Li Isotope Constraints on Meltwater Plume and Ocean Stratification after the Marinoan Snowball Earth скачать в хорошем качестве

Li Isotope Constraints on Meltwater Plume and Ocean Stratification after the Marinoan Snowball Earth

Lithium Isotope Constraints on Meltwater Plumes and Ocean Stratification after the Marinoan Snowball Earth Tian Gan University of Maryland The termination of the Marinoan Snowball Earth (~635 Ma) marks a profound reorganization of Earth’s climate and ocean chemistry. Rapid deglaciation likely delivered large volumes of continental meltwater into an ocean where the seawater had evolved beneath global ice cover, potentially producing a transient (~104 years), chemically stratified “Plumeworld” ocean. In this talk, I will present new lithium isotope (δ7Li) data from Marinoan cap dolostones across a nearshore–offshore transect on the Yangtze Platform, South China, to test this hypothesis. Lithium isotopes are well-suited for tracing meltwater input and weathering processes because they fractionate strongly during chemical weathering and are insensitive to biological and redox effects. The data reveal a systematic decrease in δ7Li from shelf to slope environments, opposite to trends observed in the modern ocean. To interpret these patterns, I integrate the observations with a lithium isotope mass-balance model, which indicates that during the synglacial period, weak continental chemical weathering combined with strong reverse weathering on the seafloor drove seawater δ7Li to low values. Following deglaciation, the delivery of isotopically heavy riverine lithium by continental meltwater generated a pronounced nearshore–offshore δ7Li gradient. Together, these results provide geochemical support for a stratified Plumeworld ocean in the aftermath of the Marinoan Snowball Earth.