Biodiversity dynamics in deep time are influenced by climatic changes. However, linking these two aspects is challenging. At a basic level, a phylogenetic tree can be directly compared to global averages of a palaeoclimate proxy of interest. This approach is only qualitative and neglects regional climate differences. In a recent article, we introduced the concept of phylogeochemistry, which links the – typically distant – topics of geochemical proxy data and comparative phylogenetics. As a case study, we applied this technique to main and trace element concentrations in belemnite rostra, showing how and at what rates these proxies change through time with respect to macroevolutionary links. Here, we introduce phylogeochemistry more broadly, explaining the motivation and background, and provide a brief overview of the methodology and potential research questions. Specifically, in a phylogenetic tree, each tip (representing, e.g., a species or population) can be associated with proxy data (e.g., oxygen isotope ratios used for the reconstruction of palaeo-seawater temperatures). Phylogenetic comparative methods can then be used to reconstruct ancestral states at internal nodes or the rate of changes. Potential applications include, e.g., testing whether temperature affects extinction rates, whether distinct warm- or cold-water clades can be identified. Due to the flexible probabilistic framework, the models can be specifically tailored to the research objectives at hand. We further discuss challenges and caveats that need to be considered in study design. Last but not least, phylogeochemistry calls for closer collaborations between geochemists and palaeobiologists for the best results.

Over the past 50 million years, Cenozoic climate cooling has coincided with rising Mg/Ca ratios in seawater. However, the connection between this shift in seawater chemistry and climate change remains debated. Magnesium isotope ratios (δ²⁶Mg) in seawater could help differentiate between possible mechanisms, such as dolomitization, formation of authigenic clays, and variations in silicate and carbonate weathering rates. Past reconstructions of paleo-seawater δ²⁶Mg using foraminifera, corals, and carbonate muds have yielded inconsistent results. In this study, we evaluate bivalves from the genus Glycymeris as alternative archives for paleo-seawater δ²⁶Mg. These bivalves possess several advantages, including evolutionary stability, thick shells, and a fossil record extending back to the Lower Cretaceous—traits that suggest consistent isotopic fractionation over time. We analyzed Mg isotope compositions from the ventral shell margins of three modern Glycymeris species (G. bimaculata, G. nummaria, G. pilosa) from the Adriatic Sea. Our data show increasing isotopic fractionation with ontogenetic age and distinct intra-shell differences depending on sampling location (center vs. margin) at the same developmental stage. Our results show that variations in precipitation rates best explain this behavior of Mg isotopes. Unaltered isotope signatures in fossil shells can thus be clearly identified. This work suggests that the rate-dependence of δ²⁶Mg in Glycymeris can be exploited to derive paleo-seawater δ²⁶Mg.

Subfossil gastropod assemblages in geological deposits can be used to reconstruct past environmental and climatic conditions. We present new results from loess-palaeosol sequences in the Armenian highlands that provide insights into multiple glacial-interglacial transitions across the past 400 ka. Hereby our main aim was to reconstruct quantitative information that can serve as reference data e.g. for cross-validating earth system models. Our approach combines stable oxygen isotope (δ¹⁸O) analysis of snail shells with the ecological interpretation of species assemblages. The latter includes mutual climatic range analysis, supported by climatic niche modelling based on modern species distribution data. The gastropod assemblages showed distinct variations within the sequences, indicating different ecosystem characteristics and associated climatic conditions. We observed a significant relationship between specific ecological groups of gastropods and oxygen isotope signals in the shells. Predominantly xerophilous assemblages linked to stadial phases showed more negative δ¹⁸O_shell signals, while mesophilous assemblages linked to warmer phases corresponded to more positive signals. δ¹⁸O_shell signals provide valuable information on the isotopic composition of ingested precipitation, which in the studied region is strongly related to average temperatures. Temperature estimation based on transfer functions indicated a difference of 5.4°C between stadial and interglacial phases. Climatic range modelling turned out to be suitable for precipitation reconstruction, pointing to mean annual precipitation amounts centering around 425+-75 mm during glacial and 775+-75 mm during interglacial phases. This study provides new evidence-based palaeoclimate data for the Caucasus region highlighting the potential of snail shells as a quantitative proxy for palaeoclimate reconstruction.

