Abstract
Reconstruction of monsoon evolution in the tropical Indian Ocean and evaluation of its influence on large-scale ocean circulation and sea-air interaction processes can help us understand climate driving mechanisms. Herein, we used a gravity core SO184-10043 to present the marine sedimentary record from the southernmost Sumatra, spanning the past 35 kyr. The age model is well constrained by 12 accelerator mass spectrometry (AMS) radiocarbon dates determined in mixed planktic foraminifera. We also measured sediment grain size and major and trace elements to reconstruct the variations in hydrodynamic conditions and chemical weathering intensity. These data were then used to reveal the evolution of the northwest (Indonesian) monsoon system over the past 35 kyr. The results showed that both monsoon current and chemical weathering coincided with summer insolation in the Northern Hemisphere and responded to glacial-interglacial climate changes in the northern Atlantic. Higher grain-size values of sensitive components, increased chemical index of alteration (CIA), and Ba/Sr ratios, together with lower CaO/MgO ratios, reflect a stronger monsoon current and chemical weathering during the late marine isotope stage 3 and Holocene. Higher intensity of chemical weathering might be attributed to a stronger northwest monsoon carrying warm and moist air from the Asian continent to Indonesian waters. Lower values of sensitive components, CIA, and Ba/Sr, along with higher CaO/MgO values, reveal a weaker monsoon current and lower intensity of chemical weathering during the last glaciation-deglaciation phase, which was controlled by a weaker monsoon system. At a millennial timescale, cold events occurred during the following intervals: 30–26 ka BP, Heinrich Stadial 1 (HS1; 18–15 ka BP), Last Glacial Maximum (LGM; 23–18 ka BP), Younger Dryas (YD; 11–10 ka BP), and 8.2 ka BP. The same cold events were identified from core SO184-10043, indicating a perfect match with climatic cooling in the Northern Hemisphere. We also observed periodicities of ~ 7.9 ka, 3.0–3.1 ka, 2.2–2.3 ka, and ~ 1.0 ka in our core records. These periodicities are coincident with solar-induced climate changes and support the hypothesis that monsoon evolution in the tropical Indian Ocean during the late Pleistocene coincided with the climate change in the Northern Hemisphere.
Highlights
Monsoonal climate dominates over the northern Indian Ocean, and marine records have revealed its close relationship with global climate changes during the late Pleistocene (Mohtadi et al 2014; Li et al 2016)
These data further support the Conclusions We conducted a paleoclimatic reconstruction for core SO184-10043 collected from the southernmost coast of Sumatra using sedimentological, geochemical, and elemental proxies in order to reconstruct the monsoon evolution and its response to the Northern Hemisphere climate changes
On a glacial-interglacial timescale, both monsoon current and chemical weathering coincided with summer insolation in the Northern Hemisphere and showed a clear response to the glacial-interglacial changes
Summary
Monsoonal climate dominates over the northern Indian Ocean, and marine records have revealed its close relationship with global climate changes during the late Pleistocene (Mohtadi et al 2014; Li et al 2016). Coastal waters of Sumatra span the equator in the northeastern Indian Ocean and are influenced by seasonal rhythms, i.e., by the southeast Malaysian-Australian monsoon and northwest Indonesian monsoon. These monsoon systems show a biennial alternation between central Asia and Australia (Tomczak and Godfrey 2001; Lückge et al 2009). Precipitation in Indonesia is relatively low between June and September, when the dominant southeast monsoon carries warm and dry air from Australia (Gingele et al 2002; Spooner et al 2005; Lückge et al 2009). During the southeast monsoon season, the SJC weakens and may even turn back to the west, feeding the South Equatorial Current (SEC) (Wyrtki 1962; Murgese et al 2008)
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