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A continuous Holocene record of ENSO variability in Southern Chile (ENSO-CHILE)
De Batist, M.; Fagel, N.; Loutre, M.F.; Chapron, E.; Berger, A.; Boës, X.; Bertrand, S.; Charlet, F.; De Vleeschouwer, F.; Juvigné, E.; Pino, M.; Renson, V.; Roche, E.; Sterken, M.; Thorez, J.; Urrutia, R.; Vargas, L.; Verleyen, E.; Vyverman, W. (2007). A continuous Holocene record of ENSO variability in Southern Chile (ENSO-CHILE). OSTC, Brussels: Brussels. 87 pp.
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  • Charlet, F., meer
  • De Vleeschouwer, F.
  • Juvigné, E.
  • Pino, M.
  • Renson, V., meer
  • Roche, E.
  • Sterken, M., meer
  • Thorez, J.
  • Urrutia, R.
  • Vargas, L.
  • Verleyen, E., meer
  • Vyverman, W., meer
Abstract
    An 11-m-long sediment core was collected in Lago Puyehue (40ºS, Lake District, Chile). The coring site was selected on basis of a thorough seismic-stratigraphic analysis that highlighted it as an area of relatively condensed, continuous and undisturbed sedimentation in this otherwise highly dynamic post-glacial lake. The 11-m core extends back to 17,915 cal. yr BP and a substantial part of it is annually laminated. An age-depth model was established by 9 AMS 14C dates, constrained by 210Pb, 237Cs, 241Am measurements, by the identification of event deposits related to earthquakes and/or volcanic eruptions, and by varve counting for the past 600 yrs. The core was submitted to a multi-proxy analysis, including sedimentology, mineralogy, grain-size, major geochemistry and organic geochemistry (C/N ratio, d13C), loss-on-ignition, magnetic susceptibility, diatom analysis, palynology and varve thickness analysis. Interpretation of the seismic data and extrapolation of the age-depth model puts the age for the onset of open-water conditions in Lago Puyehue at ca. 28,000 cal. yr BP. This contrasts with previous glacial-history reconstructions from the area based on terrestrial records, which date the complete deglaciation of the basin as ca. 14,600 cal. yr. BP. Along-core variations in sediment composition reveal that the area of Lago Puyehue was characterised since the Last Glacial Maximum (LGM) by a series of rapid climate fluctuations superimposed on a long-term warming trend. Among these climate fluctuations are: i) a first warming pulse sometime between 19,500 and 17,150 cal. yr BP, ii) a well-marked cold and humid interval at 13,100-12,300 cal. yr BP, roughly coeval with the Huelmo/Mascardi Cold Reversal (and out-of-phase with the Northern-Hemisphere Younger Dryas and the Antarctic Cold Reversal), iii) a second pulse towards warmer and dryer conditions between 12,300 and 11,800 cal. yr BP, marking the onset of the Holocene, iv) warm and dry climate conditions between 11,800 and 7,800 cal. yr BP, reflecting an early Holocene climatic optimum, v) relatively stable climate conditions since 7,800 cal. yr BP, except for vi) an interval of cold and/or humid conditions at 3,400-2,900 cal. yr BP, and vii) a wet period during the interval 1490-1700. Regional present-day climate around Lago Puyehue is dominated by the southern Westerlies and associated strong precipitation. Precipitation peaks during the transition from austral autumn to winter and during winter. Detailed re-analysis of available instrumental data shows El-Niño years to be characterized by lower-thannormal precipitation, particularly during the autumn/winter transition. Since precipitation during autumn/winter is the dominant factor controlling the thickness of the varves, varve-thickness and color-intensity records can be used as proxy for precipitation and as a tracer of El Niño activity over time. Spectral analysis of varvethickness records over the last 600 yrs reveals periodicities of 3, 3.2 and 4-4.4 yrs. The dominant period over the last 100 yrs is that of 3 yrs, which is consistent with the most common frequency of the present-day El Niño phenomenon. The record also contains multi-decadal periodicities of 15 and 41 yrs, which are consistent with other South Pacific and even North Pacific indexes (QBO, PDO, PNI or NOI). The dominant period over the last 600 yrs is 4-4.4 yrs and appears in the record during the period 1490-1700 (i.e., the Little Ice Age). The climate during the Little Ice Age thus appears to have been characterized by successive pronounced El Niño events. Varve-thickness analysis of the laminated interval at the bottom of the long core allows sub-dividing the Huelmo/Mascardi Cold Reversal into two separate cold/humid intervals, interrupted by a dryer and warmer phase. The sedimentary record obtained from Lago Puyehue provides the very first longterm, continuous, high-resolution record from the Pacific side of southern South America, and will undoubtedly emerge as a reference paleoclimate record.
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