Canada Basin Research Articles

Application of Parameter Screening to Derive Optimal Initial State Adjustments for Streamflow Forecasting

AbstractStreamflow forecasting is essential in many applications, including the management of hydropower reservoirs and of flood risks. To increase the performance of these hydrologic forecasts, a hydrological model is typically updated with optimal initial model states. These states are usually selected a priori and adjusted to obtain the optimal initial setup. The model states to adjust are generally selected by experts with deep knowledge of the model's behavior. These relationships are rarely documented and formalized, leading to difficulties in reproducibility and transferability to other models. The method here provides a fully automatized system to find the model states based on the parameter‐free sensitivity method of efficient elementary effects (EEE), which identifies the most informative variables of the hydrologic model CEQUEAU. The analysis is applied to 1,826 model setups for four Canadian basins. The identified states are formalized using clustering techniques to obtain adjustment “recipes” conditioned on given meteorological conditions. Several recipes are tested and compared to expert‐based recipes. The recipes are tested according to their ability to (a) obtain optimal initial states and (b) their forecast performance. The results show that (1) the EEE‐based recipes perform similarly or better than the expert‐based recipes in both objectives; (2) the recipes are similar across the four basins, highlighting their potential of spatial transferability; and (3) the adjustment of hydrologic model inputs significantly decreases forecast performance. The proposed approach to use EEE‐based recipes to obtain optimal initial states for forecasting is reproducible, objective, and suitable to be applied to other models and basins.

Interplay between thermal convection and compressional fault reactivation in the formation of unconformity-related uranium deposits

A number of large and high-grade unconformity-related uranium deposits formed in intracratonic Proterozoic basins, including the Athabasca Basin in Canada and the McArthur Basin in Australia. These deposits occur close to the unconformities between the Paleo- to Mesoproterozoic basinal sequences and their Archean to Paleoproterozoic metasedimentary basement, and are spatially associated with reactivated basement faults showing reverse offsets due to contractional deformation. Previous studies have suggested that fluid flow responsible for uranium mineralization in such basins may be related to thermal convection and tectonic deformation; however, the relative roles of these two driving forces, as well as their interrelationships, have not been explored in detail. In this study, two-dimensional numerical modeling of fluid flow in relation to coupled tectonic compression and heat transport was carried out to evaluate the relationships between deformation-driven flow and fluid convection, and their relative importance for uranium mineralization. The results indicate that tectonic compression at a relatively high strain rate (6.66 × 10−11 s−1) may instantaneously destroy pre-existing thermal convection developed in the sedimentary rocks in the basin, due to the rapid development of overpressure in the system. Convection may then reappear over time as deformation progresses and the overpressure wanes. By contrast, tectonic compression at a relatively low strain rate (6.66 × 10−13 s−1) does not affect pre-existing thermal convection, and deformation-driven fluid flow in the basement coexists with thermal convection in the basin. It is proposed that during an overall tectonically active period associated with a far-field tectonic event, compressional reactivation of basement faults creates permeability and causes fluid to flow toward dilatant zones accompanying individual seismic events, whereas during seismically quiet times, fluid flow driven by thermal convection dominates. The formation of the unconformity-related uranium deposits likely involves alternating relatively short-lived, deformation-driven fluid flow and relatively prolonged fluid convection events.

Potential Vorticity Dynamics of the Arctic Halocline

AbstractAn idealized two-layer shallow water model is applied to the study of the dynamics of the Arctic Ocean halocline. The model is forced by a surface stress distribution reflective of the observed wind stress pattern and ice motion and by an inflow representing the flow of Pacific Water through Bering Strait. The model reproduces the main elements of the halocline circulation: an anticyclonic Beaufort Gyre in the western basin (representing the Canada Basin), a cyclonic circulation in the eastern basin (representing the Eurasian Basin), and a Transpolar Drift between the two gyres directed from the upwind side of the basin to the downwind side of the basin. Analysis of the potential vorticity budget shows a basin-averaged balance primarily between potential vorticity input at the surface and dissipation at the lateral boundaries. However, advection is a leading-order term not only within the anticyclonic and cyclonic gyres but also between the gyres. This means that the eastern and western basins are dynamically connected through the advection of potential vorticity. Both eddy and mean fluxes play a role in connecting the regions of potential vorticity input at the surface with the opposite gyre and with the viscous boundary layers. These conclusions are based on a series of model runs in which forcing, topography, straits, and the Coriolis parameter were varied.

