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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. 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.
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This content will become publicly available on May 30, 2026
The Causes and Consequences of Ordovician Cooling
A long-term cooling trend through the Ordovician Period, from 487 to 443 Ma, is recorded by oxygen isotope data. Tropical ocean basins in the Early Ordovician were hot, which led to low oxygen concentrations in the surface ocean due to the temperature dependence of oxygen solubility. Elevated temperatures also increased metabolic demands such that hot shallow water environments had limited animal diversity as recorded by microbially dominated carbonates. As the oceans cooled through the Ordovician, animal biodiversity increased, leading to the Great Ordovician Biodiversification Event. The protracted nature of the cooling suggests that it was the product of progressive changes in tectonic boundary conditions. Low-latitude arc-continent collisions through this period may have increased global weatherability and decreased atmospheric CO2levels. Additionally, decreasing continental arc magmatism could have lowered CO2outgassing fluxes. The Ordovician long-term cooling trend culminated with the development of a large south polar ice sheet on Gondwana. The timescale of major ice growth and decay over the final 2 Myr of the Ordovician is consistent with Pleistocene-like glacial cycles driven by orbital forcing. The short duration of large-scale glaciation indicates a high sensitivity of ice volume to temperature with a strongly nonlinear response, providing a valuable analog for Neogene and future climate change.▪Oxygen isotope data record progressive and protracted cooling through the Ordovician leading up to the onset of Hirnantian glaciation.▪The gradual cooling trend is mirrored by an Ordovician radiation in biological diversity, consistent with temperature-dependent oxygen solubility and metabolism as a primary control.▪Long-term cooling occurred in concert with low-latitude arc-continent collisions and an increase in global weatherability. Although CO2outgassing may have also decreased with an Ordovician decrease in continental arc length, in the modern, CO2outgassing is variable along both continental and island arcs, leaving the relationship between continental arc length and climate uncertain.▪Evidence for significant ice growth is limited to less than 2 Myr of the Hirnantian Stage, suggesting a high sensitivity of ice growth topCO2and temperature.▪Independent estimates for ice volume, area, and sea level change during the Hirnantian glacial maximum are internally consistent and comparable to those of the Last Glacial Maximum.
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- Award ID(s):
- 2153786
- PAR ID:
- 10655561
- Publisher / Repository:
- Annual Reviews
- Date Published:
- Journal Name:
- Annual Review of Earth and Planetary Sciences
- Volume:
- 53
- Issue:
- 1
- ISSN:
- 0084-6597
- Page Range / eLocation ID:
- 651 to 685
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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