"Releases of hydrocarbon compounds from routine operations, such as shipping and oil exploration and exploitation, are relatively well regulated (e.g., through the MARPOL 73/78 Convention).
Historically, the release of hydrocarbons from catastrophic spills or tanker accidents has been of most concern. Most of the environmental consequences of catastrophic spills are relatively short-lived, although they can cause disruptions of flora and fauna, including seabird populations. These populations may be slow to recover. Weathered oil from spills at sea can become adsorbed into beach strata for several decades.
The development and installation of contingency plans and technology to counteract the effects of large oil spills reflects an awareness of the seriousness of such threats and has been a positive development, largely in response to previous tanker accidents. There are some on-going concerns about seabird mortalities in coastal and offshore areas that may be related to illegal discharges of oil or chronic contamination from maritime sources.
Future exploitation of marine oil and gas reserves will take place in many developing regions of the world. This raises concerns about abilities to provide adequate regulation and/ or enforcement and to respond to oil spills in such regions.
It is interesting to note, in this context, that studies of the Persian/Arabian Gulf suggest that the chronic and acute releases of oil that have taken place as a result of leakage from shipping activity and, most recently, acts of war, have been accommodated by that system relatively rapidly.
The potential for acute effects of oil spills is clearly one warranting stringent preventative and contingency measures to minimize damage, but the insidious introduction of low-levels of hydrocarbons from shipping, refining and runoff from parking lots is likely, overall, to be of greater biological significance. GESAMP is currently undertaking a review of the inputs of oil entering the marine environment from sea-based activities.
The overall total average influx of oil to the sea from ship traffic and offshore activities is of the order of 850,000 tonnes per year. A further 350,000 tonnes per year is estimated to be derived from coastal refineries, storage and transhipment facilities, oil seeps and other unknown sources.
Excluded from these estimates are releases from military activities and leisure craft and emissions to air of volatile organic carbons (VOCs). VOC emissions are potentially a major route of oil input to the oceans as they have been estimated to be 3,750,000 tonnes per year, principally from tankers. This latter estimate is, however, being re-evaluated taking account of the high proportion of methane in such releases.
An illustrative example of the relative contributions of oil from a variety of sources is provided in the Black Sea Assessment [in 1998c]. Of the total input of 111,000 tonnes, 53,000 tonnes (48%) enters via the Danube River. A further 30,000 tonnes is derived from domestic sources, 15,400 tonnes from industrial sources, and only 136 tonnes from accidental oil spills.
To this must be added the unquantified inputs through the discharge of oily residues from ships, which is thought to be considerable. The point is that the land-based sources of oil input are likely to the most significant even in marine areas having heavy tanker traffic. This reinforces the view that marine sources, although probably significant in the case of this sea, are probably of negligible importance on oceanic scales. It is, of course, recognized that catastrophic spills such as those from the Amoco Cadiz and Exxon Valdez will cause severe, if transient, problems within regional areas, but they are of limited significance on spatial oceanic, and long-term time, scales."
GESAMP71:23
GESAMP (IMO/FAO/UNESCO-IOC/WMO/WHO/IAEA/ UN/UNEP Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection). 2001. Protecting the oceans from land-based activities - Land-based sources and activities affecting the quality and uses of the marine, coastal and associated freshwater environment. Rep. Stud. GESAMP No. 71, 162 pp. ISBN 82-7701-011-7.