Soil formation and weathering over the past 60 kyr reconstructed using lithium isotopes from Maar records

Chemical weathering of silicate rocks is a fundamental control on the carbon cycle, although on timescales shorter than a few tens of kyr, transient carbon storage becomes more important. However, weathering can still act as an amplifier or inhibitor of the carbon cycle on these timescales. Further, weathering produces soils, a storage reservoir of carbon, although the rate at which soils can be produced is likely highly variable, and remains uncertain. Here, we use lithium isotopes in laminated maar sediments from western Germany to examine weathering and soil formation rates, principally across the rapid warming transitions of Greenland Interstadials (GI), also known as Dansgaard Oeschger (D/O) events, and rapid cooling of Greenland Stadials (GS). Our principal finding is that Li isotope ratios are higher during cooler periods, both on glacial-interglacial and GI-GS event scales. Thus, δ 7 Li values average −2.5 ± 1.6‰ during GI events, and −1.5 ± 1.5‰ in the intervening colder stadial events. Based on the evolution of Li isotopes with weathering, this suggests that there was more soil formation relative to primary mineral dissolution during cooler compared to warmer events. That is not to say that weathering rates were higher, but that clay formation was amplified relative to a given weathering rate when it was cooler, due to the combination of lower erosion rates, thermodynamically favoured conditions for clay formation, and enhanced water–rock contact times, promoting secondary mineral formation. Overall, the data show that soil formation responds even through rapid (∼100 years) climate change events.