Ocean Circulation and Geochemistry
234Th (dpm/L)
0
20
40
60 0
20
40
60
MBkarov
a
North
P
asin
ole
100
200
Diss. 234Th
Diss. 234Th
P
P
Tart. 234Th
Tart. 234Th
D tal 234Th
D tal 234Th
o
o
300
Siss. 238Th
Siss. 238Th
i (M)
i (M)
400
0
20 40 60
0 20 40 60
Si (M)
dissolved silicate in the Makarov Basin and at the North Pole.
238U activities were calculated from salinity (238U = 0.069
salinity).
productivity. On the other hand, the 234Th deficit may also reflect a scaveng-
ing "history" due to 234Th removal within the particle-rich shelf waters and
advection into the Arctic interior. In contrast, results from the North Pole
(Station 35) indicate no significant 234Th/238U disequilibrium and hence no
appreciable scavenging of 234Th.
These 234Th profiles show for the first time a marked spatial variability in
particle scavenging in the upper Arctic Ocean. Ongoing studies aim to deter-
productivity and advective transport of shelf water containing low 234Th into
the central Arctic.
Finally, the 234Th results are being used to quantify the sinking flux of
biologically produced particulate organic carbon ( POC) from the surface mixed
layer (030 m). Preliminary estimates indicate that the export flux of POC
ranges from approximately 400 mg C/m2-day in the Chukchi Sea to 110 mg
C/m2-day in the Arctic interior. These particulate carbon fluxes are compara-
ble to the limited number of carbon flux measurements obtained using sedi-
ment traps in the Arctic Ocean.
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