Time：13:30-15:00, 26th November (Monday)
Venue： Lecture Hall 221, ISESS (Building No. 16), Tianjin University
Speaker：Doctor Zhou Xiaoli
Abstract：Cenozoic climate has transitioned from a warmhouse to an icehouse, manifest as decreasing seawater temperature and atmospheric pCO2. What caused the changes in temperature and pCO2, however, has not been fully resolved. Since ocean chemistry is tightly coupled with global carbon cycle on multi-million-year timescale, studies on ocean chemistry can provide potentials to understand long-term changes in carbonate system including pCO2. Major ion concentrations such as Mg and Ca concentrations in seawater ([Mg]sw and [Ca]sw) presumably have changed over the Cenozoic, but existing proxies yielded inconsistent [Mg]sw and [Ca]sw records. To resolve this problem, here I propose to use Na/Ca in foraminifera as a proxy for [Ca]sw. This proxy is testified by culture experiments and core-top samples. The downcore Na/Ca records of three species of foraminifera are generated from multiple locations in the Atlantic and Pacific Ocean. A generally increasing trend in the Na/Ca records suggests a monotonic decrease in [Ca]sw and increase in (Mg/Ca)sw since Eocene. Such a long-term change in [Ca]sw and (Mg/Ca)sw may be a result of coupled changes in continental weathering and hydrothermal flux. High [Ca]sw suggests low carbonate ion concentration ([CO32-]) in the early Cenozoic, which may have the potential to sustain high pCO2 at that time.
