•Evapotranspiration (ET) increased largely across the Pan-Arctic during 1981–2020.•Permafrost-dominated basins showed faster increases in ET than those with less permafrost.•Permafrost thawing may ...contribute to increased evapotranspiration.
Land evapotranspiration (ET) is a key factor in the hydrological cycle and is particularly sensitive to climate change. In the past few decades, the Pan-Arctic region has witnessed a strong warming trend, causing substantial changes in ground surface conditions. However, it remains poorly understood how ET varies across such a region. Here, we investigated the spatial–temporal changes in ET over six large Pan-Arctic river basins using corrected ET estimates from GLEAM and ERA5-Land during 1981–2020. The 40-year mean annual ET in the Ob, Yenisei, Lena, Kolyma, Yukon, and Mackenzie River basins were approximately 366 mm·yr−1, 271 mm·yr−1, 228 mm·yr−1, 239 mm·yr−1, 278 mm·yr−1, and 295 mm·yr−1, respectively. Climatologically, permafrost-dominated basins tend to have lower ET than those with less permafrost. Temporally, the annual ET in permafrost-dominated basins has increased faster than that in less permafrost-developed basins over the past four decades. This increase is particularly prominent in the Kolyma River basin (completely covered by permafrost), where the significant trend in ET (7.5 mm·decade−1, p < 0.001) is the highest among the six basins. Further analyses show that intensified permafrost thawing is likely the key factor contributing to increased ET in permafrost-dominated basins, as seen from the positive relationship between the thickening in the active layer (ALT) and the change in ET. Under an amplified warming background, ET in permafrost-dominated regions is expected to continue to increase. The results reported in this study improve our understanding of the variations in ET and the associated mechanisms in the changing Arctic.
Recent advances in remote sensing and the upcoming launch of the joint NASA/CNES/CSA/UKSA Surface Water and Ocean Topography (SWOT) satellite point toward improved river discharge estimates in ...ungauged basins. Existing discharge methods rely on “prior river knowledge” to infer parameters not directly measured from space. Here, we show that discharge estimation is improved by classifying and parameterizing rivers based on their unique geomorphology and hydraulics. Using over 370,000 in situ hydraulic observations as training data, we test unsupervised learning and an “expert” method to assign these hydraulics and geomorphology to rivers via remote sensing. This intervention, along with updates to model physics, constitutes a new method we term “geoBAM,” an update of the Bayesian At‐many‐stations hydraulic geometry‐Manning's (BAM) algorithm. We tested geoBAM on Landsat imagery over more than 7,500 rivers (108 are gauged) in Canada's Mackenzie River basin and on simulated hydraulic data for 19 rivers that mimic SWOT observations without measurement error. geoBAM yielded considerable improvement over BAM, improving the median Nash‐Sutcliffe efficiency (NSE) for the Mackenzie River from −0.05 to 0.26 and from 0.16 to 0.46 for the SWOT rivers. Further, NSE improved by at least 0.10 in 78/108 gauged Mackenzie rivers and 8/19 SWOT rivers. We attribute geoBAM improvement to parameterizing rivers by type rather than globally, but prediction accuracy worsens if parameters are misassigned. This method is easily mapped to rivers at the global scale and paves the way for improving future discharge estimates, especially when coupled with hydrologic models.
Key Points
We introduce geoBAM, an improved version of a remote sensing of river discharge algorithm (BAM)
geoBAM is tested successfully on over 7,500 river reaches in the Canadian Arctic and on a suite of simulated SWOT observations
Discharge estimation accuracy is improved by using river‐specific prior information informed by classification of a large field data set
•Climate change can impact the Arctic transportation network of Mackenzie River Basin.•Investigate impact by driving a hydrologic model with downscaled RCP climate scenarios.•Navigation problems at ...Mackenzie due to projected lower water levels would increase.
