Study of Seasonal Radiocarbon Variability in the Eastern Tropical Pacific During Periods of Decadal and Interannual Climate Shifts

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In this project, investigators at the University of California at Irvine will determine the detailed changes of radiocarbon in the surface of the eastern tropical Pacific during distinctive climatic periods in the past 400 years. The researchers expect that these studies will aid in our understanding of how natural variability in climate can influence the ability of the ocean to absorb excess CO2 produced from fossil fuel and biomass burning. High-precision AMS (accelerator mass spectrometry) 14C measurements on seasonal coral bands from the eastern tropical Pacific, located in the "center of action" with respect to El Nino, will be made to determine the variability of the low 14C component of the source waters (presumably Sub-Antarctic Mode Water) from the South Pacific. Three hypotheses will be tested: 1) Wintertime 14C values in Galapagos corals are an indicator for the phase of the PDO; 2) Prolonged periods of winter-time upwelling were present at in the eastern tropical Pacific during the early 1600s and early 1800s, which were likely caused by prolonged entrainment of Sub-Antarctic Mode Water into the Equatorial Under Current; and 3) Wintertime 14C values at Galapagos reveal interannual-to-decadal variability in climate.To test these hypotheses, the following studies will be done: 1) Seasonal 14C and, in collaboration with colleagues at Stanford University, 18O will be measured in Galapagos coral bands that grew from 1900-1996 to determine if the winter-time 14C was significantly lower during recorded periods when the PDO was known to have been in a negative phase (1915-1925 and 1945-1955). A calibration experiment will be performed to demonstrate that the coral species used in this study is indeed recording the entire seasonal signal. 2) Seasonal 14C and 18O measurements of coral bands that grew from 1598-1611 and from 1804-1825 will be made to determine if the winter-time 14C was significantly lower and/or persisted for a longer period of time during these unusual climatic periods. 3) Seasonal 14C measurements will be made of coral bands from time periods that display clear interannual variability in climate (ENSO) and those that are dominated by distinct decadal variability. Collaboration with colleagues at Princeton University is planned to utilize the seasonal 14C records in his ocean circulation modeling experiments designed to calculate variability of past pCO2 and CO2 out-gassing fluxes in the equatorial Pacific.In terms of broader impacts, the project will support the work of one graduate student and two undergraduate students and provide hands-on experience that will prepare them for careers as scientists and educators. The PI is involved with developing outreach activities in conjunction with middle and high school youths. She is also on the advisory board for FCOSEE (Florida Center for Ocean Science Education Excellence COSEE) to assist in developing web-based educational classes at the college level, and participates in teaching a short course on Radiocarbon and the Carbon Cycle every summer.