Eccentricity forcing of East Asian monsoonal systems over the past 3 million years

Abstract

The East Asian summer monsoon and the precipitation it brings are relevant for millions of people. Because of the monsoon's importance, there has been a substantial amount of work attempting to describe the driving mechanisms behind its past variability. However, discrepancies exist, with speleothem-based East Asian monsoon reconstructions differing from those based on loess records from the Chinese Loess Plateau during the late Quaternary. The periodicity of wet and dry phases experienced by desert areas that lie on the periphery of the East Asian monsoon's influence offer another independent view of monsoonal variability. Here, we provide environmental records based on magnetic parameters for the last 3 million years from the Tengger Desert, China, one such marginal arid region. Our results reveal wet-dry cycles at a dominant frequency of 405 kiloyears, with drier intervals corresponding to eccentricity minima. These findings are consistent with previous reconstructions of East Asian summer and North African summer monsoon precipitation variability. Our records emphasize the dominant role of eccentricity in forcing East Asian monsoonal precipitation as well as monsoonal-derived environmental fluctuations experienced in peripheral desert areas. These results challenge the traditional view that high-latitude ice sheets are the primary driver of East Asian monsoon precipitation during the Quaternary based on Chinese loess records.

Keywords: Tengger Desert; eccentricity; environmental magnetics; monsoon.

Fig. 1.

Map showing the location of the Tengger Desert (TG) and the borehole from Chahanchi Lake. (A) Geographic location of the TG relative to other northern Chinese deserts, the Chinese Loess Plateau, and the Tibetan Plateau. The modern pattern of Asian atmospheric circulation is also shown. Luochuan and Chaona loess sites used to compare with the TG records are also shown. The green dashed line represents the current northeastern edge of the East Asian summer monsoon (EAM) (42). (B) A digital elevation model map showing the TG and surrounding mountains. The studied borehole WEDP01 is in the center of the desert.

Fig. 2.

Lithology and borehole WEDP01 magnetic parameter records on a depth scale. (A) Lithology and depositional environment (12). The four tie points used to convert depth to age are shown on the left. We used the most updated geomagnetic polarity time scale (43) to convert depth to age. The two yellow-coded lithologies correspond to eolian dune strata. E: eolian; L: lacustrine. (B) χ. (C) SIRM. (D) χ_ARM. (E) χ_ARM/χ. (F) χ_ARM/SIRM. (G) HIRM. The two orange bars indicate eccentricity minima during the past 0.5 Myr relative to the depth in borehole WEDP01.

Fig. 3.

Timeseries of insolation, Tengger Desert χ_ARM/SIRM, and East Asian speleothem oxygen isotopes and their power spectral plots over the interval of ∼310 to 90 ka. (A) 21 July insolation at 65° N (47). (B) 20 kyr and 400 kyr-band tuned χ_ARM/SIRM record. (C) Composite East Asian speleothem δ¹⁸O record (22). The dash lines indicate the amplitude variation trends. (D, E, F) Power spectral plot of A, B, and C, respectively, using orders 0 to 2 2π prolate multitapers and robust red noise modeling (41). Red, purple, and green lines indicate 90, 95, and 99% confidence limits, respectively.

Fig. 4.

Tengger Desert paleoenvironmental variations since the late Pliocene and comparison with other monsoonal records. (A) χ_ARM/SIRM records from the Chinese Loess Plateau [blue: Luochuan (31); black: Chaona (30)]. The age models of the Quaternary portion of the records are based on orbital tuning (30, 31), and the late Pliocene portion is based on paleomagnetic dating (44). (B) K/Al (counts per second ratio) from Ocean Drilling Program (ODP) Site 1143 in South China Sea (26). (C) Tengger Desert χ_ARM/SIRM record based on an orbitally tuned age model (this study). Specifically, we tuned the 400 kyr component of the record to the 400 kyr band of eccentricity (SI Appendix, Fig. S9). (D) Sapropels (gray bars) and hematite content (7) (blue line) estimated by IRM_{0.9 T}@AF120 mT for ODP Site 967 from Mediterranean Sea. (E) Benthic LR04 δ¹⁸O stack (45). (F) Eccentricity (46). The black curves in B, C, D, and F are their 400 kyr components.