Asian monsoons in a late Eocene greenhouse world

Abstract

The strong present-day Asian monsoons are thought to have originated between 25 and 22 million years (Myr) ago, driven by Tibetan-Himalayan uplift. However, the existence of older Asian monsoons and their response to enhanced greenhouse conditions such as those in the Eocene period (55-34 Myr ago) are unknown because of the paucity of well-dated records. Here we show late Eocene climate records revealing marked monsoon-like patterns in rainfall and wind south and north of the Tibetan-Himalayan orogen. This is indicated by low oxygen isotope values with strong seasonality in gastropod shells and mammal teeth from Myanmar, and by aeolian dust deposition in northwest China. Our climate simulations support modern-like Eocene monsoonal rainfall and show that a reinforced hydrological cycle responding to enhanced greenhouse conditions counterbalanced the negative effect of lower Tibetan relief on precipitation. These strong monsoons later weakened with the global shift to icehouse conditions 34 Myr ago.

The neglected Indo‐Gangetic Plains low‐level jet and its importance for moisture transport and precipitation during the peak summer monsoon

“…We also provide results from CAM5 (S1) [Neale et al, 2010]. We focus on CAM because it has been heavily used in theoretical [Sandeep and Ajayamohan, 2015;Boos and Storelvmo, 2016], idealized [Chen et al, 2014;Zhang et al, 2015], and paleoclimate studies [Huber and Goldner, 2012;Licht et al, 2014]. Additionally, the NCAR CAM physics schemes have been ported to several other climate models such as Global Environmental and Ecological Simulation of Interactive Systems [Thompson and Pollard, 1994] and FOAM [Jacob et al, 2001].…”

Oligocene ruminants from the Kızılırmak Formation, Çankırı-Çorum Basin, Central Anatolia, Turkey

“…Although collecting biases are always possible, it appears that very early during the Oligocene, the climate in Mongolia became drier or at least not favorable to the tragulids, and at lesser extent to lophiomerycids. This more seasonal and drier climate of Mongolia during the Oligocene may be related to the beginning of Tibetan Plateau uplift, and the related intensification of the Asian Moonson (Licht et al, 2014). During the late Oligocene, paleogeographic maps (Popov et al, 2004) indicate connection of Anatolia with the Asian mainland probably via complex foreand back arc basins in Eastern Anatolia and Lesser Caucasus .…”

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“…There is a lack of consensus regarding the onset or intensification of the Indian monsoon (e.g., Allen and Armstrong, 2012). Some proxy records suggest that the initial intensification occurred at ~7 to 8 Ma (e.g., Kroon et al, 1991;Prell et al, 1992), whereas others suggest a considerably earlier onset, as early as ~22 Ma (Clift et al, 2008;Guo et al, 2002) or the Eocene (Licht et al, 2014). Alternatively, events at ~8 Ma were linked to global cooling (Gupta et al, 2004) or coupled to productivity changes (Filippelli, 1997).…”