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  • 1
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    Sea-air CO2 exchange in the western Arctic coastal ocean (2015)
    Wiley
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    Publication Date: 2015-07-17
    Description: The biogeochemical seascape of the western Arctic coastal ocean is in rapid transition. Changes in sea ice cover will be accompanied by alterations in sea-air carbon dioxide (CO 2 ) exchange, of which the latter has been difficult to constrain owing to sparse temporal and spatial datasets. Previous assessments of sea-air CO 2 flux have targeted specific sub-regional areas of the western Arctic coastal ocean. Here a holistic approach is taken to determine the net sea-air CO 2 flux over this broad region. We compiled and analyzed an extensive dataset of nearly 600,000 surface seawater CO 2 partial pressure (pCO 2 ) measurements spanning 2003 through 2014. Using space-time co-located, reconstructed atmospheric pCO 2 values coupled with the seawater pCO 2 dataset, monthly climatologies of sea-air pCO 2 differences (∆pCO 2 ) were created on a 0.2° latitude x 0.5° longitude grid. Sea-air CO 2 fluxes were computed using the ∆pCO 2 grid and gas transfer rates calculated from a climatology of wind speed second moments. Fluxes were calculated with and without the presence of sea ice, treating sea ice as an imperfect barrier to gas exchange. This allowed for carbon uptake by the western Arctic coastal ocean to be assessed under existing and reduced sea ice cover conditions, in which carbon uptake increased 30% over the current 10.9 ± 5.7 Tg C (1 Tg = 10 12 g) yr −1 of sea ice adjusted exchange in the region. This assessment extends beyond previous sub-regional estimates in the region in an all-inclusive manner, and points to key unresolved aspects that must be targeted by future research.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Variation in summer nitrogen and phosphorus uptake among Siberian headwater streams (2016)
    Norwegian Polar Institute
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    Publication Date: 2016-06-07
    Description: Arctic streams are likely to receive increased inputs of dissolved nutrients and organic matter from thawing permafrost as climate warms. Documenting how Arctic streams process inorganic nutrients is necessary to understand mechanisms that regulate watershed fluxes of permafrost-derived materials to downstream ecosystems. We report on summer nitrogen (N) and phosphorus (P) uptake in streams draining upland soils from the Pleistocene, and lowland floodplain soils from the Holocene, in Siberia’s Kolyma River watershed. Uptake of N and P differed between upland and floodplain streams, suggesting topographic variation in nutrient limitation. In floodplain streams, P uptake rate and uptake velocity were higher than N, while upland streams had similar values for all N and P uptake metrics. Phosphorus uptake velocity and size of the transient hydrologic storage zone were negatively related across all study streams, indicating strong influence of hydrologic processes on nutrient fluxes. Physical sorption of P was higher in floodplain stream sediments relative to upland stream sediments, suggesting more physically driven uptake in floodplain streams and higher biological activity in upland streams. Overall, these results demonstrate that high-latitude headwater streams actively retain N and P during summer base flows; however, floodplain and upland streams varied substantially in N and P uptake and may respond differently to inorganic nutrient and organic matter inputs. Our results highlight the need for a comprehensive assessment of N and P uptake and retention in Arctic streams in order to fully understand the impact of permafrost-derived materials on ecosystem processes, and their fate in continental drainage networks. Keywords: Arctic streams; nutrient uptake; hydrologic transient storage; phosphorus sorption; coupled N and P cycling. (Published: 6 June 2016) To access the supplementary material for this article, please see the supplementary files in the column to the right (under Article Tools). Citation: Polar Research 2016, 35 , 24571, http://dx.doi.org/10.3402/polar.v35.24571
    Print ISSN: 0800-0395
    Electronic ISSN: 1751-8369
    Topics: Geography , Geosciences
    Published by Norwegian Polar Institute
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  • 3
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    Constraining the parameters of the putative supermassive binary black hole in PG 1302-102 from its radio structure (2015)
    Oxford University Press
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    Publication Date: 2015-10-03
