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.