The environmental and biogeochemical information implicated by a sediment column from the northern shelf of the South China Sea suggests that the vertical phosphorus variation in the sediment column bares a negative correlation with those of calcium carbonate and cadmium. The functional correlation between CO2 and PO43- in seawater is given by calculating a series of chemical equilibriums, indicating a coupling relationship between the accumulation of marine sedimentary P and the atmospheric CO2 change. The decreased P accumulation in marine sediments correlated to the increase of marine primary production during the glacial period might act as a key factor causing glacial atmospheric CO2 decline.