    Description: We investigate the pc-scale kinematics and kpc-scale radio morphology of the quasar PG 1302–102, which may harbour a sub-pc separation supermassive binary black hole system at its centre as inferred from optical variability. High-resolution radio interferometric measurements obtained with the Very Long Baseline Array (VLBA) in the Monitoring Of Jets in Active galactic nuclei with VLBA Experiments programme at 15 GHz at 20 epochs spanning 17 years were analysed to investigate the pc-scale radio structure. Archival observations with the Very Large Array at 1.4 and 5 GHz were obtained to study the kpc-scale morphology. We find that the pc-scale jet is inclined within ~2 $_{.}^{\circ}$ 2 to the line of sight and has a half-opening angle of ~0 $_{.}^{\circ}$ 2. The parameters derived from the pc-scale radio jet are qualitatively consistent with those obtained from the analysis of the optical light curve of PG 1302–102. We obtain at least 0.08 for the mass ratio of the two black holes in the system. We find some indication for a helical jet structure on kpc-scale, but the directions of the inner and the extended radio jets are significantly different, obstructing a straightforward connection of the pc- and kpc-scale jets within the binary scenario.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Assessing the potential impacts of declining arctic sea ice cover on the photochemical degradation of dissolved organic matter in the Chukchi and Beaufort seas (2015)
    Wiley
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    Publication Date: 2015-10-30
    Description: A warming and shifting climate in the Arctic has led to significant declines in sea ice over the last several decades. Although these changes in sea ice cover are well documented, large uncertainties remain in how associated increases in solar radiation transmitted to the underlying ocean water column will impact heating, biological and biogeochemical processes in the Arctic Ocean. In this study, six under-ice marine, two ice-free marine, and two ice-free terrestrially-influenced water samples were irradiated using a solar simulator for 72 hours (representing ~10 days of ambient sunlight) to investigate dissolved organic matter (DOM) dynamics from the Chukchi and Beaufort seas. Solar irradiation caused chromophoric DOM (CDOM) light absorption at 254 nm to decrease by 48 to 63%. An overall loss in total DOM fluorescence intensity was also observed at the end of all experiments, and each of 6 components identified by parallel factor analyses (PARAFAC) was shown to be photoreactive in at least one experiment. DOM fluorescence (FDOM) also indicated that the majority of DOM in under-ice and ice-free marine waters was likely algal-derived. Measurable changes in dissolved organic carbon (DOC) were only observed for sites influenced by riverine runoff. Losses of CDOM absorbance at shorter wavelengths suggest that the beneficial UV protection currently received by marine organisms may decline with the increased light transmittance associated with sea ice melt ponding and overall reductions of sea ice. Our FDOM analyses demonstrate that DOM irrespective of source was susceptible to photobleaching. Additionally, our findings suggest that photodegradation of CDOM in under-ice waters is not currently a significant source of carbon dioxide (CO 2 ) (i.e., we did not observe systematic DOC loss). However, increases in primary production and terrestrial freshwater export expected under future climate change scenarios may cause an increase in CDOM quantity and shift in quality throughout Arctic Ocean surface waters. As arctic temperatures continue to warm and summer sea ice further declines, examination of the resulting enhanced photodegradation processes and their impacts on the interplay between primary production, carbon cycling, and surface ocean heating processes will be paramount.
    Print ISSN: 0148-0227
    Topics: Biology , Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Divergent trajectories of Antarctic surface melt under two twenty-first-century climate scenarios (2015)
    Springer Nature
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    Publication Date: 2015-11-28
    Description: Nature Geoscience 8, 927 (2015). doi:10.1038/ngeo2563 Authors: Luke D. Trusel, Karen E. Frey, Sarah B. Das, Kristopher B. Karnauskas, Peter Kuipers Munneke, Erik van Meijgaard & Michiel R. van den Broeke Ice shelves modulate Antarctic contributions to sea-level rise and thereby represent a critical, climate-sensitive interface between the Antarctic ice sheet and the global ocean. Following rapid atmospheric warming over the past decades, Antarctic Peninsula ice shelves have progressively retreated, at times catastrophically. This decay supports hypotheses of thermal limits of viability for ice shelves via surface melt forcing. Here we use a polar-adapted regional climate model and satellite observations to quantify the nonlinear relationship between surface melting and summer air temperature. Combining observations and multimodel simulations, we examine melt evolution and intensification before observed ice shelf collapse on the Antarctic Peninsula. We then assess the twenty-first-century evolution of surface melt across Antarctica under intermediate and high emissions climate scenarios. Our projections reveal a scenario-independent doubling of Antarctic-wide melt by 2050. Between 2050 and 2100, however, significant divergence in melt occurs between the two climate scenarios. Under the high emissions pathway by 2100, melt on several ice shelves approaches or surpasses intensities that have historically been associated with ice shelf collapse, at least on the northeast Antarctic Peninsula.
