Samples from two coastal experimental ecosystems were incubated in vitro and sampled over 24 h. Production rates were measured by the 14C method, the O2 and CO, light-dark bottle methods, and the I80 method. 0, production in the experimental enclosures (volume -1.3 x lo4 liters) was also measured directly.Photosynthetic and respiratory quotients were close to 1 .O. Gross production values determined by 0, light-dark experiments, CO2 light-dark experiments, and I80 were similar. 14C production ranged from 60 to 100% of gross production measured in CO, light-dark experiments, indicating that 14C uptake is not precisely fixed with respect to other measures of community metabolism. There was no evidence that 14C or any other method underestimated the rate of primary production in vitro by more than 40%. Productivities in vitro ranged from 35 to 100% of those in the mesocosm at similar light intensities.In samples from one of the ecosystems, the rate of respiration in the light (calculated from I80 data) was an order of magnitude greater than the rate in the dark. This difference may be ascribed to either photorespiration or light enhancement of mitochondrial respiration.Turnover of microplankton populations in the ocean occurs on time scales of hours to days. Measurements of community turnover rates must be carried out with in vitro incubations, presenting two problems. First, it can never be claimed that processes oc-I

The isotopic composition (or 18O/16O ratio) of O2 produced by photosynthesis and the isotopic composition of O2 consumed during respiration are different from each other as well as from the isotopic composition of ambient dissolved O2. In a closed body of water in which photosynthesis and respiration are co‐occurring, the 18O/16O of dissolved O2 will be a function of both the rate of respiration and the gross rate of photosynthesis. Therefore gross primary production can be calculated if one determines both net O2 production and the18O/16O of dissolved O2. As a test of the feasibility of this approach, we present data on the 18O/16O ratio of dissolved O2, along with ancillary parameters, in the top 200 m of waters in the North Pacific gyre in August and September 1985. The results are shown to reflect isotope fractionation during photosynthesis and respiration. We outline the additional information needed before natural 18O/16O variations can be used to constrain quantitatively the gross production.

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Tautomeric equilibria in acetoacetic acid have been examined by *H NMR and found to be strongly solvent dependent. Values for enol tautomer range from less than 2% in deuterium oxide to 49% in carbon tetrachloride.Chemical shift data suggest that the enol tautomer is internally hydrogen bonded in the less polar solvents and that internal hydrogen bonding is unimportant for the keto tautomer. The acid probably exists in the keto form in the solid state.