JISAO Postdoc Seminar: "ENSO variability changes during the Holocene"

Start Date/Time: Friday, August 29, 2008, 1:00 PM
Location: Ocean Science Building (OSB) 425

Speaker: Matthieu Carre

"ENSO variability changes during the Holocene: reconstruction from mollusk isotopic records"

Sea surface temperatures (SST) can be reconstructed from oxygen isotopes in mollusk shells carbonates. We analyzed shells from archaeological sites on the Peruvian coast, whose climate is strongly influenced by the coastal upwelling and the El Niņo Southern Oscillation (ENSO). A random sample of shells extracted from a stratigraphic layer provides a statistical estimate of the annual SST, the seasonal SST amplitude, and the ENSO-related variability for the period of time corresponding to the layer accumulation. Climate reconstructions from archaeological shell middens involve two time scales: the monthly to interannual scale corresponding to the individual shell formation, and the centennial to millenial scale related to the midden accumulation rate.

We present here results from different periods in the Holocene showing significant changes of the ENSO activity associated to background SST changes. Monte Carlo analysis of known time series combined with a proxy model allows to quantitatively estimate the standard error of the reconstructions, which depends on the sample size, the proxy uncertainties, and the climate variability. Such data are promising for comparison with paleoclimate GCM simulations to study the relationships between the ENSO activity, the background climate conditions, and the SST seasonality in the South-East Tropical Pacific.