When oil is spilled into the sea it undergoes a number of physical and chemical changes, some of which lead to its removal from the sea surface, while others cause it to persist. The fate of spilled oil in the marine environment depends upon factors such as the quantity spilled, the oil’s initial physical and chemical characteristics, the prevailing climatic and sea conditions and whether the oil remains at sea or is washed ashore.
An understanding of the processes involved and how they interact to alter the nature, composition and behaviour of oil with time is fundamental to all aspects of oil spill response. It may, for example, be possible to predict with confidence that oil will not reach vulnerable resources due to natural dissipation, so that clean-up operations will not be necessary. When an active response is required, the type of oil and its probable behaviour will determine which response options are likely to be most effective.
This paper describes the combined effects of the various natural processes acting on spilled oil, collectively known as ‘weathering’. Factors which determine whether or not the oil is likely to persist in the marine environment are considered together with the implications for response operations. The fate of oil spilled in the marine environment has important implications for all aspects of a response and, consequently, this paper should be read in conjunction with others in this series of Technical Information Papers.