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Droplets produced in a cloud condensation nuclei chamber (CCNC) as a function of supersaturation have been separated from unactivated aerosol particles using counterflow virtual impaction. Residual material after droplets were evaporated was chemically analyzed with an Aerodyne Aerosol Mass Spectrometer (AMS) and the Particle Analysis by Laser Mass Spectrometry (PALMS) instrument. Experiments were initially conducted to verify activation conditions for monodisperse ammonium sulfate particles and to determine the resulting droplet size distribution as a function of supersaturation. Based on the observed droplet size, the counterflow virtual impactor cut-size was set to differentiate droplets from unactivated interstitial particles. Validation experiments were then performed to verify that only droplets with sufficient size passed through the counterflow virtual impactor for subsequent analysis. A two-component external mixture of monodisperse particles was also exposed to a supersaturation which would activate one of the types (hygroscopic salts) but not the other (polystyrene latex spheres or adipic acid). The mass spectrum observed after separation indicated only the former, validating separation of droplets from unactivated particles. Results from ambient measurements using this technique and AMS analysis were inconclusive, showing little chemical differentiation between ambient aerosol and activated droplet residuals, largely due to low signal levels. When employing as single particle mass spectrometer for compositional analysis, however, we observed enhancement of sulfate in droplet residuals.
Droplets produced in a cloud condensation nucleus chamber as a function of supersaturation have been separated from unactivated aerosol particles using counterflow virtual impaction. Residual material after droplets were evaporated was chemically analyzed with an Aerodyne Aerosol Mass Spectrometer and the Particle Analysis by Laser Mass Spectrometry instrument. Experiments were initially conducted to verify activation conditions for monodisperse ammonium sulfate particles and to determine the resulting droplet size distribution as a function of supersaturation. Based on the observed droplet size, the counterflow virtual impactor cut-size was set to differentiate droplets from unactivated interstitial particles. Validation experiments were then performed to verify that only droplets with sufficient size passed through the counterflow virtual impactor for subsequent analysis. A two-component external mixture of monodisperse particles was also exposed to a supersaturation which would activate one of the types (ammonium sulfate) but not the other (polystyrene latex spheres). The mass spectrum observed after separation indicated only the former, validating separation of droplets from unactivated particles. Results from atmospheric measurements using this technique indicate that aerosol particles often activate predominantly as a function of particle size. Chemical composition is not irrelevant, however, and we observed enhancement of sulfate in droplet residuals using single particle analysis.
The performance of an ion source based on corona discharge has been studied. This source is used for the detection of gaseous sulfuric acid by chemical ionization mass spectrometry (CIMS) through the reaction of NO−3 ions with H2SO4. The ion source is operated under atmospheric pressure and its design is similar to the one of a radioactive (americium-241) ion source which has been used previously. The results show that the detection limit for the corona ion source is sufficiently good for most applications. For an integration time of 1 min it is ~6×104 molecule cm−3 of H2SO4. In addition, only a small cross-sensitivity to SO2 has been observed for concentrations as high as 1 ppmv in the sample gas. This low sensitivity to SO2 is achieved even without the addition of an OH scavenger. When comparing the new corona ion source with the americium ion source for the same provided H2SO4 concentration, both ion sources yield almost identical values. These features make the corona ion source investigated here favorable over the more commonly used radioactive ion sources for most applications where H2SO4 is measured by CIMS.
The performance of an ion source based on corona discharge has been studied. This source is used for the detection of gaseous sulfuric acid by chemical ionization mass spectrometry (CIMS) through the reaction of NO3– ions with H2SO4. The ion source is operated under atmospheric pressure and its design is similar to the one of a radioactive (Americium 241) ion source which has been used previously. Our results show that the detection limit for the corona ion source is sufficiently good for most applications. For an integration time of one minute it is ~6 × 104 molecules of H2SO4 per cm3. In addition, only a small cross-sensitivity to SO2 has been observed for concentrations as high as 1 ppmv in the sample gas. This low sensitivity to SO2 is achieved even without the addition of an OH scavenger. When comparing the new corona ion source with the americium ion source for the same provided H2SO4 concentration, both ion sources yield almost identical values. These features make the corona ion source investigated here favorable over the more commonly used radioactive ion sources for most applications where H2SO4 is measured by CIMS.
