HYDROCARBONS IN THE MARINE ENVIRONMENT 



Occurrence, Formation and Degradation 



Both recent, biosynthetic, and fossil hydrocarbons occur in the sea; 

 the latter are observed increasingly along tanker routes of the open 

 ocean and in coastal areas receiving chronic spills. We lack fundamental 

 data on the residence times of hydrocarbons in the open ocean, on 

 beaches, in bottom sediments, and in organisms. The degradation and 

 solution processes that disperse and destroy hydrocarbons are unknown, 

 as is how recent and fossil hydrocarbons move through the biosphere, 

 the hydrosphere, and the marine food web. 



A closely allied problem is understanding the diagenesis of organic 

 matter in sediments that leads to hydrocarbon accumulation. Changes 

 in organic matter with depth in sediments of inland seas of the geologic 

 past have been studied, but there have been only limited studies of cores 

 from the present continental margins and deep sea. These studies 

 indicate that some of the conversion processes may be slower because 

 of lower temperatures and that different products may result because 

 of differences in amounts and type of organic matter in the open ocean 

 and in inland seas. We need more definitive studies of the mechanisms 

 and rates of change of organic constituents of open ocean sediments. 



Hydrocarbon Gases 



Inventories of hydrocarbon gases in waters and sediments have 

 been made in selected marine environments, but little is known of the 

 processes and rates of their formation, accumulation, and decomposi- 

 tion. Methane, ethylene, and propylene are commonly present in near- 

 surface waters of coastal margins and inland seas. The methane probably 

 originates from anaerobic decay of organic matter, and the low-molecu- 

 lar-weight olefins are believed to be metabolic byproducts of plankton 

 growth, but there is no clear evidence of these processes. We need studies 

 to define mechanisms and rates of hydrocarbon production from biota in 

 both shallow coastal and deep sea environments. 



In reducing waters and sediments methane, ethane, and propane are 

 the dominant hydrocarbons produced. Although the production of 

 methane by micro-organisms utilizing carbon dioxide and hydrogen is 

 established, there is no evidence of how ethane and propane are formed. 



Transport mechanisms resulting in the migration and accumulation 

 of hydrocarbons in sediments and waters are also poorly understood. 

 Hydrocarbons may migrate either as bubbles or as part of a solution 

 by convection and diffusion. In the Black Sea, methane formed in 

 sediments and bottom waters migrates through the anoxic to oxic 



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