Eurasian Arctic Rivers Research Articles

Dissolved Major and Trace Elements in the Largest Eurasian Arctic Rivers: Ob, Yenisey, Lena, and Kolyma

In contrast to fairly good knowledge of dissolved carbon and major elements in great Arctic rivers, seasonally resolved concentrations of many trace elements remain poorly characterized, hindering assessment of the current status and possible future changes in the hydrochemistry of the Eurasian Arctic. To fill this gap, here we present results for a broad suite of trace elements in the largest rivers of the Russian Arctic (Ob, Yenisey, Lena, and Kolyma). For context, we also present results for major elements that are more routinely measured in these rivers. Water samples for this study were collected during an international campaign called PARTNERS from 2004 through 2006. A comparison of element concentrations obtained for Arctic rivers in this study with average concentrations in the world’s rivers shows that most elements in the Arctic rivers are similar to or significantly lower than the world average. The mineral content of the three greatest rivers (Ob, Yenisey, and Lena) varies within a narrow range (from 107 mg/L for Yenisey to 123 mg/L for Ob). The Kolyma’s mineral content is significantly lower (52.4 mg/L). Fluxes of all major and trace elements were calculated using average concentrations and average water discharge for the 2004–2006 period. Based on these flux estimates, specific export (i.e., t/km2/y) for most of the elements was greatest for the Lena, followed by the Yenisey, Ob, and Kolyma in decreasing order. Element pairwise correlation analysis identified several distinct groups of elements depending on their sources and relative mobility in the river water. There was a negative correlation between Fe and DOC concentration in the Ob River, which could be linked to different sources of these components in this river. The annual yields of major and trace elements calculated for each river were generally consistent with values assessed for other mid-size and small rivers of the Eurasian subarctic.

Catchment and in-channel sources in three large Eurasian Arctic rivers: Combining monitoring, remote sensing and modelling data to construct Ob', Yenisey and Lena rivers sediment budget

This paper presents a comparative study of fluvial sediment budgets for the largest Siberian rivers of Northern Eurasia - Ob', Yenisey and Lena which cover over 14 % of the Eurasia continent. Each component of the sediment budget was assessed using an independent approach. The Revised Universal Soil Loss Equation model (RUSLE) was used to calculate catchment erosion based on the GMTED 2010 DEM with a resolution of 250 m. Channel erosion was quantified through automatic image decoding integrated with riverbank elevation estimated from ArcticDEM and hydromorphological 1D modeling of streamflow depths, whereas sediment yield was assessed based on a combination of long-term suspended sediment load monitoring at the outlet gauging stations and bed load estimates. Large differences between total (catchment and riverbank) erosion (1622 Mt year−1 for the Ob', 898 Mt year−1 for the Yenisey, 1218 Mt year−1 for the Lena) and yearly sediment export (58.2 Mt year−1 for the Ob', 32.5 Mt year−1 for the Yenisey and 38.6 Mt year−1 for the Lena) suggest that catchment, in-channel and overbank sediment sinks and storage dominate the sediment budget. The throughflow from the sources to the sea is less than 4 % of the suspended sediment inflow (total erosion). This data enhances the knowledge of the sediment delivery rates in large river systems. Over ∼96 % decline of sediment transport compared to catchment total erosion is explained by storage in various buffer zones of the catchment and river network including mainly hillslopes, as well as reservoirs and floodplains.

River runoff components change variably and respond differently to climate change in the Eurasian Arctic and Qinghai-Tibet Plateau permafrost regions

Cryohydrological processes in the Eurasian Arctic and Qinghai-Tibet Plateau (QTP) permafrost regions have been changing rapidly, yet the details of the river runoff changes are still obscure. Here we use multidecadal natural daily discharge data to compute annual flow duration curves (FDCs) and percentile flows for 20 Eurasian Arctic and QTP river basins with permafrost underlain. We provide detailed trends of various percentile flows that almost all runoff components change variably, either with the distinct magnitude or opposite direction or both. We demonstrate that the lower flows increase monotonically faster than higher flows. Most low flows increase while the high flows show spatial heterogeneity with both increased and decreased trends observed. The portion of deep and total groundwater flow in total discharge increases, with the deep groundwater flow increases faster. Interestingly, the river runoff components respond differently to climatic change factors. The low flows, mainly sustained by groundwater, are more sensitive to warming than high flows, while the high flows are more sensitive to precipitation than low flows. Our results may suggest an increased subsurface hydrological connectivity under the warming climate and thawing permafrost. We show that FDCs have the potential to reveal the long-term runoff components change. Future climatic change may alter the shapes and distributions of FDCs since the asynchronous changes of runoff components, which have important implications for cold region river management and mitigation under climatic change.

