ENSO and solar activity signals from oxygen isotopes in diatom silica during late glacial-Holocene transition in Central Andes (18°S)

Abstract

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 Odiatom 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 δ 18Odiatom 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.

Biogeochemical processes controlling oxygen and carbon isotopes of diatom silica in Late Glacial to Holocene lacustrine rhythmites

“…Accordingly we suggest two main scenarios for the formation of the superblooms in Lago Chungará: (1) low lake level and/or strong wind episodes that, facilitating turbulence, would select diatoms over other types of phytoplankton due to their relative buoyancy (Reynolds, 2006); and (2) extraordinary humid events that would increase runoff and therefore external nutrient loading (Bradbury et al, 2002). The ENSO cyclicity signal recorded at this time in the Lago Chungará sedimentary record (Hernández et al, 2010) provides support to the existence and prevalence of one of the two contrasting dry (El Niño) or humid (La Niña) conditions (Valero-Garcés et al, 2003).…”

“…Additionally, 11 of these samples were also analysed for δ 13 C diatom and %C diatom . Two previous studies described δ 18 O diatom data from 22 (Hernández et al, 2008) and 40 (Hernández et al, 2010) dark-green sample levels to establish the baseline environmental evolution of Lago Chungará (Fig. 2).…”

“…The onset of the Holocene is characterised by a weakening and reduction of amplitude of the ENSO (Moy et al, 2002;Rodbell et al, 1999). The establishment of a long-term La Niña pattern in the tropical Pacific during this period seems to be a consequence of the ENSO activity reduction (Hernández et al, 2010;Koutavas et al, 2002). Onset of the present day ENSO conditions occurred at about 7000 cal years BP (Moy et al, 2002;Sandweiss et al, 2001).…”

“…Moreover, decadal variations in solar activity are related to the atmospheric circulation (Christoforou and Hameed, 1997) modulating the sign and strength of the westerly wind flow, which reduces the delivery of the moisture from the east above the Altiplano (Theissen et al, 2008). Previously published data dealing with the laminated sediments of Lago Chungará suggest that (at least during the Late Glacial-Early Holocene transition) there is an interaction between the solar activity and ENSO (Hernández et al, 2010). The solar activity forcing was likely transmitted to the Andean Altiplano via ENSO modulation of the SASM.…”

“…B. δ 18 O diatom data of all the green laminae from the Late Glacial-Early Holocene transition (12,000-11,500 cal years BP). These data were used to document the moisture balance in the region for this period (Hernández et al, 2010). C. δ 18 O diatom data of all the laminae (green and white) from the Late Glacial-Early Holocene transition (12,000-11,500 cal years BP).…”