Carbon isotopes in stalagmites and drip water : Tracers of soil processes

Stalagmites in caves are new climate archives recording meteorological parameters and processes occurring in the soil above caves. Due to advances in mass spectroscopy (TIMS and ICPMS) stalagmites can be dated reliably by the 230Th/U-method. Carbon isotopes, recorded in stalagmites, are of interest because they depend on climate influenced soil processes above caves. In this thesis 14C and 13C in speleothem environments were used as tracers to investigate soil processes for the present day situation and during the Holocene. The present day situation is studied by using monthly collected drip water samples from two caves (Ernesto cave in Trentino, Italy, and Bunker cave in Sauerland, Germany), which were analysed for their carbon isotope content. To interpret the isotopic composition a drip water model including various modes of limestone dissolution with respect to carbon isotopes was developed for the first time. The modelled carbon isotope composition of the drip water agrees well with the measurements. The annual trend in the carbon isotopes, observed in the drip water samples, can be attributed to changes in the water supply in the soil for Ernesto cave and to changes of the soil air carbon isotopic composition for Bunker cave. The information about the soil-cave-systems obtained in the investigation of the present day situation was applied to interpret the carbon isotopes of Holocene stalagmites of both caves. An inverse modelling method was developed to determine the soil CO2 content from measured carbon isotope pairs (14C, 13C). The results indicate that the soil CO2 content increased during the late Holocene in the soil above Ernesto cave due to a rising vegetation density. The Bunker cave stalagmite reveals a constant soil pCO2 in the past

Special Libraries, September-October 1921

Volume 12, Issue 7-8https://scholarworks.sjsu.edu/sla_sl_1921/1006/thumbnail.jp

Bunker Cave stalagmites: an archive for central European Holocene climate variability

Holocene climate was characterised by variability on multi-centennial to multi-decadal time scales. In central Europe, these fluctuations were most pronounced during winter. Here we present a record of past winter climate variability for the last 10.8 ka based on four speleothems from Bunker Cave, western Germany. Due to its central European location, the cave site is particularly well suited to record changes in precipitation and temperature in response to changes in the North Atlantic realm. We present high-resolution records of δ18O, δ13C values and Mg/Ca ratios. Changes in the Mg/Ca ratio are attributed to past meteoric precipitation variability. The stable C isotope composition of the speleothems most likely reflects changes in vegetation and precipitation, and variations in the δ18O signal are interpreted as variations in meteoric precipitation and temperature. We found cold and dry periods between 8 and 7 ka, 6.5 and 5.5 ka, 4 and 3 ka as well as between 0.7 and 0.2 ka. The proxy signals in the Bunker Cave stalagmites compare well with other isotope records and, thus, seem representative for central European Holocene climate variability. The prominent 8.2 ka event and the Little Ice Age cold events are both recorded in the Bunker Cave record. However, these events show a contrasting relationship between climate and δ18O, which is explained by different causes underlying the two climate anomalies. Whereas the Little Ice Age is attributed to a pronounced negative phase of the North Atlantic Oscillation, the 8.2 ka event was triggered by cooler conditions in the North Atlantic due to a slowdown of the thermohaline circulation

Climate Variability in Central Europe during the Last 2500 Years Reconstructed from Four High-Resolution Multi-Proxy Speleothem Records

The Late Holocene was characterized by several centennial-scale climate oscillations including the Roman Warm Period, the Dark Ages Cold Period, the Medieval Warm Period and the Little Ice Age. The detection and investigation of such climate anomalies requires paleoclimate archives with an accurate chronology as well as a high temporal resolution. Here, we present 230Th/U-dated high-resolution multi-proxy records (δ13C, δ18O and trace elements) for the last 2500 years of four speleothems from Bunker Cave and the Herbstlabyrinth cave system in Germany. The multi-proxy data of all four speleothems show evidence of two warm and two cold phases during the last 2500 years, which coincide with the Roman Warm Period and the Medieval Warm Period, as well as the Dark Ages Cold Period and the Little Ice Age, respectively. During these four cold and warm periods, the δ18O and δ13C records of all four speleothems and the Mg concentration of the speleothems Bu4 (Bunker Cave) and TV1 (Herbstlabyrinth cave system) show common features and are thus interpreted to be related to past climate variability. Comparison with other paleoclimate records suggests a strong influence of the North Atlantic Oscillation at the two caves sites, which is reflected by warm and humid conditions during the Roman Warm Period and the Medieval Warm Period, and cold and dry climate during the Dark Ages Cold period and the Little Ice Age. The Mg records of speleothems Bu1 (Bunker Cave) and NG01 (Herbstlabyrinth) as well as the inconsistent patterns of Sr, Ba and P suggests that the processes controlling the abundance of these trace elements are dominated by site-specific effects rather than being related to supra-regional climate variability

