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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2020-272
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-272
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  10 Aug 2020

10 Aug 2020

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A revised version of this preprint is currently under review for the journal BG.

Characterizing the origin of excess dissolved organic carbon in coastal seawater using stable carbon isotope and light absorption characteristics

Heejun Han, Jeomshik Hwang, and Guebuem Kim Heejun Han et al.
  • School of Earth and Environmental Sciences/Research Institute of Oceanography, Seoul National University, Seoul, 08826, South Korea

Abstract. In order to determine the origins of dissolved organic matter (DOM) occurring in coastal seawater of the Sihwa Lake, South Korea, which is semi-enclosed by a dyke, we measured the stable carbon isotopic ratio of dissolved organic carbon (DOC-δ13C) and optical properties (absorbance and fluorescence) of the DOM in two different seasons (March 2017 and September 2018). The concentrations of DOC were generally higher in lower-salinity waters in both periods, while a significant excess of DOC was observed in 2017 in the same salinity range. The main source of DOC, dependent on salinity, was found to be from marine sediments in the freshwater-seawater mixing zone rather than from terrestrial sources based on the DOC-δ13C values (−20.7±1.2 ‰) and good correlations among DOC, humic-like fluorescent DOM (FDOMH), and NH4+ concentrations. However, the excess DOC observed in 2017 seems to originate from terrestrial sources by direct land-seawater interactions rather than from in-situ biological production, considering the lower DOC-δ13C values (−27.8 ‰ to −22.6 ‰) and higher spectral slope ratio (SR) of light absorbance, without increases in FDOMH and NH4+ concentrations. This terrestrial DOM source could have been exposed to light and bacterial degradation for a long time, resulting in nonfluorescent and low-molecular-weight DOM, as this study area is surrounded by the reclaimed land. Our results suggest that the combination of these biogeochemical tools can be a powerful tracer of coastal DOM sources.

Heejun Han et al.

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Heejun Han et al.

Heejun Han et al.

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Latest update: 26 Nov 2020
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Short summary
The main source of excess DOC occurring in coastal seawater off an artificial lake, which is semi-enclosed by a dyke, was determined using combination of various biogeochemical tools including DOC and nutrient concentrations, stable carbon isotope, and optical properties of colored dissolved organic matter (CDOM) in two different seasons (March 2017 and September 2018).
The main source of excess DOC occurring in coastal seawater off an artificial lake, which is...
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