ABSTRACT
At present, major sources of CO2 include fossil fuel combustion and deforestation, while major sinks include the atmosphere and, from models, the oceans (Randerson et al. 1997; Millero 2007). Based on analysis of boron isotopes in foraminifera, it is alleged that oceanic pH has declined over the past 20 million years from about 9.0 to present day levels of 8.2 (Sanyal et al. 1995). During the latest ice age of the recent Pleistocene, which lasted about a million years, seawater pH during the post-glacial period in the most seriously affected areas dropped by 0.3 units to 7.94-7.96 (Sanyal et al. 1995); however, these results are considered preliminary. The global oceans contain about 50 times more inorganic carbon than does the atmosphere. During glacial periods, the oceans were sinks for atmospheric CO2. During glacial-interglacial transitions the oceans were a source of CO2 to the atmosphere, although mechanisms responsible for net CO2 exchange between ocean and atmosphere remain unresolved (Raven and Falkowski 1999). The 20 ppm rise in atmospheric CO2 content over the last 8,000 years was a consequence, in part, of the 500 Gt C increase in terrestrial biomass early in the present interglacial and an early Holocene demise of the supply of excess respiration CO2 to sediment pore waters (Broecker et al. 2001).
