120 research outputs found
A Holocene black carbon ice-core record of biomass burning in the Amazon Basin from Illimani, Bolivia
The Amazon Basin is one of the major contributors to global
biomass burning emissions. However, regional paleofire trends remain
particularly unknown. Due to their proximity to the Amazon Basin, Andean ice
cores are suitable to reconstruct paleofire trends in South America and
improve our understanding of the complex linkages between fires, climate and
humans. Here we present the first refractory black carbon (rBC) ice-core
record from the Andes as a proxy for biomass burning emissions in the Amazon
Basin, derived from an ice core drilled at 6300 m a.s.l. from the Illimani
glacier in the Bolivian Andes and spanning the entire Holocene back to the
last deglaciation 13 000Â years ago. The Illimani rBC record displays a
strong seasonality with low values during the wet season and high values
during the dry season due to the combination of enhanced biomass burning
emissions in the Amazon Basin and less precipitation at the Illimani site.
Significant positive (negative) correlations were found with reanalyzed
temperature (precipitation) data for regions in eastern
Bolivia and western Brazil characterized by substantial fire activity. rBC
long-term trends indirectly reflect regional climatic variations through
changing biomass burning emissions as they show higher (lower) concentrations
during warm–dry (cold–wet) periods, in line with climate
variations such as the Younger Dryas, the 8.2 ka event, the Holocene
Climatic Optimum, the Medieval Warm Period and the Little Ice Age. The highest
rBC concentrations of the entire record occurred during the Holocene Climatic
Optimum between 7000 and 3000 BCE, suggesting that this exceptionally warm and
dry period caused high levels of biomass burning activity, unprecedented in the
context of the past 13 000Â years. Recent rBC levels, rising since 1730 CE
in the context of increasing temperatures and deforestation, are similar to
those of the Medieval Warm Period. No decrease in fire activity was observed
in the 20th century, in contradiction to global biomass burning
reconstructions based on charcoal data.</p
An 800-year high-resolution black carbon ice core record from Lomonosovfonna, Svalbard
Produced by the incomplete combustion of fossil fuel and biomass, black
carbon (BC) contributes to Arctic warming by reducing snow albedo and thus
triggering a snow-albedo feedback leading to increased snowmelt. Therefore,
it is of high importance to assess past BC emissions to better understand and
constrain their role. However, only a few long-term BC records are available
from the Arctic, mainly originating from Greenland ice cores. Here, we
present the first long-term and high-resolution refractory black carbon (rBC)
record from Svalbard, derived from the analysis of two ice cores drilled at
the Lomonosovfonna ice field in 2009 (LF-09) and 2011 (LF-11) and covering
800 years of atmospheric emissions. Our results show that rBC concentrations
strongly increased from 1860 on due to anthropogenic emissions and reached
two maxima, at the end of the 19th century and in the middle of the 20th
century. No increase in rBC concentrations during the last decades was
observed, which is corroborated by atmospheric measurements elsewhere in the
Arctic but contradicts a previous study from another ice core from Svalbard.
While melting may affect BC concentrations during periods of high
temperatures, rBC concentrations remain well preserved prior to the 20th
century due to lower temperatures inducing little melt. Therefore, the
preindustrial rBC record (before 1800), along with ammonium (NH4+),
formate (HCOO−) and specific organic markers (vanillic acid, VA, and
p-hydroxybenzoic acid, p-HBA), was used as a proxy for
biomass burning. Despite numerous single events, no long-term trend was
observed over the time period 1222–1800 for rBC and NH4+. In
contrast, formate, VA, and p-HBA experience multi-decadal peaks reflecting
periods of enhanced biomass burning. Most of the background variations and
single peak events are corroborated by other ice core records from Greenland
and Siberia. We suggest that the paleofire record from the LF ice core
primarily reflects biomass burning episodes from northern Eurasia, induced by
decadal-scale climatic variations.</p
Linear discriminant analysis reveals differences in root architecture in wheat seedlings by nitrogen uptake efficiency
Root architecture impacts water and nutrient uptake efficiency. Identifying exactly which root architectural properties influence these agronomic traits can prove challenging. In this paper approximately 300 wheat plants were divided into four groups using two binary classifications, high vs. low nitrogen uptake efficiency (NUpE), and high vs. low nitrate in medium. The root system architecture for each wheat plant was captured using 16 quantitative variables. The multivariate analysis tool, linear discriminant analysis, was used to construct composite variables, each a linear combination of the original variables, such that the score of the wheat plants on the new variables showed the maximum between-group variability. The results show that the distribution of root system architecture traits differ between low and high NUpE wheat plants and, less strongly, between low NUpE wheat plants grown on low vs. high nitrate media
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