Sea level fluctuations and silicate weathering dynamics over 450 kyr: Insights from lithium isotopes in South China sea sediments

Abstract

Silicate weathering is a key regulator of Earth's long-term carbon cycle and climate. While the influence of climate on weathering intensity is well recognized, the extent of its variability on glacial–interglacial timescales, particularly in low-latitude regions, remains poorly constrained. Here we present lithium (δ⁷Li), strontium (Sr), and neodymium (Nd) isotope data from the clay-sized siliciclastic fraction of core MD 05–2901, recovered around 200 km from the coast of central Vietnam in the South China Sea (SCS), to reconstruct silicate weathering mecanisms over the past 450 kyr. The record spans 12 marine isotope stages, capturing multiple glacial–interglacial cycles. δ⁷Li values of the silicate fraction range from −1.3 ‰ to +0.9 ‰ (2SD = 0.3 ‰) and display systematic glacial–interglacial variability, with negligible influence from grain size or diagenetic alteration. Lower δ⁷Li values (mean = −1.0 ± 0.3 ‰) occur in kaolinite-rich intervals, indicating intensified silicate weathering during glacials, likely linked to enhanced secondary mineral exchange and greater organic matter incorporation. We suggest that sea-level lowstands (∼50 m below interglacial levels) exposed continental shelves, promoting intense chemical weathering. Our results demonstrate that Li isotopes serve as a robust tracer of silicate weathering intensity on orbital timescales, assuming stable sediment provenance, and highlight the role of sea-level fluctuations in modulating weathering processes and secondary mineral formation in shelf environments.