHB coastal waters. Here there are large concentration ranges of nutrients within a small salinity range, possibly due to an alternate source water, or recirculation of HB outflow. SEHB coastal waters are largely influenced by riverine input from local r

As the global climate changes and demand for renewable electricity increases, construction of hydroelectric dams is increasing globally though the impacts of regulating the worlds rivers are still understudied. Northern Manitoba, Canada, has extensive hydroelectric development since the 1950s; fish mercury (Hg) concentrations in on-system lakes were observed to have increased above human consumption guidelines upon impoundment and have taken decades to decrease towards natural concentrations. To better understand the long-term impacts of hydroelectric regulation on Hg in fish and other biota in Northern Manitoba, we determined methylmercury (MeHg) production potential in soil from the water fluctuation zone in on- and off-system lakes through a soil flooding incubation experiment in the laboratory. We further studied the historic flux of MeHg and Hg to the sediments in on- and off-system lakes and links to organic matter in these waterbodies. We found that MeHg production was highest in the water fluctuation zone of the on-system lakes, which may represent an increased source of MeHg to the food web in these environments even decades after impoundment. In addition, sedimentation rates were found to greatly affect Hg fluxes to the sediment in those waterbodies where increased water flows result in higher erosion and sedimentation. These findings provide new insight in our understanding of the long-term recovery of Hg cycling within on-system lakes decades after impoundment.

Precipitation falling on a watershed can be stored above ground as well as in the vadose zone in the shallow subsurface or the deeper saturated zone. Examining the dynamics pertaining to the storage and release of water from these different zones is essential, not only for better hydrological process understanding, but also for biogeochemical reasons. Indeed, there are strong linkages between water storage dynamics and the persistence of contaminants in runoff and groundwater and their timing of release from terrestrial to aquatic environments. When it comes to the release of water from storage zones, two main types of dynamics are generally considered; (1) active storage release, which relates to the fast release and transfer of water from surface sources and the vadose zone, and (2) passive storage release, which rather refers to the slow release and transfer of water from the saturated zone to streams. While the literature is rich in theoretical, field and modelling studies targeting the assessment of water storage and release dynamics, few have attempted to compare different storage assessment approaches at the same site, i.e., hydrometric approaches, isotopic approaches only, or approaches that combine hydrometric and isotopic data. Undertaking a study of this nature in the Canadian prairie region is especially important in view of the numerous surface storage depressions that are naturally present, the man-made ponds built for stormwater control purposes, and the many bridges and ditches that all together modify the release and transport of water to streams in ways that are not yet fully understood. The overall goal of this PhD thesis was, therefore, to assess water storage and release dynamics within a nested system of eight prairie watersheds located in Manitoba, Canada. Through the synthesis of hydrometric and isotopic data analysis results, a conceptual framework detailing the dominant flow processes prevailing in each of the studied watersheds has been su

Mercury (Hg) is a major contaminant in the Arctic marine ecosystem, with concentrations in marine mammals and Indigenous Peoples frequently exceeding safety thresholds. The key step of Hg bioaccumulation is Hg methylation in the ocean, as the resulting monomethylmercury (MMHg) biomagnifies in the marine food webs. However, little is known about the sources and dynamics of seawater MMHg in the Arctic. In this research, high vertical resolution profiles of total Hg and methylated Hg (MeHg, sum of MMHg and dimethylmercury) were measured, for the first time, in seawater across the Canadian Arctic from the Canada Basin in the west, through the Canadian Arctic Archipelago, to Baffin Bay in the east and reaching Labrador Sea in the North Atlantic Ocean. Whereas total Hg concentrations are lower in the western Canadian Arctic, MeHg is enriched at shallow depths and its peak concentration decreases from west to east. Biological uptake of this subsurface MeHg and subsequent biomagnification can readily explain the regional gradients of biotic Hg in the Canadian Arctic. Seawater MeHg concentrations show significant correlations with nutrients and apparent oxygen utilization, but this does not necessarily support that MeHg is produced in-situ in the water column; instead, further analysis with water masses and N* reveals that the subsurface MeHg is likely originated from the Chukchi Sea sediments and advected within the Upper Halocline Water to the Canadian Arctic. The long-distance transport implies that MeHg in Arctic seawater must have a half-life much longer than previously determined from the seawater incubation approach, which is problematic in estimating Hg methylation and demethylation rates in seawater. Incubation studies with an Arctic copepod (Calanus hyperboreus) show that the microenvironments in copepod guts and fecal pellets are unlikely hotspots for Hg methylation, and that the copepod preferentially bioaccumulates MMHg over inorganic Hg and the main uptake path

