Compositional variability of Mg/Ca, Sr/Ca, and Na/Ca in the deep-sea bivalve Acesta excavata (Fabricius, 1779)

Acesta excavata (Fabricius, 1779) is a slow growing bivalve from the Limidae family and is often found associated with cold-water coral reefs along the European continental margin. Here we present the compositional variability of frequently used proxy elemental ratios (Mg/Ca, Sr/Ca, Na/Ca) measured by laser-ablation mass spectrometry (LA-ICP-MS) and compare it to in-situ recorded instrumental seawater parameters such as temperature and salinity. Shell Mg/Ca measured in the fibrous calcitic shell section was overall not correlated with seawater temperature or salinity; however, some samples show significant correlations with temperature with a sensitivity that was found to be unusually high in comparison to other marine organisms. Mg/Ca and Sr/Ca measured in the fibrous calcitic shell section display significant negative correlations with the linear extension rate of the shell, which indicates strong vital effects in these bivalves. Multiple linear regression analysis indicates that up to 79% of elemental variability is explicable with temperature and salinity as independent predictor values. Yet, the overall results clearly show that the application of Element/Ca (E/Ca) ratios in these bivalves to reconstruct past changes in temperature and salinity is likely to be complicated due to strong vital effects and the effects of organic material embedded in the shell. Therefore, we suggest to apply additional techniques, such as clumped isotopes, in order to exactly determine and quantify the underlying vital effects and possibly account for these. We found differences in the chemical composition between the two calcitic shell layers that are possibly explainable through differences of the crystal morphology. Sr/Ca ratios also appear to be partly controlled by the amount of magnesium, because the small magnesium ions bend the crystal lattice which increases the space for strontium incorporation. Oxidative cleaning with H2O2 did not significantly change the Mg/Ca and Sr/Ca composition of the shell. Na/Ca ratios decreased after the oxidative cleaning, which is most likely a leaching effect and not caused by the removal of organic matter

Potentials and limitations of multi-proxy records in speleothem research - Case studies in complex climate systems

The central goal of this dissertation is assessing the benefits and limitations of multi-proxy approaches in speleothem research with respect to paleo climate reconstruction. Hence, the aims were evaluating the environmental controls of speleothem proxies such as stable isotopes or trace elements, and the application to samples from locations affected by complex climate interactions. Thus, this thesis provides an important contribution to the recent scientific discussion in speleothem and climate research. The presented case studies comprise a Holocene stalagmite from southwestern Romania, and two speleothems from the Caribbean realm covering major parts of the last Glacial cycle. All records are based on high-precision dating methods, such as 230Th/U dating, lamina counting or radiocarbon dating. The analysis of stable isotope δ18O and δ13C composition together with trace elemental signatures enables a broad survey of past environmental changes comprising temperature and rainfall variability as well as soil and vegetation dynamics. The studies presented in this thesis demonstrate the strong benefits of the combination of several proxies in speleothems and in the investigated regions, they provide the first speleothem derived climate reconstructions, respectively, combining successfully both stable isotopes and elemental proxies. In tropical locations, the δ18O values in speleothems may be reliable recorders of past rainfall changes. However, a number of processes such as temperature variability, source effects and disequilibrium fractionation affecting the oxygen isotopic composition have to be carefully evaluated. Under certain circumstances, trace elements such as magnesium and strontium are found to constitute valuable tracers of hydrological variability, whereas phosphorus is most commonly associated with soil and vegetation dynamics. However, the interpretation of P/Ca is found to be diverse in the three case studies. To explain the non-conventional P systematics in the Cuban sample, a mechanism was devised which previously has received little attention. Stalagmite C09-2 from southwestern Romania emerged as one of the unique samples appropriate for quantitative reconstruction of past climate variability. The Mg/Ca ratio was found to be strongly connected with past winter rainfall, and the reconstructed precipitation estimates for the last 3.6 ka are in agreement with other local and supra-regional records. The δ18O record from stalagmite PR-LA-1 is one of the first speleothem derived long-term reconstructions of rainfall variability from the western tropical Atlantic realm which demonstrates the imprint of both the Heinrich stadials as well as the Dansgaard/Oeschger cycles on Puerto Rico during the last Glacial. In addition, stalagmite CM from western Cuba provides one of the longest speleothem records from the Caribbean region, and the geochemical evidence from the stable isotope and trace element signatures gives a comprehensive picture of past environmental variability over a long time interval of the last Glacial

Aerosol contributions to speleothem geochemistry

There is developing interest in cave aerosols due to the increasing awareness of their impacts on the cave environment and speleothems. This study presents the first multidisciplinary investigation into cave aerosols and their contribution to speleothem geochemistry. Modern monitoring of suspended aerosol concentrations, CO2 and temperature in Gough’s Cave, Cheddar Gorge have presented a strong relationship with cave ventilation processes. Temporal variations of aerosol levels have demonstrated the ability of aerosol monitoring to record seasonal ventilation shifts, beyond anthropogenic influences. When used in combination with more established monitoring methods, suspended aerosol monitoring is a beneficial addition to cave environmental studies Theoretical modelling and calculations based on modern aerosol monitoring have established that aerosol contributions are highly variable. Aerosol contributions are of greatest significance under slow growth or hiatus scenarios and high aerosol deposition scenarios. Marine and terrestrial aerosol contributions have been quantified in a flowstone core from New St Michaels Cave, Gibraltar. Additionally, bio-aerosol deposits and bacterial colonisation have been identified as a potential source of trace element bioaccumulation and flowstone coloration in Yarrangobilly Caves, Australia

