Did ocean warming, acidification or saturation state control coccolithophorids production through time ?

• Main Author: Menini, Alessandro
• Other Authors: Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement (LGL-TPE), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), Université de Lyon, Emanuela Mattioli, Guillaume Suan
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2020
• Subjects: PETM; Calcareous nannofossils; Biostratigraphy; Pelagic carbonate production; Carbon cycle; Calcium cycle; Paleoceanography; T-OAE; Nanofossiles calcaires; Biostratigraphie; Production de carbonate pelagique; Cycle du carbone; Cycle du calcium; Paleoceanographie; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Ocean acidification; Planktonic foraminifera
• Online Access: https://theses.hal.science/tel-03366248; https://theses.hal.science/tel-03366248/document; https://theses.hal.science/tel-03366248/file/TH2020MENINIALESSANDRO.pdf

Ongoing CO2 emissions are expected to increase global temperatures and affect ocean chemistry better known as ‘ocean acidification’. This latter is a major threat for marine calcifying biota (corals, foraminifera, coccolithophorids). However, recent works identify a particular resilience of coccolithophorids to past ocean acidification events, whereas temperature limits biocalcification. Studies on cultured coccolithophorids or surface-water samples allow understanding the response to short-term temperature, pCO2 or pH variations, but long-term species-specific resilience to environmental changes is crucial to evaluate the respective role of ocean acidification and temperature on fossil calcifying biota. We approach the long-term response of coccolithophorids to these parameters by analyzing the fossil record of two past global events showing perturbation of the carbon cycle associated to CO2 fluctuations and global warming: these are the Toarcian Oceanic Anoxic Event (T-OAE; 183 Ma) and the Paleocene-Eocene Thermal Maximum (PETM; 56 Ma). Firstly, I present new high resolution biostratigraphy for both events in order to link the bioevents to the carbon stable isotopes curve and hence to the carbon isotopes excursion defining the T-OAE and the PETM. We quantify the response of fossil cocoliths to past hyperthermal events by quantifying nannofossils accumulation rate. Both are hyperthermals, but only the former records organic matter accumulations (black shales). Besides ocean acidification, the carbonate saturation and alkalinity of the oceans have an impact on coccolithophorids; we will thus use the calcium isotope composition of the test of planktonic foraminifera to track changes in CO32- concentration across the PETM, where ocean acidification is inferred, and compare these data with analogue records for the T-OAE Les émissions de CO2 devraient augmenter les températures globales et affecter la chimie des océans, un phénomène mieux connu sous le nom d'acidification des océans. Cet dernier phénomène ...