Temporal Trend of Mercury in the Arctic ringed seal (Pusa hispida).
Supervisors: Krishna Das, Marianna Pinzone (U Liege)
Mercury (Hg) is one of the core contaminants, and some of the Hg species bioaccumulate along with food webs, making neurotoxicity to the biota. The Arctic Hg concentration is increasing due to global warming and, some Arctic top predators exceed their Hg biological thresholds limit. However, contaminants accumulation trends in the Arctic biota are not uniform due to local climate change influence and physiology of the animal. It is a vital requirement to study the climate change impacts on Hg temporal trends in the Arctic predators, identifying potential driving factors in the different arctic regions to implement proper Hg management plans in the warming Arctic. Therefore, the objective of this study was to analyse the ringed seals‟ (Pusa hispida) temporal trends of Total Mercury (THg) concentrations from the mid-1980s to 2016 in two subpopulations living in North-west and East Greenland. We analysed the influence of potential driving factors such as physical factors (i.e. Sea ice extent, North Atlantic Oscillation, Sampling year) and trophic ecology proxies (i.e. δ13C, δ15N and δ34S) on THg accumulation. We measured THg concentrations of ringed seals muscle samples through absorbance spectrometry with the DMA80 Milestone. δ13C, δ15N, and δ34S isotope values were measured by mass spectrometry in an IRMS coupled to Elemental Analyser isoprime. We applied the Multivariate Linear Mixed Models (LMM) and Stable Isotope Bayesian Ellipses in R (SIBER) to analyse the THg temporal trends & shift of trophic ecology, respectively. We assumed seals‟ muscle samples collected in 2016 represents the present status of THg concentrations and isotope values. THg concentrations in ringed seals muscles increased from the mid-1980s (994 ng.g-1 dw) to 2012 (1185 ng.g-1 dw) in East Greenland, while it decreased from 2006 (1406 ng.g-1 dw) to present (715 ng.g-1 dw) in Northwest Greenland subpopulation. LMM in East Greenland indicated a decrease of THg with more sea ice extent and positive phases in North Atlantic Oscillation, while it showed an increase of THg with more sea ice extent in North-west Greenland. The model reflected that THg levels increase with high trophic level prey in both subpopulations. Temporal patterns in trophic ecology proxies showed the shift of East Greenland ringed seals from coastal sympagic (ice-associated) food chains in the mid-1980s to pelagic food chains in offshore waters at present due to sea ice melting. Climatic and trophic ecology proxies indicated the influence of borealization, shifting ringed seals‟ prey from Arctic cod to capelin in North-west Greenland subpopulation. The local climate change impacts for the temporal feeding ecology and exposure to foodborne Hg of ringed seals in East and North-west Greenland can occur via accessibility to different prey through spatiotemporal movement patterns. There is spatial variability in THg temporal trends of ringed seals‟ subpopulations in East and North-west Greenland from the mid-1980s to present, and it depends on their habitat-specific influence on climatic and trophic ecology driving factors. Our study emerges the importance of introducing site-specific Hg monitoring plans; therefore, we recommend expanding this study for different species and locations in the Arctic region to understand the site-specific & species-specific Hg temporal trends for future Hg management efforts in the Arctic.

Key words: Arctic, Hg temporal trend, stable isotopes, borealization, sea ice, ringed seal