Laramide Orogenesis Driven by Late Cretaceous Weakening of the North American Lithosphere

AbstractThis paper investigates the causes of the Late Cretaceous transition from “Sevier” to “Laramide” orogenesis and the spatial and temporal evolution of effective elastic thickness (EET) of the North American lithosphere. We use a Monte Carlo flexural model applied to 34 stratigraphic profiles in the Laramide province and five profiles from the Western Canadian Basin to estimate model parameters which produce flexural profiles that match observed sedimentary thicknesses. Sediment thicknesses come from basins from New Mexico to Canada of Cenomanian–Eocene age that are related to both Sevier and Laramide crustal loads. Flexural models reveal an east‐to‐west spatial decrease in EET in all time intervals analyzed. This spatial decrease in EET may have been associated with either bending stresses associated with the Sevier thrust belt, or increased proximity to attenuated continental crust at the paleocontinental margin. In the Laramide province (i.e., south of ~48°N) there was a coeval, regional decrease in EET between the Cenomanian–Santonian (~98–84 Ma) and the Campanian–Maastrichtian (~77–66 Ma), followed by a minor decrease between the Maastrichtian and Paleogene. However, there was no decrease in EET in the Western Canada Basin (north of ~48°N), which is consistent with a lack of Laramide‐style deformation or flat subduction. We conclude that the regional lithospheric weakening in the late Santonian–Campanian is best explained by hydration of the North American lithosphere thinned by bulldozing by a shallowly subducting Farallon plate. The weakening of the lithosphere facilitated Laramide contractional deformation by focusing end‐loading stresses associated with flat subduction. Laramide deformation in turn may have further reduced EET by weakening the upper crust. Finally, estimates of Campanian–Maastrichtian and Paleogene EET are comparable to current estimates indicating that the modern distribution of lithospheric strength was achieved by the Campanian in response to flat subduction.

The Atlantic Water Boundary Current in the Chukchi Borderland and Southern Canada Basin

AbstractSynoptic shipboard measurements, together with historical hydrographic data and satellite data, are used to elucidate the detailed structure of the Atlantic Water (AW) boundary current system in the southern Canada Basin and its connection to the upstream source of AW in the Chukchi Borderland. Nine high‐resolution occupations of a transect extending from the Beaufort shelf to the deep basin near 152°W, taken between 2003 and 2018, reveal that there are two branches of the AW boundary current that flow beneath and counter to the Beaufort Gyre. Each branch corresponds to a warm temperature core and transports comparable amounts of Fram Strait Branch Water between roughly 200–700 m depth, although they are characterized by a different temperature/salinity (T/S) structure. The mean volume flux of the combined branches is 0.87 ± 0.13 Sv. Using the historical hydrographic data, the two branches are tracked upstream by their temperature cores and T/S signatures. This sheds new light on how the AW negotiates the Chukchi Borderland and why two branches emerge from this region. Lastly, the propagation of warm temperature anomalies through the region is quantified and shown to be consistent with the deduced circulation scheme.

The recent state and variability of the carbonate system of the Canadian Arctic Archipelago and adjacent basins in the context of ocean acidification

Abstract. Ocean acidification driven by the uptake of anthropogenic CO2 by the surface oceans constitutes a potential threat to the health of marine ecosystems around the globe. The Arctic Ocean is particularly vulnerable to acidification and thus is an ideal region to study the progression and effects of acidification before they become globally widespread. The appearance of undersaturated surface waters with respect to the carbonate mineral aragonite (ΩA<1), an important threshold beyond which the calcification and growth of some marine organisms might be hindered, has recently been documented in the Canada Basin and adjacent Canadian Arctic Archipelago (CAA), a dynamic region with an inherently strong variability in biogeochemical processes. Nonetheless, few of these observations were made in the last 5 years and the spatial coverage in the latter region is poor. We use a dataset of carbonate system parameters measured in the CAA and its adjacent basins (Canada Basin and Baffin Bay) from 2003 to 2016 to describe the recent state of these parameters across the Canadian Arctic and investigate the amplitude and sources of the system's variability over more than a decade. Our findings reveal that, in the summers of 2014 to 2016, the ocean surface across our study area served as a net CO2 sink and was partly undersaturated with respect to aragonite in the Canada Basin and the Queen Maud Gulf, the latter region exhibiting undersaturation over its entire water column at some locations. We estimate, using measurements made across several years, that approximately a third of the interannual variability in surface dissolved inorganic carbon (DIC) concentrations in the CAA results from fluctuations in biological activity. In consideration of the system's variability resulting from these fluctuations, we derive times of emergence of the anthropogenic ocean acidification signal for carbonate system parameters in the study area.

