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The world’s oceans absorb almost half of all carbon emissions, and can hold up to 50 times more CO2 than the atmosphere (Sabine et al., 2004). Increasing greenhouse gases have caused the oceans to become saturated in CO2, and so are losing the capability to act as carbon sinks. It is also having an adverse effect on oceanic pH as it is becoming more acidic, while also reducing levels of carbonate ions (CO32-). By 2100, marine CO2 levels could reach 880ppm (parts per million), which would lead to unprecedented impacts on the marine environment (EC, 2013). This would cause a drop in pH from the current 8.2 to 7.9, increasing ocean acidity by 150% since preindustrial times (Raven et al., 2005; McNeil and Matear, 2006; Feely et al., 2009). This increased acidity is thought to be to blame for major coral bleaching* events observed in the Great Barrier Reef, where losses of 25% are expected within the next 40 years if current trends continue (Wild et al., 2011).


Ocean Acidification Chart (WWW1)

Cold water corals, found off the Irish coast are also in danger from these pH alterations. Lower levels of carbonate ions create immediate dangers for many marine organisms, such as zooplankton, molluscs, and corals, and indirect threats to fish, seabirds, marine mammals, and humans. The immediate danger stems from the need for carbonate ions in the formation of shells like those of mussels and marine snails (Header Image – WWW3). Without appropriate levels these organisms become easily damaged and mortality rates increase. Not only does this reduce the biodiversity of the coastal environment, but shell and finfish aquaculture industries can be hit with serious economic losses. The fisheries industry can also suffer, as a major food source for many of their stocks could suddenly decrease, resulting in lower populations and lower quality individuals for commercial sale.

To learn more about the effects of rising oceanic temperatures see this month’s blog post on ‘Temperature and Sea Level Change

  Seán & Orla-Peach

*Coral Bleaching – may also occur due to increases in oceanic temperature levels. Coral organisms maintain a symbiotic relationship with microscopic algae known as zooxanthellae which also contribute to their vibrant colours. Rising temperatures can lead this algae to photosynthesize too quickly forcing the coral to expel them in order to protect its own tissue. If temperatures remain high for prolonged periods of time (NAOO, 2016), corals are unable to recover. In 2014 alone, a team of researches conducting expeditions in Australia’s Great Barrier Reef identified a 40% reduction in coral calcification rates when compared with those recorded in the 1970.

coral infographic

Coral Bleaching Infographic – WWW2References –


Feely, R. A., Doney, S. C., & Cooley, S. R. (2013). Ocean acidification: UK Ocean Acidification Programme. Oceanography, 22(4), 36–47.

McNeil, B. I., & Matear, R. J. (2006). Projected climate change impact on oceanic acidification. Carbon Balance and Management, 1(1), 2.

NAOO (2016)  El Nino Prolongs Longest Global Coral Bleaching Event.

Raven, J., Caldeira, K., Elderfield, H., Hoegh-Guldberg, O., Liss, P., Riebesell, U., Watson, A. (2005). Ocean acidification due to increasing atmospheric carbon dioxide. Policy Document, 5(12), 60.

Sabine, C. L., Feely, R. A., Gruber, N., Key, R. M., Lee, K., Bullister, J. L., Rios, A. F. (2004). The Oceanic Sink for Anthropogenic CO2. Science, 305(5682), 367–371.

Wild, C., Hoegh-Guldberg, O., Naumann, M. S., Colombo-Pallotta, M. F., Ateweberhan, M., Fitt, W. K., & van Woesik, R. (2011). Climate change impedes reef ecosystem engineers. Marine and Freshwater Research, 62, 205–215.

WWW1 – Ocean Acidification Chart

WWW2 –  Coral Bleaching 

WWW3 – Ocean Acidification Effects