Marine phytoplankton and sea-ice initiated convection drive spatiotemporal differences in Arctic summertime mercury rebound.

Gaseous elemental mercury (GEM) concentrations in the Arctic exhibit a distinct rebound during the summer months, with notable spatiotemporal variations observed in this phenomenon; however, the underlying mechanisms remain poorly understood. On the basis of targeted cruise observations from the Bering Strait to the North Pole, this study captured the summertime GEM rebound in the Pacific sector of the Arctic Ocean. Moreover, we identified synchronous increases in dissolved gaseous mercury (DGM) concentrations during the GEM rebound in the Marginal Ice Zone (MIZ). Combined with Generalized Additive Model (GAM) simulations, we confirm that oceanic mercury emissions from the MIZ contribute to this phenomenon. We also show that the spatiotemporal variability of dissolved organic components associated with phytoplankton, along with local atmospheric convection triggered by sea-ice melting in the MIZ, plays a crucial role in the observed spatiotemporal differences in the GEM rebound. In the context of rapid Arctic warming, with expected increases in primary productivity and more frequent local convection, the air‒sea exchange of mercury is likely to intensify, amplifying the summertime "mercury source" effect in the Arctic Ocean.