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  • 1
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    Online Resource
    A stalagmite test of North Atlantic SST and Iberian hydroclimate linkages over the last two glacial cycles
    Copernicus GmbH ; 2018
    In:  Climate of the Past Vol. 14, No. 12 ( 2018-12-11), p. 1893-1913
    Details
    In: Climate of the Past, Copernicus GmbH, Vol. 14, No. 12 ( 2018-12-11), p. 1893-1913
    Abstract: Abstract. Close coupling of Iberian hydroclimate and North Atlantic sea surface temperature (SST) during recent glacial periods has been identified through the analysis of marine sediment and pollen grains co-deposited on the Portuguese continental margin. While offering precisely correlatable records, these time series have lacked a directly dated, site-specific record of continental Iberian climate spanning multiple glacial cycles as a point of comparison. Here we present a high-resolution, multi-proxy (growth dynamics and δ13C, δ18O, and δ234U values) composite stalagmite record of hydroclimate from two caves in western Portugal across the majority of the last two glacial cycles (∼220 ka). At orbital and millennial scales, stalagmite-based proxies for hydroclimate proxies covaried with SST, with elevated δ13C, δ18O, and δ234U values and/or growth hiatuses indicating reduced effective moisture coincident with periods of lowered SST during major ice-rafted debris events, in agreement with changes in palynological reconstructions of continental climate. While in many cases the Portuguese stalagmite record can be scaled to SST, in some intervals the magnitudes of stalagmite isotopic shifts, and possibly hydroclimate, appear to have been somewhat decoupled from SST.
    Type of Medium: Online Resource
    ISSN: 1814-9332
    URL: Article
    URL: Article
    DOI: 10.5194/cp-14-1893-2018
    DOI: 10.5194/cp-14-1893-2018-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2018
    detail.hit.zdb_id: 2217985-9
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  • 2
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    A simplified isotope dilution approach for the U–Pb dating of speleogenic and other low-〈sup〉232〈/sup〉Th carbonates by multi-collector ICP-MS
    Copernicus GmbH ; 2022
    In:  Geochronology Vol. 4, No. 1 ( 2022-01-17), p. 33-54
    Details
    In: Geochronology, Copernicus GmbH, Vol. 4, No. 1 ( 2022-01-17), p. 33-54
    Abstract: Abstract. We describe a new method for the measurement of U/Pb ratios by isotope dilution multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) for the dating of geologically young clean carbonates, particularly speleothems. The method is intended for materials containing little or no initial 232Th. We illustrate and validate the method with four examples ranging from 0.57 to 20 Ma. The new method is capable of applying the 235U–207Pb and 238U–234U–206Pb chronometers, common Pb and quantifiable residual 234U/238U disequilibrium permitting. These provide an alternative to the more widely used 238U–206Pb chronometer, which can be highly inaccurate for samples that are 〈 ca. 20 million years old, owing to uncertainties in the excess initial 234U (hence, excess radiogenic 206Pb) commonly observed in speleothems.
    Type of Medium: Online Resource
    ISSN: 2628-3719
    URL: Article
    DOI: 10.5194/gchron-4-33-2022
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2022
    detail.hit.zdb_id: 2966593-0
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  • 3
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    Lignin oxidation products in soil, dripwater and speleothems from four different sites in New Zealand
    Copernicus GmbH ; 2021
    In:  Biogeosciences Vol. 18, No. 7 ( 2021-04-08), p. 2289-2300
    Details
    In: Biogeosciences, Copernicus GmbH, Vol. 18, No. 7 ( 2021-04-08), p. 2289-2300
    Abstract: Abstract. Lignin oxidation products (LOPs) are widely used as vegetation proxies in climate archives, such as sediment and peat cores. The total LOP concentration, Σ8, provides information on the abundance of vegetation, while the ratios C/V and S/V of the different LOP groups also provide information on the type of vegetation. Recently, LOP analysis has been successfully applied to speleothem archives. However, there are many open questions concerning the transport and microbial degradation of LOPs on their way from the soil into the cave system. These processes could potentially alter the original source-dependent LOP signals, in particular the C/V and S/V ratios, and thus complicate their interpretation in terms of past vegetation changes. We analyzed LOPs in leaf litter and different soil horizons as well as dripwater and flowstone samples from four different cave sites from different vegetation zones in New Zealand using ultrahigh-performance liquid chromatography coupled to high-resolution mass spectrometry. We test whether the original source-dependent LOP signal of the overlying vegetation is preserved and can be recovered from flowstone samples and investigate how the signal is altered by the transport from the soil to the cave. The LOP concentrations range from mg g−1 in the soil to ng g−1 in the flowstones. Our results demonstrate that, from the soil to the flowstone, the C/V and S/V ratios both increase, while the total lignin content, Σ8, strongly decreases. This shows that the LOP signal is strongly influenced by both transport and degradation processes. Nevertheless, the relative LOP signal from the overlying soil at the different cave sites is preserved in the flowstone. We emphasize that for the interpretation of C/V and S/V ratios in terms of past vegetation changes, it is important to compare only samples of the same type (e.g., speleothem, dripwater or soil) and to evaluate only relative variations.
