Significance

The Southeast Asian islands are a modern-day hotspot of CO₂ consumption via silicate weathering. Since ∼15 million years ago, these islands have been increasing in size at the same time that Earth’s climate has been cooling. Here, we test the hypothesis that this global cooling could have been driven by tectonic emergence of the Southeast Asian islands. Using a compilation of paleoshorelines, in conjunction with a coupled silicate weathering and climate model, we find that this emergence is associated with a large decrease in pCO₂. Without these changes in tropical island paleogeography, there would not have been large Northern Hemisphere ice sheets as a defining feature of Earth’s climate over the past 3 million years.

Abstract

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, atmospheric pCO₂ would have been significantly higher than preindustrial values, remaining above the levels necessary for initiating Northern Hemisphere ice sheets.

The full (paywalled) article appeared on the Proceedings of the National Academy of Science website at https://www.pnas.org/content/early/2020/09/23/2011033117