where k is the turbulent diffusivity and u is the fluid
velocity. The equation appears similar to that of an
ideal age tracer (A), governed by
uÁ
! rA ¼ r krA
ð
Þþ1
except for the presence of the unsteady (time derivative) term and the last term on the right. The
unsteady term arises from the fact that the parent
distributions are changing with time, and the age
distribution is adjusting accordingly. The last term
appears more as a pseudovelocity that is a direct
manifestation of the nonlinear mixing behavior exemplified in the two-water-mass thought experiment
described earlier. Although the equation appears
complex, the key point is that all the terms are observable. That is, given field observations of the
tracers, the terms can be computed to within a value
of k. The effects on the shallowest surfaces are small.
Analysis of actual distributions within the shallow
North Atlantic, for example, shows that deviations
from ‘ideal’ behavior are negligibly small. Moreover,
combining the age distributions with other tracers,
for example salinity, and with geostrophic constraints, permits the determination of absolute velocities within the main thermocline to a resolution of
order 0.1 cm s
À1 .
See also
Elemental Distribution: Overview.
Further Reading
Clarke WB, Jenkins WJ, and Top Z (1976) Determination
of tritium by mass spectrometric measurement of
3
He.
International Journal of Applied Radioisotopes 27: 515.
Doney SC, Glover DM, and Jenkins WJ (1992) A model
function of the global bomb tritium distribution in
precipitation, 1960–1986. Journal of Geophysical
Research 97: 5481--5492.
Doney SC, Jenkins WJ, and O ¨ stlund HG (1993) A tritium
budget for the North Atlantic. Journal of Geophysical
Research 98(C10): 18069--18081.
Jenkins WJ (1978) Helium isotopes from the solid earth.
Oceanus 21: 13.
Jenkins WJ (1992) Tracers in oceanography. Oceanus 35:
47--56.
Jenkins WJ (1998) Studying subtropical thermocline
ventilation and circulation using tritium and
3
He.
Journal of Geophysical Research 103: 15817--15831.
Jenkins WJ and Smethie WM (1996) Transient tracers
track ocean climate signals. Oceanus 39: 29--32.
146 TRITIUM–HELIUM DATING
velocity. The equation appears similar to that of an
ideal age tracer (A), governed by
uÁ
! rA ¼ r krA
ð
Þþ1
except for the presence of the unsteady (time derivative) term and the last term on the right. The
unsteady term arises from the fact that the parent
distributions are changing with time, and the age
distribution is adjusting accordingly. The last term
appears more as a pseudovelocity that is a direct
manifestation of the nonlinear mixing behavior exemplified in the two-water-mass thought experiment
described earlier. Although the equation appears
complex, the key point is that all the terms are observable. That is, given field observations of the
tracers, the terms can be computed to within a value
of k. The effects on the shallowest surfaces are small.
Analysis of actual distributions within the shallow
North Atlantic, for example, shows that deviations
from ‘ideal’ behavior are negligibly small. Moreover,
combining the age distributions with other tracers,
for example salinity, and with geostrophic constraints, permits the determination of absolute velocities within the main thermocline to a resolution of
order 0.1 cm s
À1 .
See also
Elemental Distribution: Overview.
Further Reading
Clarke WB, Jenkins WJ, and Top Z (1976) Determination
of tritium by mass spectrometric measurement of
3
He.
International Journal of Applied Radioisotopes 27: 515.
Doney SC, Glover DM, and Jenkins WJ (1992) A model
function of the global bomb tritium distribution in
precipitation, 1960–1986. Journal of Geophysical
Research 97: 5481--5492.
Doney SC, Jenkins WJ, and O ¨ stlund HG (1993) A tritium
budget for the North Atlantic. Journal of Geophysical
Research 98(C10): 18069--18081.
Jenkins WJ (1978) Helium isotopes from the solid earth.
Oceanus 21: 13.
Jenkins WJ (1992) Tracers in oceanography. Oceanus 35:
47--56.
Jenkins WJ (1998) Studying subtropical thermocline
ventilation and circulation using tritium and
3
He.
Journal of Geophysical Research 103: 15817--15831.
Jenkins WJ and Smethie WM (1996) Transient tracers
track ocean climate signals. Oceanus 39: 29--32.
146 TRITIUM–HELIUM DATING