해양기원 황성분 분석 기술의 개발과 해양 황순환 연구

Abstract

Dimethyl sulfide (DMS) is a volatile sulfur compound and is produced from the breakdown of dimethylsulfoniopropionate (DMSP) by microbial processes. DMS is by far the most abundant sulfurous compound emitted from the ocean and one of the major precursors for aerosols and cloud condensation nuclei in the marine boundary layer over the remote ocean. DMS is a crucial component to understand global sulfur cycle and play important role in regulating the Earth’s climate system. Various empirical relationships with biological and geophysical data have been developed to predict changes in DMS production and marine sulfur cycle. However, poor understanding on what factors control the marine sulfur cycles including DMS production and lack of continuous DMS observation limit to perform advanced study. For this dissertation study, I improved the analytical methods for oceanic and atmospheric DMS measurements. The analytical system for seawater DMS measurement include DMS extraction (both traditional sparger and microporous membrane contactor) and trapping devices, a gas chromatograph (GC) equipped with a flame photometric detector (FPD), and a data acquisition system. A complete analytical cycle takes 7 min, which is 3-4times shorter than has been achieved using sparge-trap analytical steps. The analytical system for atmospheric DMS measurement consists of the four major components including DMS (separation and) trapping and desorption devices, a gas chromatograph equipped with a pulsed flame photometric detector, and a calibration component for the DMS detector. The analysis system requires minimal weekly maintenance, and can continuously provide real-time data on the concentration of atmospheric DMS. The advantages of these two automated systems include the ability to rapidly and accurately analyze multiple samples, a low detection limit, and automated collection and display of data. The proposed DMS detection system described in this study has proved to be an efficient and continuous analysis for near real-time quantification of DMS in seawater and atmosphere. Such improved skills permit us to investigate spatiotemporal variations of DMS production simultaneously in large areas.Using the improved DMS measurement system, I investigated the effect of mixotrophic nature of dinoflagellate on DMS and DMSP production. Dinoflagellates are known to be strongest DMS and DMSP producer in marine environment and unique mixotrophic nature of dinoflagellate indicate that they are potentially important in the dynamics of oceanic DMS and DMSP. The mixotrophic dinoflagellate K. veneficum produce DMSP by photosynthesis, but the present study found that it also acquires DMSP by grazing on DMSP-containing algal species. And also significant fractions of the total DMSP injested by K. veneficum were transformed into DMS and other biochemical compounds. The results may indicate that the DMSP content of prey species affects temporal variations in the cellular DMSP content of mixotrophic dinoflagellates, and that mixotrophic dinoflagellate produce DMS though grazing on DMSP-rich preys. In order to investigate what factors affect atmospheric DMS during the Arctic Ocean spring bloom in 2010, atmospheric DMS mixing ratios were measured at approximately hourly intervals over a one-year period (April 2010–March 2011) in the Atlantic sector of the Arctic Ocean (Svalbard, Norway

78.5°N, 11.8°E). The mixing ratios varied by several orders of magnitude over time scales of less than several days, and occasionally reached 200−300 parts per trillion by volume (pptv) during the major phytoplankton growth period (May–September), whereas during the winter months (October–April) the mixing ratios were on the order of a few pptv. Our results, based on analyses using multiple data products (atmospheric DMS mixing ratios, satellite-derived ocean colors and meteorological datasets), indicated that weekly variability in the DMS mixing ratios at Svalbard was highly correlated with variability in the chl-a concentration in waters in the vicinity of Svalbard (r = 0.89). Hourly-to-daily variability in the DMS mixing ratios were largely influenced by changes in the trajectory, altitude and speed of air masses passing the DMS sources prior to reaching Svalbard. The observed coupling between DMS mixing ratios and chl-a concentration is surprising, and indicates that the variability in chl-a concentrations in the study area represents the change in the abundance of phytoplankton capable of producing DMS. The intensive monitoring of DMS levels at Svalbard enabled us to identify in situ production and the flux of oceanic DMS over the Arctic region. It thus constitutes a useful analytical tool for detecting changes in DMS production associated with variations in phytoplankton productivity resulting from changes in sea ice extent as a consequence of Arctic seasonality and warming.