Climatological distribution of aragonite saturation state in the global oceans

Aragonite saturation state (Omega(arag)) in surface and subsurface waters of the global oceans was calculated from up-to-date (through the year of 2012) ocean station dissolved inorganic carbon (DIC) and total alkalinity (TA) data. Surface Omega(arag) in the open ocean was always supersaturated (Omega>1), ranging between 1.1 and 4.2. It was above 2.0 (2.0-4.2) between 40 degrees N and 40 degrees S but decreased toward higher latitude to below 1.5 in polar areas. The influences of water temperature on the TA/DIC ratio, combined with the temperature effects on inorganic carbon equilibrium and apparent solubility product (K-sp'), explain the latitudinal differences in surface Omega(arag). Vertically, Omega(arag) was highest in the surface mixed layer. Higher hydrostatic pressure, lower water temperature, and more CO2 buildup from biological activity in the absence of air-sea gas exchange helped maintain lower Omega(arag) in the deep ocean. Below the thermocline, aerobic decomposition of organic matter along the pathway of global thermohaline circulation played an important role in controlling Omega(arag) distributions. Seasonally, surface Omega(arag) above 30 degrees latitudes was about 0.06 to 0.55 higher during warmer months than during colder months in the open-ocean waters of both hemispheres. Decadal changes of Omega(arag) in the Atlantic and Pacific Oceans showed that Omega(arag) in waters shallower than 100m depth decreased by 0.10 +/- 0.09 (-0.40 +/- 0.37%yr(-1)) on average from the decade spanning 1989-1998 to the decade spanning 1998-2010.