Carbon geochemistry of marine-derived brines: I. sup 13 C depletions due to intense photosynthesis
- Hebrew Univ., Elat (Israel)
- Hebrew Univ., Jerusalem (Israel)
The study was conducted in the evaporation pans of a solar salt production plant (simulated sabkha environment) in which ca. 50% of the evaporation area is dominated by microbial mat communities (MMC). MMC are the modern equivalents of fossil stromatolites as old as Early Archean; hence, investigation is relevant to the research of the ancient carbon cycle. Total dissolved CO{sub 2} (C(T)) decreases by ca. 50% of its original value as brine concentration increases from 1.5 to 4 times mean seawater. Roughly 70% of the original total alkalinity is precipitated as calcium carbonate at this salinity range. The relations between total alkalinity A(T) and C(T) (both normalized to salinity) suggest that the brines are depleted in C(T) by up to 50% with respect to equilibrium with atmospheric CO{sub 2}. This large C(T) deficit is driven by the intense photosynthetic activity of the MMC. Considerable depletion in {sup 13}C was observed despite the photosynthetic activity which normally causes a {sup 13}C enrichment of C(T). {delta}{sup 13}C(T) values down to {minus}9{per thousand} were observed in brine concentration range of 2 to 6 times mean seawater. Mass balance calculation is compatible with the suggested mechanism of chemically enhanced atmospheric invasion of {sup 12}C enriched CO{sub 2}. This kinetic isotope fractionation may serve as an alternative explanation to that of fresh water runoff for some negative {delta}{sup 13}C values of laminated carbonates from evaporitic sections found in the geological record. In addition, at least part of the large scatter observed in the {delta}{sup 13}C vs. age curve for carbonates and organic matter from Precambrian stromatolitic environments may be explained by this mechanism rather than by late metamorphism and maturation processes.
- OSTI ID:
- 7235654
- Journal Information:
- Geochimica et Cosmochimica Acta; (United States), Vol. 56:1; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CARBON
GEOCHEMISTRY
ATMOSPHERIC CHEMISTRY
BRINES
CALCIUM CARBONATES
CARBON 12
CARBON 13
CARBON CYCLE
CARBON DIOXIDE
DENSITY
ENRICHMENT
EXPERIMENTAL DATA
GEOLOGIC HISTORY
GEOLOGIC MODELS
MASS BALANCE
METHANE
MICROORGANISMS
OXIDATION
PH VALUE
PHOTOSYNTHESIS
PRECIPITATION
SALINITY
SULFATE-REDUCING BACTERIA
ALKALINE EARTH METAL COMPOUNDS
ALKANES
BACTERIA
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBON ISOTOPES
CARBON OXIDES
CARBONATES
CHALCOGENIDES
CHEMICAL REACTIONS
CHEMISTRY
DATA
ELEMENTS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
HYDROCARBONS
INFORMATION
ISOTOPES
LIGHT NUCLEI
NONMETALS
NUCLEI
NUMERICAL DATA
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHYSICAL PROPERTIES
SEPARATION PROCESSES
STABLE ISOTOPES
SYNTHESIS
580000* - Geosciences