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| 2. |
- Holzkämper, Steffen, 1974-, et al.
(författare)
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Late Pleistocene stalagmite growth in Wolkberg Cave, South Africa
- 2009
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Ingår i: Earth and Planetary Science Letters. - Amsterdam : Elsevier. - 0012-821X .- 1385-013X. ; 282, s. 212-221
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Tidskriftsartikel (refereegranskat)abstract
- Little is known about the sequence of climate and environmental change in southern Africa during the last glacial period, in spite of the intimations from records, such as Antarctic ice cores and archaeological sites, that very marked changes took place which would have had profound effects on vegetation and animal distributions across the sub-continent. High-resolution, (semi-) continuous climate and environmental records can be extracted from suitable cave speleothems. Speleothems are reasonably abundant in southern Africa, but their occurrence is patchy in time and space and the records can be difficult to interpret. Here we report our assessment of the stalagmite W5 from Wolkberg Cave in the northeastern part of South Africa, as an archive for glacial-period climatic and environmental shifts. The cave is located at 1450 m asl, in the dolomitic limestones of the Transvaal System in an area currently dominated by C4 grass vegetation. Nine U/Th dates show growth from 58 to 46 ka, and a second brief phase ca. 40 ka, indicating that the available moisture was sufficient to allow speleothems to form. The δ18O and δ13C values along the growth axis show variability in the order of 2‰ for the former, while variability in the latter is characterized by a shift from values near − 2‰ in the older section to + 2‰ or more in the younger part. These high δ13C values are probably the combined result of CO2 degassing of the percolating soil water prior to the carbonate precipitation in the cave chamber, the increasing dominance of C4 over C3 vegetation, and the high percentage of aragonite towards the stalagmite's top. The retrieved data point towards increasingly drier and colder conditions during the growth period of the stalagmite. Furthermore, the high-frequency variations of δ18O values indicate the presence of short term climate oscillations that are probably linked to shifts of the Intertropical Convergence Zone.
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| 3. |
- Huguet, Carme, et al.
(författare)
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Temperature and Monsoon Tango in a Tropical Stalagmite: Last Glacial-Interglacial Climate Dynamics
- 2018
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution paleoclimate data on stable isotopes in a stalagmite were coupled to glycerol dialkyl glycerol tetraethers (GDGTs). The Indian Summer Monsoon (ISM) transitioned from limited rainfall during the Last Glacial Maximum (LGM) to intense precipitation during early Holocene (22 to 6 ka). This was associated with changes in stalagmite growth, abundance of branched (br) and isoprenoid (iso) GDGTs, as well as delta O-18, delta C-13, Sr/Ca and GDGT-derived signals providing both temperature and moisture information. The reconstructed mean annual air temperature (MAAT) of the most modern stalagmite sample at similar to 19 degrees C, matches the surface and cave MAAT, but was similar to 4 degrees C lower during LGM. Warming at the end of LGM occurred before ISM strengthened and indicate 6 ka lag consistent with sea surface temperature records. The isotope records during the Younger Dryas show rapid progressions to dry conditions and weak monsoons, but these shifts are not coupled to TEX86. Moreover, change to wetter and stronger ISM, along with warmer Holocene conditions are not continuous indicating a decoupling of local temperatures from ISM.
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| 4. |
- Kalpana, M. S., et al.
