PARENT SESSION
Tuesday, August 8, 5:00-6:30 pm
Poster Session 10 - Genetics, evolution, and paleoecology
Exhibit Hall, Ballroom Level, Cook Convention Center

Pollen record of ENSO variability for the last 1500 years.

Restrepo, Alejandra^*,1, Bush, Mark B. ^*,1, ¹ Florida Institue of Technology, Melbourne, Florida

ABSTRACT- ENSO events in the tropical eastern Pacific have been recorded in coral isotopic records. However, these events also impact terrestrial biota, especially vegetation that undergoes long drought periods. Precipitation in the Galapagos Islands can increase three-fold during El Niño events compared to average annual values. In addition, the mean annual temperature increases during these events. These climate anomalies have striking effects on plant biomass production and phenology. A pollen record with three to seven years of temporal resolution was raised from EJ N-1 core (El Junco Lake, San Cristobal Island) in order to investigate ENSO variability. An age model was established for each 0.4 cm depth using calibrated radiocarbon, Pb-210, and Cs-137 measurements. Non-bioturbated sediments recorded the strength of ENSO phases at a decadal time scale. Changes in ENSO periodicity, due to the Pacific decadal oscillation and global warming forcing, are manifest for the last 200 years (2003 to 1786 AD). We tested the strength of ENSO phases during the Little Ice age and the Medieval Warm period in response to fluctuations of the Pacific zonal SST gradient. The sampled intervals range between 1743 to 1658 AD, 1366 to 1245 AD, and 1089 to 928 AD. The vegetation's responses along the four intervals are registered as taxonomic variations of the pollen assemblages, changes in pollen concentration, and in the ratio Poaceae/Cyperaceae.

Key words: ENSO variability, pollen record, decadal time scale