Arctic tidewater glaciers and ice shelves are undergoing rapid attrition, with warmer ocean temperatures playing an important role. However, the relationship between ocean temperature and ice structure retreat is complex and may change as the ocean warms and as the ice structure geometry evolves. In order to explore ice–ocean interactions and the impact of retreating ice structures in a glacial fjord, we use a numerical ocean model of Milne Fiord, which features an ice shelf and a tidewater glacier with a floating glacier tongue (part of which is detached). We model past, present, and potential future ice configurations. Our results reveal that the average submarine melting is negligible across the ice shelf (<2 cm a−1) but can dominate thinning rates (>20 cm a−1) at specific locations where the ice is thick (>50 m) along the seaward edge. Our simulations also indicate that the temperature of water reaching the grounding line does not vary significantly when the ice shelf and glacier tongue are removed. In addition, we carry out a series of simulations with increasing ocean temperature which reveal a quasi-linear relationship between ocean temperature and submarine melting at the grounding line. Using this relationship and ocean temperature predictions for different greenhouse gas emission scenarios (2020 to 2100), we estimate that Milne Glacier will continue to retreat for at least 50 years, solely in response to ocean forcing. This study highlights the vulnerability of ice structures in the Arctic, even in a region regarded as the Last Ice Area.

The ocean supplies large quantities of thermal energy to tidewater glaciers, but the mechanisms behind the heat delivery are not fully understood. To examine heat flux dynamics in glacial fjords, we run an 8-year realistic numerical simulation of Milne Fiord, validated with observations. We leverage the duration and spatial resolution of the simulation to calculate ice melt, offshore density variations, average fjord temperature, and heat fluxes at different locations along-fjord. Correlations between these quantities reveal that heat fluxes near the grounding line (<5 km) are linked to buoyancy-driven circulation while offshore forcing is linked to heat fluxes along the remainder of the fjord. Comparison to a simulation with constant offshore boundary conditions reveals that offshore forcing enhances the exchange between the coastal shelf and the fjord, increasing glacier melt rates by 18%. Including offshore forcing into numerical and box models of glacial fjords is essential for accurate melting predictions.

The exchange of heat and freshwater between glaciers and the ocean is dictated by the circulation in glacial fjords and ice shelf cavities. Therefore, our ability to estimate and predict these fluxes depends on our understanding of the circulation mechanisms inside these polar estuaries. Here, we use an exceptionally long observational data set (8+ years) to develop and validate a high-resolution realistic numerical model of Milne Fiord (Nunavut, Canada), a glacial fjord with an ice shelf at its mouth. Model results show the circulation inside Milne Fiord from 2011 to 2019 is highly three-dimensional and unsteady. Three distinct circulation modes are identified (eddy, front, barotropic). The shifts between circulation modes are driven by density variations in the offshore coastal current, which restrict vertical stretching, allowing (or not) the coastal current to develop sufficient relative vorticity to enter the fjord. The unsteadiness of the system results in an overturning estuarine circulation with mean velocities similar to 50 times smaller than the instantaneous field. Moreover, analysis of the model outputs suggest that at least 2 years of simulation are needed to yield reliable average heat flux estimates in this environment. This work highlights the value of combining long term (>1 year) observations with numerical modeling. This allowed us to uncover the spatial and temporal variability of the system, which impacts how heat and freshwater fluxes can be reliably estimated.

