Abstract
Indian-Asian monsoon has oscillated between warm/wet interglacial periods and cool/dry glacial periods with periodicities closely linked to variations in Earth’s orbital parameters. However, processes that control wet versus dry, i.e. aridity cyclical periods on the orbital time-scale in the low latitudes of the Indian-Asian continent remain poorly understood because records over millions of years are scarce. The sedimentary record from International Ocean Discovery Program (IODP) Expedition 359 provides a well-preserved, high-resolution, continuous archive of lithogenic input from the Maldives reflecting on low-latitude aridity cycles. Variability within the lithogenic component of sedimentary deposits of the Maldives results from changes in monsoon-controlled sedimentary sources. Here, we present X-ray fluorescence (XRF) core-scanning results from IODP Site U1467 for the past two million years, allowing full investigation of orbital periodicities. We specifically use the Fe/K as a terrestrial climate proxy reflecting on wet versus dry conditions in the source areas of the Indian-Asian landmass, or from further afield. The Fe/K record shows orbitally forced cycles reflecting on changes in the relative importance of aeolian (stronger winter monsoon) during glacial periods versus fluvial supply (stronger summer monsoon) during interglacial periods. For our chronology, we tuned the Fe/K cycles to precessional insolation changes, linking Fe/K maxima/minima to insolation minima/maxima with zero phase lag. Wavelet and spectral analyses of the Fe/K record show increased dominance of the 100 kyr cycles after the Mid Pleistocene Transition (MPT) at 1.25 Ma in tandem with the global ice volume benthic δ18O data (LR04 record). In contrast to the LR04 record, the Fe/K profile resolves 100-kyr-like cycles around the 130 kyr frequency band in the interval from 1.25 to 2 million years. These 100-kyr-like cycles likely form by bundling of two or three obliquity cycles, indicating that low-latitude Indian-Asian climate variability reflects on increased tilt sensitivity to regional eccentricity insolation changes (pacing tilt cycles) prior to the MPT. The implication of appearance of the 100 kyr cycles in the LR04 and the Fe/K records since the MPT suggests strengthening of a climate link between the low and high latitudes during this period of climate transition.
Highlights
Over the last two million years (Myr), the Earth’s climate has oscillated between cold and warm periods driven by semi-periodic changes of the Earth’s orbit around the Sun
Ice volume increased during glacial periods post-Mid Pleistocene Transition (MPT), ice volume and temperature maxima remained relatively constant during the interglacial periods for mid and low latitudes (Herbert et al 2010; Rodrigues et al 2017)
Scanning electron microscope Primary observations by scanning electron microscope (SEM) show the presence of dust particles
Summary
Over the last two million years (Myr), the Earth’s climate has oscillated between cold and warm periods driven by semi-periodic changes of the Earth’s orbit around the Sun. The general trend of Earth’s climate shows a shift towards colder conditions, marked by a stepped increase in the amplitude of glacial ice volume across the Mid Pleistocene Transition (MPT; for an overview, see Head and Gibbard (2015), they used the term Early-Middle Pleistocene Transition). The emergence of the 100 kyr cycles is still a matter of debate and it is unclear why the Earth’s climate system started to respond non-linearly to orbital forcing Ice volume increased during glacial periods post-MPT, ice volume and temperature maxima remained relatively constant during the interglacial periods for mid and low latitudes (Herbert et al 2010; Rodrigues et al 2017)
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