XRF analysis of Laguna Pallcacocha sediments yields new insights into Holocene El Nino development

The laminated sedimentary sequence of Ecuador's Laguna Pallcacocha is one of the most widely cited proxy records of Holocene El Nino Southern Oscillation (ENSO) variability. Previous efforts to reconstruct flood-driven laminae from Laguna Pallcacocha relied solely on sediment color, a useful but non-specific metric of flood events. We improved the chronology with Pb-210 and additional C-14 dates over the past millennium, which allows for comparison of the sedimentary record with historically documented El Nino events. Additionally, we use elemental composition derived from X-ray Fluorescence (XRF) to reconstruct flood history at Pallcacocha. A principal component analysis (PCA) of the XRF dataset identifies minerogenic flood-driven clastic laminae. The first principal component (PC1) of the XRF data and red color intensity are positively correlated over the past 7.5 kyr, but the color record fails to capture high frequency variability that is preserved in the XRF dataset during the early Holocene (approximately 7.5-11 kyr BP). The new XRF dataset indicates moderate El Nino activity during the early Holocene, suppressed El Nino activity in the middle Holocene, and enhanced El Nino activity during the late Holocene. This pattern is relatively common among other ENSO records, and has been attributed to long-term changes in tropical insolation. Some intervals-most notably between 3-2 kyr BP and during the last millennium-deviate from expected trends if insolation was the sole forcing mechanism. Previously proposed mechanisms linking ENSO to latitudinal displacement of the ITCZ and ocean-atmospheric variabilities in other ocean basins appear to play an additional role in modulating Holocene ENSO development, as demonstrated by statistically significant correlations between the revised Laguna Pallcacocha flood history and proxy records from the Atlantic. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the laminated sedimentary sequence of Laguna Pallcacocha in Ecuador and improves the chronology using Pb-210 and C-14 dating methods. By using X-ray Fluorescence and principal component analysis, the researchers reconstruct the flood history and identify patterns of El Nino activity during the Holocene. The results suggest that El Nino variability in the region is influenced by both long-term changes in tropical insolation and latitudinal displacement of the ITCZ and ocean-atmospheric variabilities in other ocean basins.