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This dataset contains the raw data associated with the manuscript entitled: Aquatic Moss δ18O as a Proxy for Seasonally Resolved Lake Water δ18O, Northwest Greenland (Puleo et al., 2024). Reconstructing past climate seasonality is fundamental to understanding the nature of past climate changes. This is especially true in the Arctic, where climate is intensely seasonal and proxies that can distinguish climate conditions of multiple seasons in a single year are relatively rare. We propose that submerged aquatic mosses, which are abundant subfossils in some Arctic lake sediments and have distinctive seasonal growth morphologies, can be used to estimate past lake water oxygen isotope composition (δ18Olw) across multiple seasons. Aquatic mosses are abundant, well preserved, and grow continuously in Arctic lakes whenever light is available, with some species displaying unique seasonal morphologies influenced by water temperature. Although Greenland paleorecords support that aquatic moss oxygen isotope values (δ18Oom) reflect the δ18O values of lake water, no modern calibration between δ18Oom and δ18Olw exists in Greenland, as aquatic moss samples are composed largely, but not entirely, of cellulose. We present a modern δ18Oom vs. δ18Olw calibration using multiple moss species or morphotypes from eight lakes and ponds near Pituffik (Thule), northwest Greenland. We find strong linear relationships between the δ18Oom and δ18Olw values of multiple species or morphotypes across the range of relatively low δ18Olw values at Pituffik, and our results indicate isotopic fractionations are similar to those found previously at lower latitudes. To assess the potential of mosses as archives of seasonal δ18Olw values, we analyzed δ18Oom in season-specific segments of moss strands, with seasons identified based upon growth morphology. Moss inferred lake water δ18O values (δ18Olwom) are higher in autumn than spring or summer, likely due to increasing contributions of isotopically heavier precipitation and the cumulative effects of lake water evaporation throughout the ice-free season. For moss subsampled throughout summer, δ18Olwom values generally increased through the season in parallel with observed δ18Olw values. Potential temperature dependent fractionation effects during biosynthesis, however, remain unconstrained and should be further addressed with future research. Overall, these findings suggest that aquatic mosses from lake sediments could be used to directly resolve climate seasonality of the past. Puleo, P.J.K., Akers, P.D., Kopec, B.G., Welker, J.M., Bailey, H., Osburn, M.R., Riis, T., Axford, Y., 2024. Aquatic moss δ18O as a proxy for seasonally resolved lake water δ18O, northwest Greenland. Quaternary Science Reviews 334, 1-11. 

The SUMup database is a compilation of surface mass balance (SMB), subsurface temperature and density measurements from the Greenland and Antarctic ice sheets. This 2023 release contains 4 490 442 data points: 1 778 540 SMB measurements, 2 706 413 density measurements and 5 489 subsurface temperature measurements. This is respectively 1 477 132, 420 825 and 4 715 additional observations of SMB, density and temperature compared to the 2022 release. This new release provides not only snow accumulation on ice sheets, like its predecessors, but all types of SMB measurements, including from ablation areas. On the other hand, snow depth on sea ice is discontinued, but can still be found in the previous releases. The data files are provided in both CSV and NetCDF format and contain, for each measurement, the following metadata: latitude, longitude, elevation, timestamp, method, reference of the data source and, when applicable, the name of the measurement group it belongs to (core name for SMB, profile name for density, station name for temperature). Data users are encouraged to cite all the original data sources that are being used. Issues about this release as well as suggestions of datasets to be added in next releases can be done on a dedicated user forum: https://github.com/SUMup-database/SUMup-data-suggestion/issues. Example scripts to use the SUMup 2023 files are made available on our script repository: https://github.com/SUMup-database/SUMup-example-scripts.