On 4 August 2014, a tailings dam failure at Mount Polley Mine in central British Columbia led to the largest short‐term release of mine waste into a lake ever recorded. Once released by the breach, slurry entered the smaller of Quesnel Lake’s two basins, called the West Basin, from which the lake drains northwest into the Quesnel River. An estimated 38,000 ± 11,000 tonnes of fine solids remained suspended in the West Basin on 10 September 2014, 37 days postspill. This decreased to within background levels (<300 tonnes) by June 2015, by which time ∼4,000 tonnes of sediment had flowed from the West Basin into the Quesnel River, and ∼31,000 tonnes had been transported east into the main basin, the direction opposed to the mean hydraulic gradient. Here, we evaluate sediment transport in Quesnel Lake following the Mount Polley tailings dam spill. We apply conservation of mass in two ways: using data collected between 12 August 2014 and 15 October 2020 to estimate suspended sediment mass and mass flows into and out of the West Basin; and using one‐ and two‐basin completely mixed models. Suspended sediment concentrations were highly elevated through the first three seasons postspill, then fluctuated within a gradually decreasing, seasonal cycle. The observed mass trend and an analytical mass balance model of a simplified, two‐basin system suggest that suspended sediment mass will fall to below the median prespill mass by 7 ± 5 years postspill.

Failures of mine tailings storage facilities (TSF) can have profound and long-lasting effects on the downstream receiving environment. Virtually all spills to date have been into river systems without large lakes that may buffer downstream impacts. In August 2014, the failure of the Mount Polley copper (Cu)-gold mine TSF in British Columbia, Canada, released ~25 × 106 m3 of water and solids; globally, this is the second largest TSF spill in history. Over 18 × 106 m3 was delivered to Quesnel Lake, which is ~9 km from the TSF and is the third deepest lake in North America, and a crucial habitat for Pacific salmon and trout populations. We determined the sediment-associated Cu concentrations and fluxes in Quesnel River, downstream of the lake, from August 2014 to February 2021 based on the analysis of >400 samples of sediment, mainly collected using a continuous-flow centrifuge. During each winter since the spill, Cu concentrations in the fluvial sediment in the upper reaches of the river (~35 km from the TSF) were elevated relative to regional background concentrations and samples collected before the spill. Maximum Cu concentrations were ~410 mg kg-1 which exceeds Canadian sediment quality guidelines for the protection of aquatic organisms (197 mg kg-1). Monitoring of Quesnel Lake since the spill shows that these annual pulses in the winter are due to resuspension of unconsolidated tailings and sediments at the bottom of Quesnel Lake, during autumnal lake turnover, which become mixed throughout the water column and subsequently flow into Quesnel River. Results show that while large lakes may buffer downstream aquatic systems from contaminated sediment, they may prolong the environmental impact. These findings are crucial in understanding how lake processes may modify the effects of TSF spills on downstream aquatic systems.

Milne Ice Shelf is located at the mouth of Milne Fiord (82.6 degrees N, 81.0 degrees W), on Ellesmere Island, Nunavut. This floating ice feature is attached to both sides of the fjord. During the melt season, the ice shelf acts as a floating barrier preventing surface runoff in Milne Fiord from flowing freely to the ocean. This results in a permanent layer of freshwater that floats on top of the seawater of the fjord, commonly known as an epishelf lake. Few studies address the physical characteristics of epishelf lakes. Here, winter data from a mooring installed in Milne Fiord epishelf lake during 2011-2019 is analyzed in the framework of a one-dimensional model in order to study mixing in the upper water column and infer the characteristics of a basal channel in the ice shelf. The results show that vertical mixing rates are higher in the epishelf lake than in the seawater below. Estimation of the Richardson number using a geostrophic balance approach reveals that enhanced mixing in the epishelf lake is associated with horizontal temperature gradients. In contrast to most studies on basal channels in Greenland and Antarctica, the results presented here show the basal channel of Milne Ice Shelf is apparently not evolving (melting) rapidly.

