Cl. Mcneil et Dm. Farmer, OBSERVATIONS OF THE INFLUENCE OF DIURNAL CONVECTION ON UPPER OCEAN DISSOLVED-GAS MEASUREMENTS, Journal of marine research, 53(1), 1995, pp. 151-169
An important example of the interaction between biological productivit
y and near-surface oceanography is the role of nocturnal convection an
d diurnal restratification in modifying the environment in which photo
synthetic activity takes place. In situ time series measurements of di
ssolved oxygen reveal the effects of photosynthetic activity, respirat
ion and redistribution by mixing. Moored thermistor time series and fr
equent CTD casts show that restratification during the day is confined
to a warmer shallow surface layer where most of the biological produc
tion is expected to occur. The depth and rate of mixing is measured wi
th neutrally buoyant floats which track the vertical excursions of con
vecting water parcels. Early in the evening, at the onset of night tim
e convection, this warm oxygenated water is mixed down and diluted by
deeper less oxygenated water. The interpretation of oxygen time series
at specified depths (here 21 m and 30 m) requires knowledge of this m
ixing process. Use is made of in situ dissolved nitrogen time series t
o infer that gas transfer at the surface is of secondary importance in
determining the diurnal dissolved oxygen budget. A qualitative couple
d biological/oceanographic model of the data is presented and discusse
d. It is concluded that a serious overestimate of daily oxygen product
ion can result from excluding diurnal convection from the interpretati
on of oxygen time series.