Atmospheric carbon dioxide is a primary driver of global temperature change, but the efforts to decrease the anthropogenic emissions from fossil fuel burning are failing. The rates of fossil fuel CO2 emissions are increasing up to 3.7% per year in the following decade, resulting in a perturbation to the carbon cycle that have no precedent in geological records. During the past 65 Myr, the Earth experienced different carbon cycle perturbations associated with large climate variations, including the transition from an ice-free planet to the onset of the Pleistocene glacial¿interglacial cycles. Volcanic activity can modify the ocean-atmosphere system by introducing gases and particulates, promoting warmer or cooler climates and perturbing the structure and chemistry of the oceans. In the fossil record, carbon cycle perturbations are recorded in the stable carbon isotope composition of carbonate rocks and organic matter. This perturbation is recorded as a C isotope excursion. The shallow carbon cycle is also strictly connected with a deep cycle, involving upper mantle dynamics, even less understood from the scientific community.
This project follows an interdisciplinary approach to analyse product of the processes linked to the climate changes and carbon cycle perturbations occurred between the middle Eocene and the Miocene. Two are the main goals of this project: 1) to individuate the processes occurring during the main climate transition starting from carbon and calcium isotope excursion and changes in the carbonate production in the shallow water domain; 2) to clarify the origin of the Ca- and CO2-rich magma origin to distinguish the involvement of carbon in terms of deep or shallow cycles.
The global perturbations of the carbon cycle are generally associated with abrupt climatic changes and extreme palaeonvironmental crises. These events, caused by natural increases of atmospheric CO2, are of great interest because they are used models to test and predict the global changes produced by the anthropogenic CO2 emissions. Approximately one third of the CO2 liberated into the atmosphere from anthropogenic activity is transferred into the oceans where it reacts to form carbonic acid causing an increase of the pH and a decrease of the carbonate saturation of the ocean. Detrimental effects on the shells of calcifying organisms have been tested in the laboratory. However, these tests suffer of the spatio-temporal limits of laboratory manipulations. On the contrary, field observations of living marine communities, the long-term impact on marine ecosystems and the adaptive potential of marine fauna and flora are best investigated by looking at the geological record of past episodes of ocean acidification. One of the goals of this project, is to understand the changes in carbonate productions by investigating the shallow water and pelagic carbonate successions. Consequently, we will approach the study of C-perturbation starting from the classical facies analysis followed by biostratigraphic analysis, isotope stratigraphy and detailed petrographic characterization of volcanic activity. This project displays the potential to observe the response of marine carbonate producing biota to the global perturbation, to analyze the impact of the perturbation on the sedimentary record and on the stable isotope signal.
In this project an integrated isotope (C, O, Sr and Ca) stratigraphy will be performed. The oxygen isotope signature of succession allows reconstructing a combined ice volume and temperature effect plus a local salinity record in their oxygen isotope signature. The carbon isotopic composition of marine carbonates serves as excellent source of information on past fertility of seawater, recording a history of changing ocean chemistry, productivity and pCO2. The strontium isotopes are widely used to correlate and to integrate the biostratigraphy. Lastly, Ca isotopes represent an innovative approach to reconstruct seawater carbonate chemistry, being this systematics particularly sensitive to ocean acidification. Indeed, the dissolution of deep-marine carbonate sediments coincides with a negative excursion in ¿44¿40Ca.
From the igneous petrological point of view, an alternative - fuzzy - approach will be adopted. Indeed, the idea of our team is to propose for the ULUD volcanic districts not a model based on a carbonatite-yes or carbonatite-no choice. Our aim is to distinguish the primary carbonate component in this small but extremely peculiar district, from that likely associated to secondary limestone and dolostones assimilation by a carbonated silicatic mantle
Last not least, the strength of this project is the interdisciplinary approach. Having two different, specialized teams working in parallel paths provides a unique opportunity to focus independently on the study of the carbonate successions and the shallow- to deep-carbon cycle. The integrated structural, stratigraphic, paleontological, petrographic, mineralogical and geochemical approach of several case studies, in collaboration with Italian and foreign top researchers with different expertise will certainly receive a very positive feedback.