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Abstract

The discovery of huge subsurface reservoirs of methane in the form of gas hydrate,
has fueled the interest in the associated seep ecosystems and their role as barriers against this
greenhouse gas. Technological advances in high-resolution mapping and optical imaging, as
well as in situ chemical analyses of the deep seafloor have helped to reveal the vast diversity of
hydrocarbon-fueled chemosynthetic ecosystems, such as pockmarks, gas chimneys, mud
volcanoes, brine ponds, and oil and asphalt seeps. In sediments impacted by fluid flow and
a high supply of methane as a carbon and energy source, steep vertical and horizontal
gradients of dissolved porewater species develop on a scale of centimeters to decimeters.
Recently, various in situ chemical sensors and incubation chambers have been developed,
which have been used to quantify the rates of microbial hydrocarbon turnover in seep
ecosystems in combination with a variety of classical methods of biogeochemistry and
microbiology.