When crude oil or petroleum products are released to the marine environment, immediate alterations in chemical and physical properties occur as a result of a variety of weathering processes. A three-year oil weathering study of Prudhoe Bay crude oil has been completed under ambient subarctic conditions at the National Oceanic and Atmospheric Administration's lower Cook Inlet field laboratory in Kasitsna Bay, Alaska. Quantitative data from outdoor wave-tank and flow-through aquaria systems were collected on seasonal and time-series measurements of compositional changes in the oil and water column due to evaporation, dissolution, and water-in-oil emulsification, as well as alterations in rheological properties of the slick. These data are used for mathematical model development and verification of computer-predicted oil weathering behavior from a variety of spill scenarios. The oil-weathering mathematical models developed in this program are based on measured physical properties data, and they generate material balances for both specific compounds and pseudo-compounds (distillation cuts) in crude oil. These models are applicable to open-ocean oil spills, spills in estuaries and lagoons where the water column is finite, and spills on land. The oil weathering processes included in the mathematical model are evaporation, dispersion of oil into the water column, dissolution, water-in-oil emulsification (mousse formation), and oil slick spreading. In most cases, very good agreement is obtained between predicted and observed weathering behavior. The material balance and weathered-oil composition predictions generated as a function of time have been very useful in providing information for contingency planning, estimating potential damage assessments and preparing environmental impact reports for outer continental shelf drilling activities.

Outdoor flow-through seawater wave tank studies and model predictions on the chemical and physical fate of Prudhoe Bay crude oil in subarctic waters are compared with field observations from the Exxon Valdez oil spill in Prince William Sound, Alaska. Excellent agreement is obtained between predicted and observed parameters, including evaporative loss of lighter distillate cuts, water content in mousse, density, viscosity, oil/water and oil/air interfacial surface tension, and chemical composition. As predicted from wave tank studies, water column samples of dispersed and dissolved oil and suspended particulate material collected from several heavily oiled sheltered coves and bays in Prince William Sound indicate that little oil reached the near-shore benthic environment during the first few weeks after the spill.

Oil-weathering processes in ice-free subarctic and Arctic waters include spreading, evaporatlon. dissolution, dispersion of whole-oil droplets into the water column, photochemical oxidation. water-in-oil emulsification, microbial degradation, adsorption onto suspended particulate material, ingestion by organisms. sinking. and sedimentation. While many of these processes also are important factors in ice-covered waters, the various forms of sea ice (depending on the active state of ice growth, extent of coverage and/or decay) impart drastic, if not controlling, changes to the rates and relative importance of different oil-weathering mechanisms. Flow-through seawater wave-tank experiments in a cold room at-35°C and studies in the Chukchi Sea in late winter provide data on oil fate and effects for a variety of potential oil spill scenarios in the Arctic. Time-series chemical weathering data are presented for Prudhoe Bay crude oil released under and encapsulated in growing first-year columnar ice through spring breakup.

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Oil‐weathering processes in ice‐free subarctic and Arctic waters include spreading, evaporation, dissolution, dispersion of whole‐oil droplets into the water column, photochemical oxidation, water‐in‐oil emulsification, microbial degradation, adsorption onto suspended particulate material, ingestion by organisms, sinking, and sedimentation. While many of these processes also are important factors in ice‐covered waters, the various forms of sea ice (depending on the active state of ice growth, extent of coverage and/or decay) impart drastic, if not controlling, changes to the rates and relative importance of different oil‐weathering mechanisms. Flow‐through seawater wave‐tank experiments in a cold room at −35°C and studies in the Chukchi Sea in late winter provide data on oil fate and effects for a variety of potential oil spill scenarios in the Arctic. Time‐series chemical weathering data are presented for Prudhoe Bay crude oil released under and encapsulated in growing first‐year columnar ice through spring breakup.