Abstract:The East Asian monsoon plays an integral role in human society, yet its geological history and controlling processes are poorly understood. Using a general circulation model and geological data, we explore the drivers controlling the evolution of the monsoon system over the past 150 million years. In contrast to previous work, we find that the monsoon is controlled primarily by changes in paleogeography, with little influence from atmospheric CO 2 . We associate increased precipitation since the Late Cretaceou… Show more
“…However, a higher plateau will increase the flux of moisture towards it due to greater thermal forcing as a deeper low-pressure system develops. Also, Farnsworth et al (2019) showed that a plateau of half the height of today's Tibetan Plateau can limit convective processes, capping them in the lower troposphere and so inhibiting precipitation as seen today on the Iranian Plateau. Fig.…”
Section: The Topographic Evolution Of the Tibetan Regionmentioning
confidence: 99%
“…Proxy data and modelling show that, although still present in the early Cretaceous, a monsoon climate all but disappeared over southern China during the late Cretaceous and early Paleocene (see Farnsworth et al., 2019 , and references therein) ( Fig. 1 b).…”
Section: Introductionmentioning
confidence: 97%
“…Like the biodiversity, the monsoon has a long history, which has shaped both the biota and the landscape. While regional topographic controls on climate are complex ( Acosta and Huber, 2020 ; Boos and Kuang, 2010 ; Molnar et al., 2010 ), it is not just the topography of the Tibetan Region but paleogeographical constraints further afield that influence monsoon dynamics ( Farnsworth et al., 2019 ). We also now know that models of Tibetan orogeny favoured a few years ago, the most recent of which envisaged the plateau expanding outward from a high Paleogene “Proto Plateau” ( Dai et al., 2012 ; Wang et al., 2014 ), require substantial revision in the light of new fossil discoveries, and that those discoveries are changing radically our knowledge of how Asian biodiversity was generated ( Spicer et al., 2020 ).…”
Section: Introductionmentioning
confidence: 99%
“…These ITCZ monsoons can, however, be variously modified and amplified by changes in astronomical drivers (Earth's axial tilt, orbital shape etc.) and the configuration of the continents and topography, but are minimally affected by atmospheric CO 2 concentrations ( Farnsworth et al., 2019 ).…”
Section: Introductionmentioning
confidence: 99%
“…In part, this was due to a globally warm climate that generated only a weak Siberian winter low pressure system, and we know the late Cretaceous continental interior of Siberia had a much-reduced mean annual range of temperature compared to that of colder times, such as the present ( Spicer et al., 2008 ). As global climate cooled in the later Cenozoic, a strong winter Siberian High re-established and the EAM strengthened to a zenith in the ‘supermonsoon’ and peak rainfall of the late Miocene and Pliocene ( Farnsworth et al., 2019 ).…”
The biodiversity of the Himalaya, Hengduan Mountains and Tibet, here collectively termed the Tibetan Region, is exceptional in a global context. To contextualize and understand the origins of this biotic richness, and its conservation value, we examine recent fossil finds and review progress in understanding the orogeny of the Tibetan Region. We examine the deep-time origins of monsoons affecting Asia, climate variation over different timescales, and the establishment of environmental niche heterogeneity linked to topographic development. The origins of the modern biodiversity were established in the Eocene, concurrent with the formation of pronounced topographic relief across the Tibetan Region. High (>4 km) mountains to the north and south of what is now the Tibetan Plateau bounded a Paleogene central lowland (<2.5 km) hosting moist subtropical vegetation influenced by an intensifying monsoon. In mid Miocene times, before the Himalaya reached their current elevation, sediment infilling and compressional tectonics raised the floor of the central valley to above 3000 m, but central Tibet was still moist enough, and low enough, to host a warm temperate angiosperm-dominated woodland. After 15 Ma, global cooling, the further rise of central Tibet, and the rain shadow cast by the growing Himalaya, progressively led to more open, herb-rich vegetation as the modern high plateau formed with its cool, dry climate. In the moist monsoonal Hengduan Mountains, high and spatially extensive since the Eocene but subsequently deeply dissected by river incision, Neogene cooling depressed the tree line, compressed altitudinal zonation, and created strong environmental heterogeneity. This served as a cradle for the then newly-evolving alpine biota and favoured diversity within more thermophilic vegetation at lower elevations. This diversity has survived through a combination of minimal Quaternary glaciation, and complex relief-related environmental niche heterogeneity. The great antiquity and diversity of the Tibetan Region biota argues for its conservation, and the importance of that biota is demonstrated through our insights into its long temporal gestation provided by fossil archives and information written in surviving genomes. These data sources are worthy of conservation in their own right, but for the living biotic inventory we need to ask what it is we want to conserve. Is it 1) individual taxa for their intrinsic properties, 2) their services in functioning ecosystems, or 3) their capacity to generate future new biodiversity? If 2 or 3 are our goal then landscape conservation at scale is required, and not just seed banks or botanical/zoological gardens.
