Latest Pliocene Northern Hemisphere glaciation amplified by intensified Atlantic meridional overturning circulation

Masahiko Sato,Yoshihiro Kuwahara,Tatsuya Hayashi,Masao Ohno,Toshiro Yamanaka,Yuki Hikasa

doi:10.1038/s43247-020-00023-4

Abstract

The global climate has been dominated by glacial–interglacial variations since the intensification of Northern Hemisphere glaciation 2.7 million years ago. Although the Atlantic meridional overturning circulation has exerted strong influence on recent climatic changes, there is controversy over its influence on Northern Hemisphere glaciation because its deep limb, North Atlantic Deep Water, was thought to have weakened. Here we show that Northern Hemisphere glaciation was amplified by the intensified Atlantic meridional overturning circulation, based on multi-proxy records from the subpolar North Atlantic. We found that the Iceland–Scotland Overflow Water, contributing North Atlantic Deep Water, significantly increased after 2.7 million years ago and was actively maintained even in early stages of individual glacials, in contrast with late stages when it drastically decreased because of iceberg melting. Probably, the active Nordic Seas overturning during the early stages of glacials facilitated the efficient growth of ice sheets and amplified glacial oscillations.

Highlights

The global climate has been dominated by glacial–interglacial variations since the intensification of Northern Hemisphere glaciation 2.7 million years ago
The primary cause of intensification of Northern Hemisphere glaciation (iNHG) has been debated, with two leading hypotheses: severe cooling induced by decreased atmospheric CO2 concentration[4,5,6], and increased rain and snow fall over Greenland and Europe attributed to the closure of the Central American Seaway (CAS)[7,8]
We propose that the active Atlantic meridional overturning circulation (AMOC) during early glacial stages facilitated the efficient growth of continental ice sheets by mitigating heat and utilizing moisture supplied by the North Atlantic Current (NAC), resulting in the amplification of Northern Hemisphere glaciation

Summary

Introduction

The global climate has been dominated by glacial–interglacial variations since the intensification of Northern Hemisphere glaciation 2.7 million years ago. Northern Hemisphere glaciation gradually developed after its onset 3.6 million years ago (Ma)[1] and further intensified after 2.7 Ma2 The latter intensification of Northern Hemisphere glaciation (iNHG) was an irreversible climatic deterioration[3], and the 41-kyr component of glacial–interglacial variations was amplified[2]. The AMOC played a dominant role in recent glacial–interglacial and stadial–interstadial climate conditions[11,12], studies based on benthic foraminiferal carbon isotopes (δ13C)[13,14], a major proxy of deep-water formation, suggested that North Atlantic Deep Water (NADW), the deep component of the AMOC, weakened after iNHG. We propose that the active AMOC during early glacial stages facilitated the efficient growth of continental ice sheets by mitigating heat and utilizing moisture supplied by the North Atlantic Current (NAC), resulting in the amplification of Northern Hemisphere glaciation

Methods

Results

Conclusion