Supplementary materials for thesis "The trace element and lithium isotope composition of planktonic foraminifera"
This dataset comprises the files contained on a CD-ROM which was attached to the thesis when it was submitted in 2004. It was uploaded to ORDO in 2024 for preservation purposes. For more information, please refer to the thesis "The trace element and lithium isotope composition of planktonic foraminifera" via ORO.
Thesis abstract
Analysis of recent planktonic foraminifera indicates that, although species-specific offsets exist, they do record the d77Li value of modern seawater. A cleaning experiment and laser ablation ICP-MS analyses indicate that only lattice bound Li is being analysed.
The Li and Li isotope composition of Neogene seawater has been established by analysis of the Li/Ca ratio and d7Li value of ancient planktonic foraminifera recovered from ODP Sites 871, 872 (equatorial West Pacific) and 1264 (sub-tropical South Atlantic). The records from each site are remarkably similar despite different diagenetic histories.
These data indicate that the d7Li value of seawater increased from a minimum of ~26‰ around the Miocene climatic optimum to ~30‰ at ~8Ma. Since 8Ma, 7Li values have remained close to 30‰. Li/Ca ratios (normalised to Orbulina) are ~9.5 mol/mol between 19 and 14Ma, then decrease to ~6 mol/mol at 6Ma before increasing to the present day (~10.5 mol/mol).
Since other work indicates that the d7Li value of river water increases with decreasing weathering intensity, the data suggest that decreasing river water Li fluxes and an increasing seawater d7Li between 14 and 6Ma reflect a decrease in global weathering intensity. Furthermore, river water Li concentration appears to be sensitive to changes in silicate weathering, suggesting that silicate weathering was reduced in the interval 14 to 6Ma. This may explain the putative increase in atmospheric carbon dioxide at this time.
From 6Ma to the present, increases in the seawater Li concentration, while seawater d7Li remains relatively constant, suggest a global increase in the intensity and rate of silicate weathering. It is interesting to note that this occurs prior to the onset of northern hemisphere glaciation.
