61 research outputs found
Temporally delineated sources of major chemical species in high Arctic snow
Long-range transport of aerosol from lower latitudes to
the high Arctic may be a significant contributor to climate forcing in the
Arctic. To identify the sources of key contaminants entering the Canadian
High Arctic an intensive campaign of snow sampling was completed at Alert,
Nunavut, from September 2014 to June 2015. Fresh snow samples collected
every few days were analyzed for black carbon, major ions, and metals, and
this rich data set provided an opportunity for a temporally refined source
apportionment of snow composition via positive matrix factorization (PMF) in
conjunction with FLEXPART (FLEXible PARTicle dispersion model) potential emission sensitivity analysis. Seven
source factors were identified: sea salt, crustal metals, black carbon,
carboxylic acids, nitrate, non-crustal metals, and sulfate. The sea salt
and crustal factors showed good agreement with expected composition and
primarily northern sources. High loadings of V and Se onto Factor 2, crustal
metals, was consistent with expected elemental ratios, implying these metals
were not primarily anthropogenic in origin. Factor 3, black carbon, was an
acidic factor dominated by black carbon but with some sulfate contribution
over the winter-haze season. The lack of K+ associated with this
factor, a Eurasian source, and limited known forest fire events coincident
with this factor's peak suggested a predominantly anthropogenic combustion
source. Factor 4, carboxylic acids, was dominated by formate and acetate
with a moderate correlation to available sunlight and an oceanic and North
American source. A robust identification of this factor was not possible;
however, atmospheric photochemical reactions, ocean microlayer reaction, and
biomass burning were explored as potential contributors. Factor 5, nitrate,
was an acidic factor dominated by NO3−, with a likely Eurasian
source and mid-winter peak. The isolation of NO3− on a separate
factor may reflect its complex atmospheric processing, though the associated
source region suggests possibly anthropogenic precursors. Factor 6,
non-crustal metals, showed heightened loadings of Sb, Pb, and As, and
correlation with other metals traditionally associated with industrial
activities. Similar to Factor 3 and 5, this factor appeared to be largely
Eurasian in origin. Factor 7, sulfate, was dominated by SO42− and
MS with a fall peak and high acidity. Coincident volcanic activity and
northern source regions may suggest a processed SO2 source of this
factor
Symbolic meanings and e-learning in the workplace: The case of an intranet-based training tool
This article contributes to the debate on work-based e-learning, by unpacking the notion of ‘the learning context’ in a case where the mediating tool for training also supports everyday work. Users’ engagement with the information and communication technology tool is shown to reflect dynamic interactions among the individual, peer group, organizational and institutional levels. Also influential are professionals’ values and identity work, alongside their interpretations of espoused and emerging symbolic meanings. Discussion draws on pedagogically informed studies of e-learning and the wider organizational learning literature. More centrally, this article highlights the instrumentality of symbolic interactionism for e-learning research and explores some of the framework’s conceptual resources as applied to organizational analysis and e-learning design. </jats:p
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Precise interpolar phasing of abrupt climate change during the last ice age
The last glacial period exhibited abrupt Dansgaard–Oeschger climatic oscillations, evidence of which is preserved in a variety of Northern Hemisphere palaeoclimate archives¹. Ice cores show that Antarctica cooled during the warm phases of the Greenland Dansgaard–Oeschger cycle and vice versa[superscript 2,3], suggesting an interhemispheric redistribution of heat through a mechanism called the bipolar seesaw[superscript 4–6]. Variations in the Atlantic meridional overturning circulation (AMOC) strength are thought to have been important, but much uncertainty remains regarding the dynamics and trigger of these abrupt events[superscript 7–9]. Key information is contained in the relative phasing of hemispheric climate variations, yet the large, poorly constrained difference between gas age and ice age and the relatively low resolution of methane records from Antarctic ice cores have so far precluded methane-based synchronization at the required sub-centennial precision[superscript 2,3,10]. Here we use a recently drilled high-accumulation Antarctic ice core to show that, on average, abrupt Greenland warming leads the corresponding Antarctic cooling onset by 218 ± 92 years (2σ) for Dansgaard–Oeschger events, including the Bølling event; Greenland cooling leads the corresponding onset of Antarctic warming by 208 ± 96 years. Our results demonstrate a north-to-south directionality of the abrupt climatic signal, which is propagated to the Southern Hemisphere high latitudes by oceanic rather than atmospheric processes. The similar interpolar phasing of warming and cooling transitions suggests that the transfer time of the climatic signal is independent of the AMOC background state. Our findings confirm a central role for ocean circulation in the bipolar seesaw and provide clear criteria for assessing hypotheses and model simulations of Dansgaard–Oeschger dynamics
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