ENSO and solar activity signals from oxygen isotopes in diatom silica during Lateglacial-Holocene transition in Central Andes (18ºS).

The Late Glacial-Holocene transition from the Lago Chungará sedimentary record in northern Chilean Altiplano (18ºS) is made up of laminated sediments composed of light and dark pluriannual couplets of diatomaceous ooze. Light sediment laminae accumulated during shortterm extraordinary diatom blooms whereas dark sediment laminae represent the baseline limnological conditions during several years of deposition. Diatom oxygen isotope data (δ18Odiatom) analyzed in 40 succesive (lamina by lamina) dark laminae, from 11,990 to 11,450 cal years BP, suggest that there occurred a series of decadal-to-centennial dry-wet oscillations. Dry periods are marked by relatively high isotope values whereas wet episodes are indicated by lower values. This interpretation agrees with the reconstructions on allochthonous inputs and regional effective moisture availability carried out in the lake. The δ18Odiatom record documents repeated effective moisture changes at a centennial-scale. Three major cycles have been established (11,990 to 11,800, 11,800 to 11,550 and 11,550 to 11,450 cal years BP). Each cycle is defined by an increasing isotope trend followed by a sudden depletion of the isotope values. In addition, several wet and dry events at a decadal scale are superimposed onto these major cycles. The spectral analyses of the δ18Odiatom values suggest that cycles and events could be triggered by both the El Niño-Southern Oscillation (ENSO) and the solar activity. Significant ENSO frequencies of 7-9 years and 15-17 years, and periodicities of the solar activity cycles such as 11 yr (Schwabe), 23 yr (Hale) and 35 yr (Brückner) have been recognized in the oxygen isotope time series. Time-frequency analysis shows that the activity of these two forces,, although was also present in the onset of the Holocene, it was more intense during the Late Glacial period. The early Holocene could be mainly governed by La Niña-like conditions that correspond to wet conditions over the Andean Altiplano