The effect of formation processes on the frequency of palaeolithic cave sites in semiarid zones: Insights from Kazakhstan

Central Asian caves with Palaeolithic deposits are few, but they provide a rich record of human fossils and cultural assemblages that has been used to model Late Pleistocene hominin dispersals. However, previous research has not yet systematically evaluated the formation processes that influence the frequency of Palaeolithic cave sites in the region. To address this deficiency, we combined field survey and micromorphological analyses in the piedmont zone of south Kazakhstan. Here, we present our preliminary results focusing on selected sites of the Qaratau mountains. Sediment cover varies among the surveyed caves, and loess-like sediments dominate the cave sequences. The preservation of cave deposits is influenced by reworking of cave sediments within the caves but also by the broader erosional processes that shape semiarid landscapes. Ultimately, deposits of potentially Pleistocene age are scarce. Our study provides new data in the geoarchaeologically neglected region of Central Asia and demonstrates that micromorphology has great analytical potential even within the limitations of rigorous survey projects. We outline some of the processes that influence the formation and preservation of cave deposits in Kazakhstan, as well as broader implications for the distribution of Palaeolithic cave sites in Central Asia and other semiarid environments.publishedVersio

Chemical characterization of clastic cave sediments and insights into particle transport and storage in karst aquifers

Abstract Chemical characterization of clastic cave sediments and insights into particle transport and storage in karst aquifers Jill L. Riddell Cave sediments can be divided into two groups: precipitates and clastics. Precipitates are speleothems, or lithologic or mineral features that are chemically precipitated in the cave environment. Clastic cave sediments are frequently described by depositional facies, sorting, and particle size (Bosch and White, 2004). Robust analytical chemical analyses of these sediments to quantify their physical and chemical components is rarely performed although some chemical characterization of mineralogy and paleomagnetism has become prevalent in recent years (Chess et al., 2010; Sasowsky et al., 2007). The organic carbon content of cave sediments can be representative of organic carbon concentrations in the larger karst system and concentrations of organic carbon in cave sediments can be used to estimate the potential retardation of organic contaminants through the entire karst system. The ability of karst sediments to be a sorbent for metals and organic contaminants, and store and transport contaminants is positively correlated with the amount of organic carbon in the sediment; yet these concentrations are rarely reported in karst sediments. This dissertation seeks to fill the gap in the mineralogy and chemical components of cave sediments; quantify the organic carbon content of cave sediments relative to depositional facies; and measure the adsorption of an organic microsphere onto a cave sediment to explore sediment-contaminant interactions. A case study from Dropping Lick Cave in Monroe County, WV, is presented where a variety of analytical techniques were used to determine the active fraction ( \u3c 2mm) mineralogy and chemical components of the sediment The sediments were silt and sand-sized particles consisting of quartz, some clay or silicate minerals, dolomite, and amorphous materials. The particle size and total carbon was within the same range reported for the \u3c 2mm fraction in other clastic cave sediments in this region, in the central United States, and in Puerto Rico. The preliminary mineralogy of the sediments is congruent with the mineralogy of surrounding siliciclastic rocks indicating that the source of the sediment is erosional products from nearby Peters Mountain and its slopes. Particle size, TOC, and total nitrogen were measured in sediments representing different facies in Butler Cave, Virginia, USA. TOC concentrations ranged from 0.08 – 0.87 weight percent and C:N molar ratio ranged from 3 – 15, indicating a possible terrestrial source of organic carbon in these sediments. TOC concentrations measured in Butler Cave were within the same range as those observed in above water, eogenetic clastic cave sediments from two caves in Puerto Rico. Estimated retardation factors calculated based on the TOC concentrations in the Butler Cave sediments indicate the range of TOC in this cave could be responsible for 39 – 987% increase in retardation of selected contaminants. This study highlights the importance of measuring the ranges of TOC in clastic cave sediments across different facies and their role in contaminant fate and transport. In this study, The adherence of carboxylated and nonfunctionalized polystyrene microspheres onto a clastic cave sediment was quantified for microsphere dilutions in three water types – deionized water, a 25 mg/L CaCO3 solution, and a karst spring water. Regardless of water type, both types of microspheres adhered to the sediment. Infrared absorbance data of different microsphere-solution-sediment mixtures indicated the potential presence of sediment minerals and microspheres in the solution. Analysis of solution pH and infrared spectra suggested pH and mineral constituents of the sediment are the most important factors in microsphere adherence. Using the adherence data, estimated KOC values for both types of microspheres were calculated and were in the same ranges as phthalates, a known contaminant in karst aquifers that is also considered a plastic, like polystyrene. The chemical and physical commonalities between microspheres and organic and microplastic (MP) contaminants warrant further investigation of microspheres as a proxy for contaminants in sediment-contaminant experiments. The results of these experiments suggest that consideration of MPs adhered to sediments should be considered when quantifying MP contamination in karst systems