Effects of air-sea exchange of reactive gases on global atmospheric chemistry system

Takashi Sekiya1, Maki Noguchi Aita2, Akitomo Yamamoto3, Fumikazu Taketani4, Yoko Iwamoto5, Katsuhiro Kawamoto6, Kengo Sudo7,8 and Yugo Kanaya4, (1)JAMSTEC Japan Agency for Marine-Earth Science and Technology, Research Institute for Global Change, Kanagawa, Japan, (2)Japan Agency for Marine-Earth Science and Technology, Research Institute for Global Change, Yokosuka, Japan, (3)JAMSTEC Japan Agency for Marine-Earth Science and Technology, Research Center for Environmental Modeling and Application, Yokohama, Japan, (4)JAMSTEC Japan Agency for Marine-Earth Science and Technology, Research Institute for Global Change, Yokohama, Japan, (5)Hiroshima University, Graduate School of Integrated Sciences for Life, Higashi-Hiroshima, Japan, (6)Kobe University, Graduate School of Maritime Sciences, Japan, (7)Nagoya University, Nagoya, Japan, (8)JAMSTEC Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
Abstract:
The ocean is non-negligible sources and sinks for atmospheric reactive trace gases relevant to climate system. Meanwhile, comprehensive effects of air-sea exchange of reactive gases on climate have not been evaluated well enough yet. We evaluate combined effects of (1) global air-sea exchanges of bromine (Br) and iodine (I) compounds, oxygenated volatile organic compounds (OVOCs), ammonia (NH3), and dimethyl sulfide (DMS) and (2) chemical ozone loss reactions with I, Br, DMS, and dissolved organic carbon (DOC) in the sea surface water on global atmospheric chemistry and radiative budget using global atmospheric chemistry model (CHASER) which includes the iodine chemistry, lower-trophic marine ecosystem model (COCO-NEMURO), and marine ecosystem component of earth-system model (MIROC-ES2L). Oceanic fluxes were estimated using the methods proposed by previous studies (Ordóñez et al., 2012; Carpenter et al., 2013; Ziska et al., 2013; Chance et al., 2014) for halocarbons and inorganic iodine compounds and using the two-phase model for other species. Chemical reactions in the sea surface water were considered in the dry deposition process following Chang et al. (2004). The model results suggested that the air-sea exchanges of I (5.0 Tg I yr-1), Br (1.3 Tg Br yr-1), OVOCs (16 Tg C yr-1), NH3(-0.4 Tg N yr-1), and DMS (13 Tg S yr-1), and enhanced ozone deposition velocity (by 70%) owing to the chemical reactions decreased global mean surface concentrations of ozone (by 13%) and nitrate aerosol (by 12%) over the ocean, whereas they increased sulfate (by 45%) and ammonium aerosols (by 10%). Compared to ship-borne measurements on the R/V Mirai and Hakuho-maru, the air-sea exchange of the reactive gases reduced positive model biases of O3 by 51% and 16% over the tropical western Pacific (1°S—30°N) and the southern Indian Ocean (20°S—0°), respectively, and negative model biases of sulfate aerosol by 53% and 20%. These changes in tropospheric ozone and aerosols led to negative radiative effects of 0.07 Wm-2 and 0.12 Wm-2, respectively. These results demonstrated that the air-sea exchange of the reactive gas have non-negligible effects on global atmospheric chemistry and climate.
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