Strong and sustained winds can drive dramatic hydrodynamic responses in density-stratified lakes, with the associated transport and mixing impacting water quality, ecosystem function, and the stratification itself. Analytical expressions offer insight into the dynamics of stratified lakes during severe wind events. However, it can be difficult to predict the aggregate response of a natural system to the superposition of hydrodynamic phenomena in the presence of complex bathymetry and when forced by variable wind patterns. Using an array of current, temperature, and water quality measurements at the upwind shore, we detail the hydrodynamic response of deep, rotationally influenced Lake Tahoe to three strong wind events during late spring. Sustained southwesterly winds in excess of 10 m s(-1) drove upwelling at the upwind shore (characteristic of non-rotational upwelling setup), with upward excursions of deep water exceeding 70 m for the strongest event. Hypolimnetic water, with elevated concentrations of chlorophyll a and nitrate, was advected toward the nearshore, but this water rapidly returned to depth with the relaxation of upwelling after the winds subsided. The relaxation of upwelling exhibited rotational influence, highlighted by an along-shore, cyclonic front characteristic of a Kelvin wave-driven coastal jet, with velocities exceeding 25 cm s(-1). The rotational front also produced downwelling to 100 m, transporting dissolved oxygen to depth. More complex internal wave features followed the passage of these powerful internal waves. Results emphasize the complexity of these superimposed hydrodynamic phenomena in natural systems, providing a conceptual reference for the role upwelling events may play in lake ecosystems.

Understanding the impact of the break-up of northern Ellesmere Island ice shelves on fjord dynamics is limited by a lack of ocean observations prior to ice loss. Based on profiling and mooring data collected between 2011 and 2019, we describe the oceanography of Milne Fiord prior to the 2020 breakup of the Milne Ice Shelf, including, sources of ambient water, under-ice hydrography, glacial modification, and seasonality. Ambient waters originate in the Canada Basin but are modified by interaction with the 100 m thick ice shelf at the fjord entrance, and extensive glacier tongue at the head. Properties within the 436 m deep fjord are depth-dependent, with freshwater surface runoff and subglacial discharge accumulating in the upper 50 m of the fjord each summer behind the ice shelf. Freshwater export is restricted to a basal channel in the ice shelf, resulting in the fjord being more stratified and warmer than waters offshore year-round. Below the ice shelf and above a 260 m deep sill unrestricted exchange allows warm Atlantic Water to penetrate to the 150 m deep glacier grounding line where submarine melting occurs. Basal meltwater spreads down-fjord close to its depth of origin due to the strong stratification. Interannual warming of fjord deepwater is likely driven by shoaling of the Arctic Ocean thermocline and spillover at the sill, highlighting the link between fjord properties and regional oceanography. Further breakup of the ice shelf is predicted to substantially alter fjord dynamics, with consequences for ocean forcing of the Milne Glacier.

Excitation of basin-scale, internal waves (i.e., internal seiches) in lakes require spatially homogeneous wind fields that vary on time scales comparable to the seiche period, which can be on the order of several days in large lakes. We evaluate 2 years (October 1, 2016 to September 30, 2018) of 15-min wind data from a shore-based meteorological station to identify strong wind episodes likely to excite internal seiches in a large and geometrically complex lake surrounded by convoluted topography, Quesnel Lake, British Columbia, Canada. Our findings include the identification of strong wind event seasonality, with peak mean monthly wind speeds in April and November, and minimum mean monthly wind speeds in August. Using geopotential heights (GPHs) from 1.5 degrees x 1.5 degrees gridded reanalysis data to reconstruct the atmospheric state for each strong wind episode, two primary synoptic patterns are identified that, in conjunction with local topographic channelling, lead to either easterlies or westerlies occurring at our sampling station, with strong easterly episodes three times more frequent than westerly episodes. This highlights the important role that developing low-pressure systems in the Northeastern Pacific Basin have in setting up the GPH gradient required for persistent strong winds at Quesnel Lake, in the hours and days before these storms make landfall. The projection of synoptic patterns of strong wind events onto a 4 x 3 self-organizing map clustered strong wind events by mean wind direction, similar to the results of a manual classification. Methods to identify the strong wind episodes and the resulting self-organizing map are both evaluated in-part by two case studies where strong winds are known to have excited a basin-scale baroclinic response in Quesnel Lake.