Potential impact of climate change on the inland waterway transport of the Mackenzie River Basin (MRB) have been investigated through simulations of the Hydrologiske Byrån avdeling för Vattenbalans (HBV) hydrological model, the HBV-light, for the baseline, 1974–2004, and future periods of 2041–2070 and 2071–2100 over the MRB driven by precipitation and air temperature data of Representative Concentration Pathways, RCP4.5 and RCP8.5 climate scenarios of 10 Global Climate Models statistically downscaled by the Pacific Climate Impacts Consortium using the Bias-Correction Spatial Disaggregation. The average onset of spring snowmelt between 2041 and 2100 is projected to occur up to two weeks earlier than the historical (1974–2004) climate. Projected warmer temperature and higher precipitation will lead to higher runoff for MRB in winter and spring, at the expense of decreased summer streamflow and water level at Fort Simpson and Arctic Red River stations partly because projected increase in evapotranspiration will offset the projected increase in precipitation. Under a warmer climate, navigation issues related to low water levels are expected to increase, e.g., under RCP8.5 at Arctic Red River station, the number of days the water level above 5 m is projected to decrease from 74 days in 1974–2000 to 42 days in the 2080s. The summer durations that water levels of MRB will be at or above 3, 4, and 5 m are projected to decrease by 2.8%–22.2%, 10.0%–34.5%, and 16.2%–43.4%, respectively, which mean navigation problems would increase because safe transit through MRB depends on its water levels.
The Mackenzie River Basin (MRB) delivers large quantities of organic carbon (OC) into the Arctic Ocean, with significant implications for the global C budgets and ocean biogeochemistry. The amount ...and properties of OC in the Mackenzie River's delta have been well monitored in the last decade, but the spatial variability in OC sources transported by its different tributaries is still unclear. Here we present new data on the radiocarbon (C-14) content of dissolved and particulate OC (Delta C-14-DOC and Delta C-14-POC) across the mainstem and major tributaries of the MRB, comprising 19 different locations, to identify factors controlling spatial patterns in riverine OC sources. The Delta C-14-DOC and Delta C-14-POC varied across a large range, from -179.9 parts per thousand to 62.9 parts per thousand, and -728.8 parts per thousand to -9.0 parts per thousand, respectively. Our data reveal a positive spatial coupling between the Delta C-14 of DOC and POC across the MRB, whereby the most C-14-depleted waters were issued from the mountainous west bank of the MRB. This C-14-depleted DOC and POC likely originates from a combination of petrogenic sources, connected with the presence of kerogens in the bedrock, and biogenic sources, mobilized by thawing permafrost. Our analysis also reveals intriguing relationships between Delta C-14 of DOC and POC with turbidity, water stable isotope ratio and catchment elevation, indicating that hydrology and geomorphology are key to understanding riverine OC sources in this landscape. A closer examination of the specific mechanisms giving rise to these relationships is recommended. For now, this study provides a road map of the key OC sources in this rapidly changing river basin.
Variations in water levels of seasonally ice-covered subarctic lakes are indicators of environmental and climatic change. Satellite altimetry enables remote sensing of these lakes, but the lake ...phenology is problematic as radar reflection surfaces include water, snow, and ice. Reflection from multiple surfaces gives rise to two-peak waveforms across ice-covered lakes. Misinterpretation of the altimetric height has caused extracted water levels to be low compared with gauge data. In this study, a modified retracker is used to determine heights from the first altimetric subwaveform. Using in situ snow depth and ice thickness, the first reflection surface is shown to correspond closely to the snow/ice interface when the lake is frozen. The modified retracker is applied to the Great Bear Lake (GBL), Great Slave Lake (GSL), and Lake Athabasca (ATL) of the Mackenzie River Basin for the period 1992-2020. Standard deviations (Std) of differences between lake levels from Jason-2 waveforms and in situ data across GBL and GSL are 0.06 m with the new methodology compared with 0.11 and 0.08 m, respectively, using the standard Ice retracker. With an Std of 0.11 m between altimetric and gauge lake levels, TOPEX/Poseidon is less accurate than the combined Jason missions (Std: 0.07 m).