    Type of Medium: Online Resource
    ISSN: 1726-4189
    URL: Article
    URL: Article
    DOI: 10.5194/bg-18-2289-2021
    DOI: 10.5194/bg-18-2289-2021-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2021
    detail.hit.zdb_id: 2158181-2
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  • 4
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    SISALv2: a comprehensive speleothem isotope database with multiple age–depth models
    Copernicus GmbH ; 2020
    In:  Earth System Science Data Vol. 12, No. 4 ( 2020-10-27), p. 2579-2606
    Details
    In: Earth System Science Data, Copernicus GmbH, Vol. 12, No. 4 ( 2020-10-27), p. 2579-2606
    Abstract: Abstract. Characterizing the temporal uncertainty in palaeoclimate records is crucial for analysing past climate change, correlating climate events between records, assessing climate periodicities, identifying potential triggers and evaluating climate model simulations. The first global compilation of speleothem isotope records by the SISAL (Speleothem Isotope Synthesis and Analysis) working group showed that age model uncertainties are not systematically reported in the published literature, and these are only available for a limited number of records (ca. 15 %, n=107/691). To improve the usefulness of the SISAL database, we have (i) improved the database's spatio-temporal coverage and (ii) created new chronologies using seven different approaches for age–depth modelling. We have applied these alternative chronologies to the records from the first version of the SISAL database (SISALv1) and to new records compiled since the release of SISALv1. This paper documents the necessary changes in the structure of the SISAL database to accommodate the inclusion of the new age models and their uncertainties as well as the expansion of the database to include new records and the quality-control measures applied. This paper also documents the age–depth model approaches used to calculate the new chronologies. The updated version of the SISAL database (SISALv2) contains isotopic data from 691 speleothem records from 294 cave sites and new age–depth models, including age–depth temporal uncertainties for 512 speleothems. SISALv2 is available at https://doi.org/10.17864/1947.256 (Comas-Bru et al., 2020a).
    Type of Medium: Online Resource
    ISSN: 1866-3516
    URL: Article
    URL: Article
    DOI: 10.5194/essd-12-2579-2020
    DOI: 10.5194/essd-12-2579-2020-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2020
    detail.hit.zdb_id: 2475469-9
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  • 5
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    Online Resource
    Pacific climate reflected in Waipuna Cave drip water hydrochemistry
    Copernicus GmbH ; 2020
    In:  Hydrology and Earth System Sciences Vol. 24, No. 6 ( 2020-07-01), p. 3361-3380
    Details
    In: Hydrology and Earth System Sciences, Copernicus GmbH, Vol. 24, No. 6 ( 2020-07-01), p. 3361-3380
    Abstract: Abstract. Cave microclimate and geochemical monitoring is vitally important for correct interpretations of proxy time series from speleothems with regard to past climatic and environmental dynamics. We present results of a comprehensive cave-monitoring programme in Waipuna Cave in the North Island of New Zealand, a region that is strongly influenced by the Southern Westerlies and the El Niño–Southern Oscillation (ENSO). This study aims to characterise the response of the Waipuna Cave hydrological system to atmospheric circulation dynamics in the southwestern Pacific region in order to assure the quality of ongoing palaeo-environmental reconstructions from this cave. Drip water from 10 drip sites was collected at roughly monthly intervals for a period of ca. 3 years for isotopic (δ18O, δD, d-excess parameter, δ17O, and 17Oexcess) and elemental (Mg∕Ca and Sr∕Ca) analysis. The monitoring included spot measurements of drip rates and cave air CO2 concentration. Cave air temperature and drip rates were also continuously recorded by automatic loggers. These datasets were compared to surface air temperature, rainfall, and potential evaporation from