Coastal Ocean Last Glacial Maximum to 2100 CO sub(2)-Carbonic Acid-Carbonate System: A Modeling Approach

• Published in: Aquatic geochemistry 2011-09, Vol.17 (4-5), p.749-773
• Main Authors: Lerman, Abraham, Guidry, Michael, Andersson, Andreas J, Mackenzie, Fred T
• Format: Article
• Language: English
• Subjects: Marine
• ISSN: 1380-6165; 1573-1421
• DOI: 10.1007/s10498-011-9146-z

Using coupled terrestrial and coastal zone models, we investigated the impacts of deglaciation and anthropogenic inputs on the CO sub(2)-H sub(2)O ; CaCO sub(3) system in global coastal ocean waters from the Last Glacial Maximum (LGM: 18,000 year BP) to the year 2100. With rising sea level and atmospheric CO sub(2), the carbonate system of coastal ocean water changed significantly. We find that 6 x 10 super(12) metric tons of carbon were emitted from the coastal ocean, growing due to the sea level rise, from the LGM to late preindustrial time (1700 AD) because of net heterotrophy and calcification processes. This carbon came to reside in the atmosphere and in the growing vegetation on land and in uptake of atmospheric CO sub(2) through the weathering of rocks on land. It appears that carbonate accumulation, mainly, but not exclusively, in coral reefs from the LGM to late preindustrial time could account for about 24 ppmv of the 100 ppmv rise in atmospheric CO sub(2), lending some support to the "coral reef hypothesis". In addition, the global coastal ocean is now, or soon will be, a sink of atmospheric CO sub(2). The temperature rise of 4-5 degree C since the LGM led to increased weathering rates of inorganic and organic materials on land and enhanced riverine fluxes of total C, N, and P to the coastal ocean of 68%, 108%, and 97%, respectively, from the LGM to late preindustrial time. During the Anthropocene, these trends have been exacerbated owing to rising atmospheric CO sub(2), due to fossil fuel combustion and land-use practices, other human activities, and rising global temperatures. River fluxes of total reactive C, N, and P are projected to increase from late preindustrial time to the year 2100 by 150%, 380%, and 257%, respectively, modifying significantly the behavior of these element cycles in the coastal ocean, particularly in proximal environments. Despite the fact that the global shoal water carbonate mass has grown extensively since the LGM, the pH sub(T) (pH values on the total proton scale) of global coastal waters has decreased from similar to 8.35 to similar to 8.18 and the carbonate ion concentration declined by similar to 19% from the LGM to late preindustrial time. The latter represents a rate of decline of about 0.028 mu mol CO sub(3) super(2-) per decade. In comparison, the decrease in coastal water pH sub(T) from the year 1900 to 2000 was about 8.18-8.08 and is projected to decrease further from about 8.08 to 7.85 between 2000 and 2