TEMPORAL VARIATIONS OF BOMB RADIOCARBON INVENTORY IN THE PACIFIC-OCEAN

The natural and anthropogenic components of the radiocarbon measuremen ts from seawater samples can be successfully separated by an improved method, which is based on a very well-defined relationship between nat ural radiocarbon and dissolved silica observed mainly during the GEOSE CS survey for waters beneath 1000 m depth. This relationship is furthe r reconfirmed by the C-14 measurements from large volume samples taken in the deep waters in the Pacific Ocean during the recent WOCE survey program. Analysis of upper ocean C-14 measurements made along 152 deg rees W, and north of 20 degrees N, in the northeastern Pacific Ocean d uring the NOAA's CGC91 cruise, which is a part of the WOCE survey prog ram, indicates that the bomb C-14 inventory in this part of the ocean has increased by 22% since the GEOSECS measurements made in 1974, This increase is consistent with the model prediction of 25% for the north ern hemisphere ocean. Change of the surface water bomb Delta(14)C valu es during this period is insignificant, This feature is also consisten t with the model simulation. Results of this new analysis will provide useful information of the temporal variations of bomb C-14 inventory in the ocean, in addition to the spatial distribution, which can be us ed as powerful constraints in calibrating the global ocean carbon cycl e models, especially those based on three-dimensional ocean general ci rculation models, for estimating the uptake of CO2 by the ocean. (C) 1 998 Elsevier Science B.V.