Eccesso di CO2 nel passato geologico: risposte del biota a cambiamenti globali di caldo estremo e acidificazione degli oceani

Anthropogenic burning of fossil fuels have introduced environmental stress that biota are forced to survive. The influence of CO2 concentration on global warming and seawater chemistry is thus subject of much scientific debate. The complex interplay between pCO2, climate change and instability, oceanic acidification and CaCO3 saturation still has to be fully understood, preventing reliable predictions of ecosystem responses. An enormous gap has separated the world of Environmental scientists who deal with time scales of day to decades, from that of Geoscientists, who think in thousands to millions of years: this has come to be an impediment to our understanding of climate and ecosystem behaviors. Understanding of the Earth system at time scales longer than human observations has become imperative, because anthropogenic activities are likely to telescope by order of magnitude the rates of climatic change that usually result from geologic processes.

The ocean is the oldest and largest ecosystem on Earth; global warming and ocean acidification are major threatens to biologic diversity and functioning of pelagic and neritic habitats. The Phanerozoic record clearly indicates that our planet has experienced similar conditions many times over geological times and sedimentary successions offer the possibility of analyzing episodes when the atmosphere and the ocean experienced pCO2 levels comparable or even higher than those projected by CO2 emission scenarios.

The general aim of our coordinated effort is to investigate the response of pelagic and carbonate platform ecosystems to paleoenvironmental perturbations associated with rapid CO2 addition to the atmosphere-ocean, and in particular to past episodes of global warming and ocean acidification: the Paleozoic-Mesozoic-Cenozoic history of planktonic and shallow-water calcifiers indicates that their biodiversity and evolution is intimately linked to the environment. We selected case-histories of past high-CO2 scenarios with geological evidence of climate change, environmental stress, biota adaptation and accelerated evolutionary rates. Specifically, we will investigate: (1) END PERMIAN- EARLY TRIASSIC (253-251 Ma); (2) TOARCIAN OAE (183-182 Ma); (3) EARLY APTIAN OAE1a (120-119 Ma); (4) LATEST CENOMANIAN OAE 2 (94-93 Ma); (5) PALEOGENE: (5a) PETM (~55.7 Ma); (5b) ETM2 (~53.7 Ma); ETM3 (~52.4 Ma); (5c) EECO (ca. 51-53 Ma) and post-EECO hyperthermals. For all these intervals there is evidence that extreme environmental changes impacted the oceanic biota but consequences on calcifying organisms remain to be fully understood. One of the key issues when looking at geological records is how to distinguish the effects of concurring agents of paleoenvironmental perturbation. To tackle this problem we will apply a full suite of biotic and geochemical proxies.

The integrated analyses of pelagic and shallow-water carbonates is designed to understand the reaction of calcifiers to excess CO2-induced global warming and ocean acidification in both pelagic and neritic habitats. To shed light on the relationship between these ecosystems, a crucial point is the application of high-resolution stratigraphies to obtain precise dating and correlations. A solid integrated stratigraphy and chronology is already available for some of the selected Permian through Paleogene pelagic and shallow water sections. The planned cyclostratigraphic analysis of complete sedimentary successions in Umbria-Marche and in the borehole to be drilled in Veneto will contribute significant results for the completion of the Paleogene Astronomical Time Scale. The main objectives of the proposed research are to: 1) date and quantify the response of calcareous plankton and shallow-water carbonate communities to global change and in particular to ocean acidification; 2) quantify the evolutionary trends of planktic and benthic calcifiers in time intervals of perturbed environmental conditions; 3) verify the sinchroneity/diachroneity of responses; 4) discriminate between adaptative morphologies, malformations and evolutionary changes; 5) date environmental variations with highest precision to estimate time-lags or coincidence between evolutionary trends and oceanic-climatic changes.

We aim at understanding the role of calcifiers evolution in the marine ecosystem. Also, we aim at modeling: a) the species-specific responses to high-pCO2, oceanic acidification and extreme climates, b) functioning during perturbation, c) variations during recovery phases, especially after acidification climax. From a very broad perspective, the overarching goal of the research is to understand if different causes may have solicited analogous responses at different times. The comparison of the various study intervals will point out if consequences are repetitive or specific of individual cases, providing potential means of validations of future predictions.