Rare earth elements (REE) as indicators of geochemical processes in permafrost systems of the Arctic Foothills, Northern Alaska

Abstract

In permafrost environments, distinct soil thermal regimes create unique influences on pedogenic processes and hydrological systems. Rare earth elements (REE) provide utility as indicators of soil geochemical cycling that can improve our understanding of permafrost soil-hydrological systems and their change over time, yet a greater understanding of the factors governing permafrost REE distribution is needed. We assess cryogenic controls on soil REE cycling in permafrost and active layer from three pedogenic environments in the Arctic Foothills of Alaska, and REE of adjacent surface waters. Soil parent material influenced the relative REE species abundance across sites while total extractable REE varied with soil material properties. REE reservoir transfer functions revealed differences in fractionation between permafrost and active layer in middle REE of a peat-rich site, and heavy REE for two sites with higher mineral content, potentially reflecting preferred degradation of heavy REE inorganic complexes in the active layer. Each soil profile revealed accumulation of REE above the near-surface permafrost table which could serve as an important sourcing zone for suprapermafrost flow. REE (<0.45 μm) of two tundra streams featured fractionation toward heavier REE that varied throughout the thaw season, likely with changing flux of species-preferred ligands driven by top-down seasonal soil thaw. Heavy REE enrichment in permafrost translated to elevated heavy REE in the surface waters of an active thermokarst, suggesting that catchment permafrost degradation may be identifiable by increased loading of heavy REE to streams at our sites. Our results demonstrate the importance of soil thermal status on influencing chemical weathering and translocation in permafrost environments and illustrate the potential utility of REE in tracking catchment permafrost stability.