Oxygen isotopes in biogenic silica (δ18O BSi) from lake sediments allow for quantitative reconstruction of past hydroclimate and proxy–model comparison in terrestrial environments. The signals of individual records have been attributed to different factors, such as air temperature (T air ), atmospheric circulation patterns, hydrological changes and lake evaporation. Here, we provide 55 composite down–core records published to date and complemented with additional lake basin parameters (e.g. lake water residence time and catchment size) to best characterize the signal properties. Records feature widely different temporal coverage and resolution ranging from decadal–scale records covering the last 150 years to records with multi–millennial scale resolution spanning glacial–interglacial cycles. Best coverage in number of records (N=37) and datapoints (N=2112) is available for northern hemispheric (NH) extra–tropic regions throughout the Holocene (corresponding to Marine Isotope Stage 1; MIS 1).

Oxygen isotopes in biogenic silica (δ18O BSi) from lake sediments allow for quantitative reconstruction of past hydroclimate and proxy–model comparison in terrestrial environments. The signals of individual records have been attributed to different factors, such as air temperature (T air ), atmospheric circulation patterns, hydrological changes and lake evaporation. Here, we provide 55 composite down–core records published to date and complemented with additional lake basin parameters (e.g. lake water residence time and catchment size) to best characterize the signal properties. Records feature widely different temporal coverage and resolution ranging from decadal–scale records covering the last 150 years to records with multi–millennial scale resolution spanning glacial–interglacial cycles. Best coverage in number of records (N=37) and datapoints (N=2112) is available for northern hemispheric (NH) extra–tropic regions throughout the Holocene (corresponding to Marine Isotope Stage 1; MIS 1).

Dataset includes depth and ¹⁴C based age-depth model of core from Lake 850 taken in March 2019. Biogenic silica, density, total organic carbon (TOC), total nitrogen content (%N) and calcium carbonate content (CaCO₃) were measured by weak-alkaline extraction, by constraining volume and weight of wet and dry bulk sediment sample and by elemental analyzed COSTECH, respectively. Further, stable carbon isotopes (d¹³C) were measured by Elemental Analyzer connected to a MAT-252 mass spectrometer at Weizmann Institute of Science, Rehovot.Mass accumulation rate (MAR) is calculated from sediment density, age-depth model and biogenic silica flux is MAR multiplied by biogenic silica content.Further, the data contains elemental composition (Al, Si, P, S, Ar, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Ge, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Te, Ba, La, Ce, Nd, Sm, Eu, Tb, Er, Tm, Yb, Hf, Ir, Pt, Au, Pb, Rn och, Rh inc, MS) of the sediment core from 2019 originating from ITRAX CS37 XRF from GLOBE Institute, Copenhagen University.

Data on core from Lake 850 sampled in 1999, including depth, ¹⁴C based age-depth model, loss-of-ignition and stable Si isotopes measured on diatom opal-A using Apex HF desolvation nebulizer connected to MC-ICP-MS at the Vegacenter, Swedish Natural History Museum, Stockholm.

¹⁴C data and age-depth models are based on ¹⁴C data from two cores sampled from Lake 850 in 1999 and 2019. Radiometric dates were calibrated with IntCal20 radiocarbon calibration dataset (Reimer et al. 2020), see doi:10.1594/PANGAEA.933321. Age-depth models are calculated using R package Bacon (Blaauw et al, 2021).

Data contains elemental composition (Al, Si, P, S, Ar, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Ge, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Te, Ba, La, Ce, Nd, Sm, Eu, Tb, Er, Tm, Yb, Hf, Ir, Pt, Au, Pb, Rn och, Rh inc, MS) of the sediment core from 2019 originating from ITRAX CS37 XRF from GLOBE Institute, Copenhagen University.

¹⁴C data and age-depth models based on ¹⁴C data from two cores sampled from Lake 850 in 1999 and 2019. Radiometric dates were calibrated with IntCal20 radiocarbon calibration dataset (Reimer et al. 2020). For age-depth models calculated using R package Bacon see doi:10.1594/PANGAEA.933325.Lake850-Core3-1999 data are from Shemesh et al., 2001.

