The silicon cycle impacted by past ice sheets

Globally averaged riverine silicon (Si) concentrations and isotope composition (δ 30 Si) may be affected by the expansion and retreat of large ice sheets during glacial−interglacial cycles. Here we provide evidence of this based on the δ 30 Si composition of meltwater runoff from a Greenland Ice Sheet catchment. Glacier runoff has the lightest δ 30 Si measured in running waters (−0.25 ± 0.12‰), significantly lower than nonglacial rivers (1.25 ± 0.68‰), such that the overall decline in glacial runoff since the Last Glacial Maximum (LGM) may explain 0.06–0.17‰ of the observed ocean δ 30 Si rise (0.5–1.0‰). A marine sediment core proximal to Iceland provides further evidence for transient, low-δ 30 Si meltwater pulses during glacial termination. Diatom Si uptake during the LGM was likely similar to present day due to an expanded Si inventory, which raises the possibility of a feedback between ice sheet expansion, enhanced Si export to the ocean and reduced CO 2 concentration in the atmosphere, because of the importance of diatoms in the biological carbon pump.