Multi-molecular tracers of terrestrial carbon transfer across the pan-Arctic: comparison of hydrolyzable components with plant wax lipids and lignin phenols

Abstract. Hydrolyzable organic carbon (OC) comprises a significant component of sedimentary particulate matter transferred from land into oceans via rivers. Its abundance and nature are however not well studied in Arctic river systems, and yet may represent an important pool of carbon whose fate remains unclear in the context of mobilization and related processes associated with a changing climate. Here, we examine the molecular composition and source of hydrolyzable compounds isolated from sedimentary particles derived from nine rivers across the pan-Arctic. Bound fatty acids (b-FAs), hydroxy FAs, n-alkane-α,ω-dioic acids (DAs) and phenols were the major components released upon hydrolysis of these sediments. Among them, b-FAs received considerable inputs from bacterial and/or algal sources, whereas ω-hydroxy FAs, mid-chain substituted acids, DAs, and hydrolyzable phenols were mainly derived from cutin and suberin of higher plants. We further compared the distribution and fate of suberin- and cutin-derived compounds with those of other terrestrial biomarkers (plant wax lipids and lignin phenols) from the same Arctic river sedimentary particles and conducted a benchmark assessment of several biomarker-based indicators of OC source and extent of degradation. While suberin-specific biomarkers were positively correlated with plant-derived high-molecular-weight (HMW) FAs, lignin phenols were correlated with cutin-derived compounds. These correlations suggest that, similar to leaf-derived cutin, lignin was mainly derived from litter and surface soil horizons, whereas suberin and HMW FAs incorporated significant inputs from belowground sources (roots and deeper soil). This conclusion is supported by the negative correlation between lignin phenols and the ratio of suberin-to-cutin biomarkers. Furthermore, the molecular composition of investigated biomarkers differed between Eurasian and North American Arctic rivers: while lignin dominated in the terrestrial OC of Eurasian river sediments, hydrolyzable OC represented a much larger fraction in the sedimentary particles from Colville River. Hence, studies exclusively focusing on either plant wax lipids or lignin phenols will not be able to fully unravel the mobilization and fate of bound OC in Arctic rivers. More comprehensive, multi-molecular investigations are needed to better constrain the land–ocean transfer of carbon in the changing Arctic, including further research on the degradation and transfer of both free and bound components in Arctic river sediments.

Differential mobilization of terrestrial carbon pools in Eurasian Arctic river basins

Mobilization of Arctic permafrost carbon is expected to increase with warming-induced thawing. However, this effect is challenging to assess due to the diverse processes controlling the release of various organic carbon (OC) pools from heterogeneous Arctic landscapes. Here, by radiocarbon dating various terrestrial OC components in fluvially and coastally integrated estuarine sediments, we present a unique framework for deconvoluting the contrasting mobilization mechanisms of surface vs. deep (permafrost) carbon pools across the climosequence of the Eurasian Arctic. Vascular plant-derived lignin phenol (14)C contents reveal significant inputs of young carbon from surface sources whose delivery is dominantly controlled by river runoff. In contrast, plant wax lipids predominantly trace ancient (permafrost) OC that is preferentially mobilized from discontinuous permafrost regions, where hydrological conduits penetrate deeper into soils and thermokarst erosion occurs more frequently. Because river runoff has significantly increased across the Eurasian Arctic in recent decades, we estimate from an isotopic mixing model that, in tandem with an increased transfer of young surface carbon, the proportion of mobilized terrestrial OC accounted for by ancient carbon has increased by 3-6% between 1985 and 2004. These findings suggest that although partly masked by surface carbon export, climate change-induced mobilization of old permafrost carbon is well underway in the Arctic.