The Paleogene succession of the Helmstedt Lignite Mining District in Northern Germany includes records of coastal peat mires from the latest Paleocene to the middle Eocene. Due to an interaction between changes in sea level, salt withdrawal in the subsurface and climate-related changes in runoff from the hinterland the area was subject to frequent changes between marine and terrestrial conditions, including peat formation. In an almost continuous section, the effects of long-term changes and short-term perturbations of the climate on the diversity and composition of plant communities can be traced by using pollen and spores as proxies. High-resolution C-isotope analyses allowed for precisely locating important short- and long-term climate events within the lower Eocene greenhouse, such as the Paleocene Eocene Thermal Maximum (PETM) and the Early Eocene Climatic Optimum (EECO). Here we present high-resolution palynological data from the lower Eocene Schöningen Formation at Schöningen to compare the wetland vegetation before, during and after these events. The focus is on the identification of short-term pulses versus long-term sustainable changes in composition and diversity of the vegetation. However, a climatic influence and the corresponding response of the ecosystems cannot simply be revealed from the microflora as documented in the studied succession. When interpreting the palynomorph record it is necessary to distinguish between changes in the vegetation that were controlled by climate or those controlled by other factors such as, for example, natural succession due to peat aggradation.

Accurate projections of climate tipping points require quantitative constraints on the nature and strength of feedbacks within the Earth’s surface carbon cycle. Among these, silicate weathering constitutes a key negative feedback by consuming atmospheric CO₂ through mineral dissolution. However, the feedback’s climatic sensitivity, expressed by the dependence of weathering rate on climate, remains poorly quantified. Basalt weathering plays an outstanding role in this process, due to basalt’s high abundance of CO₂-sequestering elements. For instance, increased basalt weathering fluxes may have caused global Cenozoic cooling. Determining weathering rates is key to this quantification. However, the quartz-free nature of basalt precludes the use of common in-situ cosmogenic nuclide approaches. We thus use the ¹⁰Be_meteoric/⁹Be cosmogenic nuclide method that has emerged as a powerful tool to simultaneously capture both physical erosion and chemical weathering in basaltic landscapes over millennial timescales.

We applied the ¹⁰Be_meteoric/⁹Be method to determine catchment-averaged denudation rates on river bedload and river waters, and local soil weathering rates on weathering profiles in the Vogelsberg (Germany). Denudation rates are consistent (~50 t km⁻² yr⁻¹ in rivers, ~40 t km⁻² yr⁻¹ in soils) and align with rates from other temperate basaltic regions. Weathering rates and intensities are high compared to other lithologies, which underlines the high reactivity of basalt. This first application of the method in basalt demonstrates its ability to simultaneously quantify denudation and weathering from multiple sample types. Extending this approach to other climates will help establish a baseline for detecting nonlinear or tipping responses in Earth’s surface carbon cycle.

Within the last 600 ka, the Guadix-Baza Basin underwent a number of significant geomorphological phases during its transformation from a flat endorheic basin towards the today´s deeply dissected erosion scenery.

Some of these phases represent turning points that introduced an entirely different geomorphic process structure such as the complex multi-phase capture of the basin. Other phases are characterized by unprecedented process intensities that, however, are leveled by opposing feedback-mechanisms such as incision and aggradation within dimensions of several tens of meters. Beside climate impact and the progressive down-cutting of the erosion base at the basin outlet, likewise tectonics exerted noticeable effects on prevalent geomorphic processes. Therefore, identifying causal factors remains a demanding task considering, furthermore, that climate archives are rare within the basin.

Here we present several examples in which way fluvial system behavior responded to certain external and internal impacts. Due to extensive geomorphological mapping and a hitherto unknown density of luminescence dating, we are able to provide a detailed picture of the fluvial evolution of the basin.