Multivariate Analysis of Petroleum Hydrocarbon Weathering in the Subarctic Marine Environment1

Abstract

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.

Oil-weathering behavior in Arctic environments

“…To assess water-column oil concentrations following the spill, 20-liter subsurface seawater samples were filtered through a 0.4-pm poresized, 293-mm diameter glass-fibre filter for analysis of the dissolved components and dispersed-and/or particulate-bound oil droplets. Chromatograms of dissolved components (Payne et al 1983). The chromatograms from filtered seawater samples collected during the early stages of the spill show very similar profiles for the lower molecular weight aromatics (Kovats Index values (Fig.…”

“…To evaluate temporal changes in the physical and chemical properties of crude oil in ice-free subarctic marine environments, a series of summer and winter outdoor flow-through seawater wavetank experiments were conducted at the NOAA field laboratory at Kasitsna Bay (Homer), Alaska. The results of the summer outdoor oil weathering experiments have been presented previously (Payne et al 1983(Payne et al ,1984Payne & McNabb 1984), and most recently they have been compared with oil weathering behavior observed in Prince William Sound after the release of 11 million gallons of North Slope crude oil from the EXXON VALDEZ (Payne et al 1991a).…”

“…This paper considers the results of NOAA-sponsored laboratory and field studies on the timedependent physical and chemical changes that occur to oil released in open-ocean and ice-covered waters. Data from these studies were used for the development and verification of computer models to predict the behavior of crude oils and refined petroleum products spilled into a variety of subarctic and Arctic marine environments (Payne et al 1983(Payne et al , 1984(Payne et al , 1987a(Payne et al ,b, 1989(Payne et al , and 1991a.…”

Use of Natural Oil Seeps for Evaluation of Dispersant Application and Monitoring Techniques

“…This reduces the amount of dispersant that is wasted through mis-targeting as often happens with other application methods, and it eliminates overdosing and under dosing. During the field trials, additional boats were to be used to deploy smoke bombs and drogues to mark the treated area, and then a series of transects through the test area were to be run over a 2-3 hour period as described by Payne et al (1991Payne et al ( , 1993 for subsurface water sampling on a continuous basis using the NOAA SMART Protocols. Aliquots of effluent from the UV/fluorescence system were also to be collected and placed on ice for subsequent toxicological testing under a separate contract funded by the Texas General Land Office.…”

The Outer Continental Shelf Environmental Assessment Program

“…Studies of the weathering of oil in the open ocean have been completed [9] and integrated into the trajectory model such that oil-component concentrations around a hypothetical trajectory can be computed. Additional studies of the interaction of oil, ice, and suspended particulates are underway and their data will be incorporated into the model allowing computation of trajectories during the sea ice freeze-up and break-up periods.…”