Cenozoic evolution of the steppe-desert biome in Central Asia

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Science Advances  09 Oct 2020:
Vol. 6, no. 41, eabb8227
DOI: 10.1126/sciadv.abb8227
  • Fig. 1 The modern Central Asian steppe-desert.

    (A) Ecological-physiognomic steppe subtypes across the Tibetan, northwestern (NW) Chinese, and Mongolian regions, with sedimentary basins and mountain ranges marked in black and white, respectively [after (1, 11, 97)]. Location of the altitudinal profile in (C) is marked in red. (B) Characteristic plant families, represented by (clockwise from top left): Ephedra sp. (Ephedraceae), Nitraria sp. (Nitrariaceae), Ceratocarpus sp. (Chenopodioideae), and Artemisia sp. (Asteraceae): all common in desert steppe and desert; Picea sp. (Pinaceae: common in forest steppe); and Achnatherum sp. (Poaceae: common in grass and shrub steppe). The latter image was photographed in the Xining Basin, Qinghai Province (photo credit: Natasha Barbolini, University of Amsterdam); all other images were taken on the southern margin of the Junggar Basin/northern slope of the Tian Shan, Xinjiang Uyghur Autonomous Region (photo credits: Hong-Xiang Zhang, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences). (C) Altitudinal profile illustrating vegetation belts of steppe subtypes shown in (A), with tundra and periglacial in gray.

  • Fig. 2 Geographic setting of Central Asian pollen records reviewed here.

    Reconstructed palaeogeographies at 40 Ma (middle-late Eocene), 20 Ma (early Miocene), and 0 Ma (Pleistocene/modern) show progressive Tibetan orogenic growth and westward retreat of the proto-Paratethys Sea from the Eocene until the modern day. Colors indicate meters above sea level (m a.s.l.); a low (≤2 km) to moderate (~3 km) elevation characterized Central Asia in the Eocene [(152, 162);], while a high elevation (~4.5 km) exists in the Tibetan region today. 1, southern Tian Shan; 2 and 3, northern Tian Shan; 4 and 5, Qaidam Basin; 6, Xining Basin; 7, Lanzhou Basin. For details of how palaeogeographic reconstructions were derived, see Materials and Methods; for individual pollen records, see fig. S1.

  • Fig. 3 High-resolution changes over the EOT in Central Asia.

    Global atmospheric carbon dioxide concentration (pCO2) variation over this period is derived from various proxies (A) (163, 164); ppm, parts per million; GTS16, Geologic Time Scale: 2016 (165). Vegetation (B) (this study; table S6) and temperature (C) [Page et al. (39)] from an extended Eocene–Oligocene reference section in NE Tibet are plotted against faunal changes in Central Asia [see Materials and Methods for details of how (D) and (E) were compiled]. Silhouette sizes indicate the proportional abundance of clades in Eocene and Oligocene mammalian communities. Net diversification rates show a strong drop in diversity (negative net rate) at the Eocene–Oligocene Boundary, followed by a rebound with strongly positive diversification rate in the early Oligocene.

  • Fig. 4 Late Eocene and early Oligocene climate simulations for Central Asia.

    The Xining Basin in NE Tibet is indicated by a black circle. Simulations show (I) mean annual temperature (MAT), (II) mean annual precipitation (MAP), (III) bare soil proportion, and (IV) conifer proportion for (A) the late Eocene, (B) the early Oligocene, and (C) changes over the EOT [expressed as Oligocene minus Eocene in degrees Celsius (C-I) and percent (C-II, C-III, and C-IV)]. All anomalies are obtained through a Student’s t test and are significant at 95% confidence. Topography is represented by thick contours (each 1000 m of elevation). Thin numbered contours refer to each plot shading. In (C-II), the white area represents persistent arid zones in simulations (<300 mm/year).

  • Fig. 5 The triphase Cenozoic history of the Central Asian steppe-desert biome.

    Vegetation changes are illustrated by a composite pollen record over the last ~43 Ma (B), within the context of global climate variation (A) and linked to net diversification rates of Central Asian mammalian communities (C). Extant Asian deserts are used as ecoregion analogs (D) for each ecosystem phase (E) and illustrated by natural view [left; images from Landsat 8 OLI (Operational Land Imager),] and hyperspectral (right) normalized difference vegetation index (NDVI) models of the (1) Gurbantunggut Desert, (2) Taklimakan Desert, and (3) Jinghe mountain–desert ecotone. Atmospheric carbon dioxide concentration (pCO2) is based on a LOESS (locally estimated scatterplot smoothing) fit through data from various proxy methods (163), enveloped by a 95% confidence interval in light gray. Global climate is represented by a nine-point moving average through the benthic foraminifera δ18O record of Cramer et al. (166). For individual pollen records, see fig. S1; for statistical support of the three ecosystem phases, see fig. S3.

  • Fig. 6 The ecological rise of grasses across the Central Asian steppe-desert.

    This occurred gradually but was more restricted in the west (A) compared to the east (B). References for pollen data are as follows: (1) Zhang and Sun (108); (2) Sun et al. (97); (3) Sun and Zhang (103); (4 and 5) Miao et al. (107), Cai et al. (109), Koutsodendris et al. (6), and this study; (6) Li et al. (110); (7) Hui et al. (99); (8) Hui et al. (98); (9) Liu et al. (100); and (10) Ma et al. (101).

Supplementary Materials

  • Supplementary Materials

    Cenozoic evolution of the steppe-desert biome in Central Asia

    N. Barbolini, A. Woutersen, G. Dupont-Nivet, D. Silvestro, D. Tardif, P. M. C. Coster, N. Meijer, C. Chang, H.-X. Zhang, A. Licht, C. Rydin, A. Koutsodendris, F. Han, A. Rohrmann, X.-J. Liu, Y. Zhang, Y. Donnadieu, F. Fluteau, J.-B. Ladant, G. Le Hir, C. Hoorn

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    • Tables S1 to S5
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