Climate Change, Acidification, & the Oceans, Conservation & Sustainable Management, Fisheries, Aquaculture, & Sustainable Seafood, Marine Life

Oceans on Acid

As we continue to burn fossil fuels, produce cement, and alter land – like clearing forests that would normally convert atmospheric carbon dioxide (CO2) into oxygen, the levels of carbon dioxide in the atmosphere continue to increase.  Between 1995 and 2004, high precision instruments have recorded an average increase of 1.9 ppm (parts per million) in atmospheric CO2.  Between 2005 and 2014, there has been a global average increase of 2.1 ppm.  At 17 February 2015, CO2 levels were 399.97 ppm, a vast increase on 1959 levels – the first year with full high precision instrument data measurements – of 315.97 ppm, and a vast increase on pre-industrial levels of around 280 ppm.  With failures of national, regional, and local governments, as well as industry and the public to take meaningful steps to reduce emissions, levels are only set to increase.  Climate change is perhaps the most well-known consequence of our continued emissions, but of increasing concern is climate change’s “evil twin” – ocean acidification.

Not all CO2 remains in the atmosphere, with around 30% being soaked up by the ocean.  When CO2 enters the ocean it forms carbonic acid (H2CO3) which in turn breaks down into bicarbonate (HCO­3) and hydrogen (H+) ions.  Bicarbonate ions can break down even further into carbonate ions (CO23) and a hydrogen ion.  It is the increase in the concentration of hydrogen ions that increases acidity levels in the ocean.  This chemical reaction is entirely natural, and it has always taken place – just not always at such magnitude, and with such rapidity.  Since the industrial revolution, surface waters of the ocean has declined by 0.1 pH units.  This deceptively small change represents a 26 – 30% increase in ocean acidity.  Projected atmospheric CO2 levels suggest that by the end of the century, ocean pH will drop by 0.3 – 0.4 units – an increase in acidity by 100 – 150%.  Numerous studies have indicated acidification will have impacts on marine life, particularly calcareous organisms like molluscs and corals.  There is a growing body of evidence that fish are also at risk.  Laboratory experiments that attempt to determine how fish may or may not be impacted by ocean acidification typically simulate past, present, or predicted future acidity levels, and even beyond into what is generally considered impossible.  Whilst studies that suggest high CO2 levels can be lethal to adult fish typically simulate levels far above that predicted in the future, more realistic scenarios suggest that long-term sub-lethal effects are possible…

The full article was published in – and can be read in – The Marine Professional, a publication of the Institute of Marine Engineering, Science & Technology (IMarEST).

Image: The map was created by the National Oceanic and Atmospheric Administration and the Woods Hole Oceanographic Institution using Community Earth System Model data. This map was created by comparing average conditions during the 1880s with average conditions during the most recent 10 years (2003–2012). Aragonite saturation has only been measured at selected locations during the last few decades, but it can be calculated reliably for different times and locations based on the relationships scientists have observed among aragonite saturation, pH, dissolved carbon, water temperature, concentrations of carbon dioxide in the atmosphere, and other factors that can be measured. This map shows changes in the amount of aragonite dissolved in ocean surface waters between the 1880s and the most recent decade (2003–2012). Aragonite saturation is a ratio that compares the amount of aragonite that is actually present with the total amount of aragonite that the water could hold if it were completely saturated. The more negative the change in aragonite saturation, the larger the decrease in aragonite available in the water, and the harder it is for marine creatures to produce their skeletons and shells. The global map shows changes over time in the amount of aragonite dissolved in ocean water, which is called aragonite saturation. Credit USA EPA/Wikipedia (Public Domain)

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