The catastrophic August 2014 Mount Polley tailings spill, the second largest ever documented, sent ~18 Mm3 of waste plunging to the bottom of the >100 m deep West Basin of Quesnel Lake, British Columbia, a critical West Coast salmon habitat. To understand the impact of the spill on the lake, including the fate of suspended solids, we examine changes in physical water properties over 11 years (2006–2017) using water column profiles, moored timeseries, and satellite imagery. Contaminated waters were initially largely confined to the hypolimnion; however, during autumn 2014 turnover, turbid waters were mixed to the surface, resulting in the clear blue lake turning bright green. Twelve months after the spill, the lake's temperature, conductivity, and turbidity temporarily returned to pre‐spill conditions; however, initiation of mine effluent discharge in late 2015 was associated with a subsequent 15 μS cm−1 conductivity increase above historic values. Importantly, a post‐spill 1–2.5 formazin turbidity unit hypolimnetic turbidity increase was observed during spring and fall turnovers of 2015–2017, which appeared to be due to resuspension of a thin layer of unconsolidated spill‐related material from the lake bed driven by large internal seiche motions. This process implies spill contaminants may be seasonally mobilized into the water column, with potentially detrimental impacts on aquatic ecology. Our findings underscore that basin‐scale physical processes, including seasonal turnover and internal seiches, must be accounted for, even in deep lakes, to understand the long‐term impact of the ever increasing number of tailings spills into aquatic ecosystems.

We investigate the seasonal evolution of stratification in a deep (100 m), high-altitude (4,730 m a.s.l.) dimictic lake on the Tibetan Plateau using three years of observation of Nam Co. The lake is situated at relatively low latitude (30 degrees N) where it receives high solar radiative forcing (observed maximum daily average 400 W m(-2)), yet the annual average air temperature is close to 0 degrees C at this high altitude. These features make Nam Co distinct from most well-documented dimictic lakes, which are usually located at higher latitude and lower altitude. We classify seasonal stratification into six phases based on strength of stratification, surface temperature relative to the temperature of maximum density, ice-cover, and heat and mixing dynamics, which we use to compare Nam Co with better-documented, higher-latitude dimictic lakes. While the three warm stratification phases (i.e. when water is warmer than the temperature of maximum density) in Nam Co are relatively cold, they are otherwise similar to that observed in high-latitude dimictic lakes. Conversely, two of Nam Co's cold stratification phases are distinct from that reported in high-latitude lakes. These two phases are characterized by the interplay between the relatively strong radiative forcing and surface heat flux, and include the following: 1) during fall turnover, persistent winds aided by radiatively driven convection prolong vertical mixing (i.e. turnover) and surface heat loss such that the entire water column cools well below the temperature of maximum density (as low as 1 degrees C); and 2) in contrast, under ice-cover with relatively little snow, the entire water column of the lake warms continuously due to through-ice solar radiative flux. The intense cooling and heating during these two phases counteract each other such that hypolimnetic temperature at spring turnover is similar to that observed in high latitude lakes. Our observations highlight the relative importance of radiatively driven convection on the seasonal stratification dynamics of Nam Co, and underscore that these dynamics must be considered when attempting to predict climate change impacts on high-altitude, low-latitude lakes, including the > 1100, largely unstudied, lakes on the Tibetan Plateau.

