Surface microlayer phenolic enrichments indicate sea surface slicks

Abstract

The realization by early investigators that oil films spread on surfaces of bodies of water could mimic slick conditions^1–3 has evolved into the present model of slicks resulting from monomolecular films that modify wave characteristics and hence reflectance properties of surfaces. However, the lipid materials postulated to form monomolecular layers constitute only a small fraction of the organic material in either bulk sea water or at the surface^4–7, may not retain their strong surface activity in the presence of natural seawater dissolved organic material (DOM)⁸, and have not been found in any consistent relationship with slicks^7,9–11. The apparent association of slicks with macroalgae has also been noted^12–15, but there has not been a demonstration of macroalgae-derived DOM in slicks. I show here that enrichments of UV-absorbing phenolic materials, consistent components of surface microlayers¹⁶, offer reliable indication of slick conditions. I then suggest that: (1) slicks result not from monomolecular films, but from viscosity changes in surface microlayers caused by more soluble organic components; and (2) the occurrence of slicks therefore depends not on absolute concentrations of surface-active materials, but on relative viscosity differences. Evidence is also given demonstrating the presence of macroalgae-derived phenolic materials in slicks.