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Hydrocarbons in seawater

in surface waters imply that the collective contribution hydrocarbons may contribute to the background
of these biogenic hydrocarbons may be substantial, levels in surface seawater, where they can then be
especially in productive regions. 24,64,65 subjected to microbial degradation or photo-oxidation
Marine bacteria and archaea also play a crucial processes, 36,37,41,48 a pathway representing a continuous,
role in producing and transforming hydrocarbons. widespread, and often diffuse input contribution to the
Some marine bacteria are known to synthesize long- overall natural hydrocarbon budget of the ocean. 1,2
chain hydrocarbons, including branched and cyclic
compounds, as components of their cell membranes 3. Anthropogenic origins of hydrocarbons in
(e.g., hopanoids) or as storage products. Moreover, seawater
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methanogenic archaea, prevalent in anaerobic marine
sediments and anoxic water columns, produce vast While sometimes attributed to natural phenomena,
quantities of biogenic methane through the anaerobic the pervasive presence of hydrocarbons in seawater is
decomposition of organic matter. This biogenic overwhelmingly dominated by anthropogenic activities.
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methane can diffuse out of sediments, forming From catastrophic oil spills to insidious chronic
methane plumes in the water column, or be oxidized discharges, human interaction with petroleum products
by methanotrophic bacteria. While methane is a potent has profoundly altered the marine environment.
1,2
greenhouse gas, its natural production and consumption Understanding the sources, quantifying their inputs,
by marine microbes are integral to the global carbon and distinguishing between types of hydrocarbons
cycle. are crucial steps in mitigating their ecological impact.
Zooplankton and other marine invertebrates can Regional variability profoundly shapes hydrocarbon
contribute to the hydrocarbon pool by accumulating and dynamics in marine environments, influencing spill
transforming lipids and hydrocarbons from their diet. impacts, response efficacy, and remediation success. In
For example, some copepod species produce certain colder climates, such as the Arctic, low temperatures
hydrocarbons, and their fecal pellets contribute to the slow oil weathering, biodegradation rates, and natural
downward flux of organic matter, including associated dispersion, leading to prolonged oil persistence and
hydrocarbons, to deeper waters and sediments. 68,69 enhanced bioaccumulation in the food web. Conversely,
On the other hand, the degradation of deceased warmer temperate and tropical waters facilitate faster
macroalgae and marine plants represents a fascinating degradation, but may promote rapid evaporation of
and environmentally significant natural process with volatile compounds, altering oil composition and
the potential to generate hydrocarbons. When these toxicity. 1,2
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organisms die, their organic matter, rich in lipids, Catastrophic oil spills leave an indelible mark on
carbohydrates, and proteins, sinks to the seabed. Under public consciousness and the environment. These
specific anoxic conditions, microbial communities incidents typically involve large-scale release of crude
play a crucial role in breaking down this complex oil or refined products, often with devastating immediate
organic material. Anaerobic decomposition prevents consequences. Tanker accidents have historically been
complete oxidation, leading to the formation of various a significant source of large-scale oil spills. 2,8,10,26 The
intermediate compounds. Over geological timescales, past 50 years have been marked by numerous nautical
these organic molecules undergo further transformation accidents that have mainly involved large oil tankers
through diagenesis and catagenesis, and the original or ships, with spillage of large quantities of mixtures
biomass is rearranged and cracked, eventually forming of crude oil or refined hydrocarbons. In 1978, the huge
liquid and gaseous hydrocarbons. 70 crude carrier Amoco Cadiz, following the breakage of a
An additional natural source of hydrocarbons in the rudder, ran aground near the coast of Portsall, Brittany,
sea is atmospheric deposition of biogenic compounds. France. About 223,000 tons of light crude oil and fuel
Terrestrial vegetation and soils are primary global sources are spilled into the sea, covering a significant ocean area
of biogenic volatile organic compounds, including and affecting about 360 km of the Brittany coastline,
isoprene and monoterpenes. These compounds, once including sandy beaches, rocky shores, salt marshes,
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emitted into the atmosphere, can undergo chemical and estuaries. The spill is estimated to have caused
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reactions, forming aerosols, and be transported long the mortality of approximately 9,000 tons of oysters,
distances before being deposited onto the ocean surface drastically affecting the region’s economy around the
through wet or dry deposition. Although difficult farming and trade of these organisms. Nearly 20,000
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to quantify, the atmospheric deposition of biogenic seabirds were recovered dead, and significant impacts

Volume 22 Issue 6 (2025) 25 doi: 10.36922/AJWEP025290224