- Email: [email protected]
Spatio-temporal variability of black carbon recorded in Greenland ice cores over the last centuries
Abstracts / Quaternary International 279-280 (2012) 346–461
amino acid geochronology. The analytical results on this species are generally more variable than for other taxa, however, prompting us to identify the origin of the variability. Eighteen samples of N. pachyderma from IODP site U1308 ranging in age from 0.2 to 1.4 Ma were analyzed two years after being extracted from sediment and stored dry (Hodell et al., 2008, Paleoceanography 23: PA4218). The results were compared with analyses of N. pachyderma from the same core levels prepared from freshly sampled mud supplied from IODP. The stored samples show unexpectedly high L-Ser concentrations and low D/L values for multiple amino acids, indicating contamination by young amino acids. In contrast, the newly prepared samples showed significantly lower L-Ser concentrations (by 62%), and an improved downcore trend of D/L values. In a second experiment, we tested the difference between the amino acid compositions of opaque versus transparent tests separated from five core layers. The results showed that transparent tests have significantly lower L-Ser/L-Asp values, by 37%, and an improved downcore trend in D/L values. Opaque tests had acceptably low L-Ser concentrations (L-Ser/LAsp < 0.8) in only 8 out of 27 replicates, versus transparent tests, which had low L-Ser in 22 out of 29 replicates. The bulk sediment from six layers contains unusually high concentrations of L-Ser, regardless of whether the associated fossils contained high or low L-Ser. Scanning electron microscopy revealed no obvious differences between the two types, nor signs of microbial degradation. These results indicate that, while the source of the L-Ser has not yet been determined, opaque tests of N. pachyderma and samples that have been stored for long periods are unsuitable for amino acid geochronology. RESPONSE OF TREES FROM HIGH-LATITUDE AND HIGH-ALTITUDE REGIONS TO EXTREME EVENTS DURING THE LAST 1500 YEARS Olga Sidorova. Paul Scherrer Institute, Switzerland E-mail address: [email protected]
Trees growing at tree line sites are very sensitive to climatic and environmental changes. The tree-ring width, tree-ring density, and cell structure chronologies provide strong summer temperature information, while the stable isotopes provide information about precipitation, relative humidity and water availability. Spatial climatic changes ranging from high latitude northeastern Yakutia (70 N, 148 E), eastern Taimyr (70 N, 103 E) and high altitudes - Siberian Altai (49 N, 86 E) are presented based on tree-ring width, cell structure, d13C, d18O chronologies from larch for the period 1900-2006 and selected extreme periods during the last 1500 years. For extreme periods, characterized by major stratospheric volcanic eruptions, we observed strongly decreasing tree-ring widths, latewood density, cell sizes and stable isotope values after each event. This isotope response might be caused by an increase of relative humidity, which resulted in higher stomatal conductance and lower photosynthetic capacity due to a reduction of solar radiation and temperature and consequently increased cloudiness. ANNUALLY RESOLVED RECORDS OF VOLCANISM FROM THE WAIS DIVIDE ICE CORE (ANTARCTICA) FOR THE EARLY AND LATE HOLOCENE Michael Sigl. Desert Research Institute, United States E-mail address: [email protected]
Volcanism is a natural climate forcing causing short-term variations. To quantify the role of volcanic eruptions in natural climate variability and to assess the human influence on climate, longer and more comprehensive records than the documentary history of volcanic eruptions are needed. Here we present a new, ice core derived record of past volcanism from the Western Antarctic Ice Sheet (WAIS) Divide. The high accumulation rates at the ice core site combined with the high sampling resolution of the continuous-flow analytical system result in records with unprecedented time resolution for Antarctica. We present (sub)-annually resolved, annual-layer-counted, non-sea-salt sulfur (nss-S) records from Western Antarctica spanning the time periods 430 BC to AD 2007 and 6100 to 9800 years BP (early Holocene). We discuss the frequency of volcanic eruptions during the two time windows.
