EPSL: Changes of deep Pacific overturning circulation and carbonate chemistry during middle Miocene East Antarctic ice sheet expansion

Xiaolin Ma^a,b, JunTian^a, Wentao Ma^a,c, Ke Li^a, Jimin Yu^a,d

a State Key Laboratory of Marine Geology, Tongji University, Shanghai, 200092, China

b State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, 710075, China

c State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, SOA, Hangzhou 310012, China

d Research School of Earth Sciences, the Australian National University, Canberra, ACT 2601, Australia

Abstract：

East Antarctic ice sheet expansion (EAIE) at ∼13.9Ma in the middle Miocene represents a major climatic event during the long-term Cenozoic cooling, but ocean circulation and carbon cycle changes during this event remain unclear. Here, we present new fish teeth isotope (εNd) and benthic foraminiferal B/Ca records from the South China Sea (SCS), newly integrated meridional Pacific benthic foraminiferal ¹⁸O and ¹³C records and simulated results from a biogeochemical box model to explore the responses of deep Pacific Ocean circulation and carbon cycle across EAIE. The εNd and meridional benthic ¹³C records reveal a more isolated Pacific Deep Water (PDW) and a sluggish Pacific meridional overturning circulation during the post-EAIE with respect to the pre-EAIE owing to weakened southern-sourced deep water formation. The deep-water [CO₃²⁻] and calcium carbonate mass accumulation rate in the SCS display markedly similar increases followed by recoveries to the pre-EAIE level during EAIE, which were probably caused by a shelf–basin shift of CaCO₃ deposition and strengthened weathering due to a sea level fall within EAIE. The model results show that the ∼1‰ positive ¹³C excursion during EAIE could be attributed to increased weathering of high-¹³C shelf carbonates and a terrestrial carbon reservoir expansion. The drawdown of atmospheric CO₂ over the middle Miocene were probably caused by combined effects of increased shelf carbonate weathering, expanded land biosphere carbon storage and a sluggish deep Pacific meridional overturning circulation.

Full article：https://www.sciencedirect.com/science/article/pii/S0012821X17307008