Enhanced poleward moisture transport and amplified northern high-latitude wetting trend

Observations and climate change projections forced by greenhouse gas emissions have indicated a wetting trend in northern high latitudes, evidenced by increasing Eurasian Arctic river discharges1, 2, 3. The increase in river discharge has accelerated in the latest decade and an unprecedented, record high discharge occurred in 2007 along with an extreme loss of Arctic summer sea-ice cover4, 5, 6. Studies have ascribed this increasing discharge to various factors attributable to local global warming effects, including intensifying precipitation minus evaporation, thawing permafrost, increasing greenness and reduced plant transpiration7, 8, 9, 10, 11. However, no agreement has been reached and causal physical processes remain unclear. Here we show that enhancement of poleward atmospheric moisture transport (AMT) decisively contributes to increased Eurasian Arctic river discharges. Net AMT into the Eurasian Arctic river basins captures 98% of the gauged climatological river discharges. The trend of 2.6% net AMT increase per decade accounts well for the 1.8% per decade increase in gauged discharges and also suggests an increase in underlying soil moisture. A radical shift of the atmospheric circulation pattern induced an unusually large AMT and warm surface in 2006–2007 over Eurasia, resulting in the record high discharge.

Change in spring snowmelt timing in Eurasian Arctic rivers

[1] Changes in the amount and timing of the discharge of major Eurasian Arctic rivers have been well documented, but whether or not these changes can be attributed to climatic factors or to the construction of manmade reservoirs remains unclear. Here we endeavor to identify the key processes (snow cover and air temperature) that have regulated seasonal streamflow fluctuations in the Eurasian Arctic over the last half-century (1958–1999) and to understand the regional coherence of timing trends, using a set of Eurasian Arctic rivers selected specifically because they are free of known effects of dams. We find a shift toward earlier onset of spring runoff as measured by a modest change in the spring pulse onset (26 of 45 stations) and a strong change in the centroid of timing (39 of 45 stations). Winter streamflows increased over the period of record in most rivers, suggesting that trends observed by others in larger regulated Eurasian Arctic rivers may not be entirely attributable to reservoir construction. Upward trends in air temperature appeared to have had the largest impact on spring and summer flows for tributaries in the coldest of the major Eurasian Arctic river basins (e.g., the Lena). While the overall duration of snow cover has not significantly changed across the Eurasian Arctic, snow cover disappearance has trended earlier in the year and appears to be related to the increased May and snowmelt season fractional flows.

Measurements of Cd, Cu, Pb and Zn in the lower reaches of major Eurasian arctic rivers using trace metal clean techniques

Concentrations of dissolved and particulate Cd, Cu, Pb and Zn were determined in samples collected in summer 1998 from the lower reaches of six major Eurasian arctic rivers: the Onega, Severnaya Dvina, Mezen, Pechora, Ob and Yenisey. These data comprise some of the earliest measurements of trace metals in Eurasian arctic rivers above the estuaries using recognized clean techniques. Significant ( α = 0.05) differences were observed among mean concentrations of particulate metals in the individual rivers ( F ≤ 0.006), with highest levels overall observed in the Severnaya Dvina and Yenisey. No significant differences were observed among mean concentrations of dissolved metals in the individual rivers ( F = 0.10–0.84). Contributions from anthropogenic sources are suggested by comparison of trace metal ratios in the samples to crustal abundances. These results establish a baseline for assessing future responses of Eurasian arctic river systems to climate-related environmental changes and shifting patterns of pollutant discharge.

Application of New Precipitation and Reconstructed Streamflow Products to Streamflow Trend Attribution in Northern Eurasia

Abstract River runoff to the Arctic Ocean has increased over the last century, primarily during the winter and spring and primarily from the major Eurasian rivers. Some recent studies have suggested that the additional runoff is due to increased northward transport of atmospheric moisture (and associated increased precipitation), but other studies show inconsistencies in long-term runoff and precipitation trends, perhaps partly due to biases in the observational datasets. Through trend analysis of precipitation, temperature, and streamflow data, the authors investigate the extent to which Eurasian Arctic river discharge changes are attributable to precipitation and temperature changes as well as to reservoir construction and operation between the years of 1936 and 2000. Two new datasets are applied: a gridded precipitation product, in which the low-frequency variability is constrained to match that of long-term bias-corrected precipitation station data, and a reconstructed streamflow product, in which the effects of reservoirs have been minimized using a physically based reservoir model. It is found that reservoir operations have primarily affected streamflow seasonality, increasing winter discharge and decreasing summer discharge. To understand the influences of climate on streamflow changes, the authors hypothesize three cases that would cause precipitation trends to be inconsistent with streamflow trends: first, for the coldest basins in northeastern Siberia, streamflow should be sensitive to warming primarily as a result of the melting of excess ground ice, and for these basins positive streamflow trends may exceed precipitation trends in magnitude; second, evapotranspiration (ET) in the warmer regions of western Siberia and European Russia is sensitive to warming and increased precipitation, therefore observed precipitation trends may exceed streamflow trends; and third, streamflow from the central Siberian basins should respond to both effects. It is found that, in general, these hypotheses hold true. In the coldest basins, streamflow trends diverged from precipitation trends starting in the 1950s to 1960s, and this divergence accelerated thereafter. In the warmest basins, precipitation trends consistently exceeded streamflow trends, suggesting that increased precipitation contributed to increases in both ET and streamflow. In the central basins, permafrost degradation and ET effects appear to be contributing to long-term streamflow trends in varying degrees for each basin. The results herein suggest that the extent and state of the permafrost underlying a basin is a complicating factor in understanding long-term changes in Eurasian Arctic river discharge.

