LIGHT NONMETHANE HYDROCARBONS IN SEAWATER

A database of dissolved C-2-C-4 hydrocarbons in the surface water of t he oceans is compiled based on more than 1000 measurements. Hydrocarbo n emission rates are calculated using a diffusive microlayer approach and climatologic wind data, This database is used to calculate average s and ranges of variation, and an attempt is made to identify the envi ronmental factors which have an impact on the hydrocarbons dissolved i n seawater. The paper focuses on data obtained in situ since other tec hniques generally contain larger uncertainties. Mean concentrations ar e 134 pmol/L for ethene, 59 pmol/L for propene, and 37 pmol/L for 1-bu tene. Alkane concentrations are lower with an average value of 22 pmol /L for ethane and less than 14 pmol/L for the other alkanes and acetyl ene, Ninety percent of the concentrations of an individual compound ge nerally ranges within an order of magnitude. Ethene concentrations are significantly anticorrelated with the transfer velocities of the sea- air exchange (r=-0.49; r(0.01)=0.29). Ethene concentrations are not co rrelated with the solar radiation, chlorophyll a, and the water temper ature. Averaged emissions of C-2-C-4 hydrocarbons extrapolated to the global ocean of 2.1 x 10(12) g/yr are calculated, with ethene alone co ntributing about 40% to the total. Thus the oceanic source is on the l ow side of previous estimates and plays a minor role in global budgets compared to continental sources.