Determination of the lithium isotopic composition of planktic foraminifera and its application as a paleo-seawater proxy

Jenney M. Hall, L. H. Chan, William F. McDonough, Karl K. Turekian

Research output: Contribution to journalArticlepeer-review

50 Citations (Scopus)

Abstract

To investigate the potential use of Li isotopes in foraminifera as a paleo-lithium seawater proxy, the Li isotopic compositions of planktic foraminifera (Orbulina universa, Globigerinoides sacculifer, Globorotalia menardii, and Globorotalia truncatulinoides) were determined by thermal ionization mass spectrometry (TIMS), using phosphate as an ion source, and multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). Rigorous cleaning procedures were employed to purify foraminiferal tests of detrital, metal oxide, and organic phases in single species analyses. Data generated using both methods reveal that δ7Li in planktic foraminifera resemble seawater such that the isotopic fractionation from the precipitation of foraminiferal calcite appears to be minimal. Down-core measurements indicate that the δ7Li of O. universa has remained constant over the last 44 ka in the North Atlantic, suggesting little change of Li isotopic composition of ocean water during the last glaciation, consistent with the long mean residence time of Li. Results suggest that planktic foraminifera may provide a reliable record of the lithium isotopic composition of ocean water in the past. The first measurements of seawater δ7Li from the Indian Ocean average 33.0 ± 1.2‰ (2σ) throughout the water column. This value is within error of values previously reported for the Atlantic and Pacific Oceans as is expected based on the long mean residence time of Li in the ocean. There is no evidence for a significant decrease in Li/Cl ratios, as reported by some workers, with Indian Ocean waters averaging 9.10 ± 0.11 μg/g.

Original languageEnglish
Pages (from-to)255-265
Number of pages11
JournalMarine Geology
Volume217
Issue number3-4
DOIs
Publication statusPublished - 2005 Jun 15
Externally publishedYes

Keywords

  • Indian Ocean
  • Lithium isotopes
  • North Atlantic
  • Planktic foraminifera
  • Sea water
  • δLi

ASJC Scopus subject areas

  • Oceanography
  • Geology
  • Geochemistry and Petrology

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