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Studies of vertical mixing in the Southern California Bight with cosmogenic radionuclides 32 P and 7 Be
Author(s) -
Lee T.,
Barg E.,
Lal D.
Publication year - 1991
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1991.36.5.1044
Subject(s) - thermocline , eddy diffusion , radiogenic nuclide , geology , radionuclide , water column , nuclide , vertical mixing , mixing (physics) , isotope , oceanography , mixed layer , atmospheric sciences , mantle (geology) , turbulence , geophysics , meteorology , nuclear physics , physics , quantum mechanics
We measured concentrations of the two cosmogenic nuclides 32 P and 7 Be and radiogenic 234 Th in the Southern California Bight during June and October 1989 in water depths up to 80 m. The depth of the mixed layer was 18 and 28 m, respectively, and the thermocline was well developed. The depth profiles of 32 P are similar to an earlier profile in September 1987 but the column inventories are ∼5 times lower. 32 P activity is fairly uniform in the mixed layer and decreases monotonically with depth below it. On the other hand, 7 Be concentrations are nearly uniform to depths of 60–80 m. The integrated inventories of both dissolved 32 P and 7 Be are appreciably lower, by factors of 5–10, than their expected secular equilibrium concentrations for their mean oceanic injection rates. We show that the low inventories of 32 P and 7 Be are not due primarily to their decreased injection rates but rather to vertical mixing. The vertical eddy diffusivity and the consequent sustained new production based on upward NO 3 ‒ fluxes have been estimated as >7 cm s and ∼1 g C m ‒2 d ‒1 from the observed profiles of 7 Be, 32 P, and NO 3 ‒ .