Trends in historical mercury deposition inferred from lake sediment cores across a climate gradient in the Canadian High Arctic

Highlights: • Sediment cores were collected from 8 Arctic lakes across microclimate gradients. • The timing of lake responses to regional climate warming varied from ∼1850 to ∼2012. • Mercury sediment depositional histories were reconstructed over hundreds of years. • In one lake, climate warming may have enhanced mercury sequestration to sediments. • Lakes unaltered by warming still show strong post-industrial mercury enrichment. Recent climate change may be enhancing mercury fluxes to Arctic lake sediments, confounding the use of sediment cores to reconstruct histories of atmospheric deposition. Assessing the independent effects of climate warming on mercury sequestration is challenging due to temporal overlap between warming temperatures and increased long-range transport of atmospheric mercury following the Industrial Revolution. We address this challenge by examining mercury trends in short cores (the last several hundred years) from eight lakes centered on Cape Herschel (Canadian High Arctic) that span a gradient in microclimates, including two lakes that have not yet been significantly altered by climate warming due to continued ice cover. Previous research on subfossil diatoms and inferred primary production indicated the timing of limnological responses to climate warming, which, due to prevailing ice cover conditions, varied from ∼1850 to ∼1990 for lakes that have undergone changes. We show that climate warming may have enhanced mercury deposition to lake sediments in one lake (Moraine Pond), while another (West Lake) showed a strong signal of post-industrial mercury enrichment without any corresponding limnological changes associated with warming. Our results provide insights into the role of climate warming and organic carbon cycling as drivers of mercury deposition to Arctic lake sediments.