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Abstract Title: Year-long monitoring of air-surface exchange of total gaseous mercury in the Canadian Arctic at Alert, Nunavut, Canada
Presenter Name: Geoff Stupple
Company/Institution: Environment and Climate Change Canada
Session: Mercury in Polar Ecosystems
Day and Session: Tuesday 26th July - Session Two
Start Time: 10:00 UTC
Co-Authors: Geoff Stupple,Katrina Macsween,Meng Si,Alexandra Steffen,Carl Mitchell

Abstract Information :

Micrometeorological measurements of total gaseous mercury (TGM) flux have been ongoing in Alert, Nunavut, Canada since June 2019. Permafrost thaw is predicted to release large amounts of mercury to the environment and, thus; this study aims to look at baseline mercury fluxes from permafrost (not experiencing rapid thaw) and the snow pack over 18-monthsto quantify the surface exchange of mercury. TGM fluxes were determined using the Modified Bowen Ratio method with temperature as the reference scalar. The vertical gradient was determined by measuring TGM concentrations at alternating inlet heights of 0.25m and 2m using a Tekran 2537x analyzer. Preliminary overall fluxes were 0.3 ñ65ngúm-3úh-1 for the June 2019-October 2020 period, similar to previous measurements at Alert. During atmospheric mercury depletion events (AMDE) in the spring of 2020 a negative flux of -1.3 ngúm-3úh-1 was observed to the snow surface. During the summer TGM fluxes were relatively small, with a mean of -0.1ñ8.1 ngúm-2úh-1. Significant re-emission fluxes were not observed until the ground surface rose above the freezing point.
Between sunrise and snowmelt (March, April), atmospheric TGM concentrations dropped below the study mean and Hg fluxes were predominantly depositional due to AMDE processes. TGM concentrations had significant positive correlations with both air and soil temperatures only during transition periods during the snowmelt (May, June) and re-freeze (September, October). In the summer period between (July, August) higher concentrations of TGM and a negative correlation between both air and soil temperatures and TGM were observed due to the emission fluxes. The major controls on TGM concentrations and fluxes appear to change when ground temperature crosses the freezing point threshold. As the Arctic continues to get warmer, the soil will stay unfrozen for longer, possibly leading to longer durations of more active air-soil TGM exchange.

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