TY - JOUR T1 - Mid- to Late-Holocene Australian–Indonesian summer monsoon variability JF - Quaternary Science Reviews Y1 - 2014 A1 - Steinke, Stephan A1 - Mohtadi, Mahyar A1 - Prange, Matthias A1 - Varma, Vidya A1 - Pittauerova, Daniela A1 - Fischer, Helmut W. AB - The Australian–Indonesian monsoon has a governing influence on the agricultural practices and livelihood in the highly populated islands of Indonesia. However, little is known about the factors that have influenced past monsoon activity in southern Indonesia. Here, we present a ∼6000 years high-resolution record of Australian-Indonesian summer monsoon (AISM) rainfall variations based on bulk sediment element analysis in a sediment archive retrieved offshore northwest Sumba Island (Indonesia). The record suggests lower riverine detrital supply and hence weaker AISM rainfall between 6000 yr BP and ∼3000 yr BP compared to the Late Holocene. We find a distinct shift in terrigenous sediment supply at around 2800 yr BP indicating a reorganization of the AISM from a drier Mid Holocene to a wetter Late Holocene in southern Indonesia. The abrupt increase in rainfall at around 2800 yr BP coincides with a grand solar minimum. An increase in southern Indonesian rainfall in response to a solar minimum is consistent with climate model simulations that provide a possible explanation of the underlying mechanism responsible for the monsoonal shift. We conclude that variations in solar activity play a significant role in monsoonal rainfall variability at multi-decadal and longer timescales. The combined effect of orbital and solar forcing explains important details in the temporal evolution of AISM rainfall during the last 6000 years. By contrast, we find neither evidence for volcanic forcing of AISM variability nor for a control by long-term variations in the El Niño-Southern Oscillation (ENSO). VL - 93 UR - http://www.sciencedirect.com/science/article/pii/S027737911400122X JO - Mid- to Late-Holocene Australian–Indonesian summer monsoon variability ER - TY - JOUR T1 - North Atlantic forcing of tropical Indian Ocean climate JF - Nature Y1 - 2014 A1 - Mohtadi, Mahyar A1 - Prange, Matthias A1 - Oppo, Delia W. A1 - De Pol-Holz, Ricardo A1 - Merkel, Ute A1 - Zhang, Xiao A1 - Steinke, Stephan A1 - ückge, Andreas KW - Palaeoceanography KW - Palaeoclimate AB - The response of the tropical climate in the Indian Ocean realm to abrupt climate change events in the North Atlantic Ocean is contentious. Repositioning of the intertropical convergence zone is thought to have been responsible for changes in tropical hydroclimate during North Atlantic cold spells1, 2, 3, 4, 5, but the dearth of high-resolution records outside the monsoon realm in the Indian Ocean precludes a full understanding of this remote relationship and its underlying mechanisms. Here we show that slowdowns of the Atlantic meridional overturning circulation during Heinrich stadials and the Younger Dryas stadial affected the tropical Indian Ocean hydroclimate through changes to the Hadley circulation including a southward shift in the rising branch (the intertropical convergence zone) and an overall weakening over the southern Indian Ocean. Our results are based on new, high-resolution sea surface temperature and seawater oxygen isotope records of well-dated sedimentary archives from the tropical eastern Indian Ocean for the past 45,000 years, combined with climate model simulations of Atlantic circulation slowdown under Marine Isotope Stages 2 and 3 boundary conditions. Similar conditions in the east and west of the basin rule out a zonal dipole structure as the dominant forcing of the tropical Indian Ocean hydroclimate of millennial-scale events. Results from our simulations and proxy data suggest dry conditions in the northern Indian Ocean realm and wet and warm conditions in the southern realm during North Atlantic cold spells. VL - 509 UR - http://www.nature.com/doifinder/10.1038/nature13196 IS - 7498 ER - TY - JOUR T1 - Glacial to Holocene swings of the Australian-Indonesian monsoon JF - Nature Geoscience Y1 - 2011 A1 - Mohtadi, Mahyar A1 - Oppo, Delia W. A1 - Steinke, Stephan A1 - Stuut, Jan-Berend W. A1 - De Pol-Holz, Ricardo A1 - Hebbeln, Dierk A1 - Lueckge, Andreas AB - The Australian-Indonesian monsoon is an important component of the climate system in the tropical Indo-Pacific region(1). However, its past variability, relation with northern and southern high-latitude climate and connection to the other Asian monsoon systems are poorly understood. Here we present high-resolution records of monsoon-controlled austral winter upwelling during the past 22,000 years, based on planktic foraminiferal oxygen isotopes and faunal composition in a sedimentary archive collected offshore southern Java. We show that glacial-interglacial variations in the Australian-Indonesian winter monsoon were in phase with the Indian summer monsoon system, consistent with their modern linkage through cross-equatorial surface winds. Likewise, millennial-scale variability of upwelling shares similar sign and timing with upwelling variability in the Arabian Sea. On the basis of element composition and grain-size distribution as precipitation-sensitive proxies in the same archive, we infer that (austral) summer monsoon rainfall was highest during the Bolling-Allerod period and the past 2,500 years. Our results indicate drier conditions during Heinrich Stadial 1 due to a southward shift of summer rainfall and a relatively weak Hadley cell south of the Equator. We suggest that the Australian-Indonesian summer and winter monsoon variability were closely linked to summer insolation and abrupt climate changes in the northern hemisphere. VL - 4 IS - 8 N1 - id: 2012; PT: J; UT: WOS:000293277100016 JO - Glacial to Holocene swings of the Australian-Indonesian monsoon ER -