Or. Flock et Mo. Andreae, PHOTOCHEMICAL AND NONPHOTOCHEMICAL FORMATION AND DESTRUCTION OF CARBONYL SULFIDE AND METHYL MERCAPTAN IN OCEAN WATERS, Marine chemistry, 54(1-2), 1996, pp. 11-26
We measured the concentration of dissolved carbonyl sulfide (COS) in t
he water column of the Northeast Atlantic (49 degrees N, 12 degrees W)
, on a cruise of the RV ''Meteor'' in January 1994 using a purge-and-t
rap GC/FPD method (Gas Chromatograph/Flame Photometric Detection). Our
results show that parts of the ocean can be undersaturated with respe
ct to the overlying atmosphere and that COS is not always vertically d
istributed homogeneously within the mixed layer. Generally, the COS co
ncentration was correlated with the under-water light intensity and de
creased with depth. Deep water contained measurable amounts of COS, su
ggesting the existence of a non-photochemical production mechanism in
addition to the photochemical mechanism operating in surface waters. D
uring daytime, pronounced vertical COS concentration gradients develop
ed. These gradients leveled off during the night probably because of h
omogenization due to mixing, hydrolytic decomposition, and the absence
of photochemical production. Increased mixed layer depths tended to d
ecrease the COS concentration due to downward mixing out of the zone o
f photochemical production (similar to 25 m). Incubation experiments s
howed that COS was formed both photochemically and non-photochemically
while methyl mercaptan (MeSH) was produced non-photochemically and de
stroyed photochemically. We calculated non-photochemical and photochem
ical production and destruction rate constants for MeSH and COS. The c
orrelation of the photo-production of COS and the photo-destruction of
MeSH suggests that there is a link between both reactions, Models are
presented which describe the COS and MeSH concentrations during the i
ncubation experiments. Laboratory incubation experiments also showed p
hotochemical formation of COS from MeSH.