Akita University, Japan

We investigated the relation between delta (super 15) N (sub org) values of organic matter and the number of nannofossil in marine sediments during a period from 300 ka to 1300 ka, using the core samples from ODP Hole 1006A, off Great Bahama Bank of the Caribbean Sea. The delta (super 15) N (sub org) values and the number of nannofossil (absolute abundance of coccoliths) fluctuate in the ranges of +0.1 ppm to +5.8 ppm and 1X10 (super 8) to 30X10 (super 8) specimens/g, respectively, with a clear positive correlation. As the number of nannofossil increases, delta (super 15) N (sub org) values become greater. These changes are closely linked to 100-ky and 41-ky variations in delta (super 18) O (sub planktonic) values of planktonic foraminifera (Globigerinoides ruber), reflecting mixing of surface water in the photic zone and bottom water brought about by the trade wind which became stronger during glacial period. delta (super 15) N (sub org) values (+0.1 to +5.8 ppm) of marine sediments from the Caribbean Sea fluctuate within a range lower than those (+4 to +10 ppm) from the Arabian Sea under the strong influence of upwelling during interglacial period. The difference in the fluctuation ranges of delta (super 15) N (sub org) values between these areas seems to reflect that in the amount of nitrate carried from bottom water to surface water under the influence of the trade wind and monsoon and its consumption rate by phytoplankton. These results corroborate the consideration that delta (super 15) N (sub org) values of marine sediments can be related directly to changes in productivity of phytoplankton.