Two centuries-long records of skeletal calcification in massive Porites colonies from Meiji Reef in the southern South China Sea and its responses to atmospheric C02 and seawater temperature

Rising atmospheric CO2 and warming of the global climate that have occurred since the industrial revolution are regarded as fatal threats to coral reefs. We analyzed the skeletal calcification rate of 14 massive Porites corals from the Meiji Reef in the southern South China Sea through X-ray photography of coral skeletons. A general pattern of change in coral skeletal calcifi- cation was determined. The change pattern of coral calcification on the Meiji Reef over the past two centuries can be divided into five periods： calcification increase in 1770-1830, 1870-1920, and 1980-2000 and calcification decline in 1830-1870 and 1920-1980. Over the past two centuries, the largest increase in calcification was 4.5%, occurring in 1770-1830, whereas the largest decline in calcification was 6.2%, occurring in 1920-1980. Coral calcification slightly increased in the recent 20 years （1980-2000）. The response relationship of coral calcification to atmospheric CO2 and sea surface temperature （SST） shows that calcification was not correlated with atmospheric CO2 but responded nonlinearly to SST with maxima at ~27.2~C in 1900-2000. On the Meiji Reef, increasing atmospheric CO2 had a negligible effect on coral growth in the past century. How- ever, rising SST improved coral growth in the early and middle 20th century, and restricted coral growth in the recent 20 years.