Rapidly changing climate is disrupting the High Arctic’s natural water systems. This disruption demands high quality monitoring of Arctic hydrology to better reconstruct past changes, track ongoing transformations, and assess future environmental threats. Water isotopes are valuable tracers of hydrological processes, but logistical challenges limit the length and scope of isotopic monitoring in High Arctic landscapes. Here, we present a comprehensive isotopic survey of 535 water samples taken in 2018–2019 of the lakes, streams, and other surface waters of the periglacial Pituffik Peninsula in far northwest Greenland. The δ18O, δ2H, and deuterium-excess values of these samples, representing 196 unique sites, grant us unprecedented insight into the environmental drivers of the region’s hydrology and water isotopic variability. We find that the spatial and temporal variability of lake isotopes is dominated by evaporation and connectivity to summer meltwater sources, while evaporation determines interannual isotopic changes. Stream isotopic compositions vary in both space and time based on the relative source balance of tundra snowpack meltwater versus surface melt from the nearby Greenland Ice Sheet. Overall, our survey highlights the diversity of isotopic composition and evolution in Pituffik surface waters, and our complete isotopic and geospatial database provides a strong foundation for future researchers to study hydrological changes at Pituffik and across the Arctic. Water isotope samples taken at individual times or sites in similar periglacial landscapes likely have limited regional representativeness, and increasing the spatiotemporal extent of isotopic sampling is critical to producing accurate and informative High Arctic paleoclimate reconstructions.

Peat carbon (C) is one of the largest pools of soil C globally and is sensitive to environmental and climatic changes. Peatlands in the Kenai National Wildlife Refuge have been studied for their hydrology, vegetation composition and succession, peat accumulation, and similar characteristics, but their mass of stored C remains unknown. We use a synthesis of soil and wetland surveying techniques to generate estimates of C mass at two sites selected for suitable topography and hydrology. Manual probing of peat depth at 208 points across both sites provided calibration for radar velocity (medians 0.039 m·ns-1 and 0.037 m·ns-1) of a low-frequency (100 MHz) ground-penetrating radar (GPR), utilized to identify peat basal horizons. GPR surveys collected data points more efficiently than probing: >26,000 traces over 4.9 km of lines in half the time. We calculated total C mass from basin volume estimates via kriging interpolation surfaces with peat core C content and bulk density values, yielding estimates of 4,172 and 3,473 metric tons C (tC) for the two sites. Nearly equal site surface areas of 2.1 hectares yielded areal densities of 1,948 and 1,628 tC per hectare, respectively. Peat core analyses of C isotopes, organic matter content, nitrogen content, and 14C dating illustrate a similar Holocene history, but site conditions vary despite proximity. Variances in bulk density, vegetation abundance and diversity, and surface water presence are likely influenced by local topography, subsurface hydrologic connectivity, and the establishment history of peat-forming vegetation.