講者:Chih-Ping Lee (Institute of Oceanography, National Taiwan University)
題目:Vertical distributions and diel variations of dissolved Arsenic species in the oligotrophic West Pacific Ocean. (Presentation in English)
時間:5月4日(五) 15:30~16:30
地點:海洋所二樓大講堂
Abstract:
Arsenic (As) is a metalloid element receiving much concern due to its toxicity. This element in the ocean shows semi-conservative vertical distributions, with a change of the concentrations mostly in surface waters above the oxygen minimum zone. Earlier studies had found that As(V) is the most dominant species, followed by As(III) and methylated As; the latter two are common in the surface of the P-stressed waters. In addition, there was no evidence of colloidal As in the ocean, even though colloids were found to be labile to microbes and could influence the partitions of other bioactive elements in seawater. Here we use cross-flow ultrafiltration and chemical speciation methods to prove and provide the first evidence on the existence of colloidal As and the molecular weight distributions of various dissolved As species in the ocean.
Dissolved inorganic As (DIAs) shows typical semi-conservative depth profiles, and 10-20% of the DIAs is HMW-DIAs, which is discovered for the first time. In a short-term study, we find clear diel variations of the HMW-DIAs in the upper euphotic zone of the West Philippine Sea, indicating a rapid turnover of As in colloidal phase. Nearly all the HMW-DIAs is As(V).
Dissolved organic As (DOAs) concentrations display decreasing trends with depth, and more than half of DOAs is in colloidal phase. Overall, our results prove that colloids play a major role in biogeochemical cycle of As in the ocean. With molecular weight fractionation and chemical methods, dissolved As species in seawater is redefined.