Due to its elevated temperatures and atmospheric CO2 concentrations, the Pliocene warm period (PWP) (5.3-2.6 million years ago) is a common analog for a future, warmer world. The El NiñoSouthern Oscillation (ENSO) is an ocean and atmosphere phenomenon punctuated by El Niño and La Niña events, changes in the distribution of warm water across the Pacific Ocean that currently occur every 2-7 years. ENSO is the strongest control on global interannual climate variability, yet the nature of ENSO during the PWP is the subject of debate, with conflicting computer models and geologically-derived reconstructions of sea surface temperature suggesting it was characterized by (1) a persistent El Niño-like state (Wara et al., 2005 Science v.309, p.758), (2) a persistent La Niña-like state (Rickaby and Halloran, 2005, Science v.307, p.1948), or (3) sea surface temperature variability consistent with modern ENSO conditions (Watanabe et al., 2011, Nature v.471, p.209). The study by Watanabe et al. (2011), which involves analysis of fossil corals from the western Pacific, differs from the other two studies which are derived from deep sea sediments spanning the tropical Pacific. Until now, no similar analysis has been performed on fossil corals from the eastern Pacific where ENSO-related sea surface temperature anomalies are most pronounced.
This research conducted a study similar to that of Wara et al. (2011) using pristine fossil corals from the Dominican Republic previously dated using U-Pb techniques (5.5±0.1 Ma) (Denniston et al., 2008, Geology, v.36, p.151). Today, the Dominican Republic is isolated from the eastern Pacific by the Central American Isthmus, but prior to ~2.7 Ma, the isthmus had not yet formed and Pacific waters flowed into the Caribbean Sea, potentially carrying ENSO signals directly into the Caribbean. The coral record suggests anomalous cold (warm) sea surface temperature excursions indicative of El Niño (La Niña) events occurred at intervals consistent with modern ENSO behavior. These findings should be integrated into paleoceanographic models at 5.5 Ma in order to better understand their connection to ENSO.
Thomas Weiss, ’16
Sponsor: Rhawn Denniston