Total organic matter in the surface microlayer

It can be seen in Table IV that DOC, DON and DOP are enriched in the microlayer by a factor of 1.5—3 on average, depending on the sampling site 

Concentrations of dissolved organic material expressed as dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) in mg m (ppb) for surface microlayer (M) and subsurface water (Sub) samples 

Concentrations of particulate organic material, expressed (POC) and particulate organic nitrogen (PON), in mg (M) and subsurface (Sub) samples 

For DOC, it can be seen that the results of Williams (1967), for example, show an extra 2.1 g m DOC in the microlayer. If the thickness of the water film obtained with the screen device is taken to be —200 pm, the surface excess of DOC can be calculated as 2.1 X 200 X 10 = 4.2 X 10 g m . A reasonable lower limit to take for the molecular weight of this extra organic material in the surface film is that of a relatively short-chain acid or alcohol with —14 carbon atoms, equivalent to —170 g mole carbon. Using this minimum value, the area per molecule in the ambient type of films sampled by Williams (1967) can be calculated as — 170/4.2 X lO X 6.02 X 10 3 = 70 A. It can be seen from Fig. 1 that for all surface film types except gaseous films, such an area per molecule has no effect on the surface tension of seawater, as measured by the spreading drop method, or on the damping of capillary waves. Moreover, only relatively water-soluble surfactants remain in the gaseous state at film pressures of —10 N m  

Taking typically 50—70% carbon in organic matter, the results in Table IV show that any specific class of organic compounds amenable to chemical analysis will have to have concentrations of the order of several g m in the 

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