Physical and chemical changes in the ocean over basin-wide zones and decadal or longer time-scales: perspectives on current and future conditions - Ocean Sustainability in the 21st Century - page 95

(Carmack et al. , 2010 ) , and predicted for the entire Arctic Ocean and large regions at high
latitudes (e.g. Steinacher et al ., 2009 ; Denman et al ., 2011 ) .
The increasing acidification ofthe oceans and the associated increase in dissolved car-
bon dioxide and decrease in saturation state for the common forms of calcium carbonate
are not due to climate change, but only to the increase of CO 2 in the atmosphere and the
invasion of roughly a third of that increase into the world ocean. This is a near-certain de-
velopment with potentially serious biological consequences. Recent observations indicate
that surface ocean pH has decreased by ~0.1 units since the start of the Industrial Revolu-
tion, 250 years ago (Bindoff et al ., 2007 ; OCB-EPOCA-UKOA, 2010 and further update).
As measured by the concentration of H + ions, ocean acidity has increased by 26%. A con-
tinued rise in the atmospheric carbon dioxide levels may lead to a further decrease in pH of
0.4 by 2100 (Meehl et al ., 2007 ) , i.e. a further increase in H + ions of 150%. This level of
ocean acidity would be higher than anything experienced during the past 120 million years.
Acidification leads to a decrease of carbonate ion, which can lead to a decrease in biologic-
al production of corals and calcifying phytoplankton and zooplankton.
How extensive might these and other changes be that may result from the increasing
acidification expected over the next century? The mass extinction in the oceans that oc-
curred at the end of the Permian period, about 250 million years ago, has been described by
Payne and Clapham ( 2012 ). They conclude that the Permian extinction (the Great Dying)
was triggered by a lack of dissolved oxygen, an excess of carbon dioxide, enhanced ocean
acidity, and warming, leading to a complete change in the dominant animals of the ocean.
Corals, sea sponges, and shelled animals were devastated. No major group of marine in-
vertebrates was spared. Substitutes included snails and bivalves like clams and scallops,
which became dominating. This shift provided the foundation for present day marine eco-
logy according to the researchers. What happened appears to have been a 'perturbation of
the global carbon cycle'. This in turn may have been due to the largest volcanic event of
the past 500 million years, which formed the Siberian Traps, and injected large amounts of
carbon gas into the atmosphere.