Linkages among runoff, dissolved organic carbon, and the stable oxygen isotope composition of seawater and other water mass indicators in the Arctic Ocean

Flow‐weighted dissolved organic carbon (DOC) concentrations and δ18O values were determined from major arctic rivers, specifically the Ob, Yenisey, Lena, Kolyma, Mackenzie, and Yukon during 2003–2004. These data were considered in conjunction with marine data for DOC, δ18O values, nutrients, salinity, and fluorometric indicators of DOC obtained during sampling at the shelf‐basin boundary of the Chukchi and Beaufort seas. On the basis of these data, freshwater in the sampled marine waters is likely derived from regional sources, such as the Mackenzie, the Bering Strait inflow, and possibly eastern Siberian rivers, including the Kolyma, or the Lena, but not rivers farther west in the Eurasian arctic. Freshwater from melted sea ice is insignificant over annual cycles, although melted sea ice was a locally dominant freshwater component following summer sea‐ice retreat in 2002. DOC concentrations were correlated with the runoff fraction, with an apparent meteoric water DOC concentration of 174 ± 1 μM. This is lower than the flow‐weighted concentrations measured at river mouths of the five largest Arctic rivers (358 to 917 μM), indicating removal of DOC during transport through estuaries, shelves and in the deep basin. Flow‐weighted DOC concentrations in the two largest North American arctic rivers, the Yukon (625 μM) and the Mackenzie (358 μM), are lower than in the three largest Eurasian arctic rivers, the Ob (825 μM), the Yenesey (858 μM), and the Lena (917 μM). A fluorometer responding to chromophoric dissolved organic matter (CDOM) was not correlated with DOC concentrations in Pacific‐influenced surface waters unlike previous observations in the Atlantic layer. Nutrient distributions, concentrations, and derived ratios suggest the CDOM fluorometer may be responding to the release of chromophoric materials from shelf sediments. Shipboard incubations of undisturbed sediment cores indicate that sediments on the Bering and Chukchi Sea shelves are a net source of DOC to the Arctic Ocean.

Increasing river discharge in the Eurasian Arctic: Consideration of dams, permafrost thaw, and fires as potential agents of change

Discharge from Eurasian rivers to the Arctic Ocean has increased significantly in recent decades, but the reason for this trend remains unclear. Increased net atmospheric moisture transport from lower to higher latitudes in a warming climate has been identified as one potential mechanism. However, uncertainty associated with estimates of precipitation in the Arctic makes it difficult to confirm whether or not this mechanism is responsible for the change in discharge. Three alternative mechanisms are dam construction and operation, permafrost thaw, and increasing forest fires. Here we evaluate the potential influence of these three mechanisms on changes in discharge from the six largest Eurasian Arctic rivers (Yenisey, Ob', Lena, Kolyma, Pechora, and Severnaya Dvina) between 1936 and 1999. Comprehensive discharge records made it possible to evaluate the influence of dams directly. Data on permafrost thaw and fires in the watersheds of the Eurasian Arctic rivers are more limited. We therefore use a combination of data and modeling scenarios to explore the potential of these two mechanisms as drivers of increasing discharge. Dams have dramatically altered the seasonality of discharge but are not responsible for increases in annual values. Both thawing of permafrost and increased fires may have contributed to changes in discharge, but neither can be considered a major driver. Cumulative thaw depths required to produce the observed increases in discharge are unreasonable: Even if all of the water from thawing permafrost were converted to discharge, a minimum of 4 m thawed evenly across the combined permafrost area of the six major Eurasian Arctic watersheds would have been required. Similarly, sensitivity analysis shows that the increases in fires that would have been necessary to drive the changes in discharge are unrealistic. Of the potential drivers considered here, increasing northward transport of moisture as a result of global warming remains the most viable explanation for the observed increases in Eurasian Arctic river discharge.

