Climate Warming Promotes Carbon Sequestration and Weathering in Tundra Landscapes and Alters Carbon Chemistry of Subarctic Lakes in Scandinavia

ABSTRACT We combined satellite data (NDVI max ) and plot‐scale field measurements to quantify effects of warming on carbon (C) sequestration by tundra vegetation in three subregions and nine subarctic catchments in northern Scandinavia. We then used long‐term data (C, sulfate, base cation concentrations) of the lakes to unravel effects of different drivers on their C chemistry. NDVI max generally showed positive trends with a marked increase during the 1990s. Total C‐sequestration for the three subregions increased by 20% during the 1990s, or from 15.45 ± 0.38 Mt during 1983–1993 to 18.51 ± 0.26 Mt during 2002–2021, but ceased in more recent years. The increase in NDVI max implied 10%–85% increases in area‐specific C‐sequestration in the catchments of our study lakes during 2001–2021 compared with 1983–1993. Despite these increases in terrestrial vegetation, total organic C (TOC) concentrations in downstream lakes showed declining trends. Conversely, inorganic C concentrations (IC alk ) showed consistent, increasing trends. Analysis of trends for major ions and multiple regressions showed that both a climate‐induced increase in weathering and declines in non‐marine SO 4 deposits in the catchments were important drivers of the temporal increase in IC alk in all lakes. Our analysis shows that warming‐induced vegetation development impacts on the C‐dynamics of tundra landscapes and downstream lakes.