RESPONSE OF CALCAREOUS NANNOPLANKTON MORPHOLOGY TO ENVIRONMENTAL PERTURBATIONS: THE LATEST CENOMANIAN OCEANIC ANOXIC EVENT 2 AND LAB SIMULATIONS
Tesi di Dottorato
Data di Pubblicazione:
2015
Citazione:
RESPONSE OF CALCAREOUS NANNOPLANKTON MORPHOLOGY TO ENVIRONMENTAL PERTURBATIONS: THE LATEST CENOMANIAN OCEANIC ANOXIC EVENT 2 AND LAB SIMULATIONS / G. Faucher ; tutor: E. Erba ; coordinatore: E. Erba. DIPARTIMENTO DI SCIENZE DELLA TERRA "ARDITO DESIO", 2015 Feb 11. 27. ciclo, Anno Accademico 2014. [10.13130/faucher-giulia_phd2015-02-11].
Abstract:
Anthropogenic emissions of carbon dioxide into the atmosphere has indirectly driven acidification and reduced carbonate saturation of the oceans. Among calcareous plankton, coccolithophore algae are the major producers of pelagic CaCO3 in the modern ocean: they are direct contributors of the ocean biogeochemical cycles and climate system and, therefore, coccolithophore sensitivity to changes in surface water conditions is of major concern. Coccolithophores build around the cell an exoskeleton of calcite (coccosphere) that consists of single platelets called coccoliths and nannoliths. This phytoplanktonic group are affected by changes in surface water temperature, fertility, salinity, light and consequently are important instrument to A) predict the future state of the ocean, particularly its carbonate chemistry B) to reconstruct changes in past surface-water conditions. This PhD thesis is aimed to combine the geological and biological approaches, quantifying tempo and mode of coccolithophore response to specific combinations of stressing environmental conditions through investigation of a geological case history and laboratory experiments trying to simulate conditions of the past.
During the Aptian Oceanic Anoxic Event 1a (OAE 1a) an extreme global perturbation of the atmosphere-ocean system was documented, with evidence of geologically rapid warming associated to ocean fertility and acidification at global scale. Erba et al. (2010) demonstrated that calcareous nannoplankton was extremely sensitive to ocean acidification during OAE 1a, allowing separation of most-, intermediate-, and least-tolerant taxa. After a major calcification failure of heavily calcified forms, ephemeral coccolith dwarfism and malformation represent the most remarkable species-specific adjustments to survive surface water acidity.
The case history I focused on, is the latest Cenomanian Oceanic Anoxic Event 2 (OAE 2, ~ 94 Ma) which represents a profound perturbation of the ocean-atmosphere system caused by natural CO2 emissions related to the emplacement of the Caribbean Plateau causing climate change, ocean fertilization and acidification. The study was performed on pelagic sediments from five localities: Eastbourne (Sussex, United Kingdom), Clot de Chevalier (France), Novara di Sicilia (Sicily, Italy) and two Western Interior sections (Pueblo, Colorado and Cuba, Kansas, USA). These five sections have been chosen based on availability of integrated stratigraphy. In fact, they all have a good time control, especially C isotopic stratigraphy and biostratigraphy, that offers the opportunity to correlate data from the different localities, discriminating between local, regional and global changes. Moreover, the selected sections represent short and long-distance locations with respect to the Caribbean Plateau paleo-position.
Morphometric analyses were performed on selected calcareous nannofossil taxa namely Biscutum constans, Zeugrhabdotus erectus, Discorhabdus rotatorius and Watznaueria barnesiae. During OAE 2 calcareous nannoplankton responded to variations in surface-water fertility, temperature and CO2-induced acidification with a calcification decline in the form of a general size reduction of coccoliths. Calcareous nannoplankton, also, was affected by dwarfism in a species-specific way: in all the five analyzed sections B. constans shows the amplest size fluctuations through the event. D. rotatorius shows a well express reduction in size while Z. erectus displays the minor size decrease. W. barnesiae doesn’t show significant changes in mean coccolith size or in morphology (e.g. ellipticity).
Coccolith size fluctuations across OAE 2 are similar and synchronous in all the analyzed sections located at great distance in different oceans and settings.
Tipologia IRIS:
Tesi di dottorato
Keywords:
OAE2; Cenomanian-Turonian; calcareous nannofossils
Elenco autori:
G. Faucher
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