Nutrient chemistry of the Ob' and Yenisey Rivers, Siberia: results from June 2000 expedition and evaluation of long-term data sets

Abstract Although containing only ∼1% of global ocean volume, the arctic Ocean receives almost 10% of global river discharge. Nutrients carried by arctic rivers influence the productivity of their estuaries and coastal seas and may serve as important indicators of changing conditions in their watersheds. The three largest arctic rivers (Yenisey, Ob', and Lena) enter the arctic Ocean from Siberia and together account for nearly 35% of river-water inputs to the arctic Ocean. Although several nutrient flux estimates have been published for Eurasian arctic rivers, recent publications have highlighted uncertainties in these estimates and have cautioned against their uncritical use, particularly with respect to ammonium data. In order to help clarify the situation and evaluate the validity of existing long-term data sets, we went to Siberia during June 2000 to collect and analyze new nutrient samples from the downstream reaches of the Yenisey and Ob' rivers. Samples were independently analyzed by as many as four groups/laboratories in order to maximize confidence in analytical results. Whereas long-term data sets report average ammonium concentrations of 710 and 360 μg N/l in the Ob' and Yenisey rivers, respectively, we measured concentrations of only 10–15 μg N/l in both rivers in June 2000. We conclude that existing long-term data sets for these two rivers are grossly in error with respect to ammonium concentrations, and by extension that other surprisingly high values of ammonium reported for Russian arctic rivers (for example Pur, Taz, Nadym, and Pechora rivers) must be considered extremely doubtful. The situation is better for nitrate and phosphate, but our one-time sampling is insufficient to fully evaluate the reliability of existing data sets for these nutrients. Because a substantial percentage of the total freshwater input to the arctic Ocean comes from Russian rivers, the large revisions in ammonium concentrations needed for the Ob', Yenisey, and probably other Eurasian arctic rivers will significantly reduce estimates of dissolved inorganic nitrogen (DIN) fluxes to the arctic Ocean as a whole.

Wind‐driven transport pathways for Eurasian Arctic river discharge

Distributions of temperature, salinity, and barium in near‐surface waters (depth ≤ 50 m) of the Laptev Sea and adjacent areas of the Arctic Ocean are presented for the summers of 1993, 1995, and 1996. The tracer data indicate that while fluvial discharge was largely confined to the shelf region of the Laptev Sea in the summer of 1993, surface waters containing a significant fluvial component extended beyond the shelf break and over the slope and basin areas north of the Laptev Sea in the summers of 1995 and 1996. These distributions of fluvial discharge are consistent with local winds and suggest two principal pathways by which river waters can enter the central Arctic basins from the Laptev Sea. When southerly to southeasterly wind conditions prevail, river waters are transported northward beyond the shelf break and over the slope and adjacent basin areas. These waters can then enter the interior Arctic Ocean via upper layer flow in the vicinity of the Lomonosov Ridge. Under other wind conditions, river waters are steered primarily along the inner Laptev shelf and into the East Siberian Sea as part of the predominantly eastward coastal current system. These waters then appear to cross the shelf and enter the interior Arctic Ocean via upper layer flow aligned roughly along the Mendeleyev Ridge. The extent to which either pathway is favored in a given year is largely determined by local wind patterns during the summer months, when fluvial discharge is greatest and shelf waters are at the lowest salinity of their annual cycle.

A survey of dissolved barium in the estuaries of major Arctic rivers and adjacent seas

Analyses for dissolved Ba have been performed on water samples obtained from the estuaries of major Arctic rivers and adjacent seas between 1993 and 1996. Complex behavior was observed in the mixing zones between fluvial and oceanic waters. In these areas, riverine dissolved Ba signals were altered by mixing with different shelf water masses and by non-conservative processes such as uptake in association with biological activity and desorption from suspended riverine particles. Despite this complexity, dissolved Ba concentrations [Ba d] measured in samples associated with the Mackenzie River (138–574 nmol L -1) were clearly much higher than those measured in samples associated with any of the Eurasian Arctic rivers (12–175 nmol L -1). While the [Ba d] signatures of Arctic rivers are subject to temporal and seasonal variability, such variability appears to be much smaller than the overall difference between [Ba d] in the Mackenzie River and Eurasian Arctic rivers. These results suggest that Ba can be used to distinguish between North American and Eurasian components of fluvial discharge to the Arctic and thus provide information not available from other oceanographic tracers currently in use.