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The modern configuration of the South East Asian Islands (SEAI) evolved over the last fifteen million years, as a result of subduction, arc magmatism, and arc-continent collisions, contributing to both increased land area and high topography.  The presence of the additional land area has been postulated to enhance convective rainfall, facilitating both increased silicate weathering and the development of the modern-day Walker circulation.  Using an Earth System Model in conjunction with a climate-silicate weathering model, we argue instead for a significant role of SEAI topography for both effects.  This dataset archives model output used in this investigation, including simulations using the Community Earth System Model version 1.2, and the climate-silicate weathering model GEOCLIM. All data are in Netcdf format, and were generated either by the Community Earth System Model 1.2 (Hurrell et al. 2013) or the climate-silicate weathering model GEOCLIM (Park et al. 2020).  Model output is organized into 4 tar files: 1) B1850C5.tar Contains model output for the fully coupled CESM1.2 runs, for 2D fields and for 3D pressure vertical velocity (W) between 10S-10N.  Monthly mean data for years 41-110 of the simulations.   Naming convention is No SEAI topography: B1850C5_noSEAItopo_y41-110.nc and B1850C5_noSEAItopo_W_y41-110.nc 50% SEAI topography: B1850C5_0.5SEAItopo_y41-110.nc and B1850C5_0.5SEAItopo_W_y41-110.nc 100% SEAI topography: B1850C5_y41-110.nc and B1850C5_W_y41-110.nc 150% SEAO topogaphy: B1850C5_1.5SEAItopo_y41-110.nc and B1850C5_1.5SEAItopo_W_y41-110.nc 2) E1850C5.tar Contains model output for the slab ocean CESM1.2 runs, for 2D fields and for 3D pressure vertical velocity (W) between 10S-10N.  Monthly mean data for years 21-50 of the simulations.  Naming convention is No SEAI topography: E1850C5_noSEAItopo_y21-50.nc and E1850C5_noSEAItopo_W_y21-50.nc 50% SEAI topography: E1850C5_0.5SEAItopo_y21-50.nc and E1850C5_0.5SEAItopo_W_y21-50.nc 100% SEAI topography: E1850C5_y21-50.nc and E1850C5_W_y21-50.nc 150% SEAO topogaphy:  E1850C5_1.5SEAItopo_y21-50.nc and E1850C5_1.5SEAItopo_W_y21-50.nc 3) GEOCLIM.tar Contains model output from the climate-silicate weathering model GEOCLIM.  Data is provided for all 573 parameter combinations.  All values are climatological annual means. All files contain these variables: GMST: global mean surface temperature (in K) atm_CO2_level: atmospheric pCO2 (in ppm) degassing: globally-integrated CO2 flux (in mol/yr) The files ending with 1xCO2.nc also contain these spatial fields: lithology fraction: fraction of land covered by a lithology class erosion: Regolith erosion rate (m/yr) weathering: Ca-Mg weathering rate (mol/m^2/yr) E1850C5_1xCO2.nc - GEOCLIM output using the Modern SEAI simulation as input, and for CO2 fixed to 286.7ppm.  E1850C5_noSEAI_1xCO2.nc - GEOCLIM output using the no SEAI simulation as input, and for CO2 fixed to 286.7ppm.  E1850C5_noSEAItopo_1xCO2.nc - GEOCLIM output using the flat SEAI simulation as input, and for CO2 fixed to 286.7ppm.  E1850C5_noSEAI_equil.nc - GEOCLIM output using the no SEAI simulation as input, and CO2 adjusted so that system is in carbon flux equilibrium.   E1850C5_noSEAItopo_flatSEAIslope_equil.nc - GEOCLIM output using the flat SEAI simulation as input, and CO2 adjusted so that system is in carbon flux equilibrium.   4) Surface.tar Contains land fraction and surface geopotential fields for the modern SEAI (Landfrac.nc) and no SEAI (Landfrac_noSEAI.nc) simulations References Hurrell, J.W., Holland, M.M., Gent, P.R., Ghan, S., Kay, J.E., Kushner, P.J., Lamarque, J.F., Large, W.G., Lawrence, D., Lindsay, K. and Lipscomb, W.H., 2013. The community earth system model: a framework for collaborative research. Bulletin of the American Meteorological Society, 94(9), pp.1339-1360. Park, Y., Maffre, P., Goddéris, Y., Macdonald, F.A., Anttila, E.S. and Swanson-Hysell, N.L., 2020. Emergence of the Southeast Asian islands as a driver for Neogene cooling. Proceedings of the National Academy of Sciences, 117(41), pp.25319-25326. 

The geography of the Southeast Asian Islands (SEAI) has changed over the last 15 million years, as a result of tectonic processes contributing to both increased land area and high topography. The presence of the additional land area has been postulated to enhance convective rainfall, facilitating both increased silicate weathering and the development of the modern‐day Walker circulation. Using an Earth System Model in conjunction with a climate‐silicate weathering model, we argue instead for a significant role of SEAItopographyfor both effects. SEAI topography increases orographic rainfall over land, through intercepting moist Asian‐Australian monsoon winds and enhancing land‐sea breezes. Large‐scale atmospheric uplift over the SEAI region increases by ∼14% as a consequence of increased rainfall over the SEAI and enhancement through dynamical ocean‐atmosphere feedback. The atmospheric zonal overturning circulation over the Indo‐Pacific increases modestly arising from dynamical ocean‐atmosphere feedback, more strongly over the tropical Indian Ocean. On the other hand, the effect of the SEAI topography on global silicate weathering is substantial, resulting in a ∼109 ppm reduction in equilibriumpCO₂and decrease in global mean temperature by ∼1.7ºC. The chemical weathering increase comes from both enhanced physical erosion rates and increased rainfall due to the presence of SEAI topography. The lowering ofpCO₂by SEAI topography also enhances the Indo‐Pacific atmospheric zonal overturning circulation. Our results support a significant role for the progressive emergence of SEAI topography in global cooling over the last several million years.

 

Steep topography, a tropical climate, and mafic lithologies contribute to efficient chemical weathering and carbon sequestration in the Southeast Asian islands. Ongoing arc–continent collision between the Sunda-Banda arc system and Australia has increased the area of subaerially exposed land in the region since the mid-Miocene. Concurrently, Earth’s climate has cooled since the Miocene Climatic Optimum, leading to growth of the Antarctic ice sheet and the onset of Northern Hemisphere glaciation. We seek to evaluate the hypothesis that the emergence of the Southeast Asian islands played a significant role in driving this cooling trend through increasing global weatherability. To do so, we have compiled paleoshoreline data and incorporated them into GEOCLIM, which couples a global climate model to a silicate weathering model with spatially resolved lithology. We find that without the increase in area of the Southeast Asian islands over the Neogene, atmosphericpCO₂would have been significantly higher than preindustrial values, remaining above the levels necessary for initiating Northern Hemisphere ice sheets.