To unravel the short-term climate variability during Marine Isotope Stage (MIS) 11, which represents a close analogue to the Holocene with regard to orbital boundary conditions, we performed microfacies and time series analyses on a ~3200-yr-long record of annually laminated Holsteinian lake sediments from Dethlingen, northern Germany. These biogenic varves comprise two sub-layers: A light layer, which is controlled by spring/summer diatom blooms, and a dark layer consisting mainly of amorphous organic matter and fragmented diatom frustules deposited during autumn/winter. Time series analyses were performed on the thickness of the light and dark layers. Signals exceeding the 95 % and 99 % confidence levels occur at periods that are near-identical to those known from modern instrumental data and Holocene palaeoclimatic records. Spectral peaks at periods of 90, 25, and 10.5 yr are likely associated with the 88-, 22- and 11-yr solar cycles, respectively. This variability is mainly expressed in the light layer spectra, suggesting solar influence on the palaeoproductivity of the lake. Significant signals at periods between 3 and 5 yr and at ~6 yr are strongest expressed in the dark layer spectra and may reflect an influence of the El Niño-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) during autumn/winter. Our results suggest that solar forcing and ENSO/NAO-like variability influenced central European climate during MIS 11 similar to the present interglacial, thus demonstrating the comparability of the two interglacial periods at sub-decadal to decadal timescales.
Owing to long-term similarities with regard to orbital climate forcing (i.e., low eccentricity and a dampened influence of precession), Marine Isotope Stage (MIS) 11 represents one of the closest astronomical analogues for present and future climate. Hence, insights into the climate variability of MIS 11 can contribute to a better understanding of the climatic evolution of the present (Holocene) interglacial as it would occur without human interference. In order to elucidate the natural climate variability during MIS 11, this study examines predominantly annually laminated lake sediments of Holsteinian age from Dethlingen, northern Germany. The Holsteinian interglacial is widely accepted to be the terrestrial equivalent of MIS 11c in central Europe and can be biostratigraphically correlated with the Hoxnian, Mazovian and Praclaux interglacials on the British Isles, in Poland and in France, respectively. These correlations yield the potential to cross-check the results from individual sites on a regional scale. This study is based on a multi-proxy approach including palynological, micropaleontological, sedimentological, geochemical and time series analyses within a wellconstrained chronological framework that has been established through varve counting and regional bio-stratigraphic correlations with other annually laminated archives of Holsteinian age. In particular, the here-presented study aims at (i) fingerprinting the long-term (centennial- to millennial-scale) and short-term (sub-decadal- to decadal-scale) climate variability during the Holsteinian interglacial, (ii) deciphering the nature, tempo and trigger mechanisms of abrupt climate change under interglacial boundary conditions, and (iii) assessing its impact on terrestrial ecosystems. With regard to long-term climate variability, the vegetation succession at Dethlingen as inferred from pollen data provides insights into the mesocratic to telocratic forest phases of a glacial-interglacial cycle spanning ~11500 (± 1000) years of the 15-16-ka-long Holsteinian interglacial. The development of temperate mixed forests suggests a general prevalence of mild climatic conditions during the Holsteinian. The older parts of the interglacial are characterised by the strong presence of boreal tree taxa (e.g., Picea), whereas the younger parts of the interglacial are marked by the expansion of sub-Atlantic to Atlantic forest elements (e.g., Abies, Buxus, Ilex, Quercus) and the decline of boreal tree taxa. This vegetation succession suggests a general warming trend and decreasing seasonality over the course of the Holsteinian interglacial. Based on the maximum pollen abundances of indicator tree taxa (e.g., Buxus and Quercus), peak warmth was reached during the later stages of the interglacial; it was accompanied by high humidity. The forest succession of the Holsteinian interglacial was punctuated by abrupt and gradual changes in the abundances of temperate plant taxa. These vegetation changes indicate considerable intra-interglacial climate variability. In particular, two marked declines of temperate taxa leading to the transient development of boreal and sub-boreal forests were triggered by centennial-scale climate oscillations, here termed Older and Younger Holsteinian Oscillations (OHO and YHO). These oscillations occurred ~6000 and ~9000 years after the onset of the interglacial pioneer forestation in central Europe, respectively. To assess the impact of abrupt climate change on terrestrial ecosystems during the Holsteinian and to investigate the underlying driving mechanisms, the intervals spanning the OHO and the YHO at Dethlingen were subjected to decadal-scale palynological and sedimentological analyses. Based on these data, the OHO comprises a 90-year-long decline of temperate taxa associated with expansion of Pinus and non-arboreal pollen, and a subsequent 130-year-long recovery of temperate taxa marked by the pioneer expansion of Betula and Alnus. Owing to its highly characteristic imprint on vegetation dynamics, the OHO can be identified in pollen records from the central European lowlands north of 50º latitude, from the British Isles to Poland. A close inspection of individual pollen records from that region reveals the prevalence of colder winters during the OHO, with a gradient of decreasing temperature and