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 6
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    Landscape-level controls on dissolved carbon flux from diverse catchments of the circumboreal (2012)
    Wiley
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    Publication Date: 2012-08-21
    Description: While much of the dissolved organic carbon (DOC) within rivers is destined for mineralization to CO2, a substantial fraction of riverine bicarbonate (HCO3−) flux represents a CO2 sink, as a result of weathering processes that sequester CO2 as HCO3−. We explored landscape-level controls on DOC and HCO3− flux in subcatchments of the boreal, with a specific focus on the effect of permafrost on riverine dissolved C flux. To do this, we undertook a multivariate analysis that partitioned the variance attributable to known, key regulators of dissolved C flux (runoff, lithology, and vegetation) prior to examining the effect of permafrost, using riverine biogeochemistry data from a suite of subcatchments drawn from the Mackenzie, Yukon, East, and West Siberian regions of the circumboreal. Across the diverse catchments that we study, controls on HCO3− flux were near-universal: runoff and an increased carbonate rock contribution to weathering (assessed as riverwater Ca:Na) increased HCO3− yields, while increasing permafrost extent was associated with decreases in HCO3−. In contrast, permafrost had contrasting and region-specific effects on DOC yield, even after the variation caused by other key drivers of its flux had been accounted for. We used ionic ratios and SO4 yields to calculate the potential range of CO2 sequestered via weathering across these boreal subcatchments, and show that decreasing permafrost extent is associated with increases in weathering-mediated CO2 fixation across broad spatial scales, an effect that could counterbalance some of the organic C mineralization that is predicted with declining permafrost.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Antarctic surface melting dynamics: Enhanced perspectives from radar scatterometer data (2012)
    Wiley
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    Publication Date: 2012-05-17
    Description: Antarctic ice sheet surface melting can regionally influence ice shelf stability, mass balance, and glacier dynamics, in addition to modulating near-surface physical and chemical properties over wide areas. Here, we investigate variability in surface melting from 1999 to 2009 using radar backscatter time series from the SeaWinds scatterometer aboard the QuikSCAT satellite. These daily, continent-wide observations are explored in concert with in situ meteorological records to validate a threshold-based melt detection method. Radar backscatter decreases during melting are significantly correlated with in situ positive degree-days as well as meltwater production determined from energy balance modeling at Neumayer Station, East Antarctica. These results support the use of scatterometer data as a diagnostic indicator of melt intensity (i.e., the relative liquid water production during melting). Greater spatial and temporal melting detected relative to previous passive microwave-based studies is attributed to a higher sensitivity of the scatterometer instrument. Continental melt intensity variability can be explained in part by the dynamics of the Southern Annular Mode and the Southern Oscillation Index, and extreme melting events across the Ross Ice Shelf region may be associated with El Niño conditions. Furthermore, we find that the Antarctic Peninsula accounts for only 20% of Antarctic melt extent but greater than 50% of the total Antarctic melt intensity. Over most areas, annual melt duration and intensity are proportional. However, regional and localized distinctions exist where the melt intensity metric provides greater insight into melting dynamics than previously obtainable with other remote sensing techniques.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    The spatial distribution of solar radiation under a melting Arctic sea ice cover (2011)
    Wiley
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    Publication Date: 2011-11-18
    Description: The sea ice cover of the Chukchi and Beaufort Seas is currently undergoing a fundamental shift from multiyear ice to first-year ice. Field observations of sea ice physical and optical properties were collected in this region during June–July 2010, revealing unexpectedly complex spatial distributions of solar radiation under the melt-season ice cover. Based on our optical measurements of first-year ice, we found the under-ice light field in the upper ocean to be spatially heterogeneous and dependent on wavelength, ice thickness, and the areal and geometric distribution of melt ponded and bare ice surfaces. Much of the observed complexity in radiation fields arose because the transmission of light through ponded ice was generally an order of magnitude greater than through bare, unponded ice. Furthermore, while many sites exhibited a consistent, exponential decay in light transmission through both ponded and bare ice surfaces, light transmission under bare ice was also observed to increase with depth (reaching maximum values ∼5–10 m below the bottom of the ice). A simple geometric model shows these transmission peaks are a result of scattering in the ice and the interspersion of bare and ponded sea ice surfaces. These new observations of complex radiation fields beneath melt-season first-year sea ice have significant implications for biological production, biogeochemical processes, and the heat balance of sea ice and under-ice ocean waters and should be carefully considered when modeling these sea ice-related phenomena.