Isotopic fingerprints of anthropogenic molybdenum in lake sediments

Anthony Chappaz, Timothy W. Lyons, Gwyneth Gordon, Ariel Anbar

Research output: Contribution to journalArticle

24 Citations (Scopus)

Abstract

We measured the molybdenum isotope compositions (δ98Mo) of well-dated sediment cores from two lakes in eastern Canada in an effort to distinguish between natural and anthropogenic contributions to these freshwater aquatic systems. Previously, Chappaz et al.1 ascribed pronounced 20th-century Mo concentration enrichments in these lakes to anthropogenic inputs. δ98Mo values in the deeper sediments (reflecting predominantly natural Mo sources) differ dramatically between the two lakes: -0.32 ± 0.17‰ for oxic Lake Tantare and +0.64 ± 0.09‰ for anoxic Lake Vose. Sediment layers previously identified as enriched in anthropogenic Mo, however, reveal significant δ98Mo shifts of ±0.3‰, resulting in isotopically heavier values of +0.05 ± 0.18‰ in Lake Tantare and lighter values of +0.31 ± 0.03‰ in Lake Vose. We argue that anthropogenic Mo modifies the isotopic composition of the recent sediments, and we determine δ 98Moanthropogenic values of 0.1 ± 0.1‰ (Lake Vose) and 0.2 ± 0.2‰ (Lake Tantare). These calculated inputs are consistent with the δ98Mo of molybdenite (MoS2) likely delivered to the lakes via smelting of porphyry copper deposits (Lake Vose) or through combustion of coal and oil also containing Mo (Lake Tantare). Our results confirm the utility of Mo isotopes as a promising fingerprint of human impacts and perhaps the specific sources of contamination. Importantly, the magnitudes of the anthropogenic inputs are large enough, relative to the natural Mo cycles in each lake, to have an impact on the microbiological communities.

Original languageEnglish (US)
Pages (from-to)10934-10940
Number of pages7
JournalEnvironmental Science and Technology
Volume46
Issue number20
DOIs
StatePublished - Oct 16 2012

Fingerprint

Molybdenum
molybdenum
Lakes
lacustrine deposit
Sediments
lake
Isotopes
isotope
sediment
Copper deposits
molybdenite
Coal
smelting
Smelting
porphyry
anthropogenic effect
Chemical analysis
sediment core
isotopic composition
combustion

ASJC Scopus subject areas

  • Chemistry(all)
  • Environmental Chemistry

Cite this

Isotopic fingerprints of anthropogenic molybdenum in lake sediments. / Chappaz, Anthony; Lyons, Timothy W.; Gordon, Gwyneth; Anbar, Ariel.

In: Environmental Science and Technology, Vol. 46, No. 20, 16.10.2012, p. 10934-10940.

Research output: Contribution to journalArticle

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