The roles of global cooling and early Tibetan Plateau uplift on the enhanced aridity in Eocene Asian inland

<p>Geological evidence shows that the Asian inland environment experienced enhanced aridity from the Early to the Late Eocene. The underlying mechanism for this enhanced Eocene aridity in the Asian inland is still not well illustrated and varies between global cooling and early Tibetan Plateau uplift. In this report, we evaluate the climate impact of three factors, global cooling, topographic uplift and land–sea reorganization, on the enhanced Eocene aridity in Asian inland, in the perspective view from paleoclimate modeling. Paleoclimate modeling supports the Eocene aridification in Asian inland explored by paleoclimate reconstruction. Both the early uplift of Tibetan Plateau and global cooling induced by atmospheric CO<sub>2</sub> reduction contributed to the enhanced aridity in Asian inland in the late Eocene. The Eocene land sea redistribution caused the precipitation increase in Asian inland and hence didn’t contribute to the enhanced aridity there. The uplift of the central Tibetan Plateau during the early stage of the India–Asia collision is emphasized more to be responsible for the long-term Asian inland aridification during the Eocene, playing at least an equally important role as the global cooling induced by decrease in atmospheric CO<sub>2</sub>. The variation of atmospheric CO<sub>2</sub> is likely more important in modulating the regional aridity, leading to the short-term fluctuations in this Eocene Asian inland aridification.</p>

The Tibetan Plateau Uplift is Crucial for Eastward Propagation of Madden-Julian Oscillation

The Tibetan Plateau (TP) and Himalayas have been treated as an essential external factor in shaping Asian monsoon and mid-latitude atmospheric circulation. In this study we perform numerical experiments with different uplift altitudes using the Nanjing University of Information Science and Technology Earth System Model to examine potential impacts of uplift of the TP and Himalayas on eastward propagation of the MJO and the associated mechanisms. Analysis of experimental results with dynamics-based MJO diagnostics indicates two potential mechanisms. First, the uplift considerably enhances low-level mean westerlies in the Indian Ocean and convection in the Maritime Continent, which in turn strengthens boundary layer moisture convergence (BLMC) to the east of the MJO convective center. The increased BLMC reinforces upward transport of moisture and heat from BL to free atmosphere and increases lower tropospheric diabatic heating by shallow and congestus clouds ahead of the MJO center, enhancing the Kelvin-Rossby wave feedback. Second, the uplift increases upper tropospheric mean easterlies and stratiform heating at the west of the MJO center, which contributes to eastward propagation of MJO by generating positive moist static energy at the east of MJO center. This study will contribute to a better understanding of the origin of the MJO and improvement in simulation of MJO propagation.

Three main stages in the uplift of the Tibetan Plateau during the Cenozoic period and its possible effects on Asian aridification: A review

The Tibetan Plateau uplift and its linkages with the evolution of the Asian climate during the Cenozoic are a research focus for numerous geologists. Here, a comprehensive review of tectonic activities across the Tibet shows that the development of the Tibetan Plateau has undergone mainly three stages of the uplift: the near-modern elevation of the central Tibet and significant uplift of the northern margins (~ 55–35 Ma), the further uplift of the plateau margins (30–20 Ma), and a rapid uplift of the plateau margins again (15–8 Ma). The first uplift of the plateau during ~ 55–35 Ma forced the long-term westward retreat of the Paratethys Sea. The high elevation of the central Tibet and/or the Himalayan would enhance rock weathering and erosion contributing to lowering of atmospheric CO2 content, resulting in global cooling. The global cooling, sea retreat coupled with the topographic barrier effect of the Tibetan Plateau could have caused the initial aridification in central Asia during the Eocene time. The second uplift of the northern Tibet could have resulted in the onset of the East Asian winter monsoon as well as intensive desertification of inland Asia, whereas the central-eastern in China became wet. The further strengthening of the East Asian winter monsoon and the inland Asian aridification during 15–8 Ma was probably associated with the Tibetan Plateau uplift and global cooling. Therefore, the uplift of the Tibetan Plateau plays a very important role in the Asian aridification.

Evolutionary response to the Qinghai-Tibetan Plateau uplift: phylogeny and biogeography ofAmmopiptanthusand tribe Thermopsideae (Fabaceae)

Previous works resolved diverse phylogenetic positions for genera of the Fabaceae tribe Thermopsideae, without a thoroughly biogeography study. Based on sequence data from nuclear ITS and four cpDNA regions (matK,rbcL,trnH-psbA,trnL-trnF) mainly sourced from GenBank, the phylogeny of tribe Thermopsideae was inferred. Our analyses support the genera of Thermopsideae, with the exclusion ofPickeringia, being merged into a monophyletic Sophoreae. Genera of Sophoreae were assigned into the Thermopsoid clade and Sophoroid clade. Monophyly ofAnagyris,BaptisiaandPiptanthuswere supported in the Thermopsoid clade. However, the genera Thermopsis and Sophora were resolved to be polyphyly, which require comprehensive taxonomic revisions. Interestingly,Ammopiptanthus, consisting ofA. mongolicusandA. nanus, nested within the Sophoroid clade, withSalweeniaas its sister.AmmopiptanthusandSalweeniahave a disjunct distribution in the deserts of northwestern China and the Hengduan Mountains, respectively. Divergence age was estimated based on the ITS phylogenetic analysis. Emergence of the common ancestor ofAmmopiptanthusandSalweenia, divergence between these two genera and the split ofAmmopiptanthusspecies occurred at approximately 26.96 Ma, 4.74 Ma and 2.04 Ma, respectively, which may be in response to the second, third and fourth main uplifts of the Qinghai-Tibetan Plateau, respectively.