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Summer CO 2 evasion from streams and rivers in the Kolyma River basin, north-east Siberia (2013)
    Norwegian Polar Institute
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    Publication Date: 2013-12-06
    Description: Inland water systems are generally supersaturated in carbon dioxide (CO 2 ) and are increasingly recognized as playing an important role in the global carbon cycle. The Arctic may be particularly important in this respect, given the abundance of inland waters and carbon contained in Arctic soils; however, a lack of trace gas measurements from small streams in the Arctic currently limits this understanding.We investigated the spatial variability of CO 2 evasion during the summer low-flow period from streams and rivers in the northern portion of the Kolyma River basin in north-eastern Siberia. To this end, partial pressure of carbon dioxide ( p CO 2 ) and gas exchange velocities ( k ) were measured at a diverse set of streams and rivers to calculate CO 2 evasion fluxes. We combined these CO2 evasion estimates with satellite remote sensing and geographic information system techniques to calculate total areal CO 2 emissions. Our results show that small streams are substantial sources of atmospheric CO 2 owing to high p CO 2 and k , despite being a small portion of total inland water surface area. In contrast, large rivers were generally near equilibrium with atmospheric CO 2 . Extrapolating our findings across the Panteleikha-Ambolikha sub-watersheds demonstrated that small streams play a major role in CO 2 evasion, accounting for 86% of the total summer CO 2 emissions from inland waters within these two sub-watersheds. Further expansion of these regional CO 2 emission estimates across time and space will be critical to accurately quantify and understand the role of Arctic streams and rivers in the global carbon budget. Keywords: Arctic streams and rivers; CO 2 evasion; inland water surface area; Kolyma River; p CO 2 ; Siberia (Published: 5 December 2013) Citation: Polar Research 2013, 32 , 19704, http://dx.doi.org/10.3402/polar.v32i0.19704
    Print ISSN: 0800-0395
    Electronic ISSN: 1751-8369
    Topics: Geography , Geosciences
    Published by Norwegian Polar Institute
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  • 10
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    Annual sea-air CO2 fluxes in the Bering Sea: Insights from new autumn and winter observations of a seasonally ice-covered continental shelf (2014)
    Wiley
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    Publication Date: 2014-09-03
    Description: High-resolution data collected from several programs has greatly increased the spatiotemporal resolution of p CO 2 data in the Bering Sea, and provided the first autumn and winter observations. Using data from 2008 – 2012, monthly climatologies of sea-air CO 2 fluxes for the Bering Sea shelf area from April through December were calculated, and contributions of physical and biological processes to observed monthly sea-air p CO 2 gradients (Δ p CO 2 ) were investigated. Net efflux of CO 2 was observed during November, December, and April, despite the impact of sea surface cooling on Δ p CO 2 . Although the Bering Sea was believed to be a moderate to strong atmospheric CO 2 sink, we found that autumn and winter CO 2 effluxes balanced 65% of spring and summer CO 2 uptake. Ice cover reduced sea-air CO 2 fluxes in December, April, and May. Our estimate for ice-cover corrected fluxes suggests the mechanical inhibition of CO 2 flux by sea-ice cover has only a small impact on the annual scale (〈 2%). An important data gap still exists for January through March, the period of peak ice cover and the highest expected retardation of the fluxes. By interpolating between December and April using assumptions of the described autumn and winter conditions, we estimate the Bering Sea shelf area is an annual CO 2 sink of ~6.8 Tg C yr -1 . With changing climate, we expect warming sea surface temperatures, reduced ice cover, and greater wind speeds with enhanced gas exchange to decrease the size of this CO 2 sink by augmenting conditions favorable for greater wintertime outgassing.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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