Publication Date:
2022-05-26
Description:
© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 478 (2017): 89-101, doi:10.1016/j.epsl.2017.08.013.
Description:
Climate has been proposed to control both the rate of terrestrial silicate weathering and
the export rate of associated sediments and terrestrial organic carbon to river-dominated margins
– and thus the rate of sequestration of atmospheric CO2 in the coastal ocean – over glacial-interglacial timescales. Focused on the Ganges-Brahmaputra rivers, this study presents records of
post-glacial changes in basin-scale Indian summer monsoon intensity and vegetation composition based on stable hydrogen (δD) and carbon (δ13C) isotopic compositions of terrestrial
plant wax compounds preserved in the channel-levee system of the Bengal Fan. It then explores
the role of these changes in controlling the provenance and degree of chemical weathering of
sediments exported by these rivers, and the potential climate feedbacks through organic-carbon
burial in the Bengal Fan. An observed 40‰ shift in δD and a 3–4‰ shift in both bulk organic-carbon and plant-wax δ13C values between the late glacial and mid-Holocene, followed by a
return to more intermediate values during the late Holocene, correlates well with regional post-glacial paleoclimate records. Sediment provenance proxies (Sr, Nd isotopic compositions) reveal
that these changes likely coincided with a subtle focusing of erosion on the southern flank of the
Himalayan range during periods of greater monsoon strength and enhanced sediment discharge.
However, grain-size-normalized organic-carbon concentrations in the Bengal Fan remained
constant through time, despite order-of-magnitude level changes in catchment-scale monsoon
precipitation and enhanced chemical weathering (recorded as a gradual increase in K/Si* and
detrital carbonate content, and decrease in H2O+/Si*, proxies) throughout the study period.
These findings demonstrate a partial decoupling of climate change and silicate weathering during
the Holocene and that marine organic-carbon sequestration rates primary reflect rates of physical
erosion and sediment export as modulated by climatic changes. Together, these results reveal the
magnitude of climate changes within the Ganges-Brahmaputra basin following deglaciation and
a closer coupling of monsoon strength with OC burial than with silicate weathering on millennial
timescales.
Description:
This work was supported by the National
Science Foundation [grant numbers OCE-1333826 and OCE-1333387].
Keywords:
Indian Monsoon
;
Bengal Fan
;
Paleoclimate
;
Sediment Provenance
;
Biomarkers
;
Stable Isotopes
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
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