New calculations done by International Pacific Research Center scientists in a recent report indicates that CO2 produced by human activity has caused an unprecedented increase in the acidity of ocean water. Acidity is measured on the pH scale, which runs from 0 to 14, seven is neutral. Over the past 300 million years, the oceans pH has been slightly basic, averaging approximately 8.2. Today, it is approximately 8.1, a drop of 0.1 pH units, representing a 25-percent increase in acidity over the past 20 years. Higher acidity has been proven to inhibit shell growth in marine animals and it even effects their reproduction cycles.
Scientists measure the concentration of aragonite (a form of calcium carbonate) in ocean water to measure the water’s acidity. Marine organisms, like corals, use aragonite to build skeletal structures using a process called calcification. As acidity of seawater increases, the saturation level of aragonite is reduced. The potential loss of an ecosystem may be caused by a reduction of the calcification rate of marine organisms which is a direct response to lower aragonite levels.
Highly acidic water can wreak havoc on marine life it can dissolve the calcium carbonate in seashells and coral reefs. Populations of large-shelled animals such as mussels and stalked barnacles will drop, whereas smaller-shelled species and noncalcareous algae (species that lack calcium-based skeletons) will become more abundant. Scott C. Doney, an oceanographer with the Woods Hole Oceanographic Institution said “I see it as a harbinger of the trends we might expect to occur in the future.”
Tobias Friedrich, an IPRC postdoctoral fellow, said “In some regions, the man-made rate of change in ocean acidity since the Industrial Revolution is a hundred times greater than the natural rate of change between the Last Glacial Maximum and pre-industrial times.” The Earth warmed slowly after the last ice age, giving marine ecosystems ample time to adjust as the CO2 rose over 6,000 years. Now, they are facing a similar increase in CO2 concentration in just 1 or 2 centuries.
Normally coral reefs are found in places where open-ocean aragonite saturation reaches levels of 3.5 or higher. These conditions exist today in approximately 50% of the ocean, mostly in the tropics. This fraction is projected to drop below 5% by the end of the 21st century. The Hawaiian Islands, sitting on the northern edge of the tropics, will be one of the very first to feel this impact.
Axel Timmermann, a professor of oceanography said “Our results suggest that severe reductions are likely to occur in coral reef diversity, structural complexity and resilience by the middle of this century."