activity and removal rate:
t sc ¼
A
t
D
J
¼
A
t
D
lðA P À A
t
D Þ
½3
Elements in this group are described below.
Thorium
230 Th is produced at a known rate from
234 U in sea water. The highly reactive element is
rapidly adsorbed onto particles and transported
down in the water column when these particles sink
out. As the adsorption is reversible, a steady-state
distribution is achieved, in which both particulate
and dissolved activities increase linearly with depth
(see Uranium-Thorium Series Isotopes in Ocean
Profiles). At any depth, disregarding horizontal
advection, the vertical flux of
230 Th XS (‘xs’ meaning
in excess of the activity supported by the parent
nuclide, in this case the small amount of
234 U on the
sinking particles) must equal its production from
222 Rn
222 Rn
222 Rn
222 Rn
228 Ra
226 Ra
228 Ra
226 Ra
228 Ra
232 Th
228 Th
232 Th
230 Th
234 Th
234 U
235 U
231 Pa
228 Th
238 U
230 Th
234 U
234 Th
238 U
Rivers:
U,Ra
210 Pb
210 Pb
210 Po
222 Rn
226 Ra
230 Th
231 Pa
227 Ac
210 Pb
238 U
210 Pb
Figure 2 Schematic diagram of radioactive decay (horizontal arrows) and typical transport processes in ocean and atmosphere that
can be traced by the nuclides described here (vertical arrows). (Adapted with permission from Ernst WG and Morin JG (eds.) 1980 The
Environment of the Deep Sea. Englewood Cliffs, NJ: Prentice Hall.)
Table 3 Isotope pairs with mobile parents and particle-reactive daughters
Mother
Daughter
Half-life
Source
Oceanographic applications
234
U
230Th
75200 y
water column
sediment trap calibration, reconstruction of past vertical
rain, sediment focusing
238
U
234Th
24.1 d
water column
export production, calibration of shallow sediment trap
resuspension budgets, bioturbation
228
Ra
228Th
1.9 y
water column, in deep sea
and continental shelf
scavenging in coastal waters, bioturbation
235
U
231
Pa
32500 y
water column
boundary scavenging, paleoproductivity, refined
sediment trap calibration
226
Ra
210
Pb
22.3 y
water column, atmosphere
boundary scavenging, bioturbation
210
Pb
210
Po
138 d
water column
scavenging in surface ocean
URANIUM-THORIUM DECAY SERIES IN THE OCEANS: OVERVIEW 205
t sc ¼
A
t
D
J
¼
A
t
D
lðA P À A
t
D Þ
½3
Elements in this group are described below.
Thorium
230 Th is produced at a known rate from
234 U in sea water. The highly reactive element is
rapidly adsorbed onto particles and transported
down in the water column when these particles sink
out. As the adsorption is reversible, a steady-state
distribution is achieved, in which both particulate
and dissolved activities increase linearly with depth
(see Uranium-Thorium Series Isotopes in Ocean
Profiles). At any depth, disregarding horizontal
advection, the vertical flux of
230 Th XS (‘xs’ meaning
in excess of the activity supported by the parent
nuclide, in this case the small amount of
234 U on the
sinking particles) must equal its production from
222 Rn
222 Rn
222 Rn
222 Rn
228 Ra
226 Ra
228 Ra
226 Ra
228 Ra
232 Th
228 Th
232 Th
230 Th
234 Th
234 U
235 U
231 Pa
228 Th
238 U
230 Th
234 U
234 Th
238 U
Rivers:
U,Ra
210 Pb
210 Pb
210 Po
222 Rn
226 Ra
230 Th
231 Pa
227 Ac
210 Pb
238 U
210 Pb
Figure 2 Schematic diagram of radioactive decay (horizontal arrows) and typical transport processes in ocean and atmosphere that
can be traced by the nuclides described here (vertical arrows). (Adapted with permission from Ernst WG and Morin JG (eds.) 1980 The
Environment of the Deep Sea. Englewood Cliffs, NJ: Prentice Hall.)
Table 3 Isotope pairs with mobile parents and particle-reactive daughters
Mother
Daughter
Half-life
Source
Oceanographic applications
234
U
230Th
75200 y
water column
sediment trap calibration, reconstruction of past vertical
rain, sediment focusing
238
U
234Th
24.1 d
water column
export production, calibration of shallow sediment trap
resuspension budgets, bioturbation
228
Ra
228Th
1.9 y
water column, in deep sea
and continental shelf
scavenging in coastal waters, bioturbation
235
U
231
Pa
32500 y
water column
boundary scavenging, paleoproductivity, refined
sediment trap calibration
226
Ra
210
Pb
22.3 y
water column, atmosphere
boundary scavenging, bioturbation
210
Pb
210
Po
138 d
water column
scavenging in surface ocean
URANIUM-THORIUM DECAY SERIES IN THE OCEANS: OVERVIEW 205