ENSO related decadal scale climate variability from the Indo-Pacific Warm Pool

The El Nino-Southern Oscillation (ENSO) is a climatic phenomenon that affects socio-economical welfare in vast areas in the world. A continuous record of Holocene ENSO related climate variability of the Indo-Pacific Warm pool (IPWP) is constructed on the basis of stable oxygen isotopes in shells of planktic foraminifera from a sediment core in the western Pacific Ocean. At the centennial scale, variations in the stable oxygen isotope signal (delta O-18) are thought be a representation of ENSO variability, although an imprint of local conditions cannot be entirely excluded. The record for the early Holocene (10.3-6 ka BP) shows, in comparison with the mid- to late Holocene, small amplitude variations in the delta O-18 record of up to 0.3 parts per thousand indicating relatively stable and warm sea surface conditions. The mid- to late Holocene (6-2 ka BP) exemplified higher variability in delta O-18 and thus in oceanic IPWP conditions. Climatically, we interpret this change (5.5-4.2 ka BP) as a phenomenon induced by variability in frequency and/or intensity changes of El Nino. In the period 4.2-2 ka BP we identified several periods, centred on 1.9, 2.1, 2.7, 3.3, 3.7 and 4.2 ka BP, with in general heavy 6180 values. During these periods, the IPWP was relocated to a more eastward position, enhancing the susceptibility for El Nino-like conditions at the core site. Over the last 2000 yr precipitation increased in the area as a response to an increase in Asian monsoon strength, resulting in a freshening of the surface waters. This study corroborates previous findings that the present-day ENSO activity started around 5.5 ka BP. (c) 2006 Elsevier B.V. All rights reserved.