Field data, a three-dimensional hydrodynamic numerical model, and modal decomposition were used to examine the baroclinic response to wind in two interconnected multiarm lakes, Knewstubb and Natalkuz Lakes (British Columbia, Canada). Similar to lakes of simpler geometry, the first-vertical first-horizontal mode (V1H1) of Knewstubb and Natalkuz Lakes was found to be the most energetic mode. This V1H1 dominance is attributed to similarity between the relatively uniform distributions of along-thalweg wind and surface-layer flow for the V1H1 mode. Two bathymetric features, the geometric constriction between Knewstubb and Natalkuz Lakes, and changes in thalweg orientation relative to the wind field act to create subbasins in which wind forcing causes local metalimnetic tilts. These subbasin scale tilts deepen the metalimnion at the downwind ends of the subbasins, raise the metalimnion at the upwind ends, and are superimposed on the lake-wide V1H1 tilt. The metalimnetic tilts in the subbasins are attributed to higher horizontal modes that are equivalent to V1H1 modes of the subbasins. Because the thickness of the metalimnion is significant, the subbasin metalimnetic tilts occur with variations in the metalimnetic thickness along the subbasins; the metalimnion is compressed at the downwind end and expanded at the other end of each subbasin. This variability in thickness leads to metalimnetic intrusions following the relaxation of wind forcing. The findings of this study contribute to characterizing the baroclinic response to wind in lakes of complex bathymetry. In particular, this study helps in understanding the effect of bathymetric features on modal composition of the baroclinic response.

The West Basin of Quesnel Lake (British Columbia, Canada) suffered a catastrophic disturbance event in August 2014 when mine tailings and scoured natural material were deposited into the lake’s West Basin due to an impoundment failure at the adjacent Mount Polley copper-gold mine. The deposit covered a significant portion of the West Basin floor with a thick layer of material. Since lake sediments host bacterial communities that play key roles in the geochemical cycling in lacustrine environments, it is important to understand which groups inhabit the newly deposited material and what this implies for the ecological function of the West Basin. Here we report a study conducted two years post-spill, comparing the bacterial communities from sediments of both disturbed and undisturbed sites. Our results show that sediments from disturbed sites differed in physical and chemical properties than those in undisturbed sites (e.g. higher pH, particle size and Cu concentration). Furthermore, bacterial communities from the disturbed sites appeared to be legacy communities from the tailings impoundment, with metabolic potential revolving mainly around the cycling of S and metals, whereas the ones from the undisturbed sites were associated with the cycling of N.

The effect of multiple arms on standing wave patterns, or seiches, present within a lake is not easy to predict. This study examines free seiche modes in fjord‐type multi‐armed lakes in order to generalize features of the response of those lakes. To do so, the study develops a simplified analytical model that predicts modal frequencies and associated mode‐shapes based on idealized lake geometries. The model demonstrates that multi‐armed lakes are subject to two different types of behavior: a full‐lake response, in which all arms are active for all modes; and a decoupled response, in which seiching is constrained to only two arms of the lake for each mode. Which of the two behaviors is expressed depends on relative values of the travel time of a progressive shallow‐water wave in each arm. In general, a decoupled response will exist if the mode‐shape along a two‐armed extent of the lake contains a node exactly at the confluence point between those two arms. We show that the period and associated mode‐shape structure of the fundamental mode in multi‐armed lakes conforms to that of a simple elongated lake as predicted by Merian's formula, but higher modes are highly impacted by lake geometry. Depth and width variation within the arms can lead to localization of mode‐shapes, but this effect is distinct from the possible decoupled behavior. In some instances, it may be possible to apply the model to baroclinic modes which would then act as having a constant bottom depth equal to the surface layer depth.

Changes in the depth of the freshwater–seawater interface in epishelf lakes have been used to infer long-term changes in the minimum thickness of ice shelves; however, little is known about the dynamics of epishelf lakes and what other factors may influence their depth. Continuous observations collected between 2011 and 2014 in the Milne Fiord epishelf lake, in the Canadian Arctic, showed that the depth of the halocline varied seasonally by up to 3.3 m, which was comparable to interannual variability. The seasonal depth variation was controlled by the magnitude of surface meltwater inflow and the hydraulics of the inferred outflow pathway, a narrow basal channel in the Milne Ice Shelf. When seasonal variation and an episodic mixing of the halocline were accounted for, long-term records of depth indicated there was no significant change in thickness of ice along the basal channel from 1983 to 2004, followed by a period of steady thinning at 0.50 m a−1 between 2004 and 2011. Rapid thinning at 1.15 m a−1 then occurred from 2011 to 2014, corresponding to a period of warming regional air temperatures. Continued warming is expected to lead to the breakup of the ice shelf and the imminent loss of the last known epishelf lake in the Arctic.