Expectations that increases in shipping and human activities may impact concentrations of hydrocarbon contaminants in northern areas have prompted study of existing baseline distributions and variability in marine sediments from Chesterfield Inlet and Wager Bay, Nunavut. Pyrogenic and petrogenic compounds likely supplied by local sources subtly influence the composition of PAHs in sections of core CI-08, retrieved close to the community of Chesterfield Inlet. However, pyrogenic PAHs indicative of long-distance atmospheric transport are the main compounds in all the cores. These concentrations are low compared to other northern areas influenced by industrial activities. n-alkanes are likely derived from both terrigenous and marine organic matter sources in both areas. The two embayments contrast in terms of physical and geochemical factors that affect the baseline hydrocarbon concentration and accumulation rates. Good correlation between post-1900 210Pb and parent PAH inventories is consistent with focusing into deeper sites in Wager Bay versus direct settling in Chesterfield Inlet. No significant degradational pattern was observed in the core profiles.

The Nelson River, a subarctic river in north-central Manitoba, is the largest river discharging to Hudson Bay and its watershed has seen extensive land-modification in the upper reaches, permafrost thaw in the lower reaches, and hydroelectric development throughout. To characterize sources of sediment and particulate organic matter (OM) in the Nelson River system, and to identify processes influencing its transport to Hudson Bay, water quality parameters, Compound-Specific Stable Isotope (CSSI) fingerprinting, and Bayesian unmixing models were employed on terrestrial and instream samples. Distinct regional, longitudinal, and temporal differences in water quality parameters and particulate OM sources were observed among all three regions of the Nelson River system (upper Nelson River, Rat-Burntwood River, lower Nelson River). The application of CSSI fingerprinting and unmixing models showed that the dominant sources of OM to suspended sediment in the lower reaches of the Nelson River are proximally derived and comprise soils, upstream suspended sediment, river bed sediment, and tributary suspended sediment.

The Arctic is undergoing rapid changes due to climatic changes. Studies show that the Arctic is not only warming, but also freshening, which can induce changes to the distribution and spreading pathways of freshwater and impact ecosystems. Here, we focus on the coast of Northeast Greenland, which lies along the primary outflow shelf of the Arctic Ocean. Long term mooring-arrays monitor the gateways of the East Greenland Current at Fram Strait and Denmark Strait, but seasonal and interannual variability of oceanographic conditions along the coast of Northeast Greenland and its impact on fjord hydrography are not well known. This is mainly due to costs and logistical constraints encountered when operating in such a harsh and remote environment, where sea ice hampers coastal navigation. For this thesis, we analyzed in-situ observations, including moorings, from Young Sound-Tyrolerfjord (74° N), to gain more knowledge on the seasonal and long-term response of the fjord system to local and regional processes inducing changes in oceanographic conditions in the fjord and in the coastal domain. Our results include a description of the variability in hydrography and circulation during the ice-covered period, an impact analysis of coastal freshening on the renewal of the fjord basin water, and a process study of the drivers of freshwater variability along the coast of Northeast Greenland. The results suggest that sea ice melt along the coast is a prominent driver of freshwater variability in the coastal domain, and that sea ice melt might be impacted by the recirculation of warm Atlantic Water. An increase of temperatures in the North Atlantic could induce more sea ice might melt at higher latitude and freshen the coastal waters of Northeast Greenland. This is important, as our data already shows that after strong costal freshening in the periods since 2005, fjord bottom renewal of Young Sound-Tyrolerfjord was prevented, which may affect the fjords ecosystem functions. This s

