Southern Hemisphere forcing of Pliocene δ¹⁸O and the evolution of Indo‐Asian monsoons

Abstract

[1] The Milankovitch paradigm links the timing (phase) of ice volume minima to summer insolation maxima in the hemisphere where ice volume dominates; consistent application of this paradigm dictates that Pliocene ice volume minima should lag Southern Hemisphere summer insolation maxima. We infer the magnitude of this lag on the basis of the phase relationship between equatorial sea surface temperature and benthic d18 O. We infer that Pliocene d18 O minima should lag obliquity maxima by 19°(2.2 ka), broadly consistent with the current global marine d18 O chronology, and precession maxima by 32°(2 ka), a difference of 160°(10.2 ka) relative to the current global marine d18 O chronology. Only in the context of this revision are Pliocene summer and winter monsoon phase relationships consistent with direct orbital forcing across the entire Indo-Asian region, including marine and terrestrial proxies from the Chinese Loess Plateau, the South China Sea, and the Arabian Sea. Strong Pliocene summer and winter monsoons were in phase with one another, strengthened at obliquity minima and precession minima; the summer monsoon was also strengthened at precession maxima, yielding a semiprecession spectral signal. Strong Pliocene monsoons at orbital extremes indicate a direct response to fast physics processes including sensible heating and cooling of the Asian landmass and, for the summer monsoon, the export of latent heat from the southern Indian Ocean. As Northern Hemisphere ice volume grew into the Pleistocene, the timing of strong winter and summer monsoons drifted apart becoming influenced by the combined effects of fast physics and slow physics (ice volume) variables. The phase of strong winter monsoons shifted toward ice maxima, and the phase of strong summer monsoons shifted toward ice minima.

High Arabian Sea productivity conditions during MIS 13 – odd monsoon event or intensified overturning circulation at the end of the Mid-Pleistocene transition?

“…The Ba and, to a lesser degree, SNW records of MD04-2881 show a high similarity with a magnetic susceptibility stack from the CLP (Clemens et al, 2008). In contrast to the Antarctic methane record and model simulation, the exceptional high productivity conditions reached during MIS 13 coincided with an exceptional thick soil horizon S5 in some loess records of the central CLP (Guo et al, 2000;Sun et al, 2006b), and with an extreme event in a monsoon record from the Tibetan plateau (Chen et al, 1999).…”

Evolution of the East Asian monsoon and its response to uplift of the Tibetan Plateau since 1.8 Ma recorded by major elements in sediments of the South China Sea

“…Pattan et al [22] attributed "excess Al" in deep-sea sediments to biogenic silicon and volcanic ash. However, for the core sediments of the ODP Site 1146, the correlation coefficient between aluminum and biogenic silicon, the concentration data of which was cited from Clemens et al [15], is just 0.3, indicating that there is no remarkable relationship between biogenic silicon and Al and that the "excess Al" is not biogenic. In fact, volcanic glass in sediments from the northern slope of the South China Sea has a greater Al/Ti ratio of up to 226 and concentrates Na 2 O [23].…”

“…R-mode analysis was performed using STSS13.0 software, and the terrestrial factor score was subsequently calculated after extraction based on element association. Both the age model and oxygen isotopic data of benthic foraminifera were directly referenced from Clemens et al [15].…”

“…In particular, there has been no study on the relationship between the evolution of the East Asian monsoon and the wholly stepwise, quick uplift of the Tibetan Plateau since the Quaternary in the South China Sea [12][13][14]. In our study, therefore, we compare the stepwise changes of the terrestrial factor, which was extracted from major-element data of fine grain-sized carbonate-free sediments (< 4 μm) of the upper 185 mcd (meters composite depth; corresponding to 1.81 Ma [15]) splice at ODP Site 1146 drilled during Leg184 in the South China Sea using R-mode analysis, with the tectonoclimatic cycles revealed by the magnetic susceptibility of Chinese loess.…”

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“…Consensus does not yet exist on the extent of the coupling or the ultimate forcing of monsoon winds and precipitation at the orbital and longer timescales Caley et al, 2011aCaley et al, , 2011bCaley et al, , 2011cCheng et al, 2009;Clemens and Prell, 2007;Clemens et al, 1996Clemens et al, , 1991Clemens et al, , 2008Ruddiman, 2006;Wang et al, 2008;Ziegler et al, 2010). Some argue for a close coupling between changes in Indian and East Asian summer monsoon winds and precipitation across the entire region spanning the Arabian Sea (Leg 117), the South China Sea (Leg 184), and terrestrial records from the Loess Plateau.…”