Research ArticleENVIRONMENTAL STUDIES

Dominant 100,000-year precipitation cyclicity in a late Miocene lake from northeast Tibet

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Science Advances  29 Mar 2017:
Vol. 3, no. 3, e1600762
DOI: 10.1126/sciadv.1600762
  • Fig. 1 Map of the study sites and atmospheric circulation pattern.

    Black dashed line depicts the Asian summer monsoon fringes at present (84). The white dashed circle represents the Siberian High in January. HTTL, Huaitoutala; LX, Linxia; JY, Jingyuan; QA, Qinan; Q, Qaidam Basin; CLP, Chinese Loess Plateau.

  • Fig. 2 Age model and lithology (19) of Late Miocene HTTL section in the Qaidam Basin.

    C3Br.1n and the reversed interval between C3Br.2n and C4n.1n are each constrained by a single data point. The bottom boundary of C4r.1n in the observed polarity has multiple possibilities. Therefore, these five reversal ages (which correspond to the dashed lines) are not used to establish the age model. VGP, virtual geomagnetic polarity (22); m, mudstone; f, fine sandstone.

  • Fig. 3 χfd/HIRM versus annual mean precipitation and temperature for surface soil samples across the CLP.

    The annual mean temperature (AMT) and the annual mean precipitation (AMP) data are from meteorological stations on the CLP. The sample sites are the same as those in the study by Nie et al. (85).

  • Fig. 4 Paleoenvironmental records during the Late Miocene.

    (A) Ocean Drilling Program (ODP) site 722 n-alkane C31 carbon isotope record (48). (B) Qinan loess magnetic susceptibility (χ) record (86). (C) Linxia lacustrine sediment oxygen isotope record (27). (D to G) Qaidam Basin HTTL section χfd/HIRM, halite content, chlorite/(hematite + goethite) [C/(H+G)] ratio, and mean grain size record. (H) Benthic oxygen isotope record from ODP Site 982, North Atlantic Ocean (50). We did not include several negative χfd/HIRM and unrealistically high χfd/HIRM and C/(H+G) values from the Qaidam records. To promote readability, wetting corresponds to the right-hand direction for the Asian monsoon records. The blue bar in (G) shows the interval that has relatively constant grain size without flooding events for over 400 ky after 8.5 Ma.

  • Fig. 5 The wavelet transform (87) (left) and the power spectrum (right) of the χfd/HIRM record from the Qaidam Basin.

    The color scale indicates power, which is scaled to percent total power, and the hatched areas illustrate the cone of influence and, hence, the edge effects of the transform. We note that warm color indicates larger power. The 400-, 100-, 40-, and 20-ky periodicities are labeled and indicated by the straight black lines. The black contour is the 20% significance level, using a red noise background spectrum.

  • Fig. 6 A comparison of the EASM variations during the Late Miocene and the Late Quaternary for a time period of ~400 ky.

    (A) The χfd/HIRM record from the Qaidam Basin during 8.18 to 7.78 Ma. (B) The χ record from Jingyuan in the northwestern CLP during the past ~400 ky (10). (C) The normalized χ record from the central CLP during the past ~400 ky (63). (D to F) The power spectrum of (A) to (C) (solid lines) and the lower limit of their 80% significance interval (dashed lines). The power spectrum was generated using the AnalySeries 2.0.4 software (88). For comparison, the eccentricity data (pink curves; higher value is upward) (89) during 8.18 to 7.78 Ma and 0.4 to 0 Ma are also shown in (A) and (B), respectively

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/3/e1600762/DC1

    fig. S1. A comparison of oxygen and carbon isotope data of the HTTL section.

    fig. S2. Unmixing of backfield IRM curves of the HTTL samples.

    fig. S3. The smoothed end-member reflectance spectra (left) and its first derivative spectra (right) for the HTTL samples.

    fig. S4. A comparison of power spectrum of full (lower) and truncated (upper) insolation for July at 35°N (73).

    fig. S5. A comparison of HIRM and L ratio for the HTTL samples.

    table S1. Age tie points used to establish the age model for the HTTL section.

    data set S1. HTTL section paleoclimatic data in Fig. 4.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. A comparison of oxygen and carbon isotope data of the HTTL section.
    • fig. S2. Unmixing of backfield IRM curves of the HTTL samples.
    • fig. S3. The smoothed end-member reflectance spectra (left) and its first derivative spectra (right) for the HTTL samples.
    • fig. S4. A comparison of power spectrum of full (lower) and truncated (upper) insolation for July at 35°N (73).
    • fig. S5. A comparison of HIRM and L ratio for the HTTL samples.
    • table S1. Age tie points used to establish the age model for the HTTL section.

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    Other Supplementary Material for this manuscript includes the following:

    • data set S1 (Microsoft Excel format). HTTL section paleoclimatic data in Fig. 4.

    Files in this Data Supplement:

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