Ocean Oil Slick Map Reveals Blanket Covering Twice The Size of Turkey

Credit: Riley/Unsplash

More than 90% of oil slicks are the result of ships and land-based human activity. Since the sources of land discharges are many and complicated, shipping should be the first focus of the solution, as reported by China Dialogue Ocean.

Marine oil contamination

The effects of oil spills on ocean ecosystems may be best illustrated by pictures of seabirds soaked in crude oil, but oil in the oceans doesn’t necessarily come from noteworthy events. Regular discharges from ships at sea and from land make up a much larger percentage and demand more care.

An article by Chinese and American academics that was published in Science earlier this year for the first time maps out a global map of marine oil contamination. According to its findings, between 2014 and 2019, anthropogenic activities were responsible for almost 94% of the total area of maritime oil slicks. The scientists discovered 21 oil slick “belts” that closely resemble busy shipping corridors.

Since the oil in these situations is typically lighter and more dispersed than oil spills, it is more difficult to clean up. The risks of these slicks, like ocean trash, are not yet fully known, but they could get worse as human activity keeps growing. Strengthening control of oil discharges from the shipping sector is very important.

What are oil slicks?

An ocean slick is a very thin layer of oil floating at sea.

At certain wind speeds, they can be spotted on radar.

This allowed the research team to process over 560,000 radar images taken between 2014 and 2019 from the Google Earth Engine, and combine these with other data to create a global oil slick dataset and map.

While the area covered by oil slicks is relatively small given the size of the ocean, the resulting harm to the environment is significant.

This in turn reduces oxygen levels and causes die-offs.

Fish and other forms of ocean life are particularly vulnerable to oil exposure early in their development.

Where does the oil come from?

Ocean oil slicks can result from natural or anthropogenic sources.

Some oil naturally seeps from fissures in the ocean floor, much like water from a spring; the rate of release is slow and local ecosystems can adapt, or even thrive.

Anthropogenic sources include oil platforms and pipelines, but releases are mainly from activities on land and from shipping.

The more recent paper, which looks at an area rather than volume, finds that natural sources account for only 6.2% of the total, with anthropogenic sources responsible for the rest.

As populations grow, so do industries, road networks and vehicle transportation.

Runoff from those activities ends up in the ocean.

How do ships contribute to slicks?

The researchers also identified 21 oil slick “belts” that match closely with busy shipping lanes.

Estimates in 2014 by World Ocean Review put the quantity of oil entering the ocean every year at 1 million tonnes, with tanker disasters accounting for only around 10% of that, and 35% coming from normal shipping activity.

An Interpol report has identified the three major types of oil pollution originating from large vessels as bilge waste, sludge-type waste and oil cargo residues.

As so many ships emit oil pollution, this type of contamination is very hard to control.

To prevent those contaminants from damaging the engine, the fuel is passed through filters, with the resulting sludge stored in tanks.

Generally, 1–2% of heavy fuel oil is a contaminant.

Fuel sludge should be retained on board until it can be properly disposed of ashore, but sometimes it is discharged illegally into the ocean.

Oil cargo transportation, meanwhile, presents particular challenges.

But even on large ships, when there is a change of cargo type – from crude to fuel oil, for example – or the vessel docks for maintenance, the tanks must be cleaned out to remove residual oil products.

The International Maritime Organization (IMO), a UN body charged with managing the shipping industry, drafted the International Convention for the Prevention of Pollution from Ships, known as MARPOL 73/78.

Rules are frequently broken, even if they are occasionally unintentional. According to an OECD analysis, data from port states shows that roughly half of the ships that underwent inspections violated at least one international environmental standard governing the loading, unloading, and handling of oils. According to the analysis, money was unquestionably the primary driver of illegal oil releases. Shipping companies can save expenses with illegal discharges and undercut more law-abiding competitors because there is little likelihood of getting detected and the fines are not very high.

Prevention is better than clean-up

While major oil spills can be tackled with containment booms, clean-up vessels and chemical treatments, or even burned-off, there is no established approach for dealing with thinner, more widely dispersed slicks.

All that can be done is to reduce discharges in the first place.

Protection of the ocean needs to focus, therefore, on prevention.

While the diversity and complexity of land-based sources make action difficult, new technology is making monitoring ship discharges easier.

Meanwhile, fines and other sanctions can have some deterrent effects.

In US waters, illegal discharges of oil from ships can be met with heavy fines: in 2021, a firm headquartered in Cyprus was fined US$2 million and placed on probation for four years after concealing illegal discharges of oily water in the Atlantic by one of its vessels.

But only a few countries worldwide are able to put effective monitoring and enforcement in place.

The new map of oil slicks provides accurate information on their locations and frequency between 2014 and 2019.

An alternative prevention measure from the OECD gets to the heart of the matter – changing the fuel used by long-distance shipping.

If the shipping sector could switch from heavy fuel oil to a cleaner source of energy much less sludge would be produced.

Similarly, in 2021 the IMO announced a ban on the use of heavy fuel oil by ships in the Arctic, to come into effect on 1 July 2024, though there were controversial exemptions.

Ship owners and operators should respect the rules and norms on discharges, while nations must monitor the problem, with strong law enforcement and punishments.


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Source: China Dialogue Ocean