HR: 09:15h
AN: OS11C-06    [Abstracts]
TI: Argon as a Tracer for Vertical Mixing and the Maintenance of the Subtropical Thermocline
AU: * Henning, C C
EM: henning@atmos.berkeley.edu
AF: University of California, Berkeley, 395 McCone Hall, #4767, Berkeley, CA 94720-4767 United States
AU: Archer, D
EM: d-archer@uchicago.edu
AF: University of Chicago, Department of the Geophysical Sciences 5734 S. Ellis Ave HGS 419, Chicago, IL 60637 United States
AU: Fung, I
EM: inez@atmos.berkeley.edu
AF: University of California, Berkeley, 395 McCone Hall, #4767, Berkeley, CA 94720-4767 United States
AB: We explore the use of Argon as a tracer of mixing in the main thermocline. After much debate, current thermocline theory suggests that the thermocline consists of an upper, adiabatic, ventilated portion and a lower, diffusive portion. Because the degree to which Argon is saturated in seawater is a nonlinear function of temperature, regions of heating due to mixing will also be regions of Argon supersaturation. We run a primitive equation model with Argon as a tracer to look at the nature of this supersaturation. Argon is forced with gas exchange at the surface with a tendency toward saturation, so the effect of bubbles is neglected. It is a passive tracer in the interior, subject to the same diffusivity as the temperature and salinity. In the main subtropical gyre away from the western boundary region, examination of the balance of terms in the temperature equation indicates a region in which diffusion is a dominant term in the balance, the so-called diffusive thermocline region. In this region, there is evidence of argon supersaturation. However, the exact depth and magnitude of the supersaturation maximum depend on the strength of the vertical diffusivity, the speed of the surface gas exchange, and the nature of the parameterized eddy mixing. In the case of the latter, eddy mixing parameterizations tend to mix heat from the warm, diffusive western boundary current region into the interior, reducing the western boundary region supersaturation and increasing the interior supersaturation at certain depths. At the equator, the supersaturation magnitude is larger, in conjunction with the larger total diffusion term in the temperature equation. Comparison with available data shows that the modeled supersaturation of Argon in the gyre is in good agreement with observations at BATS, displaying a small supersaturation indicative of weak vertical diffusivity or slow gas exchange.
DE: 4820 Gases
DE: 4203 Analytical modeling
DE: 4520 Eddies and mesoscale processes
DE: 4568 Turbulence, diffusion, and mixing processes
DE: 4576 Western boundary currents
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting