Petroleum hydrocarbons in the ocean
Petroleum hydrocarbons in the ocean refer to organic compounds composed of hydrogen and carbon, which are sourced from both point and nonpoint origins. Point sources include oil spills from vessels, pipelines, and industrial facilities, while nonpoint sources involve natural leaks from the ocean floor and activities related to marine transport. Notable incidents, such as the Deepwater Horizon oil spill in 2010, highlight the scale of these releases, with significant environmental repercussions.
Hydrocarbons impact marine ecosystems through various mechanisms, including chemical breakdown, biological degradation, and physical removal methods. While some marine organisms can adapt to hydrocarbon-rich environments, high concentrations pose stressors that can affect biodiversity, such as coral bleaching and compromised survival in waterfowl due to contaminated feathers. Moreover, methane, a potent greenhouse gas released during these events, contributes to climate change, further complicating ecosystem health.
Understanding the implications of petroleum hydrocarbons in the ocean necessitates a multidisciplinary approach, considering factors such as climate change and the bioavailability of hydrocarbons to marine organisms. The long-term effects on ocean populations and ecosystems remain challenging to assess due to the complexity of interactions at play.
Petroleum hydrocarbons in the ocean
Definition
Hydrocarbons are organic compounds formed exclusively from the elements hydrogen and carbon and are straight-chain, branched, or cyclic molecules. The types of carbon-to-carbon bonds in hydrocarbons range from single to triple. Very low mass hydrocarbons are gases. Liquid and solid hydrocarbons spread out as a floating layer, if less dense than ocean water, or sink below the ocean’s surface, if more dense.
Hydrocarbons in the ocean originate from point and nonpoint sources. Point sources include oil spills from vessels, facilities, pipelines, and rivers. In 2007, 10.6 million liters of oil were released near South Korea in a barge accident. In 2005, more than 26.5 million liters were released from petroleum refining facilities in the aftermath of Hurricane Katrina. Nonpoint sources include vents in the ocean floor and marine transport operations. The National Research Council reported in Oil in the Sea III, that 46 percent of oil released in the ocean comes from natural leaks from fissures in the ocean floor. It is a matter of debate whether these hydrocarbons come from biotic or, less likely, abiotic processes.
In 2010, the Deepwater Horizon Oil Spill occurred in the Gulf of Mexico. This disaster was considered the largest marine oil spill in history. It was caused by a blowout and subsequent explosion on the Deepwater Horizon oil platform. The spill was compounded by the failures of the first several attempts to seal the leak or contain the spill. Experts estimated that more than 210 million gallons of oil were released into the Gulf of Mexico during the incident. In 2016, BP was ruled responsible for the environmental disaster. The company was ordered to pay $20.8 billion in fines. This marked the largest environmental damage settlement in U.S. history.
Significance for Climate Change
Methane, or natural gas, is the most volatile of the hydrocarbons. Over 85 percent of methane released from deep ocean vents dissolves in the water column as a result of the high pressure and low temperature of the deep ocean. In shallow waters, methane bubbles rapidly rise to the surface. Methane is also released from landfills, oil production, and ocean oil spills. Methane is a greenhouse gas (GHG) with twenty-five times the of carbon dioxide (CO2).
Nonvolatile hydrocarbons forming ocean spills may undergo chemical, biological, or physical alteration. Chemical breakdown of surface hydrocarbons in the ocean occurs as a natural photooxidative process in which hydrocarbons, catalyzed by sunlight, react with oxygen. Because hydrocarbons do not absorb light efficiently, the reaction requires other to absorb and transfer energy to oxygen, which becomes the highly energetic and reactive species, singlet oxygen. Singlet oxygen reacts with hydrocarbons to produce alcohols, aldehydes, ketones, and carboxylic acids in a series of complex reactions. These oxidized products are more water-soluble than the parent hydrocarbon.
Less subtle is in-situ burning of oil spills. When immediate removal is important or other oil removal methods are infeasible, an oil spill can be burned to form the products CO2 and water. However, tremendous amounts of toxic carbonaceous are released into the air as a dark cloud of smoke that eventually settles on the ocean surface. Although the combustion product CO2 is a GHG and causes global warming, the smoky particulate matter deflects radiation and cools the atmosphere.
Biological breakdown of hydrocarbons occurs with bacteria, fungi, and some phytoplankton. The two pathways to breakdown hydrocarbons are oxidative phosphorylation, or respiration, and a detoxification mechanism that oxidizes the hydrocarbons to water-soluble oxygen-containing compounds that are easily excreted. Respiration of simple hydrocarbons results in the production of CO2, a GHG. Bacteria that have acclimated to environments containing hydrocarbons are faster to initiate biodegradation.
Several physical methods are used to contain and remediate oil spills, including floating boom barriers to surround an oil spill, skimming boats to remove oil, sorbent materials that transfer oil away from water, and chemical dispersants to finely divide and dilute oil spills. The method used depends on the type, amount, and location of the spill, and also weather conditions.
Some ocean flora and fauna have adapted to live near sea vents of crude oil and natural gas. However, high hydrocarbon concentration in the ocean is a stressor to other ocean flora and fauna. For example, coral appears bleached after hydrocarbon exposure destroys the pigmented of coral polyps. Bleached coral, if they survive, evince decreased exoskeleton maintenance, growth, and reproduction. In general, may be due to any number of stressors. Another likely stressor is elevated sea surface temperature associated with climate change. Attributing coral bleaching to specific stressors is complicated.
Although hydrocarbons are present in the marine environment, marine organisms are exposed only to the hydrocarbon that is bioavailable. The amount of hydrocarbon that is bioavailable depends on the partitioning of the hydrocarbon between ocean and tissues such as gills and cell membranes. Hydrocarbons can also be bioavailable when ingested (adsorbed to foods). Bioaccumulation of hydrocarbons in organisms requires desorption of hydrocarbons from foods in the gut and transport of hydrocarbons among cells. Birds and waterfowl are exposed to hydrocarbons that adsorb to feathers, skin, bills, and beaks. Even with sublethal exposure, the fitness of waterfowl may be compromised. For example, waterfowl with oily feathers cannot maneuver well enough to obtain sufficient food to survive.
The long-term effects of hydrocarbons in the ocean on populations, communities, and ecosystems are difficult to determine due to the magnitude of the studies and multiple variables. The effect of climate change must be factored into studies. Changes in CO2 concentration affect ocean while global warming affects ocean currents and ocean temperature. These factors must be included in studies of marine populations and ecosystems.
Bibliography
"Deepwater Horizon Oil Spill Settlements: Where the Money Went." NOAA, 2017, www.noaa.gov/explainers/deepwater-horizon-oil-spill-settlements-where-money-went. Accessed 20 Dec. 2024.
Guro, Weijun, et al. "Long-Term Petroleum Hydrocarbons Pollution After a Coastal Oil Spill." Journal of Marine Science and Engineering, 27 Sept. 2022, doi.org/10.3390/jmse10101380. Accessed 20 Dec. 2024.
National Research Council. Oil in the Sea III: Inputs, Fates, and Effects. Washington, D.C.: National Academy Press, 2003.
‗‗‗‗‗‗‗. Oil Spill Dispersants: Efficacy and Effects. Washington, D.C.: National Academy Press, 2005.
Proskurowski, Giora, et al. “Abiogenic Hydrocarbon Production at Lost City Hydrothermal Field.” Science 319, no. 5863 (February 1, 2008): 604-607.