Eddy Kinetic Energy in the Arctic Ocean From a Global Simulation With a 1‐km Arctic

AbstractSimulating Arctic Ocean mesoscale eddies in ocean circulation models presents a great challenge because of their small size. This study employs an unstructured‐mesh ocean‐sea ice model to conduct a decadal‐scale global simulation with a 1‐km Arctic. It provides a basinwide overview of Arctic eddy energetics. Increasing model resolution from 4 to 1 km increases Arctic eddy kinetic energy (EKE) and total kinetic energy (TKE) by about 40% and 15%, respectively. EKE is the highest along main currents over topography slopes, where strong conversion from available potential energy to EKE takes place. It is high in halocline with a maximum typically centered in the depth range of 70–110 m, and in the Atlantic Water layer of the Eurasian Basin as well. The seasonal variability of EKE along the continental slopes of southern Canada and eastern Eurasian basins is similar, stronger in fall and weaker in spring.

Circulation in the vicinity of Mackenzie Canyon from a year-long mooring array

Data from a five-mooring array extending from the inner shelf to the continental slope in the vicinity of Mackenzie Canyon, Beaufort Sea are analyzed to elucidate the components of the boundary current system and their variability. The array, part of the Marine Arctic Ecosystem Study (MARES), was deployed from October 2016 to September 2017. Four distinct currents were identified: an eastward-directed flow adjacent to the coast; a westward-flowing, surface-intensified current centered on the outer-shelf; a bottom-intensified shelfbreak jet flowing to the east; and a recirculation at the base of the continental slope within the canyon. The shelf current transports −0.12±0.03 Sv in the mean and is primarily wind-driven. The response is modulated by the presence of ice, with little-to-no signal during periods of nearly-immobile ice cover and maximum response when there is partial ice cover. The shelfbreak jet transports 0.03±0.02 Sv in the mean, compared to 0.08±0.02 Sv measured upstream in the Alaskan Beaufort Sea over the same time period. The loss of transport is consistent with a previous energetics analysis and the lack of Pacific-origin summer water downstream. The recirculation in the canyon appears to be the result of local dynamics whereby a portion of the westward-flowing southern limb of the Beaufort Gyre is diverted up the canyon across isobaths. This interpretation is supported by the fact that the low-frequency variability of the recirculation is correlated with the wind-stress curl in the Canada Basin, which drives the Beaufort gyre.

Borealization of the Arctic Ocean in Response to Anomalous Advection From Sub-Arctic Seas

An important yet still not well documented aspect of recent changes in the Arctic Ocean is associated with the advection of anomalous sub-Arctic Atlantic- and Pacific-origin waters and biota into the polar basins, a process which we refer to as borealization. Using a 37-year archive of observations (1981–2017) we demonstrate dramatically contrasting regional responses to atlantification (that part of borealization related to progression of anomalies from the Atlantic sector of sub-Arctic seas into the Arctic Ocean) and pacification (the counterpart of atlantification associated with influx of anomalous Pacific waters). Particularly, we show strong salinification of the upper Eurasian Basin since 2000, with attendant reductions in stratification, and potentially altered nutrient fluxes and primary production. These changes are closely related to upstream conditions. In contrast, pacification is strongly manifested in the Amerasian Basin by the anomalous influx of Pacific waters, creating conditions favorable for increased heat and freshwater content in the Beaufort Gyre halocline and expansion of Pacific species into the Arctic interior. Here, changes in the upper (overlying) layers are driven by local Arctic atmospheric processes resulting in stronger wind/ice/ocean coupling, increased convergence within the Beaufort Gyre, a thickening of the fresh surface layer, and a deepening of the nutricline and deep chlorophyll maximum. Thus, a divergent (Eurasian Basin) gyre responds altogether differently than does a convergent (Amerasian Basin) gyre to climate forcing. Available geochemical data indicate a general decrease in nutrient concentrations Arctic-wide, except in the northern portions of the Makarov and Amundsen Basins and northern Chukchi Sea and Canada Basin. Thus, changes in the circulation pathways of specific water masses, as well as the utilization of nutrients in upstream regions, may control the availability of nutrients in the Arctic Ocean. Model-based evaluation of the trajectory of the Arctic climate system into the future suggests that Arctic borealization will continue under scenarios of global warming. Results from this synthesis further our understanding of the Arctic Ocean’s complex and sometimes non-intuitive Arctic response to climate forcing by identifying new feedbacks in the atmosphere-ice-ocean system in which borealization plays a key role.

