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Relationship between the seasonal change in fluorescent dissolved organic matter and mixed layer depth in the subtropical western North Pacific
Author(s) -
Omori Yuko,
Hama Takeo,
Ishii Masao,
Saito Shu
Publication year - 2010
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2009jc005526
Subject(s) - dissolved organic carbon , mixed layer , subtropics , total organic carbon , environmental science , organic matter , surface water , middle latitudes , surface layer , intensity (physics) , oceanography , atmospheric sciences , environmental chemistry , geology , chemistry , layer (electronics) , ecology , physics , organic chemistry , quantum mechanics , environmental engineering , biology
Spatial and temporal distributions of marine humic‐like fluorescent dissolved organic matter (FDOM M ) were determined in the subtropical western North Pacific to evaluate the controlling factors of FDOM M behaviors. The observations were conducted at 4 stations (15–30°N) along 137°E in a subtropical area between January 2006 and April 2007. The florescence intensity of FDOM M was low (0.14–0.25 quinine sulfate units (QSU)) in the surface layer probably due to photodegradation, and increased with depth (0.90–1.10 QSU at 1000 m), irrespective of season and station. In the surface layer, the thickness of the water mass with low fluorescence intensity (<0.3 QSU) showed the seasonal change by being deeper in winter and shallower in summer, depending on the mixed layer depth (MLD). The average fluorescence intensity within the mixed layer also varied seasonally at midlatitudes; the intensity in summer was 40.8–53.8% of that in winter. Since the MLD was very much shallower in summer than in winter, FDOM M in the mixed layer would be kept within a shallow depth during the summer where intensive photodegradation could occur. The concentration of total organic carbon (TOC) was at its maximum at the water surface and decreased with depth, being adverse to FDOM M . Thus, the ratio of fluorescence intensity to TOC concentration was lowest (0.002–0.003) in surface water, which implies that FDOM M is not quantitatively important to the dissolved organic carbon pool. However, considering the possible difference in the stabilities of FDOM M against photochemical and microbial degradation, it is conceivable that photobleached FDOM M is one of the important organic groups constituting marine dissolved organic matter.

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