title: Dynamical excitation of the tropical Pacific Ocean and ENSO variability by Little Ice Age cooling.
abstract: Tropical Pacific Ocean dynamics during the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) are poorly characterized due to a lack of evidence from the eastern equatorial Pacific. We reconstructed sea surface temperature, El Niño-Southern Oscillation (ENSO) activity, and the tropical Pacific zonal gradient for the past millennium from Galápagos ocean sediments. We document a mid-millennium shift (MMS) in ocean-atmosphere circulation around 1500-1650 CE, from a state with dampened ENSO and strong zonal gradient to one with amplified ENSO and weak gradient. The MMS coincided with the deepest LIA cooling and was probably caused by a southward shift of the intertropical convergence zone. The peak of the MCA (900-1150 CE) was a warm period in the eastern Pacific, contradicting the paradigm of a persistent La Niña pattern.
authors.affiliation: Department of Engineering Science and Physics, College of Staten Island, City University of New York, Staten Island, NY 10314, USA. Doctoral Program in Earth and Environmental Sciences, Graduate Center of the City University of New York, New York, NY 10016, USA. grustic@ldeo.columbia.edu.
authors.forename: Gerald T
authors.initials: GT
authors.lastname: Rustic
authors.affiliation: Department of Engineering Science and Physics, College of Staten Island, City University of New York, Staten Island, NY 10314, USA. Doctoral Program in Earth and Environmental Sciences, Graduate Center of the City University of New York, New York, NY 10016, USA. Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, USA.
authors.forename: Athanasios
authors.initials: A
authors.lastname: Koutavas
authors.affiliation: Department of Geological Sciences and Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO 80309, USA.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Marchitto
authors.affiliation: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, USA.
authors.forename: Braddock K
authors.initials: BK
authors.lastname: Linsley