Global reorganization of atmospheric circulation during Dansgaard-Oschger cycles

Ice core records from Greenland provide evidence for multiple abrupt warming events recurring at millennial time scales during the last glacial interval. Although climate transitions strongly resembling these Dansgaard-Oeschger (DO) transitions have been identified in several speleothem records, our understanding of the climate and ecosystem impacts of the Greenland warming events in lower latitudes remains incomplete.info:eu-repo/semantics/publishedVersio

Composite data set of last glacial Dansgaard/Oeschger events obtained from stable oxygen isotopes in speleothems

Millennial scale climate variations called Dansgaard-Oeschger cycles occurred frequently during the last glacial, with their central impact on climate in the North Atlantic region. These events are, for example, well captured by the stable oxygen isotope composition in continental ice from Greenland, but also in records from other regions. Recently, it has been shown that a water isotope enabled general circulation model is able to reproduce those millennial-scale oxygen isotope changes from Greenland (Sime et al., 2019). On a global scale, this isotope-enabled model has not been tested in its performance, as stable oxygen isotope records covering those millennial scale variability were so far missing or not systematically compiled.info:eu-repo/semantics/publishedVersio

Climate-induced speleothem radiocarbon variability on Socotra Island from the Last Glacial Maximum to the Younger Dryas

In this study, the dead carbon fraction (DCF) variations in stalagmite M1-5 from Socotra Island in the western Arabian Sea were investigated through a new set of high-precision U-series and radiocarbon (14C) dates. The data reveal an extreme case of very high and also climate-dependent DCF. For M1-5, an average DCF of 56.2±3.4% is observed between 27 and 18kyrBP. Such high DCF values indicate a high influence of aged soil organic matter (SOM) and nearly completely closed-system carbonate dissolution conditions. Towards the end of the last glacial period, decreasing Mg/Ca ratios suggest an increase in precipitation which caused a marked change in the soil carbon cycling as indicated by sharply decreasing DCF. This is in contrast to the relation of soil infiltration and DCF as seen in stalagmites from temperate zones. For Socotra Island, which is influenced by the East African-Indian monsoon, we propose that more humid conditions and enhanced net infiltration after the Last Glacial Maximum (LGM) led to dense vegetation and thus lowered the DCF by increasing 14CO2 input into the soil zone. At the onset of the Younger Dryas (YD) a sudden change in DCF towards much higher, and extremely variable, values is observed. Our study highlights the dramatic variability of soil carbon cycling processes and vegetation feedback on Socotra Island manifested in stalagmite DCF on both long-term trends and sub-centennial timescales, thus providing evidence for climate influence on stalagmite radiocarbon. This is of particular relevance for speleothem studies that aim to reconstruct past atmospheric 14C (e.g., for the purposes of 14C calibration), as these would rely on largely climate-independent soil carbon cycling above the cave. © 2020 Copernicus GmbH. All rights reserved

The Ernesto Cave, northern Italy, as a candidate auxiliary reference section for the definition of the Anthropocene series

