Hydrological control of river and seawater lithium isotopes.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 35688840.
- Also identified by DOI 10.1038/s41467-022-31076-y and PMC identifier 9187753.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Seawater lithium isotopes (δ<sup>7</sup>Li) record changes over Earth history, including a ∼9‰ increase during the Cenozoic interpreted as reflecting either a change in continental silicate weathering rate or weathering feedback strength, associated with tectonic uplift. However, mechanisms controlling the dissolved δ<sup>7</sup>Li remain debated. Here we report time-series δ<sup>7</sup>Li measurements from Tibetan and Pamir rivers, and combine them with published seasonal data, covering small (<10<sup>2</sup> km<sup>2</sup>) to large rivers (>10<sup>6</sup> km<sup>2</sup>). We find seasonal changes in δ<sup>7</sup>Li across all latitudes: dry seasons consistently have higher δ<sup>7</sup>Li than wet seasons, by -0.3‰ to 16.4‰ (mean 5.0 ± 2.5‰). A globally negative correlation between δ<sup>7</sup>Li and annual runoff reflects the hydrological intensity operating in catchments, regulating water residence time and δ<sup>7</sup>Li values. This hydrological control on δ<sup>7</sup>Li is consistent across climate events back to ~445 Ma. We propose that hydrological changes result in shifts in river δ<sup>7</sup>Li and urge reconsideration of its use to examine past weathering intensity and flux, opening a new window to reconstruct hydrological conditions.