Maureen Raymo
American climate scientist and marine geologist
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Through Ocean and Carbon dioxide
Raymo has done pioneering work on the origin of the ice ages, the geologic temperature record of the Earth, and past sea level change, publishing over 100 peer-reviewed scientific articles. Her work underlies fundamental ideas in paleoceanography including the uplift weathering hypothesis, the "41,000-year problem," the Pliocene sea-level paradox, and the Lisiecki-Raymo δ18O stack.
Early life and education
Raymo was born in Los Angeles, and at age eight sailed with her family to Europe on the ocean liner S.S. United States and resolved to dedicate her life to studying the ocean. The books and films of Jacques Cousteau were also important early influences. Raymo attended Oliver Ames High School in Easton, Massachusetts, where she graduated with the Bausch and Lomb Honorary Science Award, and then attended Brown University, receiving her Sc.B. Geology in 1982. After a brief stint working in a lab, she then attended Columbia University, where she earned her M.A. in Geological sciences in 1985, M.Phil. in Geology in 1988, and Ph.D. in Geology in 1989.
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Career
Early climate research
Raymo is known for developing (with William Ruddiman and Philip Froelich) the Uplift-Weathering Hypothesis. According to this hypothesis, tectonic uplift of areas such as the Himalayas and Tibetan Plateau over the last 40 million years enhanced the chemical weathering of minerals, which removed carbon dioxide from the atmosphere and resulted in cooling that spurred the growth of large ice sheets. Over 35 years later, the hypothesis continues to be actively researched. Their proposed mechanism of CO2 removal – the chemical weathering of rock – now underpins projects to sequester anthropogenic CO2 via artificially enhanced chemical weathering.
Raymo is known for her research using deep sea cores to better understand past oceanic thermohaline circulation, as well as how Earth's Milankovitch cycles influenced ice age pacing over the Pleistocene and Pliocene. Raymo's Anti-phase Hypothesis explains the 41,000 year pacing of Earth's climate cycles from 3 to 1 million years ago as due to the out-of-phase response of the polar ice sheets to orbital precession.
Raymo has also advanced stratigraphy and dating of the past via oxygen isotope analysis of foraminifera from deep ocean sediments. This included publishing the first continuous oxygen isotope stratigraphy and time scale of the northern hemisphere ice ages from DSDP Site 607. In 2005, with her post-doc Lorraine Lisiecki, Raymo published the widely adopted 5-million-year LR04 benthic isotope stack, which remains the benchmark against which most Plio-Pleistocene studies are measured.
In 1996, Raymo used carbon isotopes of marine organic matter to produce the first paleo-CO2 estimate for the Middle Pliocene Warm Period, a time when global temperatures were about 2-3 °C above preindustrial levels. Their CO2 estimate, between 350 and 400 ppm, later inspired the name of the activist organization 350.org which advocates for a return to 350 ppm as a safe level of atmospheric carbon dioxide.
Sea level research
Raymo has also worked extensively on reconstructing sea level and ice volume during past warm climate intervals with the goal of improving predictions of future sea level rise in response to global warming. She was the lead investigator of the PLIOMAX project (2011-2018), a research project funded by the US National Science Foundation, which had the goal to deliver more accurate sea level and ice volume data for the Pliocene, a period 3 million years ago when atmospheric CO2 was at ~400 ppm. Raymo led and participated in fieldwork in Australia, South Africa, Argentina, and the U.S. to map, interpret, and date Pliocene shorelines. She also worked with Jerry X. Mitrovica to understand the role of glacial isostatic adjustment (GIA) in deforming Pliocene shorelines. They identified this process as one of the reasons for the Pliocene sea level paradox—namely the different elevations of Pliocene shorelines around the globe. Her work also contributed to the mounting evidence that dynamic topography—topography driven by convective forces in the mantle—changes over million year timescales and therefore contributes to the warping of ancient shorelines. Numerical simulations of mantle convection support these findings. New insight gained on Pliocene sea level change has since been used to calibrate the physics underpinning ice sheet simulations of the future Antarctic ice sheet change. Her work on past sea level change and ice sheet stability based on paleo shorelines is complemented by her use of ice rafted debris in marine sediment cores to understand Antarctic ice sheet evolution.
Beyond the Pliocene, Raymo has also worked on sea level change during more recent warm periods. Her work has focused on the Marine Isotope Stage (MIS) 11 interglacial, merging relative sea level indicators with glacial isostatic adjustment models to show that global mean sea level during this time reached 6–13 meters above present. She has also contributed to mapping Last Interglacial (MIS 5e) shorelines in western Australia, Bermuda, Barbados, and the Bahamas to understand how high sea level rose during this time. In particular, she co-authored several studies arguing that global mean sea level during MIS 5e peaked lower than 5m, which is below estimates used in the IPCC report, and an important hypothesis to be tested.