449
Volcanic signals reported from Antarctic low-accumulation sites (e.g. EPICA Dome C) are well recorded in the WAIS Divide ice core, allowing evaluation of the accuracy of different ice core timescales and dating approaches. Also spatial differences of volcanic sulfur fluxes between Western and Eastern Antarctica can be addressed. The high dating precision allows a direct comparison to the synchronized, annual-layer counted ice core chronology for Greenland (GICC05) so that signals from local Antarctic eruptions and large tropical eruptions can be disentangled. This geographical information is important as the distribution of volcanic fallout has implications for the climatic forcing. SPATIO-TEMPORAL VARIABILITY OF BLACK CARBON RECORDED IN GREENLAND ICE CORES OVER THE LAST CENTURIES Michael Sigl. Desert Research Institute, United States E-mail address: [email protected]
Aerosols affect the radiative forcing of Earth's climate by scattering incoming solar radiation. Black carbon (BC) is especially important to climate forcing in Greenland because of its impact on albedo. BC is emitted by forest fires, biomass burning and in recent time by fossil fuel combustion. With their short lifetimes in the atmosphere, aerosol concentrations and deposition are dominated by regional, rather than global, sources, transport processes, and pathways. However, detailed understanding of past and present concentrations, deposition rates, sources, and transport pathways of BC to Greenland is critical to the design of effective mitigation policies. At present, uncertainties in the climate forcing effects ascribed to aerosols are large. This is due to the high spatio-temporal variability of aerosol emission and deposition. As a result, arrays of historical, high-time-resolution records with a broad range of analytes are required to understand aerosol concentrations, sources, and variability while providing adequate information for evaluating global circulation, snowpack radiation, and other models. Here we present and discuss recent findings from measurements of BC and related source tracers in an array of ice cores from Greenland covering the last three centuries. YEAR-ROUND MONITORING OF TRACE ELEMENTS FROM GREENLAND ENVIRONMENTAL OBSERVATORY AT SUMMIT (GEOSUMMIT) Michael Sigl. Desert Research Institute, United States E-mail address: [email protected]
High-resolution trace element records from polar ice cores are widely used to identify proxies of dust aerosols. However, the link between measured concentrations in ice and atmospheric concentrations until aerosol deposition is not well constrained. Long-term year round sampling of the arctic atmosphere and snow provide insight to the relationship between aerosol and snow chemical composition. Current research at the Greenland Environmental Observatory Summit Station (GEOSummit) includes high temporal resolution year-round IC and ICPMS trace element measurements of surface-snow and snow-pit samples, measurement of snow accumulation and spatial variability, DRUM aerosol size and S-XRF elemental atmospheric composition and other meteorological and snow properties. These measurements allow for a better understanding of the timing and magnitude of the seasonal cycle in elemental concentrations that are deposited and preserved in the snow pack. Elemental concentration records from 2005 to 2010 were analyzed using Positive Matrix Factorization (PMF) to identify unique source factors representative of sea salt, dust and other potential sources such as biomass burning. The PMF source factors exhibit distinct seasonal cycles with significant year to year variability. The PMF source factor compositions match closely with reported source profiles from an array of Greenland ice cores. Snow accumulation rates were concurrently measured, allowing evaluation of dry and wet deposition as well as quantification of the inter-annual variability in seasonal snow accumulation. Continuous longer-term records are fundamental to analyze links between aerosol and snow chemistry to atmospheric processes with multi-year periodicities (e.g. AO, NAO).
amino acid geochronology. The analytical results on this species are generally more variable than for other taxa, however, prompting us to identify the origin of the variability. Eighteen samples of N. pachyderma from IODP site U1308 ranging in age from 0.2 to 1.4 Ma were analyzed two years after being extracted from sediment and stored dry (Hodell et al., 2008, Paleoceanography 23: PA4218). The results were compared with analyses of N. pachyderma from the same core levels prepared from freshly sampled mud supplied from IODP. The stored samples show unexpectedly high L-Ser concentrations and low D/L values for multiple amino acids, indicating contamination by young amino acids. In contrast, the newly prepared samples showed significantly lower L-Ser concentrations (by 62%), and an improved downcore trend of D/L values. In a second experiment, we tested the difference between the amino acid compositions of opaque versus transparent tests separated from five core layers. The results showed that transparent tests have significantly lower L-Ser/L-Asp values, by 37%, and an improved downcore trend in D/L values. Opaque tests had acceptably low L-Ser concentrations (L-Ser/LAsp < 0.8) in only 8 out of 27 replicates, versus transparent tests, which had low L-Ser in 22 out of 29 replicates. The bulk sediment from six layers contains unusually high concentrations of L-Ser, regardless of whether the associated fossils contained high or low L-Ser. Scanning electron microscopy revealed no obvious differences between the two types, nor signs of microbial degradation. These results indicate that, while the source of the L-Ser has not yet been determined, opaque tests of N. pachyderma and samples that have been stored for long periods are unsuitable for amino acid geochronology. RESPONSE OF TREES FROM HIGH-LATITUDE AND HIGH-ALTITUDE REGIONS TO EXTREME EVENTS DURING THE LAST 1500 YEARS Olga Sidorova. Paul Scherrer Institute, Switzerland E-mail address: [email protected]
Trees growing at tree line sites are very sensitive to climatic and environmental changes. The tree-ring width, tree-ring density, and cell structure chronologies provide strong summer temperature information, while the stable isotopes provide information about precipitation, relative humidity and water availability. Spatial climatic changes ranging from high latitude northeastern Yakutia (70 N, 148 E), eastern Taimyr (70 N, 103 E) and high altitudes - Siberian Altai (49 N, 86 E) are presented based on tree-ring width, cell structure, d13C, d18O chronologies from larch for the period 1900-2006 and selected extreme periods during the last 1500 years. For extreme periods, characterized by major stratospheric volcanic eruptions, we observed strongly decreasing tree-ring widths, latewood density, cell sizes and stable isotope values after each event. This isotope response might be caused by an increase of relative humidity, which resulted in higher stomatal conductance and lower photosynthetic capacity due to a reduction of solar radiation and temperature and consequently increased cloudiness. ANNUALLY RESOLVED RECORDS OF VOLCANISM FROM THE WAIS DIVIDE ICE CORE (ANTARCTICA) FOR THE EARLY AND LATE HOLOCENE Michael Sigl. Desert Research Institute, United States E-mail address: [email protected]
Volcanism is a natural climate forcing causing short-term variations. To quantify the role of volcanic eruptions in natural climate variability and to assess the human influence on climate, longer and more comprehensive records than the documentary history of volcanic eruptions are needed. Here we present a new, ice core derived record of past volcanism from the Western Antarctic Ice Sheet (WAIS) Divide. The high accumulation rates at the ice core site combined with the high sampling resolution of the continuous-flow analytical system result in records with unprecedented time resolution for Antarctica. We present (sub)-annually resolved, annual-layer-counted, non-sea-salt sulfur (nss-S) records from Western Antarctica spanning the time periods 430 BC to AD 2007 and 6100 to 9800 years BP (early Holocene). We discuss the frequency of volcanic eruptions during the two time windows.
