Zhimin Jian a, Haowen Dang a, Jimin Yu b c, Qiong Wu d, Xun Gong e f, Christian Stepanek f, Christophe Colin g, Lili Hu a, Gerrit Lohmann f, Xiaoli Zhou a, Sui Wan h
a State Key Laboratory of Marine Geology, Tongji University, Shanghai, China
b Laoshan Laboratory, Qingdao, 266237, China
c Research School of Earth Sciences, Australian National University, Canberra, ACT 2601, Australia
d College of Oceanography, Hohai University, Nanjing, China
e Hubei Key Laboratory of Marine Geological Resources, China University of Geosciences, 430074, Wuhan, China
f Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung, 27570 Bremerhaven, Germany
g Université Paris-Saclay, CNRS, GEOPS, 91405 Orsay, France
h South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China
Abstract：
The global climate has been gradually cooling over the Cenozoic and is punctuated by the intensification of Northern Hemisphere Glaciation (NHG) from the latest Pliocene to earliest Pleistocene (∼3.1–2.5 millions of years ago, Ma). A decline of atmospheric CO2 is supposed as a prerequisite for the NHG, but the associated carbon-cycle processes remain elusive. Here we combine foraminiferal records of neodymium isotope and boron-calcium ratio, and simulations of an Earth system model, to investigate changes in the water-mass composition and carbonate-ion concentration of the deep Pacific Ocean during the NHG. Our proxy records have revealed a significant expansion of southern-sourced waters with increased respired carbon storage into the deep Pacific during the NHG. These changes may be explained by strengthened deep-water formation and biological-pump efficiency in the Southern Ocean due to Antarctic sea-ice growth, as suggested by our model experiments and evidence from the Sub-Antarctic region. These results provide key clues for quantifying the role of the dissolved inorganic carbon content of deep Pacific waters in modulating atmospheric CO2 during the NHG.
