Major perturbations in the global carbon cycle and photosymbiont-bearing planktic foraminifera during the early Eocene

Valeria Luciani,Gerald R Dickens,Jan Backman,Roberta D'Onofrio,Claudia Agnini,Eliana Fornaciari,Luca Giusberti

doi:10.5194/cp-12-981-2016

Abstract

Abstract. A marked switch in the abundance of the planktic foraminiferal genera Morozovella and Acarinina occurred at low-latitude sites near the start of the Early Eocene Climatic Optimum (EECO), a multi-million-year interval when Earth surface temperatures reached their Cenozoic maximum. Stable carbon and oxygen isotope data of bulk sediment are presented from across the EECO at two locations: Possagno in northeast Italy and Deep Sea Drilling Project (DSDP) Site 577 in the northwest Pacific. Relative abundances of planktic foraminifera are presented from these two locations, as well as from Ocean Drilling Program (ODP) Site 1051 in the northwest Atlantic. All three sections have good stratigraphic markers, and the δ13C records at each section can be correlated amongst each other and to δ13C records at other locations across the globe. These records show that a series of negative carbon isotope excursions (CIEs) occurred before, during and across the EECO, which is defined here as the interval between the J event and the base of Discoaster sublodoensis. Significant though ephemeral modifications in planktic foraminiferal assemblages coincide with some of the short-term CIEs, which were marked by increases in the relative abundance of Acarinina, similar to what happened across established hyperthermal events in Tethyan settings prior to the EECO. Most crucially, a temporal link exists between the onset of the EECO, carbon cycle changes during this time and the decline in Morozovella. Possible causes are manifold and may include temperature effects on photosymbiont-bearing planktic foraminifera and changes in ocean chemistry.

Highlights

Cenozoic Earth surface temperatures attained their warmest long-term state during the Early Eocene Climatic Optimum (EECO)
A marked switch in the abundance of the planktic foraminiferal genera Morozovella and Acarinina occurred at low-latitude sites near the start of the Early Eocene Climatic Optimum (EECO), a multi-million-year interval when Earth surface temperatures reached their Cenozoic maximum
Significant though ephemeral modifications in planktic foraminiferal assemblages coincide with some of the short-term carbon isotope excursions (CIEs), which were marked by increases in the relative abundance of Acarinina, similar to what happened across established hyperthermal events in Tethyan settings prior to the EECO

Summary

Introduction

Cenozoic Earth surface temperatures attained their warmest long-term state during the Early Eocene Climatic Optimum (EECO). This was a 2–4 Myr time interval (discussed below) centered at ca. Several short-term (< 200 kyr) global warming events (Fig. 1) occurred before the EECO. Evidence exists for at least two other significant Eocene warming events (Cramer et al, 2003; Lourens et al, 2005; Röhl et al, 2005; Thomas et al, 2006; Nicolo et al, 2007; Agnini et al, 2009; Coccioni et al, 2012; Lauretano et al, 2015; Westerhold et al, 2015): one ca. 54.1 Ma and named H-1 or Eocene Thermal Maximum 2 (ETM-2, referred to as the Elmo event) and one Published by Copernicus Publications on behalf of the European Geosciences Union.

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