2012-2013 Schlanger Fellow – Yi Ge Zhang

Yi Ge Zhang

Yale University



Late Miocene–Pliocene Evolution of the Pacific Warm Pool and Cold Tongue: Implications for El Niño







The western Pacific warm pool of the tropical Pacific Ocean is the largest and warmest sea surface water body on Earth, whereas the eastern equatorial Pacific is characterized by strong upwelling of cold, nutrient-rich deep waters, termed the Pacific cold tongue. The warm pool and cold tongue control the circum-Pacific climate and impact the regional and globe climate through El Niño – Southern Oscillation (ENSO) teleconnections, as recognized in the IODP Science Plan for 2013-2023, which lists understanding how tropical temperatures, upwelling regimes, and El Niño variability in a high-CO2 world as a high priority. Sea surface temperature (SST) reconstructions using a single site from the warm pool (ODP 806) and two sites from the cold tongue (ODP 846, 847) suggest that the temperature of the warm pool was “stable” throughout the Plio-Pleistocene, whereas the cold tongue was much warmer in the Pliocene and cooled subsequently. The negligible Pliocene east-west Pacific temperature gradient is the basis for the “permanent El Niño” hypothesis. However, high-resolution sedimentary records show quasi-periodic climate variability (2-7 years) during the Pliocene warm period, challenging the existence of a “permanent” or invariant climate state, and suggesting that SSTs based on one or two proxies, from sites with limited spatial and temporal variability, may not be sufficient for a thorough understanding of the ENSO phenomenon in the geological past. Here I propose a multi-proxy (TEX86, Uk’ 37, Mg/Ca), multi-site reconstruction of the late Miocene-Pliocene (~12-3 Ma) SST in the Pacific warm pool (ODP Sites 769, 806, and 1143) and cold tongue (ODP 846, 849 and 850). My preliminary results show that the late Miocene-Pliocene SST evolution of the warm pool was dynamic, in contrast to the invariant character previously assumed. Interestingly, a clear, but small east-west temperature gradient persists over the studied time period, in contrast to previous results, which helps in explaining ENSO variability in Miocene-Pliocene records. Combining better resolved SST variability by proxy reconstructions with climate models, I seek to address these questions: How warm were the Pacific warm pool and cold tongue during the late Miocene-Pliocene? What was the long-term evolution of the east-west equatorial Pacific temperature gradient? How did the equatorial Pacific temperature distribution and zonal gradient control El Niño – La Niña?




I grew up in a suburb of Beijing. In my childhood, my father took me for fishing and raising animals, my mother took me to the chemistry labs, which fosters my interests in nature and science. I studied geochemistry at Nanjing University. My college life was totally changed when I first had the chance to work in a lab for my senior thesis, with the sediment samples from ODP Site 1143. I fell in love with the ocean, climate, and our Earth’s history right away and that’s something that I still enjoy doing research on today. At Yale, I benefit from the guidance of Dr. Mark Pagani on paleoceanography and organic geochemistry, Dr. Hagit Affek on clumped isotopes, Dr. Zhengrong Wang on trace elements, and Dr. Ellen Thomas on the cute little creatures of the ocean. Together we hope to produce some thrilling science, on the Neogene history of ENSO dynamics, ocean temperature and atmospheric CO2, and Earth System climate sensitivity.