22 research outputs found
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
The ST22 chronology for the Skytrain Ice Rise ice core – Part 2: An age model to the last interglacial and disturbed deep stratigraphy
We present an age model for the 651 m deep ice core from Skytrain Ice Rise,
situated inland of the Ronne Ice Shelf, Antarctica. The top 2000 years have
previously been dated using age markers interpolated through annual layer
counting. Below this, we align the Skytrain core to the AICC2012 age model
using tie points in the ice and air phase, and we apply the Paleochrono program
to obtain the best fit to the tie points and glaciological constraints. In
the gas phase, ties are made using methane and, in critical sections,
δ18Oair; in the ice phase ties are through 10Be
across the Laschamps event and through ice chemistry related to long-range
dust transport and deposition. This strategy provides a good outcome to
about 108 ka (∼ 605 m). Beyond that there are signs of flow
disturbance, with a section of ice probably repeated. Nonetheless values of
CH4 and δ18Oair confirm that part of the last
interglacial (LIG), from about 117–126 ka (617–627 m), is present and in
chronological order. Below this there are clear signs of stratigraphic
disturbance, with rapid oscillation of values in both the ice and gas phase
at the base of the LIG section, below 628 m. Based on methane values, the
warmest part of the LIG and the coldest part of the penultimate glacial are
missing from our record. Ice below 631 m appears to be of age > 150 ka.</p
Efeito dos genótipos para alphaS1-caseína sobre as frações proteicas e lipídicas do leite de cabra
Meta-analysis on the effects of the physical environment, animal traits, feeder and feed characteristics on the feeding behaviour and performance of growing-finishing pigs
Concentration of trans-vaccenic and rumenic acids in the milk from grazing cows supplemented with palm oil, rice bran or whole cottonseed
Milk saturated fatty acids, odd- and branched-chain fatty acids, and isomers of C18:1, C18:2, and C18:3n-3 according to their duodenal flows in dairy cows: A meta-analysis approach
International audienceWe sought to establish predictive response models of milk fatty acid (FA) yields or concentrations from their respective duodenal flow, rumen digestive parameters, or diet characteristics in dairy cows, with a special focus on cis and trans isomers of C18:1, C18:2, odd- and branched FA, and mammary de novo synthesized FA. This meta-analysis was carried out using data from trials with nature of forage, percentage of concentrate, supplementation of diets with vegetable oils or seeds, and marine products' animal fats as experimental factors. The data set included 34 published papers representing 50 experiments with 142 treatments. Increasing duodenal C18 FA flow induced a quadratic increase in milk total C18 yield and a linear decrease in milk C4:0 to C14:0 concentration. Intra-experirnental predictive response models of individual milk cis C18:1 isomers (Delta 11 to 15 position) from their respective duodenal flows had coefficients of determination (R-2) ranging from 0.74 to 0.99, with root mean square error varying from 0.19 to 0.96 g/d, 0.02 to 0.10% of total FA, and 0.03 to 0.29% of C18 FA. Models predicting milk trans C18:1 isomer yields or concentrations had R-2 greater than 0.90 (except for trans-4 and trans-10 C18:1) with root mean square error varying from less than 0.1 to 5.2 g/d. Linear regressions for C18:2n-6, trans-10,cis-12 CLA, and trans-11,trans-13 CLA were calculated according to their respective duodenal flows. Quadratic models of milk C18:3n-3 yield or concentration from its duodenal flow had R-2 values above 0.97. Models of amounts desaturated from C18:0 into cis-9 C18:1 and trans-11 C18:1 into cis-9,trans-11 CLA indicated that the contribution of C18:0 and trans-11 C18:1 desaturation to respective cis-9 C18:1 and cis-9,trans-11 CLA yields in milk fat was 83.8% (+/- 0.75) and 86.8% (+/- 2.8). Furthermore, when cows were fed marine products, our results could indicate a lower mammary uptake of C18:0 and trans-11 C18:1 in proportion to their respective duodenal flow, with no associated change in mammary Delta(9)-desaturase activity. Yields or concentrations of C15:0, C17:0, iso-C15:0, iso-C17:0, anteiso-C15:0, and anteiso-C17:0 were dependent on their respective duodenal flow or concentration at duodenum, but synthesis of these FA from C3 units for linear-chain odd FA, and from C2 units for branched-chain FA was suggested, respectively. Several milk C18 FA concentrations were closely related to their duodenal concentrations with slopes of the linear models close to the bisector; this could reflect a priority for the use of these duodenal C18 FA by the mammary gland to favor their high concentration in plasma triglycerides arid nonesterified FA, which are preferentially taken up by the mammary gland
In vivo prediction of goat kids body composition from the deuterium oxide dilution space determined by isotope-ratio mass spectrometry1
Abrupt CO2 release to the atmosphere under glacial and early interglacial climate conditions
Bursts of carbon dioxide, released into the atmosphere and occurring on centennial time scales, were seen during the cold periods of the last glacial cycle but not in older or warmer conditions. Nehrbass-Ahles et al. present a record of atmospheric carbon dioxide concentrations retrieved from the European Project for Ice Coring in Antarctica Dome C ice core showing that these carbon dioxide jumps occurred during both cold and warm periods between 330,000 and 450,000 years ago. They relate these pulses to disruptions of the Atlantic meridional overturning circulation caused by freshwater discharge from ice sheets. Such rapid carbon dioxide increases could occur in the future if global warming also disrupts this ocean circulation pattern.Science, this issue p. 1000Pulse-like carbon dioxide release to the atmosphere on centennial time scales has only been identified for the most recent glacial and deglacial periods and is thought to be absent during warmer climate conditions. Here, we present a high-resolution carbon dioxide record from 330,000 to 450,000 years before present, revealing pronounced carbon dioxide jumps (CDJ) under cold and warm climate conditions. CDJ come in two varieties that we attribute to invigoration or weakening of the Atlantic meridional overturning circulation (AMOC) and associated northward and southward shifts of the intertropical convergence zone, respectively. We find that CDJ are pervasive features of the carbon cycle that can occur during interglacial climate conditions if land ice masses are sufficiently extended to be able to disturb the AMOC by freshwater input