Cold seep environments are an example of a unique deep sea habitat. They differ from hydrothermal vent habitats found on Mid-ocean ridges. Cold seeps usually occur along continental margins for example, in the Gulf of Mexico. The deepest cold seeps environments have, however, been located in the sea of Japan and were found at depths between 5000 and 6000 meters. This is due to the water that emerges from hydrothermal vents is warmer than the surrounding water as it gathers heat from the magma beneath the seabed. In the case of cold seeps, the water that emerges from the seep is the same temperature as the surrounding waters. This water contains reduced inorganic compounds and organic hydrocarbons. These inorganic compounds are usually produced by sulphate-reducing and methanogenic bacteria that are present in the sediment in which the water emerges from the seep. The methane and hydrogen sulphide that is produced by these bacteria bubbles out of the sediment. The methane and hydrocarbons that are produced by the cold seep are commonly deposited in the Gulf of Mexico.

These cold seeps have previously been and are a currently exploited by humans in order to extract the hydrocarbons that are present. This has, however, cause damage to these seeps in the past and continues to threaten these environments.

Is the continued extraction of hydrocarbons from this habitat needed for human growth OR should we be doing more in order to protect these habitats?

Why should they be protected?

Since the discovery of cold seep environments in 1980 (http://www.marine.usf.edu/pjocean/packets/sp02/sp02u2p4.pdf), there have been several expeditions to these environments which have led to the discovery of many different organisms and communities that exist at these seeps. Organisms such as tube worms, clams, mussels and other bivalves all inhabit the cold seep environments. The tube worms that are present in the cold seep environments differ from those that are found and dominate hydrothermal vent systems. These tube worms are Lamellibranchia sp. and Escarpia laminata, not the Riftia pachyptila tube worms that are found at hydrothermal vent systems.

The organisms that inhabit these cold seep environments can be there in very large densities. Cold seep polychaete worms (Siboglinid tubeworms) can be present found in densities in the Barents Sea up to 7272 individuals per meter squared. Not also are these cold seep communities home to large marine fauna such as tube worms, mussels and clams, bacteria that play an important role in the survival of the large fauna and in carbon sequestration.

Carbon sequestration

Figure 1. Methane-Hydrate ice that has formed over a Cold Seep
Figure 1. Methane-Hydrate ice that has formed over a Cold Seep – Source of Image

Cold seep environments play an important role in storing carbon in the sediment surround the cold seep. This is due to the consumption of methane that is present in the seep by methanogenic bacteria in the sediment. The consumption of methane in a cold seep environment can vary from 80% in seeps that have a slow flow rate of water, to 20% or less in seeps that have a fast flow rate of water.  The methane that is present at cold seep sites can be present as methane gas or as methane-hydrate ice (Figure 1)  that forms over the surface of the sediment around the cold seep. This methane-hydrate ice forms due to the methane being placed under high pressure at depths of between 800 and 1000m depth. (Figure 2.). The methane is prevented from being released from the sediment around cold seeps via the anaerobic oxidation of the methane which is achieved by sulphate reduction. The bacteria which is present in this sediment reduce the hydrogen sulphate that is present in the sediment which is an anaerobic process. This anaerobic process oxidises the methane and fixes it in the sediment.

Figure 2. A diagram which represents the conditions required in order for methane to become methane-hydrate
Figure 2. A diagram which represents the conditions required in order for methane to become methane-hydrate – Source of Image

With methane being a prominent greenhouse gas that contributes to global climate change, it is important for these cold seep environments to be protected in order to maintain the fixation of methane into the sediment around cold seeps.

Cold Seeps as fuel source

As mentioned previously, hydrocarbons bubble out of cold of the sediments surrounding cold seeps. These hydrocarbons are present as oil. This oil is commonly used as a fuel source around the world. Hydrocarbon oil has become hard to find and is slowly becoming limited as a fuel source. This is due to the oil being forms over millions of years in the sediment around cold seeps under the high pressures associated with the deep ocean. The oil that is present in the cold seeps has previously been exploited in the Gulf of Mexico. If the reserves of oil are used up, there will be a reduction in the amount and intensity of industry that is currently present in the world. Without this level of industry, it is hard to tell if, as the human race, we would be able to support our rapid population growth.

Cold seep environments could be the key to unlocking a whole new reserve of oil if they are drilled and exploited. This could lead to the world reserves of oil not running out for a longer period of time. With the exploitation of cold seeps, however, does not come without trade-offs.

Drilling for oil in the cold seep sediments would damage the habitat for the fauna that inhabit the cold seeps. Fauna such as tube worms and clams. This damage was highlighted with the Deep Water Horizon oil spill in the Gulf of Mexico in 2010. This oil spill was responsible for covering 2900 square km of the seabed in oil.

These unique habitats should be protected in order to protect the unique fauna that inhabit cold seeps and protect the methane fixation that is provided by the bacteria in cold seeps. Alternative energy sources such as wind turbines should be developed further in order to reduce the need to drill for oil in cold seep environments.

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