Dr. Jessica Conroy has been awarded an NSF Earth Sciences Postdoctoral Fellowship to carry out a research and education plan at Georgia Institute of Technology. Dr. Conroy will carry out a multi-year precipitation and seawater sampling program to assess stable isotopes variability on diurnal, seasonal, and interannual timescales across the equatorial Pacific Ocean. This information will then be coupled with instrumental climate data to investigate the climate controls on stable isotopes in precipitation and seawater. The data produced from this project will fill a critical gap in observational networks for water isotopes, providing for rigorous comparisons to isotope-equipped global climate models and satellite-based water isotope retrievals. An improved knowledge of the relationship between large-scale climate dynamics and water isotope variability in the tropical Pacific will also allow for more accurate interpretations of key tropical Pacific proxy records across a range of timescales.
Much of the importance of stable water isotopes lies in their ability to provide information on past climate change. The vast majority of tropical Pacific paleoclimate reconstructions from corals, speleothems, lake sediments, and marine sediments are based on the stable isotope values of oxygen and/or hydrogen, which reflect changes in large-scale hydrological processes, and, in the case of carbonate archives, temperature. Accurate interpretation of these records is critically important, since climate variability in this region impacts climate across the globe, most notably through the El Niño/Southern Oscillation phenomenon. Typically, output from isotope-equipped global climate models aids in the interpretation of isotope archives of past climate information, and forward modeling of proxies provides insight into the dominant controls on isotope-based proxy climate records. However, there are few real isotope measurements from the tropical Pacific to validate climate models and incorporate into forward modeling of proxies. The new dataset generated from this project will provide these measurements, helping us to understand the controls on stable water isotope variability and accurately interpret past climate variability in this important region. The planned education activities associated with this fellowship include the development of a "Stable Isotopes and Climate" curriculum for a local public high school and student science-fair projects, and the exposure of native Pacific Islanders to scientific data collection and interpretation.
This fellowship is supported by the Paleolimate Program in the Division of Atmospheric and Geospace Scieneces.
Project Outcome Summary In places where measurements of past climate do not extend far back in time, paleoclimate records are essential to understand how climate can change and has changed over long timescales. The goal of this research was to go back and test some of the fundamental assumptions that underlie paleoclimate reconstructions, particularly those based on a key parameter of water chemistry. That key parameter, the stable isotopic composition of water, has been found to be correlated with variables like salinity in the ocean and rainfall amount, but there are so few actual measurements of stable water isotopes in some regions, like the tropical Pacific, that we can’t constrain with certainty what climate variables really drive stable water isotope variability. Incidentally, the tropical Pacific is where many water isotope-based paleoclimate reconstructions exist. During this postdoctoral fellowship, I initiated new rain and seawater collections at four sites in the tropical Pacific. Additionally, I also investigated the relationship between water isotopes and climate in a suite of global climate models. The new stable isotopic data from this project is already beginning to provide new insights into the relationship between water isotopes and climate, which is more complex than previously assumed. For example, the strength of the relationship between rain amount and water isotope values varies across the tropical Pacific. Also, in some ocean water masses, salinity and water isotope values do not have the same range of variation. One paper has been published from this 2-year fellowship, and two more are in preparation for submission. Broader Impacts During this fellowship, I trained and mentored high school student Ariana Lewis, who initiated a lake and rainwater collection program in Atlanta, conducted isotopic analysis of her water samples, and presented her results at two science fairs. She was awarded the ‘Einstein Award’ for her presentation. I also assisted local high school teacher Kori Ellis in developing lecture and curriculum material for her oceanography class--the first oceanography class to be taught at Grady High School in Atlanta.
