South Asian summer monsoon enhanced by the uplift of Iranian Plateau in Middle Miocene

Abstract

Abstract. The South Asian summer monsoon (SASM) remarkably strengthened during the Middle Miocene (16–11 Ma), coincident with the rapid uplifts of the Iranian Plateau (IP) and the Himalaya (HM). Although the development of the SASM has long been linked to the topographic changes in the Tibetan Plateau (TP) region, the effects of the HM and IP uplift are still vigorously debated, and the underlying mechanisms remain unclear. Based on Middle Miocene paleogeography, we employ the fully coupled earth system model CESM to perform a set of topographic sensitivity experiments with altered altitudes of the IP and the HM. Our simulations reproduce the strengthening of the SASM in northwestern India and over the Arabian Sea, largely attributing to the thermal effect of the IP uplift. The elevated IP insulates the warm and moist airs from the westerlies in the south of the IP and produces a low-level cyclonic circulation around the IP, which leads to the convergence of the warm and moist air in the northwestern India and triggers positive feedback between the moist convection and the large-scale monsoon circulation, further enhancing the monsoonal precipitation. Whereas the HM uplift produces orographic precipitation without favorable circulation adjustment for the SASM. We thus interpret the intensification of the Middle Miocene SASM in the western part of the South Asia as a response to the IP uplift while the subtle SASM change in eastern India reflects the effects of the HM uplift.

Phylogenomic Analysis of Target Enrichment and Transcriptome Data Uncovers Rapid Radiation and Extensive Hybridization in Slipper Orchid GenusCypripediumL

“…After dispersing to Southeast Asia, the time interval between the origin and the diversification of this new clade (i.e., stem age: 20.27 Ma; crown age: 15.93 Ma) indicates that extinctions might have taken place, which could explain why the ancestors of this lineage were limited to that region according to our analysis. The southeastern margins of the Tibetan Plateau may have provided potential refugia to Cypripedium from the cooling climate of the MMCT due to their warmer and more humid conditions owing to the intensification of the Asian monsoons (Xing and Ree, 2017; S Li et al ., 2020; Zuo et al ., 2022). Specifically, the isolation of the Cypripedium population in deep valleys between mountains, such as the Hengduan mountains, a biodiversity and endemism hotspot harboring the most species of Cypripedium (H Liu et al ., 2021 a ; J Liu et al ., 2022), could have promoted allopatric diversification at a highly dissected landscape from which several sections or lineages leading to sections diverged, producing the observed pattern of rapid radiations along the backbone of our phylogeny (Favre et al ., 2015; Xing and Ree, 2017; Spicer et al ., 2020).…”

“…17-15 Ma), especially at higher latitudes where mixed deciduous-evergreen forests dominated the vegetation type (Dutton and Barron, 1997;Herold et al, 2010;Steinthorsdottir et al, 2021) As global cooling took place following the MMCO (Frigola et al, 2018;Methner et al, 2020;RM Brown et al, 2022), a climatic dispersal barrier may have formed between the Old and the New World at higher latitudes, leading to a vicariance and allopatric diversification. The East and Ree, 2017;S Li et al, 2020;Zuo et al, 2022). Specifically, the isolation of the Cypripedium population in deep valleys between mountains, such as the Hengduan mountains, a biodiversity and endemism hotspot harboring the most species of Cypripedium (H Liu et al, 2021a;J Liu et al, 2022), could have promoted allopatric diversification at a highly dissected landscape from which several sections or lineages leading to sections diverged, producing the observed pattern of rapid radiations along the backbone of our phylogeny (Favre et al, 2015;Xing and Ree, 2017;Spicer et al, 2020).…”

“…Combining the results of the biogeographic and the phylogenetic network analyses, it appears that the lineage of Cypripedium that dispersed to the Old World had a hybrid origin. The ability of hybrids to adapt to new environments faster than their parent taxa (Kulmuni et al, 2024) (Xing and Ree, 2017;S Li et al, 2020;Zuo et al, 2022). Specifically, the isolation of the Cypripedium population in deep valleys between mountains, such as the Hengduan mountains, a biodiversity and endemism hotspot harboring the most species of Cypripedium (H Liu et al, 2021a;J Liu et al, 2022), could have promoted allopatric diversification at a highly dissected landscape from which several sections or lineages leading to sections diverged, producing the observed pattern of rapid radiations along the backbone of our phylogeny (Favre et al, 2015;Xing and Ree, 2017;Spicer et al, 2020).…”