<Li> Geological oceanography, or marine geology, is the study of the geology of the ocean floor including plate tectonics and paleoceanography . </Li> <Li> Physical oceanography, or marine physics, studies the ocean's physical attributes including temperature - salinity structure, mixing, surface waves, internal waves, surface tides, internal tides, and currents . </Li> <P> Ocean acidification describes the decrease in ocean pH that is caused by anthropogenic carbon dioxide (CO) emissions into the atmosphere . Seawater is slightly alkaline and had a preindustrial pH of about 8.2 . More recently, anthropogenic activities have steadily increased the carbon dioxide content of the atmosphere; about 30--40% of the added CO is absorbed by the oceans, forming carbonic acid and lowering the pH (now below 8.1) through ocean acidification . The pH is expected to reach 7.7 by the year 2100 . </P> <P> An important element for the skeletons of marine animals is calcium, but calcium carbonate becomes more soluble with pressure, so carbonate shells and skeletons dissolve below the carbonate compensation depth . Calcium carbonate becomes more soluble at lower pH, so ocean acidification is likely to affect marine organisms with calcareous shells, such as oysters, clams, sea urchins and corals, and the carbonate compensation depth will rise closer to the sea surface . Affected planktonic organisms will include pteropods, coccolithophorids and foraminifera, all important in the food chain . In tropical regions, corals are likely to be severely affected as they become less able to build their calcium carbonate skeletons, in turn adversely impacting other reef dwellers . </P>

Which is not a tool used by scientists to study the deep ocean