Mathematics – Logic
Scientific paper
Dec 1972
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1972gecoa..36.1337h&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 36, Issue 12, pp.1337-1357
Mathematics
Logic
14
Scientific paper
A suite of 101 surface waters from the Mackenzie River drainage basin, Canada, was collected mainly during a 3-week period in the summer of 1969 and represents an instant in time during a period of average flow for most rivers in the basin. Stable isotopes of oxygen ( 18 O / 16 O ) were determined on all these waters. Regional variations of 18 O , when compared to the distribution of both runoff as a percentage of total precipitation and of mean summer daily isotherms, suggests that the main factors controlling the 18 O content of these surface waters are the amount of evaporation to which they are subjected during both precipitation and runoff. Factor analysis was used to evaluate the relations among 14 chemical variables and the stable isotope ratio of carbon ( 13 C / 12 C ) in dissolved bicarbonate for 67 samples of surface water. We interpret the results in terms of a source of pre-existing bicarbonate from the weathering of minerals with a subsequent dominant isotope effect due to exchange of carbon isotopes with biogenic carbon dioxide--which effectively masks the carbon isotopic composition of the pre-existing bicarbonate except as revealed by factor analysis. The ratio of stable isotopes of sulphur ( 34 S / 32 S ) in dissolved sulphate was measured on 52 surface waters, which fall naturally into three major groups according to the geology of the sub-basins: 1. (1) evaporites exposed or influenced by saline springs; 2. (2) Paleozoic strata (with or without igneous rocks); 3. (3) marine Cretaceous rocks. The first two groups are characterized by positive 34 S values with variable contents of sulphate indicating a source of sulphate from gypsum, and the third group by negative 34 S values with low contents of sulphate probably indicative of the effects of microbiological fractional ion. However, microbial fractionation of sulphur isotopes is not dominant to the extent that we are unable to relate our data in the aqueous environment to geological source materials. These results indicate the extreme complexity of that portion of the hydrosphere of western Canada that has been examined and considerably more work on stable isotopes is justified.
Hitchon Brian
Krouse Roy H.
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