Annually laminated stalagmites ER77 and ER78 from Grotta di Ernesto provide an accurate annual record of environmental and anthropogenic signals for the last ~200 years. Two major transitions are recorded in the stalagmites. The first coincides with the year 1840 CE, when a change from porous and impurity-rich-laminae to clean, translucent laminae occurs. This is accompanied by a steady increase in the growth rate, a decrease in fluorescence and a sharp increase in δ13C values. These changes concur with the end of the Little Ice Age. The second transition takes place around the year 1960 CE and corresponds with an increase in both annual growth rate and sulfur concentration in stalagmite ER78 at 4.2 mm from the top, and with the deflection point in the 14C activity curve in stalagmite ER77 at 4.8 mm from the top. This latter is the stratigraphic signal proposed as the primary guide for the definition of the Anthropocene series. The following shift toward depleted δ34S–SO4 in stalagmite ER78 suggests that industrial pollution is a major source of sulfur. The interpretation of atmospheric signals (S, δ34S, 14C) in the stalagmites is affected by attenuation and time lags and the environmental signals are influenced by soil and ecosystem processes, while other anthropogenic signals (δ15N, 239Pu) are not recorded. For these reasons, the stalagmite record is here proposed as an auxiliary (reference) section rather than a global standard. In summary, Grotta di Ernesto contains one of the best stalagmite records documenting the Anthropocene, and one of only two stalagmite records where the S peak has been measured at high resolution

Monitoring of GNSS Scintillation Indices during the MOSAiC Expedition: Preliminary Results from Eight Months in the Arctic

Polar regions are of particular interest to study the interaction of space weather (solar radiation and particle precipitation) with the Earth’s atmosphere and magnetosphere. We focus here on space-weather induced irregularities of electron density in the upper atmosphere and their impact on radio signals. Such irregularities can disturb radio communication (particularly in air traffic) and radio navigation with GNSS (Global Navigation Satellite Systems) in the polar regions. The global network of GNSS stations to monitor the space weather impact is sparse at high latitudes. The permanent stations, located below 80°N, cannot reach a complete monitoring coverage in the Arctic. The MOSAiC expedition provided an excellent opportunity to collect GNSS data beyond 80°N over a long period of more than 8 months. We focus, here, on a GNSS setup that was installed aboard R/V Polarstern to study the signal’s amplitude and phase scintillation. The respective indices S4 and σφ allow to quantify the impact of space-weather induced irregularities. The MOSAiC record comprises links of three systems: GPS, GLONASS and Galileo. Preliminary GPS results show that anomalies in σφ of about 0.2 rad can be related to particle precipitation. The results indicate that a drifting GNSS setup can contribute to space weather monitoring if the ship's dynamic is carefully taken into account

Monitoring of GNSS Scintillation Indices during the MOSAiC Expedition: Preliminary Results of Ship-borne and Station-based Observations in the Arctic

Polar regions are of particular interest to study the interaction of space weather (solar radiation and particle precipitation) with the Earth’s atmosphere and magnetosphere. We focus here on space-weather induced irregularities of electron density in the upper atmosphere and their impact on radio signals. Such irregularities can disturb radio communication (particularly in air traffic) and radio navigation with GNSS (Global Navigation Satellite Systems) in the polar regions. The global network of GNSS stations to monitor the space weather impact is sparse at high latitudes. The permanent stations, located below 80°N, cannot reach a complete monitoring coverage in the Arctic. The MOSAiC expedition provided an excellent opportunity to collect GNSS data beyond 80°N over a long period of about seven months (Oct 2019 to Apr 2020). We focus, here, on the GNSS setup that was drifting with the research vessel Polarstern in the Central Arctic. Additionally, data of a GNSS scintillation station at Ny-Alesund, Svalbard (79°N) is analyzed. In general, this period (close to solar minimum) had rather calm space weather conditions and the indices S4 and σφ did not reach the thresholds of severe amplitude or phase scintillation. However, anomalies of σφ on a weak to moderate scale occur persistently for the central Artic ship setup and the Ny-Alesund station. Their comparison reveals differences in temporal distribution that are further investigated. Still, the origin of particle precipitation in the polar cap or cusp region has to be clarified. Based on the preliminary results, we found that a ship-borne GNSS setup (under moderate sea state conditions) can contribute to the detection of spaceweather induced ionospheric irregularities and we conclude that monitoring over the oceans (especially in the central Arctic) can benefit from further observations of this kind