A dual role of precipitation amount and temperature determines precipitation isotopic trends in Southeast Alaska

Southeast Alaska is one of the wettest places in the world, with some locations within the region receiving upwards of 6 metres of precipitation annually. Given the region's abundant precipitation, it is important to understand the mechanisms controlling the hydrologic cycle to better constrain past and future trends in climate. Accomplishing this requires the evaluation of isotopes in precipitation, as this is key to untangling the many drivers of the water cycle. However, there has never been a precipitation isotope study conducted in Southeast Alaska, vastly limiting our understanding of the water cycle in this region. To fill this gap, we report the first precipitation isotope results from Southeast Alaska, composed of monthly samples spanning 1 year between September 2023 and August 2024, thereby establishing an important regional baseline. We find that variations in temperature and precipitation amount during both a yearly and seasonal scale strongly influence the precipitation isotopic trends in the region, with the strength of the Aleutian Low a key factor in modulating precipitation isotopic trends.