研究業績

The solid earth plays a major role in controlling Earth’s surface climate. Volcanic degassing of carbon dioxide (CO2) and silicate chemical weathering are known to regulate the evolution of climate on a geologic timescale (>?106 yr), but the relationship between the solid earth and the shorter (<?105 yr) fluctuations of Quaternary glacial?interglacial cycles is still under debate. Here we show that the seawater osmium isotope composition (187Os/188Os), a proxy for the solid earth’s response to climate change, has varied during the past 300,000 years in association with glacial?interglacial cycles. Our marine Os isotope mass-balance simulation reveals that the observed 187Os/188Os fluctuation cannot be explained solely by global chemical weathering rate changes corresponding to glacial?interglacial climate changes, but the fluctuation can be reproduced by taking account of short-term inputs of (1) radiogenic Os derived from intense weathering of glacial till during deglacial periods and (2) unradiogenic Os derived from enhanced seafloor hydrothermalism triggered by sea-level falls associated with increases of ice sheet volume. Our results constitute the first evidence that ice sheet recession and expansion during the Quaternary systematically and repetitively caused short-term (<?105 yr) solid earth responses via chemical weathering of glacial till and seafloor magmatism. This finding implies that climatic changes on?<?105 yr timescales can provoke rapid feedbacks from the solid earth, a causal relationship that is the reverse of the longer-term (>?106 yr) causality that has been conventionally considered.