Coupled microbial bloom and oxygenation decline recorded by magnetofossils during the Palaeocene\u2013Eocene Thermal Maximum

Liao Chang,Andrew P Roberts,Xiang Zhao,Thomas A Berndt,David Heslop,Fan Zeng,Richard J Harrison

doi:10.1038/s41467-018-06472-y

Abstract

Understanding marine environmental change and associated biological turnover across the Palaeocene–Eocene Thermal Maximum (PETM; ~56 Ma)—the most pronounced Cenozoic short-term global warming event—is important because of the potential role of the ocean in atmospheric CO2 drawdown, yet proxies for tracing marine productivity and oxygenation across the PETM are limited and results remain controversial. Here we show that a high-resolution record of South Atlantic Ocean bottom water oxygenation can be extracted from exceptionally preserved magnetofossils—the bioinorganic magnetite nanocrystals produced by magnetotactic bacteria (MTB) using a new multiscale environmental magnetic approach. Our results suggest that a transient MTB bloom occurred due to increased nutrient supply. Bottom water oxygenation decreased gradually from the onset to the peak PETM. These observations provide a record of microbial response to the PETM and establish the value of magnetofossils as palaeoenvironmental indicators.

Highlights

Understanding marine environmental change and associated biological turnover across the Palaeocene–Eocene Thermal Maximum (PETM; ~56 Ma)—the most pronounced Cenozoic short-term global warming event—is important because of the potential role of the ocean in atmospheric CO2 drawdown, yet proxies for tracing marine productivity and oxygenation across the PETM are limited and results remain controversial
Magnetic measurements were made on samples across the PETM interval from Hole 1263C, core 14H, and sections 2A and CC (Supplementary Table 1), which provide strong evidence of magnetofossil occurrences within the studied PETM interval
First-order reversal curve (FORC) diagrams[42] (Fig. 2a–c) contain a major central ridge component along Bu = 0, which is an indicator of magnetofossils in sediments[43]

Summary

Introduction

Understanding marine environmental change and associated biological turnover across the Palaeocene–Eocene Thermal Maximum (PETM; ~56 Ma)—the most pronounced Cenozoic short-term global warming event—is important because of the potential role of the ocean in atmospheric CO2 drawdown, yet proxies for tracing marine productivity and oxygenation across the PETM are limited and results remain controversial. We develop a new multiscale approach based on TEM observations, magnetic properties and micromagnetic simulations to characterize trace magnetofossil concentrations preserved within PETM sediments. Quantitative IRM decomposition analysis indicates that the magnetofossil component contributes ~76% to the total remanent magnetization for the PETM onset sample (section 14H-2A, 146–147 cm interval; 335.67 metres composite depth (mcd)).

Results

Conclusion