Publication Date:
2022-05-26
Description:
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2012
Description:
The Indian monsoon affects the livelihood of over one billion people. Despite the
importance of climate to society, knowledge of long-term monsoon variability is limited.
This thesis provides Holocene records of monsoon variability, using sediment cores from
river-dominated margins of the Bay of Bengal (off the Godavari River) and the Arabian
Sea (off the Indus River). Carbon isotopes of terrestrial plant leaf waxes (δ13Cwax)
preserved in sediment provide integrated and regionally extensive records of flora for
both sites. For the Godavari River basin the δ13Cwax record shows a gradual increase in
aridity-adapted vegetation from ~4,000 until 1,700 years ago followed by the persistence
of aridity-adapted plants to the present. The oxygen isotopic composition of planktonic
foraminifera from this site indicates drought-prone conditions began as early as ~3,000
years BP. The aridity record also allowed examination of relationships between
hydroclimate and terrestrial carbon discharge to the ocean. Comparison of radiocarbon
measurements of sedimentary plant waxes with planktonic foraminifera reveal increasing
age offsets starting ~4,000 yrs BP, suggesting that increased aridity slows carbon cycling
and/or transport rates. At the second site, a seismic survey of the Indus River subaqueous
delta describes the morphology and Holocene sedimentation of the Pakistani shelf and
identified suitable coring locations for paleoclimate reconstructions. The δ13Cwax record
shows a stable arid climate over the dry regions of the Indus plain and a terrestrial biome
dominated by C4 vegetation for the last 6,000 years. As the climate became more arid
~4,000 years, sedentary agriculture took hold in central and south India while the urban
Harappan civilization collapsed in the already arid Indus basin. This thesis integrates
marine and continental records to create regionally extensive paleoenvironmental
reconstructions that have implications for landscape evolution, sedimentation, the
terrestrial organic carbon cycle, and prehistoric human civilizations in the Indian
subcontinent.
Description:
This thesis was funded by the National Science Foundation, Woods Hole Oceanographic
Institution (Arctic Research Initiative, Ocean and Climate Change Institute, Coastal
Oceans Institute, Stanley Watson Chair for Excellence in Oceanography and the
Academic Programs Office), and by the ETH Zurich.
Keywords:
Monsoons
;
Paleoclimatology
;
Holocene
;
Pelagia (Ship) Cruise 64PE300
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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