moisture availability, and increased continentality towards eastern Europe. This climate pattern points to a weakened influence of the westerlies and/or stronger influence of the Siberian High connected to the OHO. The vegetation dynamics during the YHO are characterised by a decline of temperate taxa (particularly of Carpinus) and the expansion of pioneer trees (mainly Betula). In contrast to the OHO, frost-sensitive taxa (e.g., Ilex, Buxus and Hedera) continued to thrive. This suggests that mean winter temperatures remained relatively high (>0 ºC) during the YHO pointing to a decrease of summer warmth related to the climatic deterioration. The YHO, which has a duration on the order of 300 years, is centered within a long-term (~1500-year) decline and subsequent, millennial-scale recovery of temperate taxa. Because the impact of the OHO and the YHO on the vegetation at Dethlingen was markedly different, both short-term climate oscillations may have been caused by different trigger mechanisms. For the OHO, the inferred regional-scale winter cooling over central Europe lasting for several decades points to a decrease in ocean heat transport, most likely related to a transient slowdown in North Atlantic Deep Water formation. This view is supported by the strong resemblance of the OHO to the 8.2 ka event of the Holocene with regard to the duration, imprint on terrestrial ecosystems, spatial pattern of the climatic impact, timing within the respective interglacial, and prevailing interglacial boundary conditions. In contrast, the presence of frost-sensitive taxa during the YHO appears to exclude a reduction in oceanic heat transport as postulated for the OHO. Instead, the long-lasting, gradual changes in the abundances of temperate taxa suggest a connection to orbital forcing, with the triggering mechanism causing the centennial-scale vegetation setback itself remaining unclear. The characteristics of short-term climate variability were investigated based on microfacies and time series analyses of a ~3200-year-long, annually laminated window of the Dethlingen record. The annual laminations at Dethlingen comprise biogenic varves consisting of two discrete sub-layers. The light layers, which are controlled by the intensity of diatoms blooms during spring/summer, reflect changes in the productivity of the Dethlingen palaeolake. In contrast, the dark layers, which consist predominantly of amorphous organic matter and fragmented diatom frustules, represent sediment deposition during autumn/winter. Spectral analyses of the thicknesses of the light and dark layers have revealed several peaks exceeding the 95% and 99% confidence levels that are near-identical to those known from modern instrumental data and Holocene records. Decadal-scale signals at periods of 90, 25, and 10.5 years are likely associated with the 88-, 22- and 11-year solar cycles; hence, solar activity appears to have been a forcing agent in productivity changes of the Dethlingen palaeolake. Sub-decadal-scale signals at periods between 3 and 5 years and ~6 years may reflect an influence of the El Niño-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) on varve formation during winter.
To unravel the short-term climate variability during Marine Isotope Stage (MIS) 11, which represents a close analogue to the Holocene with regard to orbital boundary conditions, we performed microfacies and time series analyses on a ~3200-yr-long record of annually laminated Holsteinian lake sediments from Dethlingen, northern Germany. These biogenic varves comprise two sub-layers: a light sub-layer, which is controlled by spring/summer diatom blooms, and a dark sub-layer consisting mainly of amorphous organic matter and fragmented diatom frustules deposited during autumn/winter. Time series analyses were performed on the thickness of the light and dark sub-layers. Signals exceeding the 95% and 99% confidence levels occur at periods that are near-identical to those known from modern instrumental data and Holocene palaeoclimatic records. Spectral peaks at periods of 90, 25, and 10.5 yr are likely associated with the 88-, 22- and 11-yr solar cycles, respectively. This variability is mainly expressed in the light sub-layer spectra, suggesting solar influence on the palaeoproductivity of the lake. Significant signals at periods between 3 and 5 yr and at ∼6 yr are strongest expressed in the dark sub-layer spectra and may reflect an influence of the El Niño-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) during autumn/winter. Our results suggest that solar forcing and ENSO/NAO-like variability influenced central European climate during MIS 11 similarly to the present interglacial, thus demonstrating the comparability of the two interglacial periods at sub-decadal to decadal timescales.
Climate change research is increasingly focusing on the dynamics among species, ecosystems and climates. Better data about the historical behaviours of these dynamics are urgently needed. Such data are already available from ecology, archaeology, palaeontology and geology, but their integration into climate change research is hampered by differences in their temporal and geographical scales. One productive way to unite data across scales is the study of functional morphological traits, which can form a common denominator for studying interactions between species and climate across taxa, across ecosystems, across space and through time—an approach we call ‘ecometrics’. The sampling methods that have become established in palaeontology to standardize over different scales can be synthesized with tools from community ecology and climate change biology to improve our understanding of the dynamics among species, ecosystems, climates and earth systems over time. Developing these approaches into an integrative climate change biology will help enrich our understanding of the changes our modern world is undergoing.
Forty two samples of the Late Eocene Kiliran oil shale, Central Sumatra Basin, Indonesia were collected from a 102 m long drill core. The oil shale core represents the deposition time of about 240.000 years. Palynofacies and geochemical analyses have been carried out to reconstruct the paleoenvironmental conditions and paleoecology during deposition of the oil shale. Amorphous organic matter (AOM) is very abundant (>76%). B. braunii palynomorphs are present (3-16%) as the only autochtonous structured organic matter and generally more abundant in the middle part of the profile. The stable carbon isotopic composition of bulk organic matter (13C) varies from -27.0 to -30.5‰ and is generally more depleted in the middle part of the profile. The ratio of total organic carbon to sulfur (TOC/S), used as salinity indicator, ranges from 2.5 to 15.8 and shows variations along the profile. Slightly less saline environments are observed in the middle part of the profile. Fungal remains are generally present only in this part with a distinct peak of abundance. The presence of fungal remains is regarded as an indication for a relatively warmer climate during deposition of the middle part of the profile. The warmer climate is thought to influence the establishment of a thermocline, limiting the supply of recycled nutrients to epilimnion. Consequently, the primary productivity in the Kiliran lake decreased during deposition of the middle part of the profile as indicated by the relatively depleted 13C values and the blooming of B. braunii. The chemocline was also shoaling during the deposition according to the higher abundance of total isorenieratane and its derivatives originated from green sulfur bacteria dwelling in the photic zone euxinia. The warmer climate is also thought to influence the slightly decrease of water salinity during deposition of the middle part of the profile. The occurrence of B. braunii in Kiliran lake is also recognized from organic geochemical data. The distribution of n-alkanes is characterized by the unusual high amount of C27 n-alkane relative to the other long-chain n-alkanes. The concentrations of C27 n-alkane vary from 30.1 to 393.7 μg/g TOC and are generally in parallel with the abundances of B. braunii palynomorphs along the profile. The 13C values of this compound are about -31‰ and up to 2‰ enriched relative to those of the adjacent long-chain n-alkanes. B. braunii race A can thus be regarded as the significant biological source of the C27 n-alkane. Lower amounts of lycopane are observed in many oil shale samples (0 to 54.7 μg/g TOC). The 13C value of this compound is 17.2‰. This strong enrichment of 13C suggests that the lycopane was derived from B. braunii race L. The concentrations of lycopane develop generally in opposite with those of C27 μalkane. It is likely that both B. braunii races bloomed in alternation in the lake, probably due to changes on specific water chemistry. Norneohop-13(18)-ene and neohop-13(18)-ene derived from methanotrophic bacteria are the dominant hopanoid hydrocarbons. The sum of their concentrations varies from 40.6 to 360.0 μg/g TOC. The 13C of these compounds are extremely depleted (-45.2 to -50.2‰). The occurrence of abundant bacteria including methanotrophic bacteria was responsible for the recycling of carbon below the chemocline of the lake. The effect of the recycling of carbon is observed by the presence of a concomitant depletion (about 7-9‰) in 13C of some specific biomarkers derived from organisms dwelling in the whole phototrophic zone. 4-Methylsterane and 4-methyldiasterene homologues occur in the oil shale as the predominant biomarkers. The sum of the concentrations of all homologues are about 40.3-1,009.2 μg/g TOC with generally higher values in the uppermost and lower parts of the profile. Calcium (Ca) accounts as the predominant element in the oil shale, ranging from 5.0 to 16.7%. This element shows generally parallel variation with the 4-methylsterane and 4-methyldiasterene homologues along the profile. This suggests that these compounds were derived from biological sources favoring more alkaline and more trophic environments. On the other hand, these compounds were less abundant in the middle part of the profile which is consistent with less alkaline and less trophic environments promoting B. braunii to bloom. Alternation between Dinoflagellates and B. braunii in ancient lacustrine environments due to water chemistry changes have been known from previous studies. In the present case, distinct alternation between B. braunii abundances and concentrations of 4-methylsterane and 4-methyldiasterene homologues along the studied oil shale profile suggest a hypothesis that these compounds were derived from freshwater Dinoflagellates although dinosterane is not present in the sediment extracts. Water alkalinity and trophic level changes were most likely responsible for the alternation of Dinoflagellates and B. braunii blooming.