The inventory of nuclear bomb produced 14C
(bomb 14C) in the ocean is a major constraint of CO2
exchange between the atmosphere and ocean in numerical models and analytical
estimates of gas exchange. New 14C data in the ocean, improved
methods of separating the bomb 14C from the natural background of 14C
in the ocean, and reassessment of previous inventories are challenging the
canonical estimates of the air-sea gas transfer. An improved method of
separating natural 14C from the observed 14C distribution
is being used to estimate the bomb 14C distribution and inventory.
We use GEOSECS 14C data to represent the global distribution in
1975, and the new WOCE dataset for 1995 to get two time representations of
inventory. To reduce the bias error for averaging zonal bomb 14C
inventories from limited observation stations during the GEOSECS times, we use
zonal averages given by Peacock [2004] for re-evaluation of 1975 air-sea CO2
exchange rates. Zonal inventories for 1995 will be from GLODAP mapping results
using WOCE data [Key et al. 2004]. Lateral
transport models developed by Broecker et al. [1985] are used to assess the
regional air-sea CO2 exchange rates as well as an appropriately
weighted global mean. Four independent methods of estimating bomb 14C
inventory in the ocean show that the original estimate by Broecker et al. [1995]
could be about 25% too high, the air-sea CO2 exchange rates derived
from this original bomb 14C inventory could also be too high by a
similar amount. Results of this assessment will be presented.
Author: T.-H. Peng, R. Wanninkhof, R.M. Key, A. Macdonald (Tsung-Hung dot Peng at noaa dot gov)
Filesize: 16.72 Kb