Research ArticleCLIMATOLOGY

Past East Asian monsoon evolution controlled by paleogeography, not CO2

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Science Advances  30 Oct 2019:
Vol. 5, no. 10, eaax1697
DOI: 10.1126/sciadv.aax1697
  • Fig. 1 Data-model precipitation, pCO2, and HTR trend through time.

    (A) Normalized quantitative precipitation proxy data trend (solid black line) is shown in conjunction with two qualitative proxy data compilations for the Cretaceous (31) and for the Paleogene and Neogene (4, 6) within 16°N to 41°N, 75°E to 130°E. Both colored panels in (A) are independent of either of the left y axis and indicate the intensity of the hydrologic cycle. The dashed red line (32) is a compilation of proxies from ocean drilling program sites 1146 and 1148 indicating monsoonal conditions. See the Supplementary Materials for details. (B) EA modeled mean annual precipitation (mm) for each geologic stage (region: fig. S4) at idealized CO2 (closed blue circle), sensitivity CO2 (open blue circle) concentrations, and alternative paleogeography (red square). The mean annual precipitation minus evaporation (mm) for each geologic stage at idealized CO2 (closed green star) and sensitivity CO2 (open green star) concentrations is shown. Black horizontal bar represents model-derived monsoonal conditions present. Orange triangle represents the mean annual (1979–2011) precipitation for the monsoon region from CMAP observations. (C) Mean orographic height (m) between 27.5°N and 45°N, 71.25°E and 101.25°E for each geologic stage (diamonds) and CO2 concentrations (circle/square) for each simulation. Shaded blue band signifies range in proxy CO2 uncertainty (3). Red vertical boxes (B and C) represent the three synthesized key periods investigated in this study. PALEAOC, Paleocene epoch; OLIG, Oligocene epoch; and PLE, Pleistocene epoch.

  • Fig. 2 Atmosphere-ocean dynamics of three key periods.

    Wettest month 500-mbar geopotential height (isolines), wind field (black arrows), and precipitation in the Hauterivian (A), Santonian (B), and Zanclean (C) (paleo-rotated region in blue line). Wettest month zonal cross-sectional (0°N to 60°N, 105°E to 112.5°E) vertical velocity in the Hauterivian (D), Santonian (E), and Zanclean (F) depicting the position of the Hadley circulation; negative values indicate vertical ascent, positive values indicate vertical descent, and vertical black lines depict maximum and minimum latitudinal extent of rotated EAM region. Mean annual meridional (10°S to 10°N) depth profile ocean temperature (°C) for the Hauterivian (G), Santonian (H), and Zanclean (I) depicting the location of the Pacific warm pool. Red circles denote region of interest highlighted in the main text.

  • Fig. 3 EA summer (June–August) sea-breeze and maximum Hadley circulation extent.

    Zonal (June–August) sea-breeze circulation (left-hand column) indicated by wind barbs showing direction and magnitude (m/s; color scale) for the Danian (A), Lutetian (B), Rupelian (C), Tortonian (D), and preindustrial (E). Vertical black lines depict the maximum and minimum longitudinal extent of the EAM region (mean, 38.75°N to 20°N). Meridional vertical velocity (Pa/s; right-hand column) cross section (mean, 105°E to 112.5°E) in the EAM region showing the maximum northerly extent of the Hadley circulation in the boreal summer. Negative values indicate vertical ascent, while positive values indicate vertical descent for the Danian (F), Lutetian (G), Rupelian (H), Tortonian (I), and the preindustrial (J).

  • Fig. 4 Conceptualized model of each key period.

    Schematic of the key processes leading to the weak monsoon in the Hauterivian (A), dry period of the Santonian (B), and super monsoonal conditions in the Zanclean (C) in the EAM region depicting a collation and synergy of model data. The wettest month of the monsoon season sea surface temperatures (SSTs) (°C) and zonal wind cross section (m/s; mean, 105°E to 112.5°E) is depicted. Arrow thickness represents the intensity of the process. Blue arrows indicate advection of air masses. WWC, western Walker cell; EWC, eastern Walker cell; STJ, subtropical jet; TEJ, tropical easterly jet with both its entrance and exit zone shown. The white “cloud” represents the region of deep organized convection, where the atmospheric dynamics highlighted in these schematic produces conditions for intense rainfall. PWP indicates the position of the Pacific warm pool. The white landmass with red outline represents the paleo-rotated location of EAM. The vertical axis on the left-hand indicates both atmospheric pressure (hPa) and height (m). The height of the HTR is also indicated on the cross section between the left-hand y axis and latitudinal x axis.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/10/eaax1697/DC1

    Supplementary Text

    Table S1. Proxy precipitation data in the East Asia Monsoon region.

    Table S2. Summary and comparison of proxy paleoaltimetry and model paleogeography.

    Table S3. GCM sensitivity simulations for each geologic stage-specific simulation June–September (JJAS) data for the strength of the Hadley circulation (vertical velocities; Pa/s) over 21.75°N to 38.75°N and between 1000 and 200 hPa in EA.

    Table S4. Correlations between different processes during all geologic stages, Cretaceous stages, Paleogene stages, and Neogene stages.

    Fig. S1. Orography and bathymetry.

    Fig. S2. EA proxy paleoaltimetry data versus prescribed paleogeography.

    Fig. S3. Precipitation seasonality.

    Fig. S4. Monsoonal regions.

    Fig. S5. Simulation spin-up of SST and zonal 1.5-m air temperature (°C).

    Fig. S6. Preindustrial mean fields.

    Fig. S7. Wind profiles and vertical velocities in the Hauterivian, Santonian, and Zanclean.

    Fig. S8. Mean SLLJ strength and alternative paleogeographies.

    References (61132)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Text
    • Table S1. Proxy precipitation data in the East Asia Monsoon region.
    • Table S2. Summary and comparison of proxy paleoaltimetry and model paleogeography.
    • Table S3. GCM sensitivity simulations for each geologic stage-specific simulation June–September (JJAS) data for the strength of the Hadley circulation (vertical velocities; Pa/s) over 21.75°N to 38.75°N and between 1000 and 200 hPa in EA.
    • Table S4. Correlations between different processes during all geologic stages, Cretaceous stages, Paleogene stages, and Neogene stages.
    • Fig. S1. Orography and bathymetry.
    • Fig. S2. EA proxy paleoaltimetry data versus prescribed paleogeography.
    • Fig. S3. Precipitation seasonality.
    • Fig. S4. Monsoonal regions.
    • Fig. S5. Simulation spin-up of SST and zonal 1.5-m air temperature (°C).
    • Fig. S6. Preindustrial mean fields.
    • Fig. S7. Wind profiles and vertical velocities in the Hauterivian, Santonian, and Zanclean.
    • Fig. S8. Mean SLLJ strength and alternative paleogeographies.
    • References (61132)

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