Final Report Summary - ISMAGIC (Ice ages, Sea level, and Magmatism: Coupled oscillations) There is widespread recognition of the connectivity of different components of the Earth system, but many of these connections have not been studied. This is certainly true of connections between climate and the solid Earth. Glacial cycles move about 5x10^19 kg of water between continental ice sheets and the oceans, driving changes of ~100 m in average sea level (SL). The submarine mid-ocean ridge volcanic system, which constitutes 80% of global volcanism, is sensitive to these changes. The ERC project Ice Ages, Sea Level and Volcanism: Coupled Oscillations (ISMAGiC), studied the effects of varying SL on mid-ocean ridge volcanism. Melting beneath mid-ocean ridges occurs by pressure release, as solid mantle rock slowly upwells beneath the ridge. Variations in SL cause pressure changes in the rock too – at a level of about 10% of that due to upwelling. Theoretical models developed by the ISMAGiC team showed that glacial cycles and the associated SL variations affect melt production and volcanic output significantly, and that this should be observable in bathymetry and crustal thickness variations. While the former prediction has been generally accepted, the latter has touched off a debate in the scientific community, with some arguing that variation in magma supply cannot affect the topography of the sea floor, which is largely created by brittle faulting. But measurements of bathymetry show the fingerprint of glacial cycles. Whatever the outcome of this debate, we'll have learned a lot by the time it is resolved.The ISMAGiC project has gone further, to ask whether mid-ocean-ridge volcanism can have a feedback on glacial cycles. The mantle contains 1000–10000 times more CO2 than the atmosphere and ocean combined. Global variations in the flux of CO2 out of the mantle via mid-ocean ridges have the potential to affect global climate, which is sensitive to the concentration of CO2 in the atmosphere. Again using theoretical models, ISMAGiC showed that SL variations, while they drive variations in mantle melting at mid-ocean ridges, can also drive variations in the emission of CO2 from ridges by about 10% globally. Crucially, these changes would be delayed by about 50ka from the SL change that caused them. This allows them to act as a negative feedback on climate change. Climate models that have been adapted by ISMAGiC to study this possibility show that the effect is potentially significant and may explain a puzzling conundrum: why have ice ages appeared every ~100ka over the past ~1Ma, when orbital variations of 41ka seem to be the primary driver? ISMAGiC results suggest that the delayed feedback of mid-ocean ridges could encourage the ice-age oscillation to skip one or two beats of the orbital cycle and lock into a 100ka oscillation. Although this now appears plausible, it will require much more testing before it becomes accepted. If it proves to be true, it will represent a profound discovery and demonstrate that the climate system and the solid Earth are tightly coupled indeed!