(författare)
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Sources, Distribution and Paleoenvironmental Application of Fatty Acids in Speleothem Deposits From Krem Mawmluh, Northeast India
- 2021
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Ingår i: Frontiers in Earth Science. - : Frontiers Media SA. - 2296-6463. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Integrated multiproxy geochemical studies are essential to reconstruct the paleoenvironment through different time scales. Pristine terrestrial archives such as speleothems provide an excellent opportunity to study these changes by measuring the stable isotope and biomarker trends preserved in these records. Here, we investigated fatty acids in drip water, moonmilk, and a stalagmite (KM-1) retrieved from Krem Mawmluh in northeast India to constrain the sources and distribution of these compounds. Besides, we tested their compatibility with established glycerol dialkyl glycerol tetraethers and stable isotope proxies in KM-1 to probe the use of fatty acid-derived proxies for paleoclimate reconstruction. We observe a similar composition of fatty acids in drip water as well as the cave deposits with significantly higher concentrations of fatty acids in drip water (10.6-124 mu g/L) and moonmilk (1.32-16.5 mu g/g) compared to the stalagmite (0.67-2.09 mu g/g). In KM-1 stalagmite, fatty acids and the presence of azelaic acid transported from surface soils indicate that these compounds are derived from bacterial activity both within the cave and the overlying soil cover. The branched C-15 fatty acid index (iso+anteiso C-15/nC(15)) increases during the Holocene, suggesting enhanced microbial production under warm/wet conditions. Fluctuations in the fatty acid indices coincide with abrupt shifts in the TEX86 and BIT proxies reflecting the warm/wet Holocene and cold/dry Late Pleistocene. These trends imply the potential use of fatty acids for reconstructing past climate changes in speleothems but need more analytical reference points to provide statistical data.
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| 5. |
- Lundblad, Katarina, 1967-
(författare)
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Studies on Tropical Palaeo-variation in Climate and Cosmic Ray Influx : Geochemical data from stalagmites collected in Tanzania and northern South Africa
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main aims of this project were to contribute to the knowledge about tropical climate variations, and to investigate the possibilities of obtaining cosmic ray influx data from stalagmites.Stalagmites from Tanzania and northern South Africa were palaeoclimatologically analysed.U-series dating, combined with previously published 14C-data (Goslar et al. 2000), shows that one of the Tanzanian stalagmites was precipitated during the latter half of the latest glacial, between approximately 39 and 27 ka. Results from stable isotope analysis (δ13C and δ18O) were interpreted as indicating millennial-scale fluctuations in atmospheric CO2-level during that time. These fluctuations show a pattern which is similar to that of the δ18O records from the GRIP and Byrd ice-cores – suggesting that the stalagmite record captures a global climate signal.U-series dating shows that the largest of the South African stalagmites covers most of the last 25 ka. The δ13C- and δ18O-data indicate millennial-scale variation in the South African climate throughout the time of the formation of this stalagmite. Because of similarities to Antarctic records (Steig et al. 2000), the driving force for these variations was suggested to be atmospheric circulation changes associated with change in the Southern Hemisphere circumpolar westerly wind vortex. Like the Tanzanian results, these South African data lend further support to the theory about global persistent millennial-scale climate-fluctuations.A beryllium isotope study was then performed on the two stalagmites described above. This study assesses, for the first time, the potential of the cosmogenic isotope 10Be as a tool in stalagmite studies. As a control, 9Be-analysis was also made on each 10Be-sample.The aim of the study was to test the idea that stalagmites could be a new source of well-dated and directly climate-proxy synchronized information about past variations in cosmic ray influx intensity – i.e., a source that would serve as a new tool for general improvement of the knowledge about past variations in cosmic ray influx, and that could possibly also provide further clues to whether such variations can affect Earth’s climate.The main excursions/fluctuations in the 10Be-and 9Be-data from these stalagmites do not coincide. Hence, the excursions in 10Be-content may be interpreted as indicating excursions in cosmic ray influx. The 10Be-data show three pronounced peaks at around 38, 35 and 21 ka respectively; plausibly corresponding to the peaks previously observed at approximately 39, 32 and 23 ka in cosmogenic isotope data from sediments and ice.In glacial parts of the stalagmite material, the 9Be-concentration fluctuates on a millennial-scale; inversely synchronized with fluctuations in δ13C-data from the same material. This indicates that 9Be could, apart from being a necessary control for 10Be-results, also function as a palaeoclimatological proxy in stalagmite studies.In order to improve dating facilities for stalagmites, a procedure for high-precision measurements of U and Th isotope ratios was also developed, using an IsoProbe® Multi Collector Inductively Coupled Plasma Mass Spectrometer (MC-ICPMS). The 230Th/232Th ratio for the thorium concentration-standard Alfa Th was determined to 7.96 (±0.012) × 10-7 (2σ), and the δ234U obtained for the uranium standard SRM950a was 18.4 ±0.6(2σ). The thorium results show, that even extremely biased isotope ratios, in low-concentration samples, can be measured with remarkably good precision. The quality of each sample measurement can also easily be evaluated. However, due to repeated technical problems with the instrument, it has not yet been possible to use the developed procedure for routine analysis and dating of samples.
