RADON FLUXES MEASURED WITH THE MANOP BOTTOM LANDER
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At five Pacific Ocean sites, radon fluxes were determined from water samples collected by the MANOP Lander, from measurements of 222Rn and 226Ra concentrations in Lander-collected box core sediments, and from measurements of excess radon in the water column. At MANOP sites H and M, fluxes (all in atoms m-2 s-1) determined with Lander water samples (2200 and 1540 480) agree within the measurement uncertainty with water column standing crop measurements (2220 450, 2040 470). At MANOP site C, the diffusive flux calculated from measurements of 226Ra in box core sediments (550 20), the integrated deficiency of 222Rn in the sediments (720 90), and the water column standing crop (500 160) are in agreement, but all are about twice as large as the single Lander water measurement of the radon flux (330). At MANOP site S radon fluxes from measurements of Lander water (3000 260) are in agreement with the predicted diffusive flux from site S sediments (2880), and both fluxes are close to the lower end of the range of water column standing crop measurements (3000-5170). In San Clemente Basin, California, the Lander water flux measurements at four different sites vary by a factor of 3 due to variability in the sediment radium distribution, but the average (1030 190) is close to the water column standing crop value (780 230). Because there is excellent agreement between the fluxes measured with Lander water samples and the predicted diffusive fluxes in most cases, diffusion must be the primary process controlling benthic exchange of radon at the sites studied. The agreement between the Lander water flux estimates and the water column standing crop estimates indicates that the MANOP Lander functions as an accurate benthic flux chamber in water depths ranging from 1900 to 4900 m. In San Clemente Basin, surficial sediments are enriched in manganese and radium, due to manganese cycling near the sediment-water interface. Molecular diffusion of radon from this radium-rich surficial layer is sufficient to obscure any effect of macrofaunal irrigation on the standing crop of radon in this basin. 1987.