Nutrient‐Rich Gravity Current Formed by Upwelling in Barrow Canyon: High‐Resolution Observations

AbstractThe distribution of nutrients influences the Chukchi Sea's rich ecosystems and affectsthe biogeochemistry of the central Arctic. Nutrients that become limiting in the late summer can be replenished episodically by physical processes that are likely to change in concert with Arctic climate trends. Here we report on unique, simultaneous, physical, and biogeochemical measurements of one such process: upwelling in Barrow Canyon. High‐resolution transects of a towed vehicle, which was equipped with physical, turbulence, and biogeochemical sensors, captured the upwelling of dense, salty, and nitrate‐rich waters into the shallow regions of Barrow Canyon. Upwelling drastically modifies the nitrate distribution of Barrow Canyon through the vertical advection of Atlantic Water from the Canada Basin and through turbulent flux across the nutricline. Upwelled waters form a highly sheared gravity current that is susceptible to both baroclinic and symmetric instabilities. The current exhibits transverse circulation common to frictional gravity currents. Our observations suggest that rapid and dramatic nutrient changes in Barrow Canyon can be accomplished by upwelling; the subsequent formation of unstable jets and fronts enhances the irreversible flux of upwelled nutrients to less dense waters in the Chukchi sea.

Review of spatial and inter-annual changes in the zooplankton community structure in the western Arctic Ocean during summers of 2008–2017

Reduction in summer sea ice coverage has recently been observed in the western Arctic Ocean. Changes in the coverage and timing of sea ice retreat are expected to have a great impact on the marine ecosystem. In this study, we evaluated inter-annual changes in the spatial distribution of zooplankton communities in the western Arctic Ocean, during the summers of 2008, 2010, 2012–2017. A total of 339 casts were conducted to collect zooplankton by vertical hauls at 22–63 stations per year in the western Arctic Ocean, between August 26 and October 13, 2008, 2010, 2012–2017. Based on cluster analysis, four zooplankton communities (basin, slope, shelf, and new-shelf) were identified. Horizontal distribution of the zooplankton communities corresponded with the depth of the sea floor. No significant interannual variability in zooplankton and copepod abundance was observed in the Canada basin; however, a decline in the abundance of dominant copepods associated with an enhanced freshening of seawater was suggested by a General Linear Model analysis. The shelf assemblage was characterized by a high abundance of Pacific species that was predicted by the length of the open water period. The new-shelf assemblage, located between the shelf and the slope, showed low species diversity and abundance and was observed only in 2012, 2015, 2016 and 2017 when the melting day of sea ice was significantly earlier than in the other years. Our study indicates that different changes in each region can be expected in response to the possible environmental changes in the Pacific Arctic.

Sea-ice loss amplifies summertime decadal CO2 increase in the western Arctic Ocean

Rapid climate warming and sea-ice loss have induced major changes in the sea surface partial pressure of CO2 ($$p_{{\mathrm {CO}}_2}$$). However, the long-term trends in the western Arctic Ocean are unknown. Here we show that in 1994–2017, summer $$p_{{\mathrm {CO}}_2}$$ in the Canada Basin increased at twice the rate of atmospheric increase. Warming and ice loss in the basin have strengthened the $$p_{{\mathrm {CO}}_2}$$ seasonal amplitude, resulting in the rapid decadal increase. Consequently, the summer air–sea CO2 gradient has reduced rapidly, and may become near zero within two decades. In contrast, there was no significant $$p_{{\mathrm {CO}}_2}$$ increase on the Chukchi Shelf, where strong and increasing biological uptake has held $$p_{{\mathrm {CO}}_2}$$ low, and thus the CO2 sink has increased and may increase further due to the atmospheric CO2 increase. Our findings elucidate the contrasting physical and biological drivers controlling sea surface $$p_{{\mathrm {CO}}_2}$$ variations and trends in response to climate change in the Arctic Ocean. Surface CO2 concentrations in the western Arctic Ocean differ due to local processes. During the period 1994–2017, the Canada Basin has shown rapid increases as warming and ice loss enhance air–sea exchange of CO2, whereas the Chukchi Shelf has strong biological activity, resulting in a CO2 sink.

Changes in the Arctic Ocean Carbon Cycle With Diminishing Ice Cover.

Less than three decades ago only a small fraction of the Arctic Ocean (AO) was ice free and then only for short periods. The ice cover kept sea surface pCO2 at levels lower relative to other ocean basins that have been exposed year round to ever increasing atmospheric levels. In this study, we evaluate sea surface pCO2 measurements collected over a 6‐year period along a fixed cruise track in the Canada Basin. The measurements show that mean pCO2 levels are significantly higher during low ice years. The pCO2 increase is likely driven by ocean surface heating and uptake of atmospheric CO2 with large interannual variability in the contributions of these processes. These findings suggest that increased ice‐free periods will further increase sea surface pCO2, reducing the Canada Basin's current role as a net sink of atmospheric CO2.

Ventilation in the Arctic Ocean and the Role of Pacific Inflow Deduced From Transient Tracer Measurements

AbstractDuring the seventh Chinese National Arctic Research Expedition, measurements of CFC‐12 and SF6 were used to estimate ventilation time scales and anthropogenic CO2 (Cant) concentrations in the Arctic Ocean and Bering Sea based on the transit time distribution (TTD) method. The profile distribution showed that there was a high CFC tongue entering through the Canada Basin in the intermediate layer (27.6 kg m−3 < σθ < 28 kg m−3), at latitudes between 75 and 85°N, related to the inflow of Atlantic water. The result shows that both intermediate and deep/bottom waters are better ventilated in the Arctic Ocean than in the Bering Sea. The mean age gradient of the Bering Sea Surface Water and Pacific water core of the southwest Canada Basin (24.7 < σθ < 26.2) could be a consequence of intensive mixing and entrainment of the inflow water from the Bering Sea. An expected difference in age between these areas was interpreted to reflect the transit time for the given water layers. Thus, a mean transit time from the Bering Sea (175.2–179.9°E, 59.7–61.6°N) to the western Arctic Ocean (151.6–158°W, 73.1–74.8°N) of 14.6 ± 4.6 years was estimated. The mean Cant column inventory in the upper 2,000 m was higher (~45 mol m−2) in the Arctic Ocean than in the Bering Sea (~25 mol m−2).

Isolating different natural and anthropogenic PAHs in the sediments from the northern Bering-Chukchi margin: Implications for transport processes in a warming Arctic

Polycyclic aromatic hydrocarbons (PAHs) have become the dominating burden in the Arctic ecosystems, but their transport pathways and relative importance of different sources in the Arctic remained unclear, and this would be further complicated by climate change. Here we interpreted 27 PAHs in 34 surface sediments from the northern Bering-Chukchi margin. We integrated source apportionment methods (including diagnostic ratios, principal component analysis, hierarchical analysis, and positive matrix factorization (PMF) model) together with geochemistry parameters, which reveal a gradually clear picture of the spatial patterns of different sources. The total PAH concentrations (50.4 to 896.0 ng/g dw) exhibited a “hilly” shape with the increase of latitude, showing the highest level of PAHs in the northeast Chukchi Sea. The total BaP toxic equivalent quotient (TEQ) for carcinogenic compounds was from 1.06 to 33.3 ng TEQ/g. Most PAHs showed positive correlations with silt content, total organic carbon, stable carbon isotopes and black carbon (p < 0.01 or 0.05). Generally, source apportionment methods revealed an increasing petrogenic source of PAHs with latitudes. The PMF model further differentiated two petrogenic (36.7%), two pyrogenic (softwood and fossil fuel combustion, 35.5%) and one in-situ biogenic source (Perylene, 27.8%). An extremely high petrogenic signal was captured in the Canada Basin margin, possibly originating from the Mackenzie River via ice drifting with Beaufort Gyre, while another petrogenic source may come from coal deposit erosion by deglaciation. Softwood combustion (characterized by Retene) exhibited exclusively higher contribution in the northeast Chukchi Sea and might result from the increasing wildfire in Alaska due to climate change, whereas fossil fuel combustion exhibited similar contributions across different latitudes. Our results revealed natural PAHs as important “inside sources” in the Arctic, which are highly sensitive to global warming and deserves more attention.

