Lithium isotope composition of Quaternary and Tertiary biogene carbonates and a global lithium isotope balance

The lithium isotope composition of thirty-nine foraminifera samples and twenty-one carbonate oozes from the Atlantic and the Indian oceans (0 to 81 Ma) has been determined by thermionic mass spectrometry. Using ocean water as external standard, Lithium isotope variations of about 40 parts per thousand have been observed. Holocene foraminifera samples possess a well-defined mean lithium isotope composition of +13 parts per thousand relative to ocean water, whereas Tertiary foraminifera show a total variation range from -10 to +30 parts per thousand. This variability of the lithium isotope signature may be interpreted as reflecting shifts in the paleo-ocean water composition, although the influence of diagenetic effects cannot totally be excluded. In a steady state system variations of the lithium input to the ocean cannot cause shifts in the delta(6)Li of ocean water exceeding 15 parts per thousand. To match the mean variation range observed in foraminifera, a nonsteady-state ocean has to be assumed and that the input fluxes varied by about a factor of 2 throughout time. Copyright (C) 1997 Elsevier Science Ltd.