Nonstationary Phase of the Plio-Pleistocene Asian Monsoon

Abstract

Paleoclimate records indicate that the strength of the Asian summer monsoon is sensitive to orbital forcing at the obliquity and precession periods (41,000 and 23,000 years, respectively) and the extent of Northern Hemisphere glaciation. Over the past 2.6 million years, the timing (phase) of strong monsoons has changed by approximately 83 degrees in the precession and approximately 124 degrees in the obliquity bands relative to the phase of maximum global ice volume (inferred from the marine oxygen isotope record). These results suggest that one or both of these systems is nonstationary relative to orbital forcing.

The middle Pleistocene transition: characteristics, mechanisms, and implications for long-term changes in atmospheric pCO2

“…Dwyer et al (1995) Changes in other components of the climate system indicate differing sensitivities to the changes in global ice volume and deep-water temperature that occurred during the MPT. The onset of the MPT was accompanied by decreases in sea surface temperatures (SSTs) in the North Atlantic (Ruddiman et al, 1989) and tropical-ocean upwelling regions (Schefus et al, 2004;Liu and Herbert, 2004;McClymont and Rossel-Mele, 2005) and by an increase in African (Tiedemann et al, 1994) and Asian aridity and monsoonal intensity (Clemens et al, 1996;Williams et al, 1997;Sun et al, 2006). The low-frequency component of North Atlantic SSTs and proxies of Asian and African monsoon and aridity also appeared at this time.…”

“…Similarly, ODP Site 722 in the Arabian Sea indicates no change in the percent of dust derived from northeast African and Arabian sources associated with Indian monsoon surface winds (not shown), but an increase in eolian flux is clearly apparent at $1350 ka ( Fig. 8c) (Clemens et al, 1996). Sun et al (2006) interpret the Chinese loess grain size record to identify an increase in the mean intensity and amplitude of the winter monsoon at the start of the MPT (Fig.…”

“…10c). In this Dd 13 C (AÀP) record, the change to more depleted glacial d 13 C values seen in the Site 607 record at (Tiedemann et al, 1994), (c) Flux of terrigenous (eolian) sediments in ODP Site 722 (Clemens et al, 1996), (d) Stacked record of normalized mean grain size of quartz (MGSQ) from loess sequences on the Chinese Loess Plateau (Sun et al, 2006), (e) Percent biogenic silica from Lake Baikal, south-central Siberia (Williams et al, 1997). Broad light-gray vertical bar shows timing of the MPT (Fig.…”

“…10b). (Clemens et al, 1996) (window length ¼ 300 kyr, sliding window length ¼ 30 kyr, data interpolated at 0.5 kyr, high-pass filter with corner frequency 0.00125), (c) Spectrogram of stacked mean grain size record from Chinese Loess Plateau (Sun et al, 2006) (window length ¼ 300 kyr, sliding window length ¼ 30 kyr, data interpolated at 1.0 kyr, high-pass filter with corner frequency 0.0025), (d) Spectrogram of percent biogenic silica from Lake Baikal, south-central Siberia (Williams et al, 1997) (window length ¼ 300 kyr, sliding window length ¼ 30 kyr, data interpolated at 0.5 kyr, high-pass filter with corner frequency 0.0025). All records are shown on their published age models.…”

“…The percent and flux of eolian sediments to adjacent oceans is a proxy for aridity of the source area (Tiedemann et al, 1994;deMenocal, 1995;Clemens et al, 1996), whereas monsoon wind strength can be estimated from the grain size of wind-blown lithogenic sediments deposited in the oceans and on the loess plateau of China (Clemens et al, 1996;Sun et al, 2006). Lastly, Williams et al (1997) interpret the sedimentary record of biogenic silica in Lake Baikal, south-central Siberia, as a proxy for temperature, with high biogenic silica percentages associated with warmer waters in the lake.…”