Contemporary cnidarian-algae symbioses are challenged by increasing CO2 concentrations (ocean warming and acidification) affecting organisms' biological performance. We examined the natural variability of carbon and nitrogen isotopes in the symbiotic sea anemone Anemonia viridis to investigate dietary shifts (autotrophy/heterotrophy) along a natural pCO2 gradient at the island of Vulcano, Italy. delta 13C values for both algal symbionts (Symbiodinium) and host tissue of A. viridis became significantly lighter with increasing seawater pCO2. Together with a decrease in the difference between delta 13C values of both fractions at the higher pCO2 sites, these results indicate there is a greater net autotrophic input to the A. viridis carbon budget under high pCO2 conditions. delta 15N values and C/N ratios did not change in Symbiodinium and host tissue along the pCO2 gradient. Additional physiological parameters revealed anemone protein and Symbiodinium chlorophyll a remained unaltered among sites. Symbiodinium density was similar among sites yet their mitotic index increased in anemones under elevated pCO2. Overall, our findings show that A. viridis is characterized by a higher autotrophic/heterotrophic ratio as pCO2 increases. The unique trophic flexibility of this species may give it a competitive advantage and enable its potential acclimation and ecological success in the future under increased ocean acidification.

Uptake of anthropogenic CO2 by the oceans is altering seawater chemistry with potentially serious consequences for coral reef ecosystems due to the reduction of seawater pH and aragonite saturation state (omega arag). The objectives of this long-term study were to investigate the viability of two ecologically important reef-building coral species, massive Porites sp. and Stylophora pistilata, exposed to high pCO2(or low pH) conditions and to observe possible changes in physiologically related parameters as well as skeletal isotopic composition. Fragments of Porites sp. and S. pistilata were kept for 6-14 months under controlled aquarium conditions characterized by normal and elevated pCO2 conditions, corresponding to pHTvalues of 8.09, 7.49, and 7.19, respectively. In contrast with shorter, and therefore more transient experiments, the long experimental timescale achieved in this study ensures complete equilibration and steady state with the experimental environment and guarantees that the data provide insights into viable and stably growing corals. During the experiments, all coral fragments survived and added new skeleton, even at seawater omega arag <1, implying that the coral skeleton is formed by mechanisms under strong biological control. Measurements of boron (B), carbon (C) and oxygen (O) isotopic composition of skeleton, C isotopic composition of coral tissue and symbiont zooxanthellae, along with physiological data (such as skeletal growth, tissue biomass, zooxanthellae cell density and chlorophyll concentration) allow for a direct comparison with corals living under normal conditions and sampled simultaneously. Skeletal growth and zooxanthellae density were found to decrease, whereas coral tissue biomass (measured as protein concentration) and zooxanthellae chlorophyll concentrations increased under high pCO2 (low pH) conditions. Both species showed similar trends of delta11B depletion and delta18O enrichment under reduced pH, whereas the delta13C results imply species-specific metabolic response to high pCO2 conditions. The skeletal delta11B values plot above seawater delta11B vs. pH borate fractionation curves calculated using either the theoretically derived deltaB value of 1.0194 (Kakihana et al., Bull. Chem. Soc. Jpn. 50(1977), 158) or the empirical deltaB value of 1.0272 (Klochko et al., EPSL 248 (2006), 261). However, the effective deltaB must be greater than 1.0200 in order to yield calculated coral skeletal delta11B values for pH conditions where omega arag >1. The delta11B vs. pH offset from the literature seawater delta11B vs. pH fractionation curves suggests a change in the ratio of skeletal material laid down during dark and light calcification and/or an internal pH regulation, presumably controlled by ion-transport enzymes. Finally, seawater pH significantly influences skeletal delta13C and delta18O. This must be taken into consideration when reconstructing paleo-environmental conditions from coral skeleton

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