Browning Lakes in a Greening Arctic: A Sediment- and Satellite-Based Circum-Arctic Synthesis

Climate change is amplified in the Arctic, which is warming four times faster than the globe. Lakes are abundant across Arctic landscapes, integral to hydrological cycles and associated ecosystem functions and services, and act as sentinels of environmental change in the region. 
Across the terrestrial Arctic, widespread but spatially heterogeneous greening trends have been documented through remote sensing, linked to field-observed increases in vegetation growth, range expansion, and altered community composition. Concurrently, increases in terrestrial organic matter loading have been reported in some Arctic lakes, associated with browning, while other lakes are greening, linked to enhanced algal growth under shifting nutrient and thermal conditions.
While the theoretical basis for recent catchment vegetation and lake-water quality shifts is clear, circum-Arctic evidence linking the two phenomena remains scarce. 
Here, we assess coupled greening and browning trends of terrestrial vegetation and aquatic indicators (total organic carbon, TOC; chlorophyll-a, ChlA) in ~100 circum-Arctic lake-catchment systems across Alaska, Canada, Greenland, Fennoscandia, and Russia. TOC and ChlA are reconstructed from sediment records using visible–near infrared spectroscopy (VNIRS)-based inference. Catchment vegetation change is quantified based on annual peak greenness and growing-season length, using spectral vegetation indices (NDVI, EVI2, and NIRv) from Landsat, AVHRR, and MODIS satellites over 1984–2025. Patterns in vegetation trends are described and analyzed using a custom land-cover reclassification, aboveground biomass, and vegetation height datasets. 
Our remote-sensing results indicate widespread greening of catchments since the 1980s, at heterogeneous rates across Arctic regions and vegetation zones. Early sediment-based reconstructions indicate TOC increases in numerous lakes over the same period; ChlA is generally increasing but not consistently coupled to TOC. The greening-browning relationship will be evaluated through multivariate association analyses, accounting for physiographic and bioclimatic setting (e.g., latitude, topography, temperature/precipitation, vegetation type, hydrological connectivity). Our presentation will summarize catchment vegetation and lake-water TOC and ChlA trajectories across the Arctic, and identify the conditions under which they are linked most strongly.