Sr-Nd Isotopes for Weathering Studies

Continental weathering is an important part of the global carbon cycle. Material eroded from rock at the earth’s surface is transported through river systems and eventually to the ocean, where it is deposited within benthic sediments, serving as an important CO2 sink. Due to the intimate link between weathering and CO2 flux, significant research has been focussed on reconstructing the causes and consequences of erosion activity within major river systems. 

The measurements of strontium (87Sr/86Sr) and neodymium (143Nd/144Nd) isotopes have been especially important in this research domain. The signature of Sr and Nd isotopes are analogous in both the solid rock and the dissolved phase, allowing one to trace the source of erosion (i.e. the rock in question) and tie it to the movement of sediment through a river system, to the eventual accumulation on the seafloor. The Sr and Nd radiogenic isotopes are particularly useful in this method due to the fact that they remain in relatively constant composition through time, as they do not undergo fractionation as readily as other more common isotopes.

Since Sr and Nd isotopes are accurate tracers of rock origin, they are also used to trace the origin of soils as well as overlying vegetation – providing a proxy for paleodiets and migration. 

Read more about Sr-Nd-Hf geochemistry

Read more about the application of Sr isotopes in provenancing and forensics

Strontium isotopes measured in marine barite
Figure 1. Strontium isotopes (87Sr/86Sr, δ88/86Sr) measured in marine barite (BaSO4) used to estimate the origin and deposition rate of weathered rock in the ocean. In this research, Paytan et al. (2021) revealed how oceanic strontium sources and sinks changed over the past 35 million years. 

References

Paytan, A., Griffith, E.M., Eisenhauer, A., Hain, M.P., Wallmann, K. and Ridgwell, A., (2021). A 35-million-year record of seawater stable Sr isotopes reveals a fluctuating global carbon cycle. Science, 371(6536), pp.1346-1350. DOI: 10.1126/science.aaz9266