“…However, a higher plateau will increase the flux of moisture towards it due to greater thermal forcing as a deeper low-pressure system develops. Also, Farnsworth et al (2019) showed that a plateau of half the height of today's Tibetan Plateau can limit convective processes, capping them in the lower troposphere and so inhibiting precipitation as seen today on the Iranian Plateau. Fig.…”
Section: The Topographic Evolution Of the Tibetan Regionmentioning
confidence: 99%
“…Proxy data and modelling show that, although still present in the early Cretaceous, a monsoon climate all but disappeared over southern China during the late Cretaceous and early Paleocene (see Farnsworth et al., 2019 , and references therein) ( Fig. 1 b).…”
Section: Introductionmentioning
confidence: 97%
“…Like the biodiversity, the monsoon has a long history, which has shaped both the biota and the landscape. While regional topographic controls on climate are complex ( Acosta and Huber, 2020 ; Boos and Kuang, 2010 ; Molnar et al., 2010 ), it is not just the topography of the Tibetan Region but paleogeographical constraints further afield that influence monsoon dynamics ( Farnsworth et al., 2019 ). We also now know that models of Tibetan orogeny favoured a few years ago, the most recent of which envisaged the plateau expanding outward from a high Paleogene “Proto Plateau” ( Dai et al., 2012 ; Wang et al., 2014 ), require substantial revision in the light of new fossil discoveries, and that those discoveries are changing radically our knowledge of how Asian biodiversity was generated ( Spicer et al., 2020 ).…”
Section: Introductionmentioning
confidence: 99%
“…These ITCZ monsoons can, however, be variously modified and amplified by changes in astronomical drivers (Earth's axial tilt, orbital shape etc.) and the configuration of the continents and topography, but are minimally affected by atmospheric CO 2 concentrations ( Farnsworth et al., 2019 ).…”
Section: Introductionmentioning
confidence: 99%
“…In part, this was due to a globally warm climate that generated only a weak Siberian winter low pressure system, and we know the late Cretaceous continental interior of Siberia had a much-reduced mean annual range of temperature compared to that of colder times, such as the present ( Spicer et al., 2008 ). As global climate cooled in the later Cenozoic, a strong winter Siberian High re-established and the EAM strengthened to a zenith in the ‘supermonsoon’ and peak rainfall of the late Miocene and Pliocene ( Farnsworth et al., 2019 ).…”
The biodiversity of the Himalaya, Hengduan Mountains and Tibet, here collectively termed the Tibetan Region, is exceptional in a global context. To contextualize and understand the origins of this biotic richness, and its conservation value, we examine recent fossil finds and review progress in understanding the orogeny of the Tibetan Region. We examine the deep-time origins of monsoons affecting Asia, climate variation over different timescales, and the establishment of environmental niche heterogeneity linked to topographic development. The origins of the modern biodiversity were established in the Eocene, concurrent with the formation of pronounced topographic relief across the Tibetan Region. High (>4 km) mountains to the north and south of what is now the Tibetan Plateau bounded a Paleogene central lowland (<2.5 km) hosting moist subtropical vegetation influenced by an intensifying monsoon. In mid Miocene times, before the Himalaya reached their current elevation, sediment infilling and compressional tectonics raised the floor of the central valley to above 3000 m, but central Tibet was still moist enough, and low enough, to host a warm temperate angiosperm-dominated woodland. After 15 Ma, global cooling, the further rise of central Tibet, and the rain shadow cast by the growing Himalaya, progressively led to more open, herb-rich vegetation as the modern high plateau formed with its cool, dry climate. In the moist monsoonal Hengduan Mountains, high and spatially extensive since the Eocene but subsequently deeply dissected by river incision, Neogene cooling depressed the tree line, compressed altitudinal zonation, and created strong environmental heterogeneity. This served as a cradle for the then newly-evolving alpine biota and favoured diversity within more thermophilic vegetation at lower elevations. This diversity has survived through a combination of minimal Quaternary glaciation, and complex relief-related environmental niche heterogeneity. The great antiquity and diversity of the Tibetan Region biota argues for its conservation, and the importance of that biota is demonstrated through our insights into its long temporal gestation provided by fossil archives and information written in surviving genomes. These data sources are worthy of conservation in their own right, but for the living biotic inventory we need to ask what it is we want to conserve. Is it 1) individual taxa for their intrinsic properties, 2) their services in functioning ecosystems, or 3) their capacity to generate future new biodiversity? If 2 or 3 are our goal then landscape conservation at scale is required, and not just seed banks or botanical/zoological gardens.
Wendlandia, as currently circumscribed, is a genus of Rubiaceae comprising about 90 species mainly in tropical and subtropical Asia. By sampling species from all four series (Clavigerae, Euexsertae, Montigenae, Subinclusae) and all tribes in the subfamily Dialypetalanthoideae, we examined the monophyly of Wendlandia based on phylogenetic reconstruction using the nuclear ribosomal internal transcribed spacer and four plastid DNA regions. Wendlandia was resolved as biphyletic, consisting of two distantly related lineages that correspond to the monotypic series Clavigerae (Wendlandia pendula), sister to the Chinese endemic genus Trailliaedoxa, and a clade containing the remainder sampled members of Wendlandia. Based on the isolated phylogenetic position of W. pendula and its unique morphological characteristics compared to the recognized tribes of the Vanguerieae alliance, we herein erect a new monotypic genus, Clavistigma, and a new tribe, Clavistigmeae to accommodate the unique species. The secondary pollen presentation and the unique seed morphology were firstly described for the species. The divergence time between Clavistigma and Trailliaedoxa was dated back to 13.8 mya, coinciding with the climate change in northwestern Yunnan driven by the uplift Tibet Plateau and the river incision in the Hengduan Mountains during the Miocene and Late Pliocene.
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