Contribution of Oceanic Sulfur to Coastal Ecosystem using Isotope Ratio in Lichens: Formulating Distance-decay and Applying Model Selection Approach

Sea fog as advection fog carries various oceanic materials to coastal land. Using of sulfur among major elements of transported materials for detecting deposition itself and evaluating the impact of oceanic deposition has benefits: 1) concentrations into biotic tissue or abiotic materials are high enough for detection, 2) ratio of several stable isotopes are reasonably distinguishable among different sources, and 3) methods for field-sampling, quantifying and measurement of stable isotopes in laboratory are established well. However, carried oceanic sulfur settle as both dry and wet deposition, and it makes challenging for evaluation of fog as vector of oceanic sulfur independent from dry deposition. It must be possible by applying synoptic-scale cline of probability of fog emergence along ocean that is known in several regions, which including Pacific coast of Hokkaido, Japan, where Oyashio flows at its offshore. We measured stable isotope ratio of sulfur in lichen on trees at three transects from coastline toward inland in Pacific coast of Hokkaido, Japan. δ ³⁴ S of lichen commonly showed exponential decrease with distance from coastline at each transects. Intercept of estimated exponential-curve was highest at transect where the highest probability of fog. Asymptotes of each estimated curve were commonly converged at all transect with ca. 5 per mil that is almost same as the global mean of the value of precipitation. Highest value of estimated intercept was lower than sea salt, but anthropogenic contamination was neglected from trajectory analysis. Both the highest value was close to that of DMS and higher oceanic primary production in offshore of sampling site suggests DMS-originated sulfur is major sulfur source at coastal area of eastern Hokkaido. Clear difference of contribution of oceanic sulfur into deposit among sites implies advection fog works effectively for more deposition would be happen.