Meridional distribution of 226Ra in the eastern Pacific along GEOSECS cruise tracks

Details Meridional distribution of 226Ra in the eastern Pacific along GEOSECS cruise tracks Meridional distribution of 226Ra in the eastern Pacific along GEOSECS cruise tracks

Sep 1980

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1980e%26psl..49..293k&link_type=abstract

Earth and Planetary Science Letters, Volume 49, Issue 2, p. 293-308.

Physics

6

Scientific paper

We present the distribution of 226Ra in eight vertical profiles from the eastern Pacific. The profiles are located along a meridional trend near 125°W, from 43°S to 29°N. Surface 226Ra concentrations are about 7 dpm/100 kg, except for the two stations south of 30°S where the higher values are due to the Antarctic influence. Deep waters show a distinctive south-to-north increase in the 226Ra content, from about 26 to 41 dpm/100 kg near the bottom. Unlike in the Atlantic and Antarctic Oceans, the effect of 226Ra injection from bottom sediments is clearly discernible in the area. The presence of this primary 226Ra can be traced up to at least 1-1.5 km above the ocean floor, making this part of the sea bed among the strongest source regions for the oceanic 226Ra. Numerical solutions of a two-dimensional vertical advection-diffusion model applied to the deep (1.2-4 km) 226Ra data give the following set of best fits: upwelling velocity (Vz) = 3.5 m/yr, vertical eddy diffusivity (Kz) = 0.6 cm2/s, horizontal (north-south) eddy diffusivity (Ky) = 1 × 107 cm2/s, and water-column regeneration flux of 226Ra (J) = 3.3 × 10-5 dpm kg-1 yr-1 as an upper limit. These parametric values are in general agreement with one-dimensional (vertical) model fits for the Ra-Ba system. However, consideration of 226Ra balance leads us to suspect the appropriateness of describing the vertical exchange processes in the eastern Pacific with constant Vz and Kz. If future modeling is attempted, it may be preferable to treat the area as a diffusion-dominant mixing regime with depth-dependent diffusivities.
Present address: Rockwell International, Rocketdyne Division, Canoga Park, CA 91304, U.S.A.

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