Radiocarbon wiggle matching of Swedish lake varves reveals asynchronous climate changes around the 8.2 kyr cold event     

IAN SNOWBALL  RAIMUND MUSCHELER  LOVISA ZILLÉN  PER SANDGREN  TANIA STANTON  KARL LJUNG 《Boreas: An International Journal of Quaternary Research》2010,39(4):720-733

Snowball, I., Muscheler, R., Zillén, L., Sandgren, P., Stanton, T. & Ljung, K. 2010: Radiocarbon wiggle matching of Swedish lake varves reveals asynchronous climate changes around the 8.2 kyr cold event. Boreas, Vol. 39, pp. 720–733. 10.1111/j.1502‐3885.2010.00167.x. ISSN 0300‐9483. A series of nine radiocarbon measurements obtained at increments of 50 years was used to wiggle match varved sediments in Lake Kälksjön (west central Sweden) to the calendar year time scale provided by the tree‐ring‐derived radiocarbon calibration curve. The anchor point for a series of 400 varves known to span the ‘8.2 kyr cold event’ was derived from a combination of correlation analysis, Monte Carlo statistics and Bayesian age modelling. The GRIP and NorthGRIP ice‐cores were matched to the same absolute time scale by comparing ¹⁰Be data and tree‐ring Δ¹⁴C. The radiocarbon‐based wiggle match, organic carbon measurements, mineral magnetic parameters and XRF data reconstruct a distinct period of enhanced erosion in Kälksjön's catchment between 8066 ± 25 and 7920 ± 25 cal. yr BP. Prior to human impact, the increased erosion in the boreal environment is assigned to increased winter precipitation in the form of snow, which caused spring meltwater discharge to intensify. Our results suggest that the abrupt onset of increased winter precipitation in west central Sweden started at least 50 years after the onset of the ‘8.2 kyr cold event’ as defined by oxygen isotope data from Greenland. The study highlights the value of synchronized time scales in the reconstruction of abrupt climate changes based on proxy data.  相似文献   

Occurrence of varved lake sediment sequences in Varmland, west central Sweden: lake characteristics, varve chronology and AMS radiocarbon dating     

LOVISA ZILLÉN  IAN SNOWBALL  PER SANDGREN  TANIA STANTON 《Boreas: An International Journal of Quaternary Research》2003,32(4):612-626

Varved lake sediments can be used to set multiple environmental proxies within a calendar year time scale. We undertook a systematic survey of lakes in the Province of Värmland, west central Sweden, with the aim of finding continuous varved lake sediment sequences covering the majority of the Holocene. In Fennoscandia, such sediments have previously only been recorded in northern Sweden and in southern and central Finland. By following a selective process and fieldwork we discovered three new varved sites (i.e. Furskogstjärnet, Mötterudstjärnet and Kälksjön). We found that lakes with varved sediments have several common lake morphometry properties and lake catchment characteristics such as maximum water depth, maximum water depth/lake surface area ratio, catchment soil types, altitude and number of inflows. Varve chronologies, supported by AMS-¹⁴C dating and tephrochronology were established for two of the sediment profiles. These varve chronologies are the longest geological records with an annual resolution known to exist in Sweden. In Furskogstjärnet, the AMS- ¹⁴C dates based on terrestrial plant macrofossils at several levels deviate significantly from the varve based time-depth curve. In Motterudstjarnet, a fully reasonable time-depth model based on the ¹⁴C dates gives older ages in the lower part of the sequence compared to the varve chronology. These results highlight that seemingly acceptable AMS radiocarbon dates may be erroneous. They also point to the fact that varved lake sediments are reliable geological archives with respect to chronological control and accuracy. Thus, these archives should be of prime interest for studies of climate and environmental change undertaken with the aim of providing sub-decadal resolution proxy data sets.  相似文献   

An experimental set-up for carbon isotopic analysis of atmospheric CO 2 and an example of ecosystem response during solar eclipse 2010     

TANIA GUHA  PROSENJIT GHOSH 《Journal of Earth System Science》2013,122(3):623-638

We present here, an experimental set-up developed for the first time in India for the determination of mixing ratio and carbon isotopic ratio of air-CO₂. The set-up includes traps for collection and extraction of CO₂ from air samples using cryogenic procedures, followed by the measurement of CO₂ mixing ratio using an MKS Baratron gauge and analysis of isotopic ratios using the dual inlet peripheral of a high sensitivity isotope ratio mass spectrometer (IRMS) MAT 253. The internal reproducibility (precision) for the δ ¹³C measurement is established based on repeat analyses of CO₂±0.03‰. The set-up is calibrated with international carbonate and air-CO₂ standards. An in-house air-CO₂ mixture, ‘OASIS AIRMIX’ is prepared mixing CO₂ from a high purity cylinder with O₂ and N₂ and an aliquot of this mixture is routinely analyzed together with the air samples. The external reproducibility for the measurement of the CO₂ mixing ratio and carbon isotopic ratios are ±7 (n?=?169) $\upmu $ mol·mol^???1 and ±0.05 (n?=?169) ‰ based on the mean of the difference between two aliquots of reference air mixture analyzed during daily operation carried out during November 2009–December 2011. The correction due to the isobaric interference of N₂O on air-CO₂ samples is determined separately by analyzing mixture of CO₂ (of known isotopic composition) and N₂O in varying proportions. A +0.2‰ correction in the δ ¹³C value for a N₂O concentration of 329 ppb is determined. As an application, we present results from an experiment conducted during solar eclipse of 2010. The isotopic ratio in CO₂ and the carbon dioxide mixing ratio in the air samples collected during the event are different from neighbouring samples, suggesting the role of atmospheric inversion in trapping the emitted CO₂ from the urban atmosphere during the eclipse.  相似文献   

The Effects of a Foehn Wind on Human Thermal Exchange: The Canterbury Nor'wester     

STANTON E. TULLER 《New Zealand geographer》1980,36(1):11-19

  相似文献   

Garnet Compositions at Broken Hill, New South Wales, as Indicators of Metamorphic Processes     

STANTON  R. L.; WILLIAMS  K. L. 《Journal of Petrology》1978,19(3):514-529

Electron microprobe analyses of garnets in the finely bedded‘banded iron formations’ (BIF) of the Willyama Complexat Broken Hill reveal marked compositional changes from onegarnet to the next on a scale of 1–2 mm. Further, systematicanalytical traverses across bedding and along bedding show thecompositions of the garnets to change markedly from one finebed to the next, but to remain extremely uniform within individualbeds. In view of the minuteness of the domains involved it appearsevident that compositional variation cannot be attributed tovariations in metamorphic pressures, temperatures or oxygenfugacities. Neither can they be attributed to variation in garnet-matrixpartition functions, as most of the garnets occur in one simplematrix—quartz. It is concluded that in spite of the high (sillimanite) gradeof the relevant metamorphism, any equilibration of garnet compositions,and hence any associated inter-grain metamorphic diffusion,has been restricted to a scale of less than 1 mm; that garnetcompositions here reflect original rock composition on an ultra-finescale, and have no connotations concerning metamorphic grade;that, hence, the garnets must derive from a single precursormaterial, earlier suggested to be a manganiferous chamositicseptechlorite; and that the between-bed variation: within-beduniformity of garnet composition reflects an original patternof chemical sedimentation—a pattern preserved with theutmost delicacy through a period of 1800 x 10⁶ years and a metamorphicepisode of sillimanite grade.  相似文献