Ocean acidification

Carbon dioxide (CO2) is one of the major gases contained in the atmosphere which affects the radiative, heat balance of the earth. High levels of combustion from fossil fuels, cement production, agriculture and deforestation have increased the global concentrations of CO2 in the atmosphere (figure 6).

As carbon dioxide is absorbed by oceanic water, carbonate ion neutralizes free hydrogen, causing carbonate concentrations to decrease (Image by Univeristy of Maryland).

Figure 6: As carbon dioxide is absorbed by oceanic water, carbonate ion neutralizes free hydrogen, causing carbonate concentrations to decrease (Image by Univeristy of Maryland).

Anthropogenic or human induced pollution occurs when energy or foreign materials are directly or indirectly introduced to the marine environment. This process causes an unbalance to the qualities and properties of the ocean. Due to the increase of carbon dioxide in oceanic waters, ocean acidification has become a large impact on marine habitats of the ocean, most importantly the extreme CWC reefs.Over decades of CO2 increase, levels have risen high enough to affect the survival rates of these deep sea organisms. Oceanic surface pH has dropped by 0.1 units in comparison to pre-industrial levels. These levels have been shown to decrease to 0.3-0.4 units in the future. Over the last century, the average temperature of the sea surface has increase by 0.74 degrees Celsius (Burdett et al, 2014). CWCs are majorly affected by ocean acidification as it impacts on the ecological and physiological characteristics.

With time, the marine environment is becoming less saturated with calcium carbonate (CaC03) causing corals to build weaker skeletons. The change in ocean chemistry can alter an important process called calcification. This term describes the deposition of the calcium carbonate minerals that are a main source required in building coral reef structure (Buddemeier., 2004). CWCs are also known to be affected first as they already contain a low carbonate concentration, so exposure to under-saturated conditions is harsh on their growth and survival. CWCs are characterized by their aragonite saturation state (below 2.5). With oceanic waters becoming more and more acidic, the aragonite saturation levels of CWC are becoming shallower and will continue to do so.

As ocean acidification increases, so does the depth of the saturation horizon up to the sea surface. The saturation horizon has elevated 80-400m since preindustrial times and is predicted to rise another 2000 m by the end of the century from projected models (Form & Riebesell, 2012). This further affects the range of habitat for CWC which they are adapted to for survival. The Mediterranean Sea is in even more of a threat as it naturally contains a high level of alkalinity causing absorption of anthropogenic CO2 to become higher in these waters. This causes a greater sensitivity to ocean acidification (Movilla et al, 2014).

 

 

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