Wet Deposition Fluxes of Ions Contributed by Cyclone-, Stationary Front- and Typhoon-associated Rains at the Southwestern Japan Coast

Wet deposition fluxes of ions at a coastal site in southwestern Japan in the period 1996–2003 were investigated to quantify the respective contributions of cyclone-, stationary front- and typhoon-associated rains. On average, the deposition fluxes of terrigenous-origin ions, nss-SO 4 2 − , NO 3 − , NH 4 + and nss-Ca 2+ were 37.6±7.3, 16.3±4.2, 19.0±3.4 and 9.6±4.8 meq m −2 yr −1 , and those of Na + and Cl − , the major ions in sea water, were 97.0±38.2 and 115.2±48.2 meq m −2 yr −1 , respectively. Cyclone-associated rain constituted more than 50% of the fluxes of the terrigenous ions in almost all years. Stationary front-associated rain also contributed significantly, although the contribution was lower than the contribution by Cyclone-associated rain in almost all years. In particular, the wet deposition flux of nitrogen compounds of NO 3 − and NH 4 + , which are important nutrients for micro-bioactivities in sea surface water, was dominated by cyclone-associated rain. Due to the extreme abundance of Na + and Cl − in the rainwater of typhoons, the fluxes of Na + and Cl − were contributed substantially by typhoons in years with typhoons’ passage although cyclones were still the largest contributor to the fluxes. These results indicate the dominance of cyclones in the wet deposition to the East China Sea areas and the necessity to take rain types into account for a more accurate elucidation of the temporal and spatial variation of the wet deposition.