Hokkaido University · Earth and Planetary Sciences
Professor Youhei Yamashita's research lab specializes in aquatic organic geochemistry, focusing on the sources, transformations, and environmental behavior of dissolved organic matter (DOM) in marine and estuarine systems. The lab employs advanced optical techniques—particularly excitation-emission matrix (EEM) fluorescence spectroscopy combined with parallel factor analysis (PARAFAC)—to characterize fluorescent components of DOM and their interactions with metals such as Cu(II) and Hg(II). Key research directions include understanding the origins and mixing dynamics of DOM in coastal environments, assessing the role of in situ production versus terrestrial inputs in shaping chromophoric DOM (CDOM) distributions, and evaluating the impact of photobleaching and biological degradation on CDOM spectral properties. The lab also investigates the biogeochemical significance of DOM in global oceanic cycles, particularly in tropical and marginal seas.
Figures are computed from collected data and may differ slightly.
Natural dissolved organic matter (DOM) is composed of a variety of organic compounds, which can interact with metals in aquatic environments. The interactions between DOM and two metals of environmental concern (Cu(II) and Hg(II)) were studied using fluorescence quenching titrations combined with excitation-emission matrix (EEM) spectra and parallel factor analysis (PARAFAC). This allowed characterizing the specific interactions between eight fluorescent components in DOM and two metals. Triplic
The distributions of fluorescent components in dissolved organic matter (DOM) from Ise Bay, Japan, were determined by excitation emission matrix (EEM) fluorescence spectroscopy combined with parallel factor analysis (PARAFAC). Three terrestrial humic‐like, one marine humic‐like, and three non‐humic‐like fluorescent components were identified by PARAFAC, and the environmental dynamics of individual fluorescent components in the bay area were evaluated. The observed linear relationships between sa
Tropical rivers are an important source of dissolved organic matter (DOM) to coastal oceans. However, temporal and spatial variability of DOM composition and thus its quality in such rivers, on landscape and basin scales, have not been well documented. In this study, we present data on the spatial distribution of DOM quantity and quality based on source, molecular weight, and composition using optical properties including excitation emission matrix fluorescence with parallel factor analysis. We
The horizontal and vertical distribution of marine humic‐like fluorophore, namely, chromophoric dissolved organic matter (CDOM) fluorescence, was surveyed in Ise Bay, Japan. The distribution patterns of salinity and marine humic‐like fluorescence intensity suggested that riverine humic‐like fluorophore conservatively distributed along with fresh‐sea water mixing in surface water at Ise Bay. However, analysis of mixing behavior of riverine CDOM implied that the 25.1 ± 10.6% in average of bulk mar
Abstract. Chromophoric dissolved organic matter (CDOM) ubiquitously occurs in marine environments and plays a significant role in the marine biogeochemical cycles. Basin scale distributions of CDOM have recently been surveyed in the global ocean and indicate that quantity and quality of oceanic CDOM are mainly controlled by in situ production and photobleaching. However, factors controlling the spectral parameters of CDOM in the UV region, i.e., spectral slope of CDOM determined at 275–295 nm (S
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