The effects of recent climate change are accelerating permafrost thaw, including ice‐rich landscapes of the western Canadian Arctic. However, regional drivers of permafrost slope failure in ...hillslopes with warm, thin permafrost remain poorly understood. Repeat satellite imagery (1984–2020) indicates rapid increases in retrogressive thaw slumps (RTSs) and deep‐seated permafrost landslides (DSPLs) since 2004, indicating a change in slope stability thresholds in an area that otherwise appeared thaw stable. The widespread occurrence of DSPL represents a contrasting geomorphic response to the RTS‐dominated ice‐rich permafrost landscapes. In this study area, RTS and DSPL occur predominantly in areas that were burned by forest fires in the 1990s, indicating a legacy thermal disturbance that preconditioned permafrost hillslopes for failure. The relations between historic fires and the later development of widespread permafrost slope failures represent an outstanding example of the complex interactions between inherited landscape sensitivity in ice‐rich terrain and ongoing climate change.
Plain Language Summary
We characterize the type and nature of permafrost slope failures in the central Mackenzie Valley, NWT and find hillslope failures have increased rapidly over the past ∼15 years. This growth occurred in conjunction with increasing air temperatures and summer precipitation but the distribution of permafrost slope failures in this area is largely constrained by forest fire extents that affected the area in the 1990s. These fires have led to increased landscape sensitivity of this ice‐rich terrain through their impacts on ground temperatures.
Key Points
Recent increases in permafrost mass‐wasting frequency (278%) and magnitude (602%) reveal a permafrost landscape in geomorphic transition
More than 80% of failures occur in areas burned in the 1990s
Compounding effects of legacy thermal disturbance and climate drivers of thaw likely to increase slope instability of warm permafrost
The main scope of this study is to investigate parameters controlling chemical weathering rates for a large river system submitted to subarctic climate. More than 110 river water samples from the ...Mackenzie River system (northern Canada) have been sampled and analyzed for major and trace elements and Sr isotopic ratios in the dissolved phase. The three main morphological units are reflected in water chemistry. Rivers from the Canadian Shield are very dilute, dominated by silicate weathering (Millot et al., 2002), whereas the rivers of the Rocky and Mackenzie Mountains as well as the rivers of the sedimentary Interior Platform are dominated by carbonate weathering and are SO
4 rich. Compared to the rivers of the Mackenzie and Rocky Mountains, the rivers of the interior plains are organic, silica, and Na rich and constitute the dominant input term to the Mackenzie River mainstream. Rivers of the Canadian Shield area do not significantly contribute to the Mackenzie River system. Using elemental ratios and Sr isotopic ratios, a mathematical inversion procedure is presented that distinguishes between solutes derived from silicate weathering and solutes derived from carbonate weathering. Carbonate weathering rates are mostly controlled by runoff, which is higher in the mountainous part of the Mackenzie basin. These rates are comparable to the carbonate weathering rates of warmer areas of the world. It is possible that part of the carbonate weathering is controlled by sulfide oxidative weathering, but its extent remains difficult to assess. Conversely to what was stated by Edmond and Huh (1997), overall silicate weathering rates in the Mackenzie basin are low, ranging from 0.13 to 4.3 tons/km
2/yr (Na + K + Ca + Mg), and confirm the negative action of temperature on silicate weathering rates for river basins in cold climates. In contrast to what has been observed in other large river systems such as the Amazon and Ganges Rivers, silicate weathering rates appear 3 to 4 times more elevated in the plains than in the mountainous headwaters. This contradicts the “Raymo hypothesis” (Raymo and Ruddiman, 1992). Isotopic characterization of suspended material clearly shows that the higher weathering rates reported for the plains are not due to the weathering of fine sediments produced in the mountains (e.g., by glaciers) and deposited in the plains. Rather, the relatively high chemical denudation rates in the plains are attributed to lithology (uncompacted shales), high mechanical denudation, and the abundance of soil organic matter derived from incomplete degradation and promoting crystal lattice degradation by element complexation. The three- to fourfold factor of chemical weathering enhancement between the plains and mountains is similar to the fourfold factor of enhancement found by Moulton et al. (2000) between unvegetated and vegetated watershed. This study confirms the negative action of temperature on silicate weathering for cold climate but shows that additional factors, such as organic matter, associated with northern watersheds are able to counteract the effect of temperature. This acceleration by a factor of 4 in the plains is equivalent to a 6°C increase in temperature.