Floating ice hazards are a risk to safe navigation in both the Arctic and the Southern Ocean as a result of changing ice conditions and increased marine traffic in recent years. These hazards include icebergs and ice islands (a type of iceberg in the Arctic that is tabular in shape and up to several km in length). Under the influence of climate change, calving (break-off) rates of tidewater glaciers, floating glacier tongues and ice shelves, the source of icebergs and ice islands, appear to be increasing, particularly in the Arctic. Understanding the drift and deterioration of these ice features is a key challenge to the ice community and tends to be limited by a paucity of observational data from around Newfoundland and Labrador, where water temperatures are significantly warmer and interaction with sea ice is less common than in Arctic waters. Observations of drifting ice islands that calved from the Petermann Glacier in NW Greenland were attempted in 2011 in the Canadian High Arctic (69-75oN) to examine draft, surface roughness and basal features using an Autonomous Underwater Vehicle (AUV) to help improve numerical ice hazard drift models. The AUV was successfully deployed under a grounded ice island, yet key challenges for future deployments involve mapping ice that is both drifting and rotating. Acoustic localization, combined with terrain-relative navigation, is proposed to deal with this motion, enabling accurate in situ measurements of the underside and sidewalls of the ice. This data is required to help understand the drift, deterioration and ultimate fate of these ice hazards in a changing global climate.

Below the temperature of maximum density (TMD) in freshwater lakes, heating at the lateral margins produces gravity currents along the bottom slope, akin to katabatic winds in the atmosphere and currents on continental shelves. We describe axisymmetric basin-scale circulation driven by heat flux at the shorelines in polar Lake Kilpisjarvi. A dense underflow originating near the shore converges toward the lake center, where it produces warm upwelling and return flow across the bulk of lake water column. The return flow, being subject to Coriolis force, creates a lake-wide anticyclonic gyre with velocities of 2-4cms(-1). While warm underflows are common on ice-covered lakes, the key finding is the basin-scale anticyclonic gyre with warm upwelling in the core. This circulation mechanism provides a key to understanding transport processes in (semi) enclosed basins subject to negative buoyancy flux due to heating (or cooling at temperatures above TMD) at their lateral boundaries.

Quantitative tools for deciphering the environment of microbialite formation are relatively limited. For example, the oxygen isotope carbonate-water geothermometer requires assumptions about the isotopic composition of the water of formation. We explored the utility of using 'clumped' isotope thermometry as a tool to study the temperatures of microbialite formation. We studied microbialites recovered from water depths of 10-55 m in Pavilion Lake, and 10-25 m in Kelly Lake, spanning the thermocline in both lakes. We determined the temperature of carbonate growth and the (18)O/(16)O ratio of the waters that microbialites grew in. Results were then compared to current limnological data from the lakes to reconstruct the history of microbialite formation. Modern microbialites collected at shallow depths (11.7 m) in both lakes yield clumped isotope-based temperatures of formation that are within error of summer water temperatures, suggesting that clumped isotope analyses may be used to reconstruct past climates and to probe the environments in which microbialites formed. The deepest microbialites (21.7-55 m) were recovered from below the present-day thermoclines in both lakes and yield radioisotope ages indicating they primarily formed earlier in the Holocene. During this time, pollen data and our reconstructed water (18)O/(16)O ratios indicate a period of aridity, with lower lake levels. At present, there is a close association between both photosynthetic and heterotrophic communities, and carbonate precipitation/microbialite formation, with biosignatures of photosynthetic influences on carbonate detected in microbialites from the photic zone and above the thermocline (i.e., depths of generally <20 m). Given the deeper microbialites are receiving <1% of photosynthetically active radiation (PAR), it is likely these microbialites primarily formed when lower lake levels resulted in microbialites being located higher in the photic zone, in warm surface waters.