Date of Award

Spring 1984

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean/Earth/Atmos Sciences

Program/Concentration

Oceanography

Committee Director

George T. F. Wong

Committee Member

Michael P. Bacon

Committee Member

William M. Dunstan

Committee Member

Curtis R. Olsen

Committee Member

Terry L. Wade

Abstract

Integrated monthly wet-only and bulk precipitation samples for Be-7 and Pb-210 analysis were collected from November 1982 through October 1983 at two sites in lower Chesapeake Bay. Atmospheric deposition fluxes for Be-7 in wet-only and bulk precipitation averaged 0.013 and 0.014 pCi/cm2/d, respectively, and for Pb-210 averaged 0.36 and 0.40 pCi/cm2/yr, respectively, suggesting that dry deposition makes only a minor contribution to the total fluxes.

A seasonal trend was observed in the depositional flux of Be-7, with a pronounced maximum in the Spring. Approximately 40 percent of the annual Be-7 deposition occurred between February and April, with a maximum in March. This is consistent with the injection of Be-7 of statospheric origin into the tropopause during the vernal tropopause break. Pb-210 exhibited a slightly weaker seasonal trend, with ca. 35 percent delivered between February and April, which appears to be related to the rate at which its parent, Rn-222, emanates from the earth. The average deposition velocities for Be-7 and Pb-210 in bulk precipitation were 1.5 and 0.8 cm/s, respectively.

The removal behaviors of two atmospherically-derived radionuclides, Pb-210 and Be-7, have been examined in real-time following their deposition to a shallow coastal bay by four precipitation events. In general, there was a marked elevation in the water column concentrations following a precipitation event and the concentrations decreased with time. The removal residence times of these radionuclides were on the order of several days. Po-210 exhibited similar behavior. Since the atmospheric flux of Po-210 is small, the elevated concentrations of Po-210 following a precipitation event may result from the mobilization of Po-210, in the dissolved form, from sediments.

Vertical profiles of dissolved Po-210, Pb-210, and Ra-226 were obtained from the Orca Basin, an anoxic, hypersaline and yet non-sulfide bearing basin. At the seawater-brine interface at 2230 m, a sharp maximum was observed in the profiles of Po-210 and Pb-210, reaching concentrations of 56.0 and 28.3 dpm/l00 kg, respectively. These are some of the highest values reported for the open ocean. These sharp maxima may be caused by a combination of the dissolution of hydrous manganese oxides and the decomposition of biogenic particulate material. Below the interface, concentrations decreased to ca. 9 and 6 dpm/100 kg, respectively. These concentrations are much higher than those observed in sulfide-bearing anoxic basins. The residence time of Pb-210 in the brine is estimated to be ca. 1 year.

DOI

10.25777/avna-s278

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