Ko. Buesseler et al., REGIONAL ESTIMATES OF THE EXPORT FLUX OF PARTICULATE ORGANIC-CARBON DERIVED FROM TH-234 DURING THE JGOFS EQPAC PROGRAM, Deep-sea research. Part 2. Topical studies in oceanography, 42(2-3), 1995, pp. 777
The upper ocean Th-234 activity distribution at 77 stations was measur
ed between 12 degrees N and 10 degrees S, and 95 degrees W and 170 deg
rees W in the spring and autumn of 1992. A regional scavenging model w
as used to estimate vertical export of particulate Th-234. Given the r
elatively high upwelling rates in this region, particularly at equator
ial latitudes near 140 degrees W, it was necessary to include upwellin
g of Th-234 in our model in order to quantify particulate export. Usin
g this export flux and the measured organic C or N to Th-234 ratio on
particles, one can empirically determine POC and PON fluxes for this r
egion. The estimated particulate organic C flux varies spatially and t
emporally within this: region, ranging from 1 to 7 mmol C m(-2) day(-1
), with enhanced export occurring over the equator. Fluxes are also en
hanced along 95 degrees W coincident with a low temperature/high nutri
ent peak at 4 degrees S. Along 140 degrees W, particulate organic C ex
port from the upper 100 m is on the order of 2 mmol C m(-2) day(-1) at
latitudes beyond 4 degrees N and 4 degrees S, with an equatorial peak
of 3-5 mmol C m(-2) day(-1) in both spring and fall. These results su
ggest that a relatively small per cent of the total production is expo
rted locally on sinking particles (particle export/primary production
<5-10%). This finding of low particle export is relatively insensitive
to the chosen upwelling rates or particulate organic C/Th-234 ratios.
Given the measured C/N ratio, particulate N Auxes from the upper 100
m would be 6 times lower than for POC.