Multi-proxy reconstruction of seawater chemistry across K-Pg boundary; tracking weathering feedbacks in response to extreme carbon cycle perturbation

Author(s): Misra, S.; Elderfield, H.
Author Affiliation(s): Primary:
University of Cambridge, Cambridge, United Kingdom
Volume Title: AGU 2014 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2014; American Geophysical Union 2014 fall meeting, San Francisco, CA, Dec. 15-19, 2014. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: On geologic time scales concentrations of atmospheric CO2, a greenhouse gas and critical mediator of Earth's surface temperature and climate, is thought to be controlled by a balance between CO2 input from mantle degassing through volcanism and metamorphism and consumption via temperature-sensitive chemical weathering of tectonically uplifted continental rocks. This interplay between global climate and tectonic uplift also controls the delivery of cations to the oceans. Hence, past changes in seawater chemistry provide a powerful archive of the interplay and feedback between climate and tectonics. Mass Extinction Events, like that at K-Pg boundary, are characterized by rapid, global Carbon Cycle Perturbations either from increased mantle degassing or by incineration of the continents due to extra-terrestrial impact. It is hypothesized that enhanced chemical weathering of continental silicate rocks consumes this excess CO2 and restores steady-state. Lithium, B, and Mg are conservative ions in seawater that are isotopically homogeneous with a residence time much longer than the oceanic mixing time. As a result, δ7LiSW, δ11BSW, and δ26MgSW, recorded by marine calcites reflect a global picture and secular variations in isotopic composition of these elements within periods shorter than their residence time must thus reflect imbalances between the sources and sinks of these elements to and from the ocean. Cenozoic δ7LiSW shows an abrupt 5 ppm drop across the K-Pg boundary, simultaneous with the seawater Ir and Os isotope spikes. This rapid decrease in δ7LiSW is due to a large instantaneous delivery of isotopically light Li to the oceans and cannot be produced by an impactor nor by Deccan trap volcanism, suggesting large-scale continental denudation. We will create high-resolution δ7LiSW, δ11BSW, and δ26MgSW records across K-Pg boundary using planktonic and benthic foraminifera from multiple ODP/DSDP sites to quantify the amount of C excursion and the response of continental weathering feedbacks to regain climatic steady states. This multi-proxy approach will help quantify the extent of CCP; time scale and magnitude of continental chemical weathering response; and the contribution of both carbonate rock and silicate rock weathering in CO2 drawdown across carbon cycle excursion episodes.
Year of Publication: 2014
Research Program: DSDP Deep Sea Drilling Project
ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Carbon; Carbon cycle; Cenozoic; Cretaceous; Deep Sea Drilling Project; Geochemical cycle; K-T boundary; Lower Paleocene; Marine sediments; Mesozoic; Ocean Drilling Program; Paleocene; Paleogene; Sediments; Stratigraphic boundary; Tertiary; Upper Cretaceous
Record ID: 2015117272
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by, and/or abstract, Copyright, American Geophysical Union, Washington, DC, United States

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