Abyssal oceanic circulation and acidification during the Middle Eocene Climatic Optimum (MECO)

Luigi Jovane,Flaminia Cornaggia,André Istvan M Nagy,Gabriel L X Silva,Martino Giorgioni,Simone Bernardini

doi:10.1038/s41598-020-63525-3

Abstract

The Middle Eocene Climatic Optimum (MECO) is a global warming event that occurred at around 40 Ma and lasted about 500 kyr. We study this event in an abyssal setting of the Tasman Sea, using the IODP Core U1511B-16R, collected during the expedition 371. We analyse magnetic, mineralogical, and chemical parameters to investigate the evolution of the sea bottom conditions at this site during the middle Eocene. We observe significant changes indicating the response to the MECO perturbation. Mn oxides, in which Mn occurs under an oxidation state around +4, indicate a high Eh water environment. A prominent Mn anomaly, occurring just above the MECO interval, indicates a shift toward higher pH conditions shortly after the end of this event. Our results suggest more acid bottom water over the Tasman abyssal plain during the MECO, and an abrupt end of these conditions. This work provides the first evidence of MECO at abyssal depths and shows that acidification affected the entire oceanic water column during this event.

Highlights

The Eocene (~56–34 Ma) was characterized by a gradual climatic cooling, accompanied by decreasing atmospheric pCO2 and culminating with the onset of the Antarctic glaciation in the early Oligocene (33 Ma)[1,2,3,4,5]
In this work we study bulk, clay, and oxide minerals within the Middle Eocene Climatic Optimum (MECO) interval in a core from the IODP Core U1511B-16R, which offers a unique opportunity to study how the Southern Ocean (SO) system responded to the MECO at abyssal depths
X-Ray Fluorescence (XRF)-scanner data show a change in chemical composition in the 266.5–264.8 mbsf interval, which corresponds to the stratigraphic position of the MECO (Fig. 1 and S3)

Summary

Introduction

The Eocene (~56–34 Ma) was characterized by a gradual climatic cooling, accompanied by decreasing atmospheric pCO2 and culminating with the onset of the Antarctic glaciation in the early Oligocene (33 Ma)[1,2,3,4,5]. The separation of Australia from Antartica during the middle-late Eocene profoundly affected the circulation and made this region sensitive to paleoceanographic changes[4,15]. In this complex geological framework, the study of iron and manganese oxides in the sediments can provide important information, as they are strongly controlled by redox conditions and circulation[16]. Our results show that a major change in deep-water circulation occurred over the TAP

Methods

Results

Conclusion