DIAGRAM 1: Ocean Carbon Cycle DIAGRAM 2: Terrestrial Carbon Cycle

DIAGRAM 1: Ocean Carbon Cycle DIAGRAM 2: Terrestrial Carbon Cycle

DIAGRAM 3: Ocean Monthly CO 2 Flux Molecules of CO 2 enter the ocean by diffusing into the sea surface waters and dissolving a physio-chemical process. The amount of CO 2 that diffuses and dissolves in the sea surface water depends on variables such as wind, sea surface mixing, concentrations of CO 2, and the temperature of the water. o o o Purple to blue colors indicate areas of the ocean where more CO2 is diffusing into sea surface water than is diffusing from sea surface water out to the atmosphere. Thus, these areas are acting as a carbon sink. Green colors indicate that the movement of CO2 into and out of the ocean is fairly equal. Yellow to red colors indicate areas of the ocean where more CO2 is diffusing out to the atmosphere than is diffusing into sea surface water. Thus, this area is acting as a carbon source to the atmosphere.

DIAGRAM 4: Physical Carbon Pump In the physical carbon pump, carbon compounds can be transported to different parts of the ocean in downwelling and upwelling currents Downwelling currents occur in areas where cold, denser water sinks. These downwelling currents bring dissolved CO 2 down to the deep ocean. Once there, the CO 2 moves into slow-moving deep ocean currents staying there for hundreds of years. Eventually, these deep ocean currents return to the surface in a process called upwelling. Many upwelling currents occur along coastlines. When upwelling currents bring deep, cold ocean water to the surface, the water warms and some of the dissolved CO 2 is released back to the atmosphere. Downwelling and upwelling currents are important components of the deep ocean conveyor belt and are important in physically transporting carbon compounds to different parts of the oceans.

DIAGRAM 5: Ocean's Conveyor Belt of Deep Ocean and Surface Currents

Diagram 6: Simplified Oceanic Biological Pump Phytoplankton are small photosynthetic organisms that move carbon into the oceanic biological pump The oceanic biological carbon pump is driven by organisms that live in the ocean. Just like the terrestrial carbon cycle, the oceanic biological carbon pump is all about photosynthesizing, respiring, eating, producing waste products, dying and decomposing. The biological pump plays a major role in: transforming carbon compounds into new forms of carbon compounds moving carbon throughout the ocean moving carbon down to sea floor sediments Phytoplankton (Greek for drifting plants) are microscopic, one-celled organisms that drift in the sunlit surface areas of the world's oceans and are key to bringing carbon down into the ocean biological pump from the atmosphere via the process of photosynthesis. Just like land plants, phytoplankton capture Sun's energy for photosynthesis. Using light energy from the Sun, they convert the carbon dioxide and water into sugars and other carbon compounds. These carbon compounds enter the marine food web and some carbon eventually ends up in deep ocean currents and seafloor sediments. Phytoplankton return CO 2 and O 2 to the atmosphere when they respire. Over 50% of the world's oxygen needed by us to breathe is produced by phytoplankton.

Diagram 7: The ocean carbonate system is essential to marine organisms such as coral, oysters, clams and lobsters building their shells The ocean naturally contains many dissolved chemicals, which are especially important to the ocean carbon cycle and the shell-building organisms that live in the oceans. When CO 2 dissolves in the ocean, it combines with water molecules and then enters into a series of reversible chemical reactions that produce bicarbonate ions (HCO 3- ), hydrogen ions (H + ) and carbonate (CO 3 2- ) ions. The carbonate ions are especially important to marine organisms because they combine with calcium ions (Ca 2+ ) to form calcium carbonate (CaCO 3 ). Shell-building organisms such as coral, oysters, lobsters, pteropods, sea urchins, and some species of plankton use calcium carbonate to build their shells, plates, and inner skeletons.

Diagram 8: Sinking Shells Bring Carbon Down to the Deep Ocean When shell-builders die and sink, the carbon in their shells is transported down to the deep ocean where the carbon can become part of deep ocean currents and seafloor sediments. Many shells dissolve before reaching the seafloor sediments, a process that releases CO2 into deep ocean currents. Shells that do not dissolve build up slowly on the sea floor forming calcium carbonate (CaCO3) sediments. Eventually, tectonic processes of high heat and pressure transform these sediments into limestone. This process locks massive amounts of carbon away for millions of years. Some of the smallest shell-builders transport the most carbon down to seafloor sediments. Microscopic shell-building unicelluar coccolithophores and foraminifera reproduce quickly when nutrients are available. When nutrients have been used up, trillions of these tiny shellbuilders die and sink, bringing carbon down to the deep. The White Cliffs of Dover on the coast of England pictured in the image on the above are a famous example of limestone calcium carbonate sediments that were deep under the ocean millions of years ago. Over very long time scales, tectonic forces have pushed these sediments above water. If you examined a sample of sediments from these cliffs, you would find shells of microscopic coccolithophores and foraminifera that lived, died and then sank to the sea floor millions of years ago. Over time, these sediment layers such as the White Cliffs of Dover eventually return carbon to the oceans by weathering and erosion.