Extreme sup 13 C depletions in seawater-derived brines and their implications for the past geochemical carbon cycle

Journal Article · Sat Dec 01 00:00:00 EST 1990 · Geology; (USA)

DOI:https://doi.org/10.1130/0091-7613(1990)018<1191:ECDISD>2.3.CO;2· OSTI ID:5679952

Lazar, B; Erez, J ^[1]

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1. Hebrew Univ. of Jerusalem (Israel)

Extreme depletions in the {sup 13}C content of the total dissolved inorganic carbon (C{sub T}) were found in brines overlying microbial mat communities. Total alkalinity (A{sub T}) and C{sub T} in the brines suggest that intense photosynthetic activity of the microbial mat communities depletes the C{sub T} from the brine. The authors suggest that this depletion drives a large, kinetic, negative fractionation of carbon isotopes similar to that observed in highly alkaline solutions. In brines of extreme salinity where microbial mat communities no longer exist, the {sup 13}C content of the C{sub T} increases, probably because photosynthesis no longer dominates the gas-exchange processes. This mechanism explains light carbon-isotope compositions of carbonate rocks from evaporitic sections and bears on the interpretation of {delta}{sup 13}C values in bedded stromatolitic limestones that are ca. 3.5 b.y. old.

• OSTI ID: 5679952
• Journal Information: Geology; (USA), Vol. 18:12; ISSN 0091-7613
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CARBON CYCLE
GEOLOGIC HISTORY
BRINES
CARBON
CARBON 13
CARBONATE ROCKS
GEOCHEMISTRY
ISOTOPE RATIO
LIMESTONE
LOSSES
MICROORGANISMS
PH VALUE
PHOTOSYNTHESIS
SALINITY
SEAWATER
CARBON ISOTOPES
CHEMICAL REACTIONS
CHEMISTRY
ELEMENTS
EVEN-ODD NUCLEI
HYDROGEN COMPOUNDS
ISOTOPES
LIGHT NUCLEI
NONMETALS
NUCLEI
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
ROCKS
SEDIMENTARY ROCKS
STABLE ISOTOPES
SYNTHESIS
WATER
580000* - Geosciences