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East Antarctic ice sheet expansion (EAIE) at ∼13.9 Ma 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 ( ε Nd) and benthic foraminiferal B/Ca records from the South China Sea (SCS), newly integrated meridional Pacific benthic foraminiferal δ 18 O and δ 13 C records and simulated results from a biogeochemical box model to explore the responses of deep Pacific Ocean circulation and carbon cycle across EAIE. The ε Nd and meridional benthic δ 13 C 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 [CO 2 − 3 ] 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 CaCO 3 deposition and strengthened weathering due to a sea level fall within EAIE. The model results show that the ∼1‰ positive δ 13 C excursion during EAIE could be attributed to increased weathering of high- δ 13 C shelf carbonates and a terrestrial carbon reservoir expansion. The drawdown of atmospheric CO 2 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. [ABSTRACT FROM AUTHOR]

We present astronomically tuned high time resolution (3–4 kyr) benthic foraminiferal δ 18 O and δ 13 C records between 9 Ma and 5 Ma from Ocean Drilling Program (ODP) Site 1143 in the southern South China Sea (SCS). We found that the late Miocene ocean carbon shift (LMOCS) which was linked with the late Miocene/early Pliocene “Biogenic Bloom” also occurred in the northern and southern SCS. A marked deep-water δ 13 C gradient as much as ~ 1.0‰ of the northern and southern SCS was observed between 6.5 Ma and 5.9 Ma, which was probably caused by the significant difference in paleoproductivity between the northern and southern SCS. The deep δ 13 C gradient was likely produced by rapid tectonic subsidence in the northern SCS at ~ 6.0 Ma and the final formation of the Bashi Strait at ~ 6.5 Ma. A reversed benthic δ 13 C gradient of the northern and southern SCS was also observed between 1.2 Ma and 0.35 Ma, which was probably caused by the consecutive closures of the interarc water gates within the Bashi strait at ~ 3.0 Ma and ~ 1.2 Ma. Closures of the interarc water gates within the Bashi strait at ~ 3.0 Ma and ~ 1.2 Ma further semi-enclosed the SCS basin and made the paleoproductivity the major factor influencing the deep water δ 13 C, leading to the reversed deep water δ 13 C gradient of the northern and southern SCS between 1.2 Ma and 0.35 Ma. [ABSTRACT FROM AUTHOR]

Currently mechanisms for the onset of the widespread aeolian dust accumulation in the Chinese Loess Plateau since 8–7 Ma remain elusive. In this study, we compile 11 records of climate (14–7 Ma) and tectonic activity of the Tibetan Plateau and its adjacent areas (15–6 Ma). The results suggest that strong tectonic activity in the northeastern Tibetan Plateau has produced massive debris and dust, which was deposited in the piedmont basins and reworked by weathering and fluviolacustrine erosion. At the same time, global cooling and uplift of the Tibetan Plateau over the period of 14–7 Ma intensified the East Asian winter monsoon and westerly winds (westerlies) while weakening the Asian summer monsoon, which led to the spread of dry land vegetation and aridification in interior China. Sediments in the piedmont basins were then exposed in the aridity and transported by the westerlies to the Chinese Loess Plateau and the North Pacific. We suggest that tectonic activity in the northeastern Tibetan Plateau and shifting global climate together triggered the widespread aeolian dust accumulation in the Chinese Loess Plateau and the North Pacific since 8–7 Ma. [ABSTRACT FROM PUBLISHER]

The Middle Miocene (~16–11.6 Ma) had atmospheric CO 2 levels comparable to the present day, and thus the mechanisms controlling the interactions of the climate system and the carbon cycle during the Middle Miocene may have significant implications for future climate change. In this study, we examined the phase relationship between benthic foraminiferal δ18O and δ13C records, within the 100-kyr band, during the Late Quaternary and the Middle Miocene. Our results suggest that benthic foraminiferal δ18O and δ13C were highly coherent and in-phase within the 100-kyr band during the Middle Miocene, in contrast to the anti-phased relationship during the Late Quaternary. However, the causes of this contrast remain elusive. We used a biogeochemical box model to explore the mechanisms of the in-phase relationship in the 100-kyr band during the Middle Miocene. The model results show that the in-phase relationship can be attributed to two mechanisms: (1) a shelf-basin carbonate shift regulated by sea-level fluctuations which originated from the growth and decay of the Antarctic ice sheet, within the 100-kyr band; and (2) changes in terrestrial carbon inputs and the biological pump driven by the discharge of riverine nutrients, which was regulated by precipitation variability in low latitudes, within the eccentricity-modulated precessional band. Thus, we propose that both high- and low-latitude processes played critical roles in the Middle Miocene carbon cycle, within the 100-kyr band. We further show that chemical weathering played a potential role in regulating the atmospheric p CO 2 on the orbital time scale during the Middle Miocene. • Phase relationships between benthic δ18O and δ13C records in the 100-kyr band are reinvestigated. • Terrestrial inputs explain the in-phase relationship of benthic δ18O and δ13C in the 100-kyr band over the Middle Miocene. • Both changes of Antarctic ice sheet and low-latitude precipitation played critical roles in the Middle Miocene carbon cycle. [ABSTRACT FROM AUTHOR]

[Display omitted] Global warming during the Miocene Climate Optimum (MCO, ∼17–14 million years ago) is associated with massive carbon emissions sourced from the flood basalt volcanism and ocean crustal production. However, the perturbation of tectonic carbon degassing on the interaction between climate change and carbon cycle remains unclear. Here, through time-evolutive phase analysis of new and published high-resolution benthic foraminiferal oxygen (δ 18O) and carbon (δ 13C) isotope records from the global ocean, we find that variations in the marine carbon cycle lead the climate-cryosphere system (δ 13C-lead- δ 18O) on 405,000-year eccentricity timescales during the MCO. This is in contrast to the previously reported climate-lead-carbon (δ 18O-lead- δ 13C) scenario during most of the Oligo-Miocene (∼34–6 million years ago). Further sensitivity analysis and model simulations suggest that the elevated atmospheric CO 2 concentrations and the resulting greenhouse effect strengthened the low-latitude hydrological cycle during the MCO, accelerating the response of marine carbon cycle to eccentricity forcing. Tropical climate processes played a more important role in regulating carbon-cycle variations when Earth's climate was in a warm regime, as opposed to the dominant influence of polar ice-sheet dynamics during the Plio-Pleistocene (after ∼6 million years ago). [ABSTRACT FROM AUTHOR]