A 2000-year high-resolution lacustrine record of El Niño Southern Oscillation from the center of the Eastern Equatorial Pacific region (Genovesa crater lake, Galapagos Islands)

Abstract:

High-resolution El Niño Southern Oscillation (ENSO) records from the Eastern Equatorial Pacific (EEP) are rare. Most sediment records are located on the edge of the EEP, while paleocoral records from the central EEP, are intermittent records of ENSO variability. We present a continuous 2000-year lacustrine record of ENSO variability from the center of the EEP. Genovesa crater lake is a hypersaline crater lake located on the arid island of Genovesa in the northern Galapagos archipelago. A deciduous Bursera graveolens forest dominates the island’s vegetation and the lake is rimmed by Rhizophora mangle, which is not precipitation dependent. Rainfall is limited to the brief wet season or El Niño events, making the lake an ideal site to record precipitation and ENSO variability. Variations in sediment grayscale intensity were subjected to wavelet analysis to detect periods of significant ENSO periodicity (4-8-years). Bursera and Rhizophora pollen percentages were used to compare plant productivity with ENSO variability. Sediment grayscale variability and peaks in Bursera percent abundance were consistent with historical records of ENSO. On longer timescales, these proxies suggest that ENSO was relatively reduced within the Medieval Climate Anomaly (MCA). Peaks in Bursera percentages, however, become more pronounced than elsewhere in the record. Overall ENSO activity may have been reduced during the MCA, but large droughts and floods appear to have been a feature of the climate. The Little Ice Age (LIA) has been described as a period of increased ENSO activity and strength. However, ENSO periodicity in our record is weak throughout this period, compared with the period after the LIA (1850 CE to modern). Bursera percentages are lower overall during the LIA (1550-1850 CE) than in the MCA, potentially outlining background arid conditions. New geochemical data from the Galapagos suggests a potential dry La Niña-like period during the LIA (Thompson et al. in review, Conroy et al. in review). A persistent La Niña-like period would reduce Bursera productivity and account for the reduction in a significant ENSO periodicity. Our data highlight the probable variability in ENSO within the EEP over the last 2000 years and indicate that the MCA may be a stronger climatic feature than the LIA in this region.