Mercury Isotope Variability in Pyrenean Lake Sediments during the Late Holocene: Sources, Deposition, and Environmental Controls.

Atmospheric mercury (Hg) emissions represent a persistent global threat to ecosystems and human health. Stable Hg isotopes have emerged as powerful tools to trace historical pollution sources and reconstruct depositional pathways in natural archives. In this study, we present a 4000-year reconstruction of Hg isotopic composition from two Pyrenean lake sediment records (Lake Marboré and Lake Estanya) located along an altitudinal gradient and compare them with those of a nearby ombrotrophic peatland (Estibere mire). Both lakes exhibit a long-term increase in Hg accumulation rates and shifts in isotope values since the onset of the Modern Period (∼16th century), consistent with intensified anthropogenic emissions. However, the isotopic patterns differ: Lake Estanya, located in a lowland area with historical land-use changes, reflects a more localized Hg signal, whereas the high-elevation, remote Lake Marboré preserves a broader regional atmospheric imprint, dominated by wet deposition. The comparison with Estibere mirepristine and situated within the same air mass trajectory as Marboréreveals a consistent offset in ΔHg values yet strikingly similar temporal trends, indicating a shared regional source signal modulated by ecosystem-specific processes. This multiarchive and multialtitude framework provides a rare opportunity to disentangle Hg source signatures from depositional and postdepositional transformations. Moreover, variations in even-MIF (ΔHg) in the alpine lake show the potential to reflect past climate phases, highlighting the additional value of Hg isotopes as paleoclimatic proxies. Our results underscore the importance of integrating different ecosystem archives to improve reconstructions of atmospheric Hg dynamics and to refine interpretations of legacy pollution and climate interactions.