The benthic zone or realm is subdivided on the basis of depth into different zones which extend from high tide to the continental shelf and deep-sea realm. The continental shelf is a gently sloping benthic region that extends away from the land mass. At the continental shelf edge, usually about 200 meters deep. The deep-sea realm includes the sediment surface and some sub-surface layers. Organisms living in this zone generally live in close relationship with the substrate bottom; many such organisms are permanently attached to the bottom.
The living organisms that live down in the benthic zone must rely on decaying animals for food or the hydrothermal vents. The hydrothermal vents get their energy from chemical reactions and spew hot mineral rich water into the environment.
The consumption of phytoplankton production by the organisms in the benthic layer is an important component of organic carbon budgets for continental shelves. Sediment texture is a major factor regulating benthic processes because fine sediment areas are sites of enhanced deposition from the water column, resulting in increased organic content, bacterial biomass and community metabolism.
Fish, whales, dolphins, crabs, seabirds, and just about everything else that makes a living in or off of the oceans owe their existence to phytoplankton, one-celled plants that live at the ocean surface.
Phytoplankton are at the base of what scientists refer to as oceanic biological productivity, the ability of a water body to support life such as plants, fish, and wildlife.
"A measure of productivity is the net amount of carbon dioxide taken up by phytoplankton," said Jorge Sarmiento, a professor of atmospheric and ocean sciences at Princeton University in New Jersey.
The one-celled plants use energy from the sun to convert carbon dioxide and nutrients into complex organic compounds, which form new plant material. This process, known as photosynthesis, is how phytoplankton grow.
Robert Frouin, a research meteorologist with the Scripps Institution of Oceanography in La Jolla, California, said understanding the process by which phytoplankton obtains ocean nutrients is important to understanding the link between the ocean and global climate.
"Marine biogeochemical processes both respond to and influence climate," Frouin said. "A change in phytoplankton abundance and species may result from changes in the physical processes controlling the supply of nutrients and sunlight availability."
Oxygen Supply At Risk
Phytoplankton need two things for photosynthesis and thus their survival: energy from the sun and nutrients from the water. Phytoplankton absorb both across their cell walls.
In the process of photosynthesis, phytoplankton release oxygen into the water. Half of the world's oxygen is produced via phytoplankton photosynthesis. The other half is produced via photosynthesis on land by trees, shrubs, grasses, and other plants.
As green plants die and fall to the ground or sink to the ocean floor, a small fraction of their organic carbon is buried. It remains there for millions of years after taking the form of substances like oil, coal, and shale.
"The oxygen released to the atmosphere when this buried carbon was photosynthesized hundreds of millions of years ago is why we have so much oxygen in the atmosphere today," Sarmiento said.
The air we breathe is approximately 21 percent oxygen and phytoplankton and terrestrial green plants maintain a steady balance in the amount of the Earth's atmospheric oxygen.
Marine biologist Stephen Mottram says that the current toxic load in the Gulf which is venturing well out into Atlantic waters will eventually threaten a large percentage of the world's phytoplankton community. "The balance and concentration of phytoplankton in the upper benthic layer is critical to the a major portion of world's oxygen and this community is now being exposed to major threat from the BP disaster and so-called clean up."
Mottram estimates that if there is as little as a 20% reduction in phytoplankton populations, a catastrophic sequence of global cooling would occur. "Toxins in the Gulf and surrounding waters will eventually create carbon dioxide deficiencies in the oceans and the result will be a dramatically reduced phytoplankton population...this will cause a cascade of phenomenon that will eventually affect almost every organism in the world." Mottram added that "climate would inevitably change globally as reductions in phytoplankton would directly influence temperate climates causing them to shift to cooler tempertures."
Mottram's primary concern is that the increased number of dead zones in the Gulf will spread to the entire Atlantic ocean and beyond in due time. "It is a literal poisoning and suffocation of the ocean and all marine life. Once nutrient cycling slows down or comes to a halt for the primary producers, more than 90% of marine life will die and the consequences to all mammals (including humans) will be devastating."