Long-term variations of river ice breakup timing across Canada and its response to climate change

River ice breakup has extensive implications on cold-region hydrological, ecological and river morphological systems. However, spatial and temporal breakup patterns under the changing climate are not well explored on large scale. This study discusses the spatial-temporal variations of breakup timing over terrestrial ecozones and five selected river basins of Canada based on long-term (1950–2016) data record. The link between the discovered patterns and climatic drivers (including air temperature, snowfall and rainfall), as well as elevation and anthropogenic activities are analyzed. An overall earlier breakup trend is observed across Canada and the spring air temperature is found to be the main driver behind it. However, the most pronounced warming trends across Canada is observed in winter. Spring warming trend is not as strong as winter warming and even becomes weak as period changes from 1950–2016 to 1970–2016, resulting in more stations showing later and significant later breakup during 1970–2016. Breakup pattern also displays evident spatial differences. Significant earlier breakup trends are mainly seen in western Canada (e.g. the Nelson River basin) and Arctic where spring warming trends are evident. Later and mixed breakup trends are generally identified in regions with weak warming or even cooling trends, such as Atlantic Canada and the St. Lawrence River basin. Spring snowfall generally delays breakup. Spring rainfall usually advances breakup dates while winter-rainfall can also delay breakup through refreezing. The increased snowfall in the north and increased rainfall in the south may be the reason why breakup timing is more sensitive to climatic warming in lower latitude regions than in higher latitude regions. Additionally, breakup timing in main streams and large rivers appears to be less sensitive to the warming trend than the headwaters and small tributaries. Elevation and flow regulation are also found to be contributing factors to the changes in breakup timing.

Replication of the Arctic Ocean surface layer with horizontal variations using a box model implemented with a probability distribution function (PDF)

The 200 m-thick surface layer of the Arctic Ocean contains a lower salinity part in the Canadian Basin, receiving fresher water from the Pacific Ocean as well as rivers, and also a higher salinity part in the Eurasian Basin, receiving saltier water from the Greenland Sea. This surface layer receives atmospheric forcing, and also partially mixes with the subsurface layer. Thus, thermohaline circulation is a fundamental pattern, under the influences of mesoscale features (∼10 km) and small-scale plumes (∼1 km).The one-box model of the surface layer possesses a salinity-driven state, and also a convected state with the subsurface layer as another solution. The new modeling is proposed with a probability distribution function (PDF) on the temperature–salinity (T–S) plane, which can represent horizontal gradients and small scale features as well. The T–S distribution retains only the probabilities of different water types, while their locations are discarded. Time progressions of the PDF are calculated with mechanisms of box-mean progression, heterogeneity generation, horizontal mixing in the box and convection with the subsurface layer. As either the subsurface layer becomes fresher, or the heterogeneity is intensified, the solution near the salinity-driven state increases convection, shifting toward the convected state. The additional PDF box model is made for the Eurasian Basin, which receives fresher water from the Canadian Basin instead of the Pacific Ocean, and provides a more restricted solution with convection, mainly controlled by the fresher subsurface layer.The original PDF box model of the entire Arctic Ocean is extended to the wider horizontal variability case: i.e., the inflow from the Greenland Sea is distributed over the higher salinity portion only, and then, the lower salinity water from the Pacific Ocean is supplied to a particular T–S point, (Tp, Sp), mixing within the lower salinity portion only. The low salinity core is retained near (Tp, Sp), even though convection develops in the higher salinity portion. Thus, this advanced PDF box model is a useful tool to judge a high resolution basin-scale circulation model, whether small-scale plumes and mesoscale features play an important role on thermohaline circulation or not.

