Photolysis and the Dimethylsulfide (DMS) Summer Paradox in the Sargasso Sea

Apparent quantum yields and rates of dimethylsulfide (DMS) photolysis were determined from Sargasso Sea seawater with the goal of assessing the extent to which photoreactions affect the unusually elevated upper ocean concentrations of DMS during the summer, the so-called DMS summer paradox. Apparent...

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Bibliographic Details
Published in:Limnology and oceanography 2003-05, Vol.48 (3), p.1088-1100
Main Authors: Toole, Dierdre A., Kieber, David J., Kiene, Ronald P., Siegel, David A., Nelson, Norman B.
Format: Article
Language:English
Subjects:
Absorption spectra
Absorptivity
Earth sciences
Earth, ocean, space
Exact sciences and technology
External geophysics
Geochemistry
Irradiance
Marine
Mineralogy
Oceans
Paradoxes
Photolysis
Physical and chemical properties of sea water
Physics of the oceans
Sea water
Seas
Silicates
Summer
Water geochemistry
Wavelengths
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Summary:Apparent quantum yields and rates of dimethylsulfide (DMS) photolysis were determined from Sargasso Sea seawater with the goal of assessing the extent to which photoreactions affect the unusually elevated upper ocean concentrations of DMS during the summer, the so-called DMS summer paradox. Apparent quantum yields determined with monochromatic radiation decrease exponentially with increasing wavelength and indicate that DMS photolysis is driven by ultraviolet (UV) radiation. The relative spectral partitioning differs between samples collected from the surface mixed layer (15 m) and from the chlorophyll a maximum (80 m), presumably because of differences in chromophoric dissolved organic matter (CDOM) quality (e.g., apparent degree of bleaching). Quantum yields are also temperature dependent, and an approximate doubling of photolysis rates occurs for a 20°C increase in temperature. The significance of DMS photolysis to upper ocean sulfur budgets is explored using a multiyear (1992-1994) DMS time series, concurrent irradiance determinations and temperature profiles, and estimates of CDOM absorption. Depth-integrated, mixed-layer DMS photolysis rates peak in the summer (15-25$\mu mol\>m^{-2}\>d^{-1}$) and decline to$\mu mol\>m^{-2}\>d^{-1}$in the winter. These rates correspond to specific turnover rates of ~0.29 d-1in the summer and
ISSN:0024-3590
1939-5590
DOI:10.4319/lo.2003.48.3.1088