The high-latitude regions of the Northern Hemisphere are a nexus for the interaction between land surface physical properties and their exchange of carbon and energy with the atmosphere. At these ...latitudes, two carbon pools of planetary significance – those of the permanently frozen soils (permafrost), and of the great expanse of boreal forest – are vulnerable to destabilization in the face of currently observed climatic warming, the speed and intensity of which are expected to increase with time. Improved projections of future Arctic and boreal ecosystem transformation require improved land surface models that integrate processes specific to these cold biomes. To this end, this study lays out relevant new parameterizations in the ORCHIDEE-MICT land surface model. These describe the interactions between soil carbon, soil temperature and hydrology, and their resulting feedbacks on water and CO2 fluxes, in addition to a recently developed fire module. Outputs from ORCHIDEE-MICT, when forced by two climate input datasets, are extensively evaluated against (i) temperature gradients between the atmosphere and deep soils, (ii) the hydrological components comprising the water balance of the largest high-latitude basins, and (iii) CO2 flux and carbon stock observations. The model performance is good with respect to empirical data, despite a simulated excessive plant water stress and a positive land surface temperature bias. In addition, acute model sensitivity to the choice of input forcing data suggests that the calibration of model parameters is strongly forcing-dependent. Overall, we suggest that this new model design is at the forefront of current efforts to reliably estimate future perturbations to the high-latitude terrestrial environment.
The hydrogen isotopic composition (2H/1H, or δ2H) of palmitic acid (PA) was measured in surface sediments from the Laptev and Kara Seas in the Russian Arctic to evaluate its use as a ...paleohydrographic proxy. δ2HPA values in surface sediments varied by 118‰ over a 21 ppt range in mean annual surface salinity, and the two properties were highly correlated (R2 = 0.8, p < 0.001) according to the relationship δ2HPA = 4.22 (±0.60)*S - 338 (±15). In contrast, δ2H values of vascular plant wax n-alkanes (nC27, nC29, nC31) did not change systematically with salinity. These differing lipid δ2H trends support the interpretation of PA as derived primarily from marine microalgae at these sites. Both the range and absolute values of δ2HPA compared favorably to those predicted from published Arctic Ocean salinity and water isotope data and the expected response of δ2HPA to salinity in cultured phytoplankton. Some 64–74% of the observed sedimentary δ2HPA increase is estimated to have resulted from increasing δ2Hwater values, with the remainder resulting from decreased 2H-discrimination during lipid biosynthesis at higher salinities. The large signal and high sensitivity of δ2HPA to surface salinity changes in the Russian Arctic was exploited to test the hypothesis that floodwaters emanated from the Mackenzie River during the late deglacial period. Measurements of δ2HPA were performed in a sediment core from the continental slope off the Mackenzie River in the Canadian Arctic. In samples from the top Bølling/Allerød-Younger Dryas period, reconstructed surface salinities (and δ2HPA values) off the Mackenzie River declined from 20 (−253‰) to 16 (−269‰) before rebounding to 24 (−236‰) in the early Holocene, close to the modern value of ∼25. A large salinity depression in the Canadian Arctic just prior to the start of the Younger Dryas would support the hypothesis of a northern routing of flood-waters from glacial Lake Agassiz via the Mackenzie River as a trigger for the Younger Dryas event.
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