Intensification of the East Asian winter monsoon during the late Miocene
ID：1529
Poster Presentation
2027-01-15 16:15 （China Standard Time）
Session：Session 17 - Modern and past processes of ocean-atmosphere-climate interactions in the low-latitude Pacific and Indian Ocean
Abstract
The late Miocene (~11.6–5.3 million years ago) represents a key interval within the long-term Cenozoic cooling trend toward the Pleistocene ice ages. During this time, drastic climatic and ecological changes occurred in both terrestrial and marine environments. The most spectacular landscape change was probably the spread of C4 grasslands at the expense of C3-dominated ecosystems in large areas of the tropics and subtropics. Here we present upper ocean hydrographic reconstructions, i.e., the depth of the mixed layer, at Ocean Drilling Program (ODP) Site 1146 in the northern South China Sea during the late Miocene (~8–6.5 Ma). Surface/mixed layer and thermocline water temperatures were reconstructed using Mg/Ca-derived temperature estimates of surface/mixed layer-dwelling planktic foraminifera species Trilobatus sacculifer and Globigerinoides extremus and the thermocline-dwelling planktic foraminifera species Neogloboquadrina acostaensis, respectively, in order to estimate the upper ocean thermal gradient (ΔT). The upper ocean thermal gradient (ΔT) allows to study changes in the upper surface water column structure, i.e., mixed layer depth (MLD) and thus EAM wind strength variability. The reconstructed ΔT(˚C) between surface/mixed-layer dwelling planktic foraminifera T. sacculifer and G. extremus and thermocline-dwelling planktic foraminifera species N. acostaensis reveal a deeper mixing and a less stratified water column after ~7.5 Ma, most likely indicating a strengthening of the East Asian winter monsoon (EAWM).
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Jan 30
2026
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Jan 12–15
2027
XMAS 2027