449
Volcanic signals reported from Antarctic low-accumulation sites (e.g. EPICA Dome C) are well recorded in the WAIS Divide ice core, allowing evaluation of the accuracy of different ice core timescales and dating approaches. Also spatial differences of volcanic sulfur fluxes between Western and Eastern Antarctica can be addressed. The high dating precision allows a direct comparison to the synchronized, annual-layer counted ice core chronology for Greenland (GICC05) so that signals from local Antarctic eruptions and large tropical eruptions can be disentangled. This geographical information is important as the distribution of volcanic fallout has implications for the climatic forcing. SPATIO-TEMPORAL VARIABILITY OF BLACK CARBON RECORDED IN GREENLAND ICE CORES OVER THE LAST CENTURIES Michael Sigl. Desert Research Institute, United States E-mail address: [email protected]
Aerosols affect the radiative forcing of Earth's climate by scattering incoming solar radiation. Black carbon (BC) is especially important to climate forcing in Greenland because of its impact on albedo. BC is emitted by forest fires, biomass burning and in recent time by fossil fuel combustion. With their short lifetimes in the atmosphere, aerosol concentrations and deposition are dominated by regional, rather than global, sources, transport processes, and pathways. However, detailed understanding of past and present concentrations, deposition rates, sources, and transport pathways of BC to Greenland is critical to the design of effective mitigation policies. At present, uncertainties in the climate forcing effects ascribed to aerosols are large. This is due to the high spatio-temporal variability of aerosol emission and deposition. As a result, arrays of historical, high-time-resolution records with a broad range of analytes are required to understand aerosol concentrations, sources, and variability while providing adequate information for evaluating global circulation, snowpack radiation, and other models. Here we present and discuss recent findings from measurements of BC and related source tracers in an array of ice cores from Greenland covering the last three centuries. YEAR-ROUND MONITORING OF TRACE ELEMENTS FROM GREENLAND ENVIRONMENTAL OBSERVATORY AT SUMMIT (GEOSUMMIT) Michael Sigl. Desert Research Institute, United States E-mail address: [email protected]
High-resolution trace element records from polar ice cores are widely used to identify proxies of dust aerosols. However, the link between measured concentrations in ice and atmospheric concentrations until aerosol deposition is not well constrained. Long-term year round sampling of the arctic atmosphere and snow provide insight to the relationship between aerosol and snow chemical composition. Current research at the Greenland Environmental Observatory Summit Station (GEOSummit) includes high temporal resolution year-round IC and ICPMS trace element measurements of surface-snow and snow-pit samples, measurement of snow accumulation and spatial variability, DRUM aerosol size and S-XRF elemental atmospheric composition and other meteorological and snow properties. These measurements allow for a better understanding of the timing and magnitude of the seasonal cycle in elemental concentrations that are deposited and preserved in the snow pack. Elemental concentration records from 2005 to 2010 were analyzed using Positive Matrix Factorization (PMF) to identify unique source factors representative of sea salt, dust and other potential sources such as biomass burning. The PMF source factors exhibit distinct seasonal cycles with significant year to year variability. The PMF source factor compositions match closely with reported source profiles from an array of Greenland ice cores. Snow accumulation rates were concurrently measured, allowing evaluation of dry and wet deposition as well as quantification of the inter-annual variability in seasonal snow accumulation. Continuous longer-term records are fundamental to analyze links between aerosol and snow chemistry to atmospheric processes with multi-year periodicities (e.g. AO, NAO).