Neogene Cooling

Related publications:

  • Park, Y., Maffre, P., Goddéris, Y., Macdonald, F. A., Anttila, E. S. C., Swanson-Hysell, N. L., 2020, Emergence of the Southeast Asian islands as a driver for Neogene cooling: Proceedings of the National Academy of Sciences, vol. TBD, pp. TBD, doi:10.1073/pnas.2011033117.

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Steep topography, a tropical climate, and mafic lithologies contribute to efficient chemical weathering and carbon sequestration in the Southeast Asian islands (SEAIs). 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 (Fig. 1). 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 (Fig. 1). We seek to evaluate the hypothesis that the emergence of the SEAIs 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 (Fig. 2). We find that without the increase in area of the SEAIs over the Neogene, atmospheric pCO2 would have been significantly higher than pre-industrial values, remaining above the levels necessary for initiating Northern Hemisphere ice sheets (Fig. 3).

Emergence of the Southeast Asian islands.
Figure 1: The emergence of the SEAIs from the mid-Miocene to present. Past shorelines at 5, 10, and 15 Ma are shown in A, with associated land area summarized in B. A significant increase in area over the past 5 million years is coincident with cooling and the onset of Northern Hemisphere glaciation, as reflected in the benthic oxygen isotope record shown in C.
GEOCLIM chemical weathering and regolith thickness maps.
Figure 2: Examples of chemical weathering and regolith thickness maps produced by GEOCLIM.
GEOCLIM pCO2 estimates.
Figure 3: Steady-state pCO2 estimates from GEOCLIM for various scenarios (see article for details). For each of the seven scenarios, each point represents an estimate from one of the 573 unique parameter combinations that most closely matched estimates of present-day CO2 consumption in 80 watersheds around the world. The box encloses the middle 50% of the pCO2 estimates (i.e., the interquartile range), and the notch represents the median with its 95% confidence interval. The whiskers extend to the 2.5th and 97.5th percentile values. Glaciation thresholds are shown on the axis.