The fate of terrestrial organic carbon (OC) in the global ocean is largely unknown and it is speculated to be rapidly degraded in the coastal waters. Arctic marine waters, especially Hudson Bay, have a disproportionally large terrestrial dissolved organic carbon (tDOC) input compared to the global ocean, which is increasing due to climate change. The findings of these first studies of microbial degradation of terrestrial OC in Hudson Bay have revealed the presence of high Apparent Oxygen Utilization in a subsurface, winter-ventilated water mass that cannot be explained by respiration of settling marine-produced OC as currently understood. I hypothesize that tDOC deposited into coastal waters ultimately gets degraded (consuming oxygen) under the ice cover. The findings from incubation experiments that 20-50% of the tDOC deposited into Hudson Bay by southern rivers in late winter is biodegradable within a few weeks are consistent with this hypothesis.

Increasing complexity in human-environment interactions at multiple watershed scales presents major challenges to sediment source apportionment data acquisition and analysis. Herein, we present a step-change in the application of Bayesian mixing models: Deconvolutional-MixSIAR (D-MIXSIAR) to underpin sustainable management of soil and sediment. This new mixing model approach allows users to directly account for the ‘structural hierarchy’ of a river basin in terms of sub-watershed distribution. It works by deconvoluting apportionment data derived for multiple nodes along the stream-river network where sources are stratified by sub-watershed. Source and mixture samples were collected from two watersheds that represented (i) a longitudinal mixed agricultural watershed in the south west of England which had a distinct upper and lower zone related to topography and (ii) a distributed mixed agricultural and forested watershed in the mid-hills of Nepal with two distinct sub-watersheds. In the former, geochemical fingerprints were based upon weathering profiles and anthropogenic soil amendments. In the latter compound-specific stable isotope markers based on soil vegetation cover were applied. Mixing model posterior distributions of proportional sediment source contributions differed when sources were pooled across the watersheds (pooled-MixSIAR) compared to those where source terms were stratified by sub-watershed and the outputs deconvoluted (D-MixSIAR). In the first example, the stratified source data and the deconvolutional approach provided greater distinction between pasture and cultivated topsoil source signatures resulting in a different posterior distribution to non-deconvolutional model (conventional approaches over-estimated the contribution of cultivated land to downstream sediment by 2 to 5 times). In the second example, the deconvolutional model elucidated a large input of sediment delivered from a small tributary resulting in differences in the reported contr

West Reflex Lake is a hypersaline lake in the Canadian Great Plains. The lake contains four types of shoreline carbonate structures: isolated pinnacles, bioherms (aggregates of pinnacles), laminated coatings, and beachrock. This study investigates the processes of formation of West Reflex Lake’s shoreline carbonates. A variety of petrographic and geochemical techniques were used to characterize the texture, mineralogy, and chemistry of the carbonates. The shoreline carbonates formed as a result of biotic and abiotic precipitation at the site of saline springs that supply Ca2+ to the lake. Evidence for biologically-influenced precipitation includes strong epifluorescence, presence of micrite cements, and abundance of microbial filaments. Abiotically-precipitated cements formed due to groundwater inflow. The isolated pinnacles and bioherms formed as a result of groundwater percolating through a framework of microbial filaments, whereas the laminated coatings formed as a result of calcification of coherent microbial mats adhering to a substrate.

A greater understanding of hydrological processes is needed to interpret spatial and temporal water quality dynamics, specifically within intensely managed prairie watersheds. This M.Sc. thesis looks at two years (2013 and 2014) of water quality and water level data, collected from 12 sub-watersheds outlets within the Catfish Creek Watershed (CCW). The CCW is located in southeastern Manitoba, is a tributary of Lake Winnipeg, and spans 642 km2, with a near-even mix of forest and agricultural land. The first data chapter (i.e., Chapter 2) analyzes correlations between each sub-watershed’s weekly water quality parameters (electrical conductivity, nitrate and phosphate concentrations) and their characteristics (e.g., topography and morphology, land use and land cover, and geology). The second research chapter (i.e., Chapter 4) conducts concentration-discharge (c-q) analyses using daily water quality measurements from four sub-watersheds. Findings indicate that the water quality dynamics within the CCW are both spatially and temporally diverse.