Late Miocene weakening of the South Asian Monsoon: Insights from the Siwalik of Nepal

Purushottam Adhikari; Gaurav Srivastava; Alexander Farnsworth; Harshita Bhatia; Sadanand; Sujata Poudel; Robert A. Spicer; Lalit K. Rai; Su Tao; Paul J. Valdes; Khum N. Paudayal

doi:10.1016/j.palaeo.2025.112789

Late Miocene weakening of the South Asian Monsoon: Insights from the Siwalik of Nepal

Purushottam Adhikari^*, Gaurav Srivastava, Alexander Farnsworth, Harshita Bhatia, Sadanand, Sujata Poudel, Robert A. Spicer, Lalit K. Rai, Su Tao, Paul J. Valdes, Khum N. Paudayal

^*Corresponding author for this work

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Abstract

The South Asian Monsoon (SAM) is the strong summer monsoon within the Asian Monsoon System, driven by the thermal gradient between the warmer Asian landmass and the cooler Indian Ocean. High-resolution marine proxies indicate a decline in SAM strength after approximately 10 million years ago (Ma); however, terrestrial evidence has been limited. We present high-resolution and well-dated leaf assemblages from the Lower and Middle Siwalik of central Nepal, supported by paleoclimate modelling, which suggest a weakening of the SAM between 10.24 and 8.5 Ma. This decline is linked to a reduction in moisture supply, possibly due to a weakening of the Somali Jet. Our study highlights the potential of leaf physiognomy to reconstruct monsoon strength.

Original language	English
Article number	112789
Number of pages	14
Journal	Palaeogeography, Palaeoclimatology, Palaeoecology
Volume	664
Early online date	7 Feb 2025
DOIs	https://doi.org/10.1016/j.palaeo.2025.112789
Publication status	Published - 15 Apr 2025

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Publisher Copyright:
© 2024

Keywords

Leaf flora
Neogene
Somali Jet
Summer monsoon

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title = "Late Miocene weakening of the South Asian Monsoon: Insights from the Siwalik of Nepal",

abstract = "The South Asian Monsoon (SAM) is the strong summer monsoon within the Asian Monsoon System, driven by the thermal gradient between the warmer Asian landmass and the cooler Indian Ocean. High-resolution marine proxies indicate a decline in SAM strength after approximately 10 million years ago (Ma); however, terrestrial evidence has been limited. We present high-resolution and well-dated leaf assemblages from the Lower and Middle Siwalik of central Nepal, supported by paleoclimate modelling, which suggest a weakening of the SAM between 10.24 and 8.5 Ma. This decline is linked to a reduction in moisture supply, possibly due to a weakening of the Somali Jet. Our study highlights the potential of leaf physiognomy to reconstruct monsoon strength.",

keywords = "Leaf flora, Neogene, Somali Jet, Summer monsoon",

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T1 - Late Miocene weakening of the South Asian Monsoon

T2 - Insights from the Siwalik of Nepal

AU - Adhikari, Purushottam

AU - Srivastava, Gaurav

AU - Farnsworth, Alexander

AU - Bhatia, Harshita

AU - Sadanand,

AU - Poudel, Sujata

AU - Spicer, Robert A.

AU - Rai, Lalit K.

AU - Tao, Su

AU - Valdes, Paul J.

AU - Paudayal, Khum N.

PY - 2025/4/15

Y1 - 2025/4/15

N2 - The South Asian Monsoon (SAM) is the strong summer monsoon within the Asian Monsoon System, driven by the thermal gradient between the warmer Asian landmass and the cooler Indian Ocean. High-resolution marine proxies indicate a decline in SAM strength after approximately 10 million years ago (Ma); however, terrestrial evidence has been limited. We present high-resolution and well-dated leaf assemblages from the Lower and Middle Siwalik of central Nepal, supported by paleoclimate modelling, which suggest a weakening of the SAM between 10.24 and 8.5 Ma. This decline is linked to a reduction in moisture supply, possibly due to a weakening of the Somali Jet. Our study highlights the potential of leaf physiognomy to reconstruct monsoon strength.

AB - The South Asian Monsoon (SAM) is the strong summer monsoon within the Asian Monsoon System, driven by the thermal gradient between the warmer Asian landmass and the cooler Indian Ocean. High-resolution marine proxies indicate a decline in SAM strength after approximately 10 million years ago (Ma); however, terrestrial evidence has been limited. We present high-resolution and well-dated leaf assemblages from the Lower and Middle Siwalik of central Nepal, supported by paleoclimate modelling, which suggest a weakening of the SAM between 10.24 and 8.5 Ma. This decline is linked to a reduction in moisture supply, possibly due to a weakening of the Somali Jet. Our study highlights the potential of leaf physiognomy to reconstruct monsoon strength.

KW - Leaf flora

KW - Neogene

KW - Somali Jet

KW - Summer monsoon

UR - https://www.scopus.com/pages/publications/85217966304

U2 - 10.1016/j.palaeo.2025.112789

DO - 10.1016/j.palaeo.2025.112789

M3 - Article (Academic Journal)

AN - SCOPUS:85217966304

SN - 0031-0182

VL - 664

JO - Palaeogeography, Palaeoclimatology, Palaeoecology

JF - Palaeogeography, Palaeoclimatology, Palaeoecology

M1 - 112789

ER -

Late Miocene weakening of the South Asian Monsoon: Insights from the Siwalik of Nepal

Abstract

Bibliographical note

Keywords

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