Forecast of streamflows to the Arctic Ocean by a Bayesian neural network model with snowcover and climate inputs

Abstract Increasing water flowing into the Arctic Ocean affects oceanic freshwater balance, which may lead to the thermohaline circulation collapse and unpredictable climatic conditions if freshwater inputs continue to increase. Despite the crucial role of ocean inflow in the climate system, less is known about its predictability, variability, and connectivity to cryospheric and climatic patterns on different time scales. In this study, multi-scale variation modes were decomposed from observed daily and monthly snowcover and river flows to improve the predictability of Arctic Ocean inflows from the Mackenzie River Basin in Canada. Two multi-linear regression and Bayesian neural network models were used with different combinations of remotely sensed snowcover, in-situ inflow observations, and climatic teleconnection patterns as predictors. The results showed that daily and monthly ocean inflows are associated positively with decadal snowcover fluctuations and negatively with interannual snowcover fluctuations. Interannual snowcover and antecedent flow oscillations have a more important role in describing the variability of ocean inflows than seasonal snowmelt and large-scale climatic teleconnection. Both models forecasted inflows seven months in advance with a Nash–Sutcliffe efficiency score of ≈0.8. The proposed methodology can be used to assess the variability of the freshwater input to northern oceans, affecting thermohaline and atmospheric circulations.

Dissolved iron and manganese in the Canadian Arctic Ocean: On the biogeochemical processes controlling their distributions

Dissolved iron (DFe) and manganese (DMn) are essential micronutrients involved in vital phytoplankton physiological pathways, and their deficit can limit primary production in otherwise nutrient-replete surface ocean waters. In this work we present the spatial distributions and biogeochemical cycling of these metals across the Canadian GEOTRACES transect in the Canadian Arctic Ocean during the summer and autumn of 2015. Surface concentrations are dominated by freshwater inputs showing a strong negative correlation with salinity, especially for DMn which behaves more conservatively than DFe. The highest surface concentrations were measured in the Canadian Arctic Archipelago (Fe: 0.401–1.91 and Mn: 4.33–9.54 nmol kg−1) and the Canada Basin (Fe: 0.225–0.479 and Mn: 3.93–7.02 nmol kg−1), regions highly influenced by riverine inputs, whereas the lowest values were found in the Labrador Sea (Fe: 0.106–0.362 and Mn: 0.450–1.09 nmol kg−1) where freshwater inputs diminished and phytoplankton uptake increased. Subsurface and deep water distributions for both metals are largely controlled by a complex balance between sources (advective inputs and organic matter remineralization) and removal processes. The subsurface peaks (∼100–300 m) observed in the Canada Basin (Fe: 0.541 ± 0.060 and Mn: 1.38 ± 0.42 nmol kg−1) and Baffin Bay (Fe: 0.753–1.03 nmol kg−1) were advected from the Chukchi Sea and the Canadian Arctic Archipelago respectively, where DFe and DMn are released from the benthic boundary layer in these shelf-dominated environments. Advective sources associated with the Arctic Circumpolar Boundary Current, rather than vertical fluxes of DFe and DMn in sinking particles, dominate metal distributions in the deep Canada Basin waters (>300 m). In the highly productive Baffin Bay and the Labrador Sea, organic matter remineralization is a notable source of DFe and DMn to deep waters. In the deepest waters (>1000 m), scavenging of DFe and DMn govern their vertical distributions; a pseudo-first order scavenging model explained the continuous removal of DMn in the Canada Basin, where the concentrations reach uniformly low concentrations (0.150 ± 0.004 nmol kg−1) after ∼400 years. Applying this DMn scavenging model we were able to estimate the age (120–190 years) of deep Baffin Bay waters, a topic of discussion for many years.

The economic impacts of water supply restrictions due to climate and policy change: A transboundary river basin supply-side input-output analysis

Finding sustainable pathways to efficiently allocate limited available water resources among increasingly competing water uses has become crucial due to climate-change-induced water shortages and increasing water demand. This has led to an urgent need for the inclusion of economic principles, models, and methods in water resources management. Although several studies have developed macro-economic models to evaluate the economic impacts of alternative water allocation strategies, many if not most ignore the hydrological boundaries of transboundary river basins. Furthermore, of those using input-output (IO) models, only a handful have applied supply-side IO models. In this paper, we present one of the first attempts to develop an inter-regional, supply-side IO modelling framework for a multi-jurisdictional, transboundary river basin to assess the direct and indirect economic impacts of water supply restrictions due to climate and policy change. Applying this framework to the Saskatchewan River Basin in Canada encompassing three provinces, we investigate the economic impacts of two different water supply restriction scenarios on the entire river basin and its sub-basins individually. We find that in the face of climate-change-induced water shortage, economic losses can be reduced by almost 50% by adopting appropriate management practices, including prioritization of water allocation, using alternative water sources, and water re-use technologies.