Steps in the Marine Carbon Cycle

on May 26 at 06:29 PM

The Ocean’s Role in the Movement of Carbon

The marine carbon cycle helps explain how animals, plants, land and water are all interconnected.

Carbon is the fourth most abundant element on Earth. It is found in all organic substances and is considered the building block for life. Understanding the carbon cycle is important in understanding the relationship between different organisms and various ecosystems. It is also important in understanding humanity’s impact on global warming trends. The ocean covers a majority of the Earth’s surface making the marine carbon cycle a significant player in the movement of this important element.

Carbon Cycles Between the Atmosphere and the Ocean

Although there is no first step in a cycle, the exchange of carbon between the atmosphere and the ocean is a good place to start. On the NASA Science website, the article “Carbon Cycle” describes how carbon dioxide in the atmosphere dissolves into the upper ocean as air mixes with the surface water. Carbon dioxide is more soluble in cold water, so it enters the ocean in greater quantities near the poles. The cold water sinks, entering the oceans’ “conveyor belt” of currents. After hundreds of years of traveling along the oceans’ deep currents, the carbon comes up in the tropics and is returned to the atmosphere. Carbon is released in the tropics because water has a lower capacity to hold gases at high temperatures. This is just one aspect of the marine carbon cycle; carbon dissolved into the ocean may also be used for photosynthesis.

Phytoplankton and the Ocean’s Carbon Cycle

John Roach describes the importance of phytoplankton in his June 7, 2004 National Geographic article “Source of Half Earth’s Oxygen Gets Little Credit”. Phytoplankton are single-celled plants that produce half the world’s oxygen and form the base for many food webs. They absorb the nutrients they need across their cell walls, taking carbon and the like from the ocean. They do not gain their carbon dioxide from the atmosphere, but rather absorb nutrients that are on their way back to the surface from the ocean’s depths.

Marine Animals and the Marine Carbon Cycle

Similar to land animals, aquatic animals do breathe. Although fish have a different apparatus for breathing – namely gills instead of lungs. Fish take in dissolved oxygen from the ocean and release carbon dioxide in return. Other animals including corals also respire and are part of the marine carbon cycle. Interestingly, the January 19, 2009 ScienceDaily article “Fish Guts Explain Marine Carbon Cycle Mystery” describes how fish have another role in the marine carbon cycle. Fish create three to fifteen percent of marine calcium carbonate, a substance that is important to ecosystems such as coral reefs, helps maintain the ocean’s acidic balance, and controls how much carbon the ocean absorbs from the atmosphere.

The Carbon Cycle and Fossil Fuels

Eventually all organisms die. In the ocean some of these organisms sink to the bottom where they can become fossil fuels. NASA’s “Carbon Cycle” article says that marine animals buried in the ocean bottom over millions of years can eventually become oil or coal. These animals contained carbon within them, thus taking carbon out of the cycle for quite some time. Naturally the sediments can be uplifted and weathered over time so that carbon returns to the system. However, at a much quicker pace, humans are finding fossil fuels and burning them. This releases great quantities of carbon into the atmosphere, having drastic effects on marine and terrestrial environments.