TY - JOUR
T1 - Hydrologic Changes Drove the Late Miocene Expansion of C4 Grasslands on the Northern Indian Subcontinent
AU - Polissar, Pratigya J.
AU - Uno, Kevin T.
AU - Phelps, Samuel R.
AU - Karp, Allison T.
AU - Freeman, Katherine H.
AU - Pensky, Jennifer L.
N1 - Funding Information:
The authors thank John Barry and Kay Behrensmeyer for updated ages on Pakistani Siwalik soil carbonates, Jay Quade for sharing the correlation of his Surai Khola measurements to older stratigraphy, current and former members of the Harvard University Siwaliks Research team, especially Michele Morgan for sharing tooth enamel data and Sherry Nelson for sharing data and sampling details from Siwalik equids, and Nicole deRoberts for laboratory assistance. The authors also thank two anonymous reviewers and editor Matthew Huber for their thoughtful comments that greatly strengthened the manuscript. This research used samples and data provided by the International Ocean Discovery Program (IODP) and its predecessors, supported by funding from the U.S. National Science Foundation and other member nations. This research was supported by the U.S. National Science Foundation through graduate research fellowships to S.R.P (DGE 16‐44869) and A.T.K (DGE 12‐55832) and undergraduate student participation through the LDEO intern program (OCE 13‐59194), an LDEO Climate Center grant (funded by the Vetlesen Foundation), and by the Center for Climate and Life at Columbia University (P.J.P. and K.T.U.).
Funding Information:
The authors thank John Barry and Kay Behrensmeyer for updated ages on Pakistani Siwalik soil carbonates, Jay Quade for sharing the correlation of his Surai Khola measurements to older stratigraphy, current and former members of the Harvard University Siwaliks Research team, especially Michele Morgan for sharing tooth enamel data and Sherry Nelson for sharing data and sampling details from Siwalik equids, and Nicole deRoberts for laboratory assistance. The authors also thank two anonymous reviewers and editor Matthew Huber for their thoughtful comments that greatly strengthened the manuscript. This research used samples and data provided by the International Ocean Discovery Program (IODP) and its predecessors, supported by funding from the U.S. National Science Foundation and other member nations. This research was supported by the U.S. National Science Foundation through graduate research fellowships to S.R.P (DGE 16-44869) and A.T.K (DGE 12-55832) and undergraduate student participation through the LDEO intern program (OCE 13-59194), an LDEO Climate Center grant (funded by the Vetlesen?Foundation), and by the Center for Climate and Life at Columbia University (P.J.P. and K.T.U.).
Publisher Copyright:
© 2021. American Geophysical Union. All Rights Reserved.
PY - 2021/4
Y1 - 2021/4
N2 - Modern tropical and subtropical C4 grasslands and savannas were established during the late-Miocene and Pliocene, over 20 Myr after evolutionary originations of the C4 photosynthetic pathway. This lag suggests environmental factors first limited and then favored C4 plants. Here, we examine the timing and drivers for the establishment of C4 grasslands on the Indian Subcontinent using carbon and hydrogen isotope signatures of plant-wax n-alkanes recovered from turbidites in the Bengal Fan. Like prior studies, we find C4 ecosystems in the Ganges-Brahmaputra catchment first emerged at 7.4 Ma and subsequently expanded between 6.9 to ∼6.0 Ma. Hydrogen isotope values varied from 10.2 to 7.4 Ma and then increased after 7.4, which suggests intermittent drying began before the establishment of C4 grasslands with further drying at the onset of C4 expansion. Synthesis of published plant fossil data from the Siwalik Group of the Himalayan foreland basin documents an ecosystem trajectory from evergreen tropical forests to seasonally deciduous forests, and then expansive C4 grasslands. This trajectory coincided with a seasonally uneven drying trend due to both increased evaporation of plant leaf and soil waters and reduced rainfall, as identified in soil carbonate and tooth enamel data sets. Collectively the fossil, biomarker, and isotopic evidence reveal the development of modern C4 ecosystems on the Indian Subcontinent followed a series of ecosystem transformations driven by drying and fire feedbacks, and possibly declining atmospheric pCO2, beginning at 10.2 Ma and strengthening through the late Miocene.
AB - Modern tropical and subtropical C4 grasslands and savannas were established during the late-Miocene and Pliocene, over 20 Myr after evolutionary originations of the C4 photosynthetic pathway. This lag suggests environmental factors first limited and then favored C4 plants. Here, we examine the timing and drivers for the establishment of C4 grasslands on the Indian Subcontinent using carbon and hydrogen isotope signatures of plant-wax n-alkanes recovered from turbidites in the Bengal Fan. Like prior studies, we find C4 ecosystems in the Ganges-Brahmaputra catchment first emerged at 7.4 Ma and subsequently expanded between 6.9 to ∼6.0 Ma. Hydrogen isotope values varied from 10.2 to 7.4 Ma and then increased after 7.4, which suggests intermittent drying began before the establishment of C4 grasslands with further drying at the onset of C4 expansion. Synthesis of published plant fossil data from the Siwalik Group of the Himalayan foreland basin documents an ecosystem trajectory from evergreen tropical forests to seasonally deciduous forests, and then expansive C4 grasslands. This trajectory coincided with a seasonally uneven drying trend due to both increased evaporation of plant leaf and soil waters and reduced rainfall, as identified in soil carbonate and tooth enamel data sets. Collectively the fossil, biomarker, and isotopic evidence reveal the development of modern C4 ecosystems on the Indian Subcontinent followed a series of ecosystem transformations driven by drying and fire feedbacks, and possibly declining atmospheric pCO2, beginning at 10.2 Ma and strengthening through the late Miocene.
UR - http://www.scopus.com/inward/record.url?scp=85105002528&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85105002528&partnerID=8YFLogxK
U2 - 10.1029/2020PA004108
DO - 10.1029/2020PA004108
M3 - Article
AN - SCOPUS:85105002528
SN - 2572-4517
VL - 36
JO - Paleoceanography and Paleoclimatology
JF - Paleoceanography and Paleoclimatology
IS - 4
M1 - e2020PA004108
ER -