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| 6. |
- Sundqvist, Hanna S., et al.
(författare)
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Stable oxygen isotopes in a stalagmite from Jämtland, NW Sweden, record large temperature variations over the last 4000 years
- 2010
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Ingår i: Boreas. - : John Wiley & Sons, Inc.. - 0300-9483 .- 1502-3885. ; 39:1, s. 77-86
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Tidskriftsartikel (refereegranskat)abstract
- This study of a 4000-year-old stalagmite from Korallgrottan in northwestern Sweden highlights the potentials and challenges when using stable isotopes in stalagmites as climate proxies, as well as the fact that the relationship between climate and proxy may change through time. Both the oxygen and the carbon isotopes display an overall trend of enrichment together with decreasing growth rates over the time period covered by the stalagmite, which is considered a generally cooling period according to current palaeoclimate understanding. The stable isotope records show enriched isotopic values during the, for Scandinavia, comparatively cold period AD 1300–1700 and depleted values during the warmer period AD 800–1000. The indication of a negative relationship between measured d18O and surface temperature concurs with earlier reported stalagmite records from regions with a seasonal snow cover and is further supported by the fact that the stalagmite d18 O record shows general similarities with both regional and hemispheric temperature reconstructions available for the past 500 and 2000 years, respectively. Compared with a stable isotope record of lacustrine carbonates from northern Sweden, however, shifting correlations over time between the two records indicate that a local hydrological change may have taken place at Korallgrottan, or at the lake, compared with around 1000 years ago. The earlier part of the stalagmite d18O might thus be influenced, to some extent, by another process than the later part, which means that a negative relationship between d18O and surface temperature might not hold for the entire 4000-year-old record.
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| 7. |
- Sundqvist, Hanna, et al.
(författare)
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Stable isotopes in a stalagmite from NW Sweden documentenvironmental changes over the past 4000 years.
- 2009
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Ingår i: Boreas. - : Elsevier. - 0300-9483 .- 1502-3885.
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Tidskriftsartikel (refereegranskat)abstract
- This study of a 4000-year-old stalagmite from Korallgrottan in northwestern Sweden highlights the potentials and challenges when using stable isotopes in stalagmites as climate proxies, as well as the fact that the relationship between climate and proxy may change through time. Both the oxygen and the carbon isotopes display an overall trend of enrichment together with decreasing growth rates over the time period covered by the stalagmite, which is considered a generally cooling period according to current palaeoclimate understanding. The stable isotope records show enriched isotopic values during the, for Scandinavia, comparatively cold period AD 1300–1700 and depleted values during the warmer period AD 800–1000. The indication of a negative relationship between measured δ18O and surface temperature concurs with earlier reported stalagmite records from regions with a seasonal snow cover and is further supported by the fact that the stalagmite δ18O record shows general similarities with both regional and hemispheric temperature reconstructions available for the past 500 and 2000 years, respectively. Compared with a stable isotope record of lacustrine carbonates from northern Sweden, however, shifting correlations over time between the two records indicate that a local hydrological change may have taken place at Korallgrottan, or at the lake, compared with around 1000 years ago. The earlier part of the stalagmite δ18O might thus be influenced, to some extent, by another process than the later part, which means that a negative relationship between δ18O and surface temperature might not hold for the entire 4000-year-old record.
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