What can nutrients tell us about the Pliocene equatorial Pacific Ocean and the future of El Niño?

Wednesday, 17 December 2014: 9:45 AM
Patrick A Rafter1, John Richard Southon2, Stefano M Bernasconi3, Gerald Hermann Haug3, Daniel Mikhail Sigman4 and Fabian Batista5, (1)University of California Irvine, Irvine, CA, United States, (2)Univ California, Irvine, CA, United States, (3)ETH Swiss Federal Institute of Technology Zurich, Zurich, Switzerland, (4)Princeton University, Princeton, NJ, United States, (5)University of California Santa Cruz, Santa Cruz, CA, United States
Global-scale climate variability associated with the El Niño-Southern Oscillation (ENSO) is produced by relatively small adjustments of the upper equatorial Pacific Ocean. However, despite being one of the most important contributors to global climate variability, we are still unsure how the current increase in greenhouse gas concentrations will affect ENSO. One way this ocean-atmosphere relationship can be tested is by reconstructing upper equatorial Pacific Ocean conditions during the Pliocene—a time period when greenhouse gases were as high as today. To date, most studies use sea surface temperature (SST) proxies in sediments to reconstruct Pliocene ocean conditions, but contradicting results have highlighted the possible short-comings and limitations of this approach. Here, we bypass this controversy by using measurements of the modern and Pliocene equatorial Pacific to link surface nutrient variability to upper ocean variability. This alternate reconstruction suggests there was no change in the mean state of nutrients since the late Pliocene and we explore this surprising result by discussing potential changes in the thermocline / nutricline relationship.