Abstract
Abstract. The role of the Tibetan Plateau (TP) in maintaining the large-scale overturning circulation in the Atlantic and Pacific is investigated using a coupled atmosphere–ocean model. For the present day with a realistic topography, model simulation shows a strong Atlantic meridional overturning circulation (AMOC) but a near absence of the Pacific meridional overturning circulation (PMOC), which are in good agreement with the present observations. In contrast, the simulation without the TP depicts a collapsed AMOC and a strong PMOC that dominates deep-water formation. The switch in deep-water formation between the two basins results from changes in the large-scale atmospheric circulation and atmosphere–ocean feedback over the Atlantic and Pacific. The intensified westerly winds and increased freshwater flux over the North Atlantic cause an initial slowdown of the AMOC, while the weakened East Asian monsoon circulation and associated decreased freshwater flux over the North Pacific give rise to the initial intensification of the PMOC. The further decreased heat flux and the associated increase in sea-ice fraction promote the final AMOC collapse over the Atlantic, while the further increased heat flux leads to the final PMOC establishment over the Pacific. Although the simulations were performed in a cold world, it still importantly implicates that the uplift of the TP alone could have been a potential driver for the reorganization of PMOC–AMOC between the late Eocene and early Oligocene.
Highlights
The uplift of the Tibetan Plateau (TP) was a major tectonic event that had occurred throughout the Cenozoic, and its gradual growth had exerted a strong influence on the atmospheric circulation and climate (Molnar et al, 2010)
With MTP, the Atlantic meridional overturning circulation (AMOC) stabilizes at around 17 Sv (Sv = 106 m3 s−1) for more than 1000 years (Fig. 1d, 1–1100 years, red line), which agrees with the observation of 18.7 ± 5.6 Sv for 2004–2005 (Cunningham et al, 2007), but with NTP there is a continual weakening of the AMOC until the point of quasi-collapse
The Pacific meridional overturning circulation (PMOC) of NTP begins at a sluggish level from MTP (Fig. 1d, 1–1100 years, purple line) and takes as long as 1200 years to reach an equilibrium state that is comparable to the level of the AMOC
Summary
The uplift of the Tibetan Plateau (TP) was a major tectonic event that had occurred throughout the Cenozoic, and its gradual growth had exerted a strong influence on the atmospheric circulation and climate (Molnar et al, 2010). Since the pioneering work of Bolin (1950), the impacts of mountain uplift on regional and global climate have been extensively investigated. Most studies have emphasized the role of mountain ranges on atmosphere dynamics, while quantifications of the associated impact on ocean dynamics have been rare. Simulations have recently been applied to investigate the effect of mountain uplift in the context of the atmosphere–ocean system, and a few studies have proposed that the uplift of the Andes (Sepulchre et al, 2009) and Rocky Mountains (Seager et al, 2002) is closely linked to the evolution of oceanic circulations, including the Gulf Stream and Humboldt Current, and the El Niño–Southern Oscillation system (Feng and Poulsen, 2014).
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