Monsoon-influenced variation in productivity and lithogenic sediment flux since 110 ka in the offshore Mahanadi Basin, northern Bay of Bengal

The Indian monsoon drives seasonal changes in precipitation and weathering across India as well as circulation and productivity in the northern Indian Ocean. Variation in paleo-monsoon intensity and its effect on productivity and lithogenic fluxes is poorly constrained in the Bay of Bengal. In this...

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Bibliographic Details
Published in:Marine and petroleum geology 2014-12, Vol.58, p.502-525
Main Authors: Phillips, Stephen C., Johnson, Joel E., Giosan, Liviu, Rose, Kelly
Format: Article
Language:English
Subjects:
Basins
Bay of Bengal
Bulk density
C4 plant
Calcium carbonate
Grain size
India
Indian Ocean
Magnetic susceptibility
Marine
Mass accumulation rate
Monsoons
Organic carbon
Productivity
Southwest
Zr/Rb
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Summary:The Indian monsoon drives seasonal changes in precipitation and weathering across India as well as circulation and productivity in the northern Indian Ocean. Variation in paleo-monsoon intensity and its effect on productivity and lithogenic fluxes is poorly constrained in the Bay of Bengal. In this paper, we present analysis of a sediment record from the offshore Mahanadi Basin recovered during the Indian National Gas Hydrate Program Expedition 01 (Site NGHP-01-19B). We reconstruct variation in biogenic and lithogenic components during the last 110 kyr using measurements of total organic carbon (TOC), total nitrogen (TN), TOC/TN, CaCO3, biogenic silica (BSi), δ13TOC, δ15TN, bulk mineralogy from X-ray diffraction, bulk and lithogenic grain size distribution, magnetic susceptibility, bulk density, and Ca, Br, and Zr/Rb from x-ray fluorescence (XRF). The mass-accumulation rate (MAR) of CaCO3, a function of marine productivity, drastically increased between 70 and 10 ka and is correlated to previously-documented elevated Asian dust fluxes and increased Bay of Bengal salinity during a weakened southwest monsoon. Decreased freshwater input over this period likely diminished stratification, allowing for increased mixing and nutrient availability, thus enhancing productivity despite weaker southwest monsoon winds. The MAR of lithogenic material is highest during the Holocene suggesting that sediment supply driven by monsoon intensity is a stronger control on margin sedimentation than sea level at the Mahanadi Basin. Over the entire record, magnetic susceptibility and XRF Zr/Rb are strongly correlated with CaCO3, suggesting higher primary mineral input under a weakened southwest monsoon. TOC/TN and δ13TOC also increase under glacial conditions, suggesting higher relative input of terrestrial C4 organic matter. These results highlight the Mahanadi Basin as a supply-dominated margin where terrigenous sedimentation is strongly influenced by monsoon intensity, and that productivity is limited by variation in monsoon-driven stratification on glacial-interglacial timescales rather than a direct response to monsoon winds. •Enhanced northern Bay of Bengal productivity 70–10 ka.•Lithogenic mass accumulation rates higher during Holocene compared to 110–12 ka.•Lithogenic mass accumulation rates correlate to solar insolation since 23 ka.•C4 plant and terrigenous organic matter abundant 86–11 ka and 107–100 ka.•Zr/Rb and magnetic susceptibility vary with regional chemical weath
ISSN:0264-8172
1873-4073
DOI:10.1016/j.marpetgeo.2014.05.007