The silicon cycle impacted by past ice sheets

Globally averaged riverine silicon (Si) concentrations and isotope composition (delta Si-30) 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 delta Si-30 composition of meltwater runoff from a Greenland Ice Sheet catchment. Glacier runoff has the lightest delta Si-30 measured in running waters (-0.25 +/- 0.12 parts per thousand), significantly lower than nonglacial rivers (1.25 +/- 0.68 parts per thousand), such that the overall decline in glacial runoff since the Last Glacial Maximum (LGM) may explain 0.06-0.17 parts per thousand of the observed ocean delta Si-30 rise (0.5-1.0 parts per thousand). A marine sediment core proximal to Iceland provides further evidence for transient, low-delta Si-30 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 CO2 concentration in the atmosphere, because of the importance of diatoms in the biological carbon pump.