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Vertical diffusion rates determined by tritium tracer experiments in the thermocline and hypolimnion of two lakes 1, 2
Author(s) -
Quay P. D.,
Broecker W. S.,
Hesslein R. H.,
Schindler D. W.
Publication year - 1980
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.1980.25.2.0201
Subject(s) - thermocline , hypolimnion , tracer , diffusion , eddy diffusion , water column , geology , atmospheric sciences , chemistry , oceanography , turbulence , physics , meteorology , thermodynamics , nuclear physics , organic chemistry , nutrient , eutrophication
Vertical diffusion rates ( K ( K z ) were determined by measuring for several weeks the vertical spread of an injection of tritiated water into the thermoclines and hypolimnia of Lake 227 and Lake 224 in the Experimental Lakes Area (ELA) of northwestern Ontario. K z values of 5×10 −5 and 8×10 −4 cm 2 · s −1 were determined from the tracer experiments in the thermoclines of L227 and L224; in the hypolimnia, similar K z determinations of 1.7×10 −3 and 1.8×10 −2 cm 2 ·s −1 are 20−30 times greater than the thermocline rates. Vertical diffusion rates of heat were determined over the same time and depth intervals as the tracer experiments. In each lake, heat is diffusing vertically faster than mass in the thermocline and at more equal rates in the hypolimnion. The low K z values and the greater diffusion rate of heat than mass (tritium) indicate that molecular diffusion is important in determining the rate of vertical transport in the thermoclines of these highly stratified lakes. Vertical eddy diffusion rates ( K z ') determined by the tracer experiments show an inverse proportionality to the static stability of the water column (N 2 ), such that K z ′ ∝ (N 2 ) −0 · 8 . However, K z ′ values determined by measuring the hypolimnetic heating rates of eight ELA lakes (including L227 and L224) and three lakes outside ELA indicate that K z ′ ∝ (N 2 ) −0.44 . These observations suggest that in the absence of large shear where K z ′ < 10 −2 cm 2 · s −1 the vertical diffusion rates of mass and heat show different inverse correlations to the static stability of the water column.