Characterizing ocean surface contamination: Composition, film thickness, and rheology

Area of Science:

• Oceanography
• Fluid Dynamics
• Environmental Science

Background:

• The air-sea interface plays a critical role in momentum and energy exchange.
• Contamination at this interface, such as from oil spills, significantly impacts wave dissipation.

Purpose of the Study:

• To investigate the composition, vertical extent, and rheological behavior of interfacial layers at the ocean-atmosphere boundary.
• To determine if these complex interfacial layers exhibit non-Newtonian fluid properties.

Main Methods:

• Laboratory preparation of fluid samples mimicking interfacial layers (water-oil emulsions, Phormidium sp. strain in artificial seawater).
• Rheological characterization of prepared samples using a rheometer to analyze behavior under varying temperature and shear rates.

Main Results:

• Interfacial layers can range from hundreds of nanometers to millimeters in thickness.
• The investigated samples, modeling interfacial layers, consistently exhibited shear thinning behavior.
• The complex composition of interfacial layers suggests inherent non-Newtonian characteristics.

Conclusions:

• Ocean interfacial layers are composed of diverse substances including oil, emulsions, plankton, and chemical compounds.
• These layers possess non-Newtonian properties, specifically shear thinning behavior.
• Accurate wave dissipation models must incorporate the finite thickness and non-Newtonian nature of interfacial fluid layers for improved air-sea interaction modeling.