title: Convective forcing of mercury and ozone in the Arctic boundary layer induced by leads in sea ice.
abstract: The ongoing regime shift of Arctic sea ice from perennial to seasonal ice is associated with more dynamic patterns of opening and closing sea-ice leads (large transient channels of open water in the ice), which may affect atmospheric and biogeochemical cycles in the Arctic. Mercury and ozone are rapidly removed from the atmospheric boundary layer during depletion events in the Arctic, caused by destruction of ozone along with oxidation of gaseous elemental mercury (Hg(0)) to oxidized mercury (Hg(II)) in the atmosphere and its subsequent deposition to snow and ice. Ozone depletion events can change the oxidative capacity of the air by affecting atmospheric hydroxyl radical chemistry, whereas atmospheric mercury depletion events can increase the deposition of mercury to the Arctic, some of which can enter ecosystems during snowmelt. Here we present near-surface measurements of atmospheric mercury and ozone from two Arctic field campaigns near Barrow, Alaska. We find that coastal depletion events are directly linked to sea-ice dynamics. A consolidated ice cover facilitates the depletion of Hg(0) and ozone, but these immediately recover to near-background concentrations in the upwind presence of open sea-ice leads. We attribute the rapid recoveries of Hg(0) and ozone to lead-initiated shallow convection in the stable Arctic boundary layer, which mixes Hg(0) and ozone from undepleted air masses aloft. This convective forcing provides additional Hg(0) to the surface layer at a time of active depletion chemistry, where it is subject to renewed oxidation. Future work will need to establish the degree to which large-scale changes in sea-ice dynamics across the Arctic alter ozone chemistry and mercury deposition in fragile Arctic ecosystems.
authors.affiliation: 1] Division of Atmospheric Sciences, Desert Research Institute, Reno, Nevada 89523, USA [2].
authors.forename: Christopher W
authors.initials: CW
authors.lastname: Moore
authors.affiliation: 1] Division of Atmospheric Sciences, Desert Research Institute, Reno, Nevada 89523, USA [2].
authors.forename: Daniel
authors.initials: D
authors.lastname: Obrist
authors.affiliation: Air Quality Processes Research Section, Environment Canada, Toronto, Ontario M3H 5T4, Canada.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Steffen
authors.affiliation: Air Quality Processes Research Section, Environment Canada, Toronto, Ontario M3H 5T4, Canada.
authors.forename: Ralf M
authors.initials: RM
authors.lastname: Staebler
authors.affiliation: US Army Cold Regions Research and Engineering Laboratory, Fort Wainwright, Alaska 99703, USA.
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Douglas
authors.affiliation: Institute of Environmental Physics, University of Bremen, Bremen 28359, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Richter
authors.affiliation: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA.
authors.forename: Son V
authors.initials: SV
authors.lastname: Nghiem
mesh_terms: D000413:Alaska; D001110:Arctic Regions; D001272:Atmosphere / Q000737:chemistry*; D017753:Ecosystem; D046448:Ice Cover / Q000737:chemistry*; D008628:Mercury / Q000032:analysis*; D010126:Ozone / Q000032:analysis*; D012914:Snow
chemical_list: D010126:Ozone; D008628:Mercury