433 research outputs found
Quantifying exchangeable base cations in permafrost: a reserve of nutrients about to thaw
Permafrost ecosystems are limited in nutrients for
vegetation development and constrain the biological activity to the active
layer. Upon Arctic warming, permafrost thaw exposes large amounts of soil
organic carbon (SOC) to decomposition and minerals to weathering but also
releases organic and mineral soil material that may directly influence the
soil exchange properties (cation exchange capacity, CEC, and base saturation,
BS). The soil exchange properties are key for nutrient base cation supply
(Ca2+, K+, Mg2+, and Na+) for vegetation growth and
development. In this study, we investigate the distributions of soil exchange
properties within Arctic tundra permafrost soils at Eight Mile Lake
(Interior Alaska, USA) because they will dictate the potential reservoir of
newly thawed nutrients and thereby influence soil biological activity and
vegetation nutrient sources. Our results highlight much lower CEC density in
surface horizons (∼9400 cmolc m−3) than in the mineral
horizons of the active layer (∼16 000 cmolc m−3)
or in permafrost soil horizons (∼12 000 cmolc m−3). Together, with the overall increase in CEC density with depth and
the overall increase in BS (percentage of CEC occupied by exchangeable base
cations Ca2+, K+, Mg2+, and Na+) with depth (from
∼19 % in organic surface horizons to 62 % in permafrost soil
horizons), the total exchangeable base cation density (Ca2+, K+,
Mg2+, and Na+ in g m−3) is up to 5 times higher in the
permafrost than in the active layer. More specifically, the exchangeable
base cation density in the 20 cm upper part of permafrost about to thaw is
∼850 g m−3 for Caexch, 45 g m−3 for
Kexch, 200 g m−3 for Mgexch, and 150 g m−3 for
Naexch. This estimate is needed for future ecosystem prediction models
to provide constraints on the size of the reservoir in exchangeable
nutrients (Ca, K, Mg, and Na) about to thaw. All data described in this paper are stored in Dataverse, the online repository of Université catholique de Louvain, and are accessible through the following DOI: https://doi.org/10.14428/DVN/FQVMEP (Mauclet et al., 2022b).</p
The AARTFAAC All-Sky Monitor: System Design and Implementation
The Amsterdam-ASTRON Radio Transients Facility And Analysis Center (AARTFAAC)
all sky monitor is a sensitive, real time transient detector based on the Low
Frequency Array (LOFAR). It generates images of the low frequency radio sky
with spatial resolution of 10s of arcmin, MHz bandwidths, and a time cadence of
a few seconds, while simultaneously but independently observing with LOFAR. The
image timeseries is then monitored for short and bright radio transients. On
detection of a transient, a low latency trigger will be generated for LOFAR,
which can interrupt its schedule to carry out follow-up observations of the
trigger location at high sensitivity and resolutions. In this paper, we
describe our heterogeneous, hierarchical design to manage the 240 Gbps raw data
rate, and large scale computing to produce real-time images with minimum
latency. We discuss the implementation of the instrumentation, its performance,
and scalability.Comment: Submitted to Journal of Astronomical Instrumentation, Special issue
on 'Digital Signal Processing (DSP) in Radio Astronomy
Deep Yedoma permafrost: A synthesis of depositional characteristics and carbon vulnerability
Permafrost is a distinct feature of the terrestrial Arctic and is vulnerable to climate warming. Permafrost degrades in different ways, including deepening of a seasonally unfrozen surface and localized but rapid development of deep thaw features. Pleistocene ice-rich permafrost with syngenetic ice-wedges, termed Yedoma deposits, are widespread in Siberia, Alaska, and Yukon, Canada and may be especially prone to rapid-thaw processes. Freeze-locked organic matter in such deposits can be re-mobilized on short time-scales and contribute to a carbon cycle climate feedback. Here we synthesize the characteristics and vulnerability of Yedoma deposits by synthesizing studies on the Yedoma origin and the associated organic carbon pool. We suggest that Yedoma deposits accumulated under periglacial weathering, transport, and deposition dynamics in non-glaciated regions during the late Pleistocene until the beginning of late glacial warming. The deposits formed due to a combination of aeolian, colluvial, nival, and alluvial deposition and simultaneous ground ice accumulation. We found up to 130 gigatons organic carbon in Yedoma, parts of which are well-preserved and available for fast decomposition after thaw. Based on incubation experiments, up to 10% of the Yedoma carbon is considered especially decomposable and may be released upon thaw. The substantial amount of ground ice in Yedoma makes it highly vulnerable to disturbances such as thermokarst and thermo-erosion processes. Mobilization of permafrost carbon is expected to increase under future climate warming. Our synthesis results underline the need of accounting for Yedoma carbon stocks in next generation Earth-System-Models for a more complete representation of the permafrost-carbon feedback
