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| Fig. 1: Seismic Airgun Blasting (Source: Wikimedia Commons) |
As the United States looks to enlarge offshore exploration of oil and natural gas in federal waters, the Trump administration recently approved the use of seismic gun blasting to find oil and natural gas deposits buried deep in the ocean floor in the coast of Alaska. [1] It is believed that the largest untapped onshore supply of oil lies underneath the Arctic National Wildlife Refuge along the coast of Beaufort Sea and while years of protection and opposition to drilling have kept the area largely off- limits to oil companies, it is all about to change. [1] As seismic gun blasting is only the beginning of the governmental efforts towards offshore drilling, it raises several environment concerns, not least concerning marine life and climate change.
Seismic instruments refer to technology that releases energy into the earthin this case, into the oceanin the form of controlled seismic waves. [2] Marine seismic sources thus release seismic waves into the ocean to explore a given marine environment via reflection and refraction surveys. Once these seismic waves and reflected and refracted, they are recorded by seismic sensors, such as geophones or hydrophone. [2,3] These data are then gathered and analyzed for information about locations of potential petroleum reservoirs and mineral deposits. The most commonly used marine seismic source is the seismic air gun, which is fired from the bottom of a ship usually, as shown in Fig. 1. Seismic air guns are often made up of two chambers and a shuttle, which looks very similar to a piston. Highly pressurized air moves from the bottom chamber to the top chamber through the shuttle and eventually, forces the top chamber upwards, resulting in the firing of highly pressurized air into the ocean. [4]
The use of seismic air guns has significant environmental implications. Seismic air guns are fired every ten seconds for 24 hours every day and it could last from anywhere to days to several weeks in a row. [5] According to a report by the Bureau of Ocean and Energy Management, seismic airgun testing could injure up to 138,000 whales and dolphins. [5] Five species with the highest amount of impact are bottlenose dolphins (up to 11,748 individuals/year), short-beaked common dolphin (up to 6,147 individuals/year), Atlantic spotted dolphin (up to 5,848 individuals/year), short-finned pilot whale (up to 4,631 individuals/year), and striped dolphin (up to 3,993 individuals/year). [5] This is due to the fact that seismic blasts loud sound, which travels very long distances. Before reaching the sound reflection surfaces, the seismic waves will first reach marine animals, which will result in severe injuries and even death in some cases. For marine animals like whales and dolphins who primarily use sound for communication, feeding, and mating, seismic airgun blasts have the potential to disrupt all three processes. Furthermore, these sounds could easily scare away fish from their normal habitat and result in temporary and permanent hearing loss in several animals, severely disrupting marine ecosystem. They can also directly kill fish eggs and larvae. As the United States looks to use seismic airgun blasting to look for oil and natural gas reservoirs near Alaska coasts, they must also think about how to prevent these severe damages to the marine ecosystem from happening, which is only the beginning of the larger health consequences that will be sure to come once oil drilling begins.
© Anika Kim. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] H. Fountain and S. Eder, "In the Blink of an Eye, a Hunt for Oil Threatens Pristine Alaska," New York Times, 3 Dec 18.
[2] R. E. Sheriff, Encyclopedic Dictionary of Exploration Geophysics, 3rd Ed. (Society of Exploration, 1991).
[3] E. Onajite, Seismic Data Analysis Techniques in Hydrocarbon Exploration (Elsevier, 2013).
[4] M.-H. Zhao et al., "Large Volume Air-Gun Sources and Its Seismic Waveform Characters," Chinese J. Geophys. 51, 400 (2008).
[5] "Atlantic OCS Proposed Geological and Geophysical Activities," U.S. Bureau of Ocean Energy Management, BOEM 2014-001, Vol. I and Vol. II, February 2014.
