{ "142379-21890775": { "datetime_modified":"20251204T101544", "datetime_start":"20251212T130000", "datetime_end":"20251212T140000", "has_end_time":1, "date_start":"2025-12-12", "date_end":"2025-12-12", "time_start":"13:00:00", "time_end":"14:00:00", "time_zone":"America\/Detroit", "event_title":"Daeun Lee Dissertation Defense", "occurrence_title":"", "combined_title":"Daeun Lee Dissertation Defense: Decoupling Climate Signals: Ocean Equilibria, Tectonic Uplift, and Hydroclimate Dynamics from the Miocene to Modern Africa", "event_subtitle":"Decoupling Climate Signals: Ocean Equilibria, Tectonic Uplift, and Hydroclimate Dynamics from the Miocene to Modern Africa", "event_type":"Lecture \/ Discussion", "event_type_id":"13", "description":"Africa\u2019s hydroclimate and environments from the Miocene (~23\u20135 million years ago) to present-day have been shaped by dynamic interactions among ocean circulation, tectonic evolution, atmospheric chemistry, and hydroclimatic processes. Understanding these shifts offers vital context for reconstructing ancient environments and the evolution of tropical ecosystems. However, persisting challenges remain in explaining the decoupling of global climate signals from regional hydrology, especially in Africa, a continent central to human evolution and biodiversity.\r\n\r\nThis dissertation integrates climate modeling, proxy analyses, and novel isotope measurements to investigate: (1) how multiple equilibrium states in ocean circulation, particularly the Atlantic Meridional Overturning Circulation (AMOC), contribute to the decoupling of atmospheric CO\u2082 and regional climate signals during the Middle Miocene Climate Transition (MMCT); (2) the impact of tectonic uplift and valley formation within the East African Rift System (EARS) on Miocene rainfall patterns, moisture transport, and water-isotope signals, and the influence of AMOC on African hydroclimate; and (3) the seasonal and spatial controls on modern rainwater isotopic composition across tropical Africa, improving proxy calibration for paleoclimate reconstructions.\r\n\r\nChapter 2 focuses on the global perspective, investigating how multiple equilibrium states in ocean circulation, particularly the AMOC, contribute to the decoupling of atmospheric CO\u2082 and regional climate signals during the MMCT. MMCT simulations, using the isotope-enabled Community Earth System Model (iCESM), reveal that initial ocean conditions induce divergent equilibrium states that modulate AMOC strength, sea surface temperature gradients, and precipitation. These findings provide a mechanistic explanation for the frequent asynchrony observed between global pCO\u2082 and regional SST proxies (UK'37) during the Miocene.\r\n\r\nChapter 3 zooms into Africa to identify the driving mechanisms of flora and faunal changes during the Late Cenozoic (23\u201315 million years ago), by examining the impact of tectonic uplift and valley formation within the EARS on Miocene rainfall patterns, moisture transport, and water-isotope signals. High-resolution paleoclimate modeling demonstrates how sequential tectonic uplift amplifies orographic precipitation, intensifies low-level jets, generates rain-shadow effects, and modulates water-isotope signatures; these simulated results can be validated against regional proxy archives (e.g., leaf-wax \u03b4D, paleosol carbonates \u03b418O, tooth enamel \u03b418O), which are very limited for this time interval in eastern Africa. Sensitivity experiments in this chapter also explore the additional influence of AMOC state in controlling continental climate variance.\r\n\r\nChapter 4 then shifts the focus to modern hydroclimate, presenting new stable water isotope datasets from tropical Africa collected at multiple sites. By analyzing biweekly rainwater isotope records, this chapter disentangles the seasonal and spatial controls on meteoric water isotopes and challenges canonical interpretations of the \u201camount effect.\u201d The data emphasize the significance of shifts in moisture source, convective activity, and dynamic atmospheric boundaries as primary drivers of isotopic variability. This new observation could help refine proxy calibration for hydroclimate reconstructions.