Leading Order Temporal Asymptotics of the Modified Non-Linear Schrodinger Equation: Solitonless Sector
Using the matrix Riemann-Hilbert factorisation approach for non-linear
evolution equations (NLEEs) integrable in the sense of the inverse scattering
method, we obtain, in the solitonless sector, the leading-order asymptotics as
tends to plus and minus infinity of the solution to the Cauchy
initial-value problem for the modified non-linear Schrodinger equation: also
obtained are analogous results for two gauge-equivalent NLEEs; in particular,
the derivative non-linear Schrodinger equation.Comment: 29 pages, 5 figures, LaTeX, revised version of the original
submission, to be published in Inverse Problem
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The Impact of Boreal Forest Fire on Climate Warming
We report measurements and analysis of a boreal forest fire, integrating the effects of greenhouse gases, aerosols, black carbon deposition on snow and sea ice, and postfire changes in surface albedo. The net effect of all agents was to increase radiative forcing during the first year (34 ± 31 Watts per square meter of burned area), but to decrease radiative forcing when averaged over an 80-year fire cycle (–2.3 ± 2.2 Watts per square meter) because multidecadal increases in surface albedo had a larger impact than fire-emitted greenhouse gases. This result implies that future increases in boreal fire may not accelerate climate warming
Permafrost Landscape History Shapes Fluvial Chemistry, Ecosystem Carbon Balance, and Potential Trajectories of Future Change
Intensifying permafrost thaw alters carbon cycling by mobilizing large amounts of terrestrial substrate into aquatic ecosystems. Yet, few studies have measured aquatic carbon fluxes and constrained drivers of ecosystem carbon balance across heterogeneous Arctic landscapes. Here, we characterized hydrochemical and landscape controls on fluvial carbon cycling, quantified fluvial carbon fluxes, and estimated fluvial contributions to ecosystem carbon balance across 33 watersheds in four ecoregions in the continuous permafrost zone of the western Canadian Arctic: unglaciated uplands, ice-rich moraine, and organic-rich lowlands and till plains. Major ions, stable isotopes, and carbon speciation and fluxes revealed patterns in carbon cycling across ecoregions defined by terrain relief and accumulation of organics. In previously unglaciated mountainous watersheds, bicarbonate dominated carbon export (70% of total) due to chemical weathering of bedrock. In lowland watersheds, where soil organic carbon stores were largest, lateral transport of dissolved organic carbon (50%) and efflux of biotic CO2 (25%) dominated. In watersheds affected by thaw-induced mass wasting, erosion of ice-rich tills enhanced chemical weathering and increased particulate carbon fluxes by two orders of magnitude. From an ecosystem carbon balance perspective, fluvial carbon export in watersheds not affected by thaw-induced wasting was, on average, equivalent to 6%–16% of estimated net ecosystem exchange (NEE). In watersheds affected by thaw-induced wasting, fluvial carbon export approached 60% of NEE. Because future intensification of thermokarst activity will amplify fluvial carbon export, determining the fate of carbon across diverse northern landscapes is a priority for constraining trajectories of permafrost region ecosystem carbon balance
Tundra microbial community taxa and traits predict decomposition parameters of stable, old soil organic carbon.
The susceptibility of soil organic carbon (SOC) in tundra to microbial decomposition under warmer climate scenarios potentially threatens a massive positive feedback to climate change, but the underlying mechanisms of stable SOC decomposition remain elusive. Herein, Alaskan tundra soils from three depths (a fibric O horizon with litter and course roots, an O horizon with decomposing litter and roots, and a mineral-organic mix, laying just above the permafrost) were incubated. Resulting respiration data were assimilated into a 3-pool model to derive decomposition kinetic parameters for fast, slow, and passive SOC pools. Bacterial, archaeal, and fungal taxa and microbial functional genes were profiled throughout the 3-year incubation. Correlation analyses and a Random Forest approach revealed associations between model parameters and microbial community profiles, taxa, and traits. There were more associations between the microbial community data and the SOC decomposition parameters of slow and passive SOC pools than those of the fast SOC pool. Also, microbial community profiles were better predictors of model parameters in deeper soils, which had higher mineral contents and relatively greater quantities of old SOC than in surface soils. Overall, our analyses revealed the functional potential of microbial communities to decompose tundra SOC through a suite of specialized genes and taxa. These results portray divergent strategies by which microbial communities access SOC pools across varying depths, lending mechanistic insights into the vulnerability of what is considered stable SOC in tundra regions
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