Search

Abstract: We present stable isotope data (δ18O, δ13C) from a detrital rich stalagmite from Kapsia Cave, the Peloponnese, Greece. The cave is rich in archeological remains and there are reasons to believe that flooding of the cave has directly affected humans using the cave. Using a combination of U–Th and 14C dating to constrain a site-specific correction factor for (232Th/238U) detrital molar ratio, a linear age model was constructed. The age model shows that the stalagmite grew during the period from ca. 950BC to ca. AD 830. The stable oxygen record from Kapsia indicates cyclical changes of close to 500yr in precipitation amount, with rapid shifts towards wetter conditions followed by slowly developing aridity. Superimposed on this signal, wetter conditions are inferred around 850, 700, 500 and 400–100BC, and around AD 160–300 and AD 770; and driest conditions are inferred to have occurred around 450BC, AD 100–150 and AD 650. Detrital horizons in the stalagmite indicate that three major floods took place in the cave at 500BC, 70BC and AD 450. The stable carbon isotope record reflects changes in biological activity being a result of both climate and human activities. [Copyright &y& Elsevier]

Sundqvist, H. S., Holmgren, K., Moberg, A., Spötl, C. & Mangini, A. 2009: Stable isotopes in a stalagmite from NW Sweden document environmental changes over the past 4000 years. Boreas, 10.1111/j.1502-3885.2009.00099.x. ISSN 0300-9483. 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. [ABSTRACT FROM AUTHOR]

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 δ 18O and δ 13C 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 δ 13C 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 δ 18O values indicate the presence of short term climate oscillations that are probably linked to shifts of the Intertropical Convergence Zone. [Copyright &y& Elsevier]

Two fast-growing stalagmites from a cellar vault in Uppsala, southeast Sweden, are analysed for their luminescent properties. The results indicate that variations in luminescence intensity in the stalagmites are annual. Due to problems in finding a suitable absolute dating method this assumption cannot yet be firmly tested; however, results from radiocarbon dating of one of the stalagmites do not contradict the proposal that the laminae are annual. If so, the speleothems have been growing for 10–15 years with a growth rate of 3–8 mm per year, which is a similar rate to other fast-growing speleothems in Great Britain that have formed from the reaction of lime mortar and carbon dioxide. It is likely that the assumed annual laminae of the luminescence record represent a flush of organic material. [ABSTRACT FROM AUTHOR]

The aim of this study was to assess the potential of Tanzanian stalagmites as palaeoclimatic archives. Twelve stalagmites were collected in cave systems in the coastal areas. U-series dating, combined with published 14C-data, shows that one of the stalagmites was precipitated during the latter half of the latest glacial, between approximately 39 and 27 ka. Stable isotope analysis results indicate millennial-scale fluctuations in atmospheric CO2 level during that time; and these fluctuations show a pattern very similar to that of the δ18O variations in the GRIP and Byrd ice-cores. The other stalagmites analysed turned out to be too porous and/or contained too much detritus to allow for reliable U-series dating. Due to low uranium content, the precision of the dating results is generally also poor. Samples from the five most compact and clean specimens yielded ages from c. 105 ka to c. 17 ka, though sometimes with an inverse age stratigraphy, indicating that the stalagmite precipitates were partly not compact enough to prevent post-depositional uranium leakage. [ABSTRACT FROM AUTHOR]

Data from stalagmites in the Makapansgat Valley, South Africa, document regional climatic change in southern Africa in the Late Pleistocene and Holocene. A new TIMS U-series dated stalagmite indicates speleothem growth from 24.4 to 12.7 ka and from 10.2 to 0 ka, interrupted by a 2.5 ka hiatus. High-resolution oxygen and carbon stable isotope data suggest that postglacial warming was first initiated ∼17 ka, was interrupted by cooling, probably associated with the Antarctic Cold Reversal, and was followed by strong warming after 13.5 ka. The Early Holocene experienced warm, evaporative conditions with fewer C4 grasses. Cooling is evident from ∼6 to 2.5 ka, followed by warming between 1.5 and 2.5 ka and briefly at ∼AD 1200. Maximum Holocene cooling occurred at AD 1700. The new stalagmite largely confirms results from shorter Holocene stalagmites reported earlier. The strongest variability superimposed on more general trends has a quasi-periodicity between 2.5 and 4.0 ka. Also present are weaker ∼1.0 ka and ∼100-year oscillations, the latter probably solar induced. Given similarities to the Antarctic records, the proximate driving force producing millennial- and centennial-scale changes in the Makapansgat record is postulated to be atmospheric circulation changes associated with change in the Southern Hemisphere circumpolar westerly wind vortex. [Copyright &y& Elsevier]

Mainland Southeast Asia experiences complex and variable hydroclimatic conditions, mainly due to its location at the intersection of Asian monsoon subsystems. Predicting future changes requires an in-depth understanding of paleoclimatic conditions that is currently hindered by a paucity of records in some regions. In this paper, we present the first speleothem stable isotope records from western Thailand detailing the Bølling-Allerød interstadial, Younger Dryas termination, and early- to mid-Holocene period. We find evidence of higher precipitation during the Bølling-Allerød (14,321–12,824 years before present (1950: BP)) compared to a Younger Dryas termination that starts 11,702–11,674 BP, has a rapid shift centered on 11,660–11,641 BP, and ends 11,603–11,589 BP. In addition, our records show Holocene monsoon intensity peaking at 8250 BP or before, a multi-millennia delay from the Northern Hemisphere summer insolation peak, followed by a trend to drier conditions until at least 750 BP. Assessment of the timing of the Younger Dryas termination in paleoclimate records across Southeast Asia reveals an earlier shift of the Indian Summer Monsoon to global climate shifts when compared to East Asian Summer Monsoon records. The causes of this are currently unknown. Some potentially important aspects include: an Indian Summer Monsoon influence on East Asian Summer Monsoon strength via the Indian Ocean Dipole climate pattern, the role of the Tibetan Plateau in monsoon dynamics, and exposure of the Sundaland shoreline. More high-resolution paleoclimate records, especially on the pathway of Indian Summer Monsoon to East Asian Summer Monsoon, are required for further discussion on the mechanisms controlling the differences between climate regimes. • We present two new speleothem stable isotope records from western Thailand. • Conditions trend wetter during the Bølling-Allerød. • Early and abrupt termination of the Younger Dryas (11,675–11,600 BP, ±73 years). • Change Point Analysis of records finds earlier rapid shift in Indian Summer Monsoon. • Distinct trend of increasing δ18O and δ13C values throughout Holocene. [ABSTRACT FROM AUTHOR]