21-10 Planktic Foraminiferal Response to Middle Miocene Hadley Cell Dynamics

Session: Insights from Microfossils and Their Modern Analogs: From Traditional to Emerging Approaches

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Abstract:

Planktic foraminifera have undergone three major diversification events in the last 130 million years, with the most recent occurring across the Miocene Epoch. The step-wise increase in diversity in the Middle Miocene coincided with an expansion of the Hadley Cell and poleward shift of the Westerlies in the southwest Pacific Ocean as inferred from X-ray fluorescence data from International Ocean Discovery Program Expedition 371 Site U1510. Numerous paleontological studies have attributed the Middle Miocene diversity increase to growth of the Antarctic ice sheet during the early to Middle Miocene, which led to a distinct warmer mixed-layer and cooler thermocline, likely forming new niche spaces for species to evolve into. Additionally, other studies note that several Late Neogene planktic foraminiferal species first evolved in the Southern Hemisphere, further hinting that the interplay of atmospheric dynamics and Antarctic ice sheet expansion may have a large part to play in marine plankton evolution, but few studies have attempted to link these processes. This study builds on prior research conducted at Site U1510 by tracking the long-term paleoecological response of marine plankton to ascertain if atmospheric processes paced by Milankovitch cyclicity can be linked to macroevolution in the planktic foraminifera. Grain size of biogenic ooze sediments from 15.3–14.0 Ma were quantified on a Laser Particle Size Analyzer to track the sizes of planktic foraminifera. Preliminary analyses indicate a reduction in test size across the Miocene Climate Optimum (MCO; 17–14.7 Myr), likely related to warmer waters crossing the size due to Hadley Cell expansion. Test size increase occurred across the Middle Miocene Climate Transition (MMCT; 14.7–13.8 Myr) associated with cooler waters over the site as the Hadley Cell re-contracted and pulled the Westerlies back towards the mid-latitudes. Further analyses will be conducted to more finely constrain the dominant species driving size changes, interpret where the first appearance of new species occurred geographically and temporally, and use cutting-edge ecological techniques to delve deeper into the drivers of marine plankton evolution.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8036

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