Hydrological control of river and seawater lithium isotopes

Abstract

Seawater lithium isotopes (δ7Li) 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 δ7Li remain debated. Here we report time-series δ7Li measurements from Tibetan and Pamir rivers, and combine them with published seasonal data, covering small (<102 km2) to large rivers (>106 km2). We find seasonal changes in δ7Li across all latitudes: dry seasons consistently have higher δ7Li than wet seasons, by −0.3‰ to 16.4‰ (mean 5.0 ± 2.5‰). A globally negative correlation between δ7Li and annual runoff reflects the hydrological intensity operating in catchments, regulating water residence time and δ7Li values. This hydrological control on δ7Li is consistent across climate events back to ~445 Ma. We propose that hydrological changes result in shifts in river δ7Li and urge reconsideration of its use to examine past weathering intensity and flux, opening a new window to reconstruct hydrological conditions.

Subaerial volcanism broke mid-Proterozoic environmental stasis

“…The magnitudes of detrital δ 7 Li excursions are closely linked to paleotopography and surface runoff flux ( 61 ). Modern comparisons of riverine δ 7 Li across diverse geomorphic settings reveal that rivers draining flat lowlands at middle and high latitudes exhibit higher δ 7 Li values (associated with intermediate W/D) compared to those originating from mountainous regions (characterized by low W/D) ( 61 , 62 ).…”

“…The magnitudes of detrital δ 7 Li excursions are closely linked to paleotopography and surface runoff flux ( 61 ). Modern comparisons of riverine δ 7 Li across diverse geomorphic settings reveal that rivers draining flat lowlands at middle and high latitudes exhibit higher δ 7 Li values (associated with intermediate W/D) compared to those originating from mountainous regions (characterized by low W/D) ( 61 , 62 ). Another explanation for the detrital δ 7 Li excursion involves secondary materials primarily formed from surface and, more likely, pore waters within the catchment area, adsorbing Li from various sources.…”

Weathering Incongruence in Mountainous Mediterranean Climates Recorded by Stream Lithium Isotope Ratios

“…A recent isotope-enabled RTM suggested that fluid travel times exert an influential control over the extent of secondary mineral formation within a given system and thus the resulting fluid δ 7 Li composition (Winnick et al, 2022). This inference is empirically supported by hydrologic sensitivity in δ 7 Li over a global assessment of seasonal river Li signatures, illustrating a consistent negative correlation between annual runoff and fluid δ 7 Li across a range of spatial and temporal scales (F. Zhang et al, 2022). These studies imply a variety of intermediate weathering intensity environments and the capacity for RTMs embedding the lithium isotope system to offer quantitative and predictive frameworks for these settings.…”

An efficient Li dual-column system and high-precision Li isotope measurement of high matrix and low-Li samples by MC-ICP-MS

“…1–4 Lithium and its isotopes are useful tracers for chemical weathering, clay formation, and hydrothermal alteration as well as cosmochemistry processes. 5–11 Over the last decade, emerging studies have been focused on using marine carbonates as Li isotope archives to shed light on climate change, chemical weathering and clay formation in the Earth's history. 6,8,11–32 Although analytical methods to determine Li isotope ratios have been well developed using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), existing methods are often challenged by carbonates and other high matrix and low-Li samples like seawater, hydrothermal fluids, and altered oceanic crust.…”