Oil slicks can cause great harm to the natural environment and are often a by-product of our dependence on oil and gas resources. Until now, it has been a challenge to map and know where oil slicks are at a global scale, while also capturing information on large and relatively small oil slicks found often in shipping lanes.
New research using Sentinel-1 synthetic aperture radar (SAR) satellite imagery has now mapped and demonstrated where oil slicks have been found and enables us to respond to these environmental threats.
Oil slicks can be natural seepages and can be found in various places; however, in recent work by Dong et al. (2022), the vast majority of oil slicks are now traced to anthropogenic causes, with about 94% of all oil slicks related to our dependence on oil and gas resources.
Analyzing Satellite Imagery to Map Oil Slicks
This work utilized 563,705 Sentinel-1 images that covered the period between 2014-2019. Oil slicks were detected by using synoptic data provided by SAR imagery, which was applied in previous methods such as the detection of spills from the Deepwater Horizon Spill.
Where do oil slicks come from?
It was previously thought that natural seepage constituted nearly 46% of oil slicks; however, now the new research has demonstrated that oil found naturally, usually from hydrocarbon reservoirs releasing oil, is a relatively small percentage. In fact, shipping appears to be the major activity contributing most to oil slicks, with 21 distinct regions of high concentration, with offshore oil and gas development also contributing.
About 50% of these slicks can be found within 38 km from the coastline. Over 30% of oil slicks are found in the Java Sea, Mediterranean, and South China Sea, which are all among the most active shipping regions in the world.
When normalizing for area of concentration, the Gulf of Guinea shows that it is among the highest concentrations of oil slicks.
Since 1983, the International Convention for the Prevention of Pollution from Ships has been in place to limit and restrict shipping-related oil pollution. However, this work has now highlighted that shipping remains a major component of oil slick pollution, demonstrating that this agreement has not resulted in rapidly diminishing oil slicks from human activity.
Given the difficulty of cleaning oil leakages and seepage, this work highlights the need for rapid response by regulators and governments to have more stringent control of shipping and oil platforms that contribute heavily to the slicks observed.
Mapping and Monitoring Oil Slicks
Other research had previously highlighted that oil slick pollution might be increasing, although they did not quantify this as clearly as Dong et al. Nevertheless, work by Bukin et al. (2021) has also highlighted the need to now better monitor oil slicks.
One way to do this in a more rapid fashion is to use unmanned aerial vehicles (UAVs) that monitor active shipping zones more frequently. In this case, using computer vision and deep learning techniques, it is now possible to autodetect oil slicks as they emerge from ships and leakages found on imagery could inform authorities if given ships are substantially leaking oil.
Other research has also highlighted developments in the use of chemical and biological dispersants, which have shown some efficacy in breaking up oil slicks before they reach shore or cause significant marine life damage. However, these options are still often limited and not easy in rapidly distributing to respond to leakages or slicks.
While such developments are welcome and needed, it might also be easier to improve shipping standards and enforcements of existing laws to more greatly limit slicks. Fines and major penalties could be introduced as potential short-term solutions to help enforce existing laws better.
What existing research has recently demonstrated is that shipping and our continued exploration and dependence on oil and gas resources have been creating a substantially large proportion of oil slicks in our oceans. While we had known some of this before, the extent of this is now better understood given the use of a global-scale mapping effort conducted by scientists.
The challenge will be to mitigate and limit future slicks. While there are solutions such as using UAVs to automate monitoring of shipping lanes or even dispersants that can breakup slicks, we may also need to better enforce existing maritime laws and take seriously our impact on marine life and the natural environment. This could be in the form of major fines or penalties given to shipping companies or oil and gas operators that create even relatively small slicks.
With the results demonstrated using Sentinel-1 imagery, we now at least known what regions are contributing heavily to oil slick pollution found around the world.
 For more on the mapping and distribution of oil slicks between 2014-2019, see: Dong, Y.; Liu, Y.; Hu, C.; MacDonald, I.R.; Lu, Y. Chronic Oiling in Global Oceans. Science 2022, 376, 1300–1304, doi:10.1126/science.abm5940.
 For more on methods used to detect oil spills and slicks, see: Leifer, I.; Lehr, W.J.; Simecek-Beatty, D.; Bradley, E.; Clark, R.; Dennison, P.; Hu, Y.; Matheson, S.; Jones, C.E.; Holt, B.; et al. State of the Art Satellite and Airborne Marine Oil Spill Remote Sensing: Application to the BP Deepwater Horizon Oil Spill. Remote Sensing of Environment 2012, 124, 185–209, doi:10.1016/j.rse.2012.03.024.
 For more information on using UAVs to monitor oil slicks, see: Bukin, O.; Proschenko, D.; Korovetskiy, D.; Chekhlenok, A.; Yurchik, V.; Bukin, I. Development of the Artificial Intelligence and Optical Sensing Methods for Oil Pollution Monitoring of the Sea by Drones. Applied Sciences 2021, 11, 3642, doi:10.3390/app11083642.
 For more on biological or chemical options used as dispersants to limit the effects of oil slicks, see: Zhu, Z.; Merlin, F.; Yang, M.; Lee, K.; Chen, B.; Liu, B.; Cao, Y.; Song, X.; Ye, X.; Li, Q.K.; et al. Recent Advances in Chemical and Biological Degradation of Spilled Oil: A Review of Dispersants Application in the Marine Environment. Journal of Hazardous Materials 2022, 436, 129260, doi:10.1016/j.jhazmat.2022.129260.