\r\n\r\nBy synthesizing isotope-enabled Earth System Modeling, proxy archives, and modern stable isotope datasets, this work advances understanding of global to regional climate driving mechanisms, tectonic-hydroclimate feedbacks, and controls on African rainwater isotope variability. Africa\u2019s dynamic tectonics and climatic transitions during the Miocene uniquely shaped rainfall patterns and water isotope signals, offering key insights into the evolving climate system we are facing today.", "occurrence_notes":null, "guid":"142379-21890775@events.umich.edu", "permalink":"http:\/\/events.umich.edu\/event\/142379", "building_id":"1000188", "building_name":"1100 North University Building", "campus_maps_id":"628", "room":"2540", "location_name":"1100 North University Building", "has_livestream":0, "cost":"", "tags":["Dissertation","Earth And Environmental Sciences"], "website":"", "sponsors":[ { "group_name":"Earth and Environmental Sciences", "group_id":"3170", "website":"http:\/\/www.lsa.umich.edu\/earth" } ], "image_url":"https:\/\/events.umich.edu\/media\/attachments\/2025\/12\/event_142379_original-1.png", "styled_images":{ "event_thumb":"https:\/\/events.umich.edu\/media\/cache\/event_thumb\/media\/attachments\/2025\/12\/event_142379_original-1.png", "event_large":"https:\/\/events.umich.edu\/media\/cache\/event_large\/media\/attachments\/2025\/12\/event_142379_original-1.png", "event_large_2x":"https:\/\/events.umich.edu\/media\/cache\/event_large_2x\/media\/attachments\/2025\/12\/event_142379_original-1.png", "event_large_lightbox":"https:\/\/events.umich.edu\/media\/cache\/event_large_lightbox\/media\/attachments\/2025\/12\/event_142379_original-1.png", "group_thumb":"https:\/\/events.umich.edu\/media\/cache\/resolve\/group_thumb\/media\/attachments\/2025\/12\/event_142379_original-1.png", "group_thumb_square":"https:\/\/events.umich.edu\/media\/cache\/resolve\/group_thumb_square\/media\/attachments\/2025\/12\/event_142379_original-1.png", "group_large":"https:\/\/events.umich.edu\/media\/cache\/resolve\/group_large\/media\/attachments\/2025\/12\/event_142379_original-1.png", "group_large_lightbox":"https:\/\/events.umich.edu\/media\/cache\/resolve\/group_large_lightbox\/media\/attachments\/2025\/12\/event_142379_original-1.png", "event_large_crop":"https:\/\/events.umich.edu\/media\/cache\/resolve\/event_large_crop\/media\/attachments\/2025\/12\/event_142379_original-1.png", "event_list":"https:\/\/events.umich.edu\/media\/cache\/resolve\/event_list\/media\/attachments\/2025\/12\/event_142379_original-1.png", "event_list_2x":"https:\/\/events.umich.edu\/media\/cache\/event_list_2x\/media\/attachments\/2025\/12\/event_142379_original-1.png", "event_grid":"https:\/\/events.umich.edu\/media\/cache\/event_grid\/media\/attachments\/2025\/12\/event_142379_original-1.png", "event_grid_2x":"https:\/\/events.umich.edu\/media\/cache\/resolve\/event_grid_2x\/media\/attachments\/2025\/12\/event_142379_original-1.png", "event_feature_large":"https:\/\/events.umich.edu\/media\/cache\/resolve\/event_feature_large\/media\/attachments\/2025\/12\/event_142379_original-1.png", "event_feature_thumb":"https:\/\/events.umich.edu\/media\/cache\/event_feature_thumb\/media\/attachments\/2025\/12\/event_142379_original-1.png" }, "occurrence_count":1, "first_occurrence":21890775 } , "141878-21889587": { "datetime_modified":"20251227T123054", "datetime_start":"20251212T130000", "datetime_end":"20251212T140000", "has_end_time":1, "date_start":"2025-12-12", "date_end":"2025-12-12", "time_start":"13:00:00", "time_end":"14:00:00", "time_zone":"America\/Detroit", "event_title":"Resume Lab", "occurrence_title":"", "combined_title":"Resume Lab", "event_subtitle":"", "event_type":"Careers \/ Jobs", "event_type_id":"2", "description":"*RSVP required to attend. Click \"Join Event\" here:\u00a0https:\/\/umich.joinhandshake.com\/edu\/events\/1862645Just getting started building a resume? Have a draft but not sure how to make it better? Want to learn about resources available to revise your resume? Wherever you\u2019re at Resume Lab is a great next step for you.\u00a0Get real-time, personalized support in a small group setting by checking out the Resume Lab.\u00a0We will discuss and educate you on\u2026- Design and format- Writing a great bullet point- Targeting your resume for specific internships\/jobs\u00a0If you're a Graduate Student or Recent Grad, please make a 1:1 appointment instead of attending the Lab because this event is designed for undergraduates.\u00a0Note: This event's information is shown in Handshake as well as on theHappening @ Michigan calendar so that it will be seen by a larger number of U-M Students.#UCC", "occurrence_notes":null, "guid":"141878-21889587@events.umich.edu", "permalink":"http:\/\/events.umich.edu\/event\/141878", "building_id":"", "building_name":"", "campus_maps_id":"", "room":"", "location_name":"", "has_livestream":0, "cost":"", "tags":[], "website":"", "sponsors":[ { "group_name":"University Career Center UCC", "group_id":"1140", "website":"http:\/\/careercenter.umich.edu" } ], "image_url":"", "styled_images":{ "event_thumb":"", "event_large":"", "event_large_2x":"", "event_large_lightbox":"", "group_thumb":"", "group_thumb_square":"", "group_large":"", "group_large_lightbox":"", "event_large_crop":"", "event_list":"", "event_list_2x":"", "event_grid":"", "event_grid_2x":"", "event_feature_large":"", "event_feature_thumb":"" }, "occurrence_count":1, "first_occurrence":21889587 } }