Sub-Orbital Scale variations in the Intensity of the Arabian Sea Monsoon
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Date
07/2005Author
Ivanochko, Tara S
Metadata
Abstract
A high-resolution multi-proxy reconstruction of the Arabian Sea
Summer Monsoon (ASSM) intensity over the past 90,000 years has been
determined using two marine sediment cores: one from the Somali margin
and one from the Indian margin. This reconstruction indicates that changes in
monsoon- induced upwelling, primary productivity and denitrification have
varied in synchrony with Dansgaard-Oeschger (D-O) cycles. Increased
monsoon intensity correlates with warm climate events (interstadials) and
decreased monsoon intensity, which coincides with stadials and Heinrich
Events, is confirmed by elevated dust concentrations in the marine cores.
A comparison of the Somali and Indian margin cores with previously
reported studies from the Northern and Western Basin allows the identification
of discrete sediment signals from the Indus River, the Arabian Peninsula and
from local riverine runoff. Sedimentary deposition on the Indian margin during
interglacials is dominated by local terrestrial runoff, whereas during glacial
periods increased dust input from the Arabian Peninsula is evident. Both
signals are related to changes in the intensity of the ASSM.
Monsoon intensity has decreased during the Holocene as the
Intertropical Convergence Zone (ITCZ) has moved to a more southerly
position. The ASSM-ITCZ relationship (increased ASSM intensity and a
northern ITCZ, decreased ASSM intensity and a southern ITCZ) has
remained consistent over the last glacial cycle suggesting that global
millennial scale climatic variability is in part driven by modulations in tropical
hydrological cycle. This ASSM reconstruction provides evidence that
rearrangements in the tropical convection system affected atmospheric dust
concentrations as well as the concentration and location of atmospheric water
vapour. In addition to modulating terrestrial and marine emissions of
greenhouse gases, variation in the tropical hydrological cycle provides a
mechanism of amplifying and perpetuating millennial-scale climatic changes.