nearby meteorological stations to test the degree of signal transfer and expression of surface environmental conditions in Waipuna Cave hydrochemistry. Based on the drip response dynamics to rainfall and other characteristics, we identified three types of discharge associated with hydrological routing in Waipuna Cave: (i) type 1 – diffuse flow, (ii) type 2 – fracture flow, and (iii) type 3 – combined flow. Drip water isotopes do not reflect seasonal variability but show higher values during severe drought. Drip water δ18O values are characterised by small variability and reflect the mean isotopic signature of precipitation, testifying to rapid and thorough homogenisation in the epikarst. Mg∕Ca and Sr∕Ca ratios in drip waters are predominantly controlled by prior calcite precipitation (PCP). Prior calcite precipitation is strongest during austral summer (December–February), reflecting drier conditions and a lack of effective infiltration, and is weakest during the wet austral winter (July–September). The Sr∕Ca ratio is particularly sensitive to ENSO conditions due to the interplay of congruent or incongruent host rock dissolution, which manifests itself in lower Sr∕Ca in above-average warmer and wetter (La Niña-like) conditions. Our microclimatic observations at Waipuna Cave provide a valuable baseline for the rigorous interpretation of speleothem proxy records aiming at reconstructing the past expression of Pacific climate modes.
    Type of Medium: Online Resource
    ISSN: 1607-7938
    URL: Article
    URL: Article
    DOI: 10.5194/hess-24-3361-2020
    DOI: 10.5194/hess-24-3361-2020-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2020
    detail.hit.zdb_id: 2100610-6
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  • 6
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    Past fire dynamics inferred from polycyclic aromatic hydrocarbons and monosaccharide anhydrides in a stalagmite from the archaeological site of Mayapan, Mexico
    Copernicus GmbH ; 2023
    In:  Biogeosciences Vol. 20, No. 15 ( 2023-08-08), p. 3249-3260
    Details
    In: Biogeosciences, Copernicus GmbH, Vol. 20, No. 15 ( 2023-08-08), p. 3249-3260
    Abstract: Abstract. Speleothems (cave stalagmites) contain inorganic and organic substances that can be used to infer past changes in local and regional paleoenvironmental conditions. Specific biomarkers can be employed to elucidate the history of past fires, caused by interactions among climate, regional hydrology, vegetation, humans, and fire activity. We conducted a simple solid–liquid extraction on pulverised carbonate samples to prepare them for analysis of 16 polycyclic aromatic hydrocarbons (PAHs) and three monosaccharide anhydrides (MAs). The preparation method requires only small samples (0.5–1.0 g); PAHs and MAs were measured by GC–MS and LC–HILIC–MS, respectively. Detection limits range from 0.05–2.1 ng for PAHs and 0.01–0.1 ng for MAs. We applied the method to 10 samples from a ∼ 400-year-old stalagmite from Cenote Ch'en Mul, at Mayapan (Mexico), the largest Postclassic Maya capital of the Yucatán Peninsula. We found a strong correlation (r = 0.75, p 〈 0.05) between the major MA (levoglucosan) and non-alkylated PAHs (Σ15). We investigated multiple diagnostic PAH and MA ratios and found that although not all were applicable as paleo-fire proxies, ratios that combine PAHs with MAs are promising tools for identifying different fire regimes and inferring the type of fuel burned. In the 1950s and 1960s, levoglucosan and Σ15 concentrations roughly doubled compared to other times in the last 400 years, suggesting greater fire activity at Mayapan during these two decades. The higher concentrations of fire markers may have been a consequence of land clearance at the site and exploration of the cave by Carnegie Institution archaeologists.
    Type of Medium: Online Resource
    ISSN: 1726-4189
    URL: Article
    URL: Article
    DOI: 10.5194/bg-20-3249-2023
    DOI: 10.5194/bg-20-3249-2023-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2023
    detail.hit.zdb_id: 2158181-2
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