Fig 1.
(a) The location of Rano Raraku on Rapa Nui (Easter Island). Base map and data from ESRI and OpenStreetMap Foundation. (b) Aerial view of the crater lake with the positions of the samples collected. Map provided by Base map and data from ESRI and OpenStreetMap Foundation. (c) Picture of the Rano Raraku basin on 7 Sep 2017. The photo was taken on the SW section of the lake and photo is taken by Dario Battistel facing NE.
Fig 2.
Geological representation of Rano Raraku a) picture of the lake (7 Sep 2017) with facies, b) cross section of the crater lake with the past lake level maximum at 17,000 cal yr. BP and at the time of the sampling [6–8, 10–12].
Table 1.
Characteristics of samples collected at Rano Raraku.
Fig 3.
Isotopic composition of rainfall on Rapa Nui (black dots; from Herrera and Custodio [42]) and Rano Raraku water in 2017 (red dots). Mean meteoric water line (blue), rainfall best fit (black line), and equation straight line derived from the evaporation model (red line).
Fig 4.
Monthly precipitation at Mataveri, Rapa Nui (Easter Island) (Center for Climate and Resilience Research, http://www.cr2.cl/datos-de-precipitacion/?cp_Precipitacion=1).
The red line is a 10-year moving average.
Fig 5.
Mean Mn/Fe (blue) and Cr/V (green) ratios with standard deviations of the analysed matrices: Water, SPM (suspended particulate matter), WSI (water-sediment interface), bed sed. (bed sediment), topsoil.
Fig 6.
Scheme of the fractionation process of Mn and Fe in Rano Raraku.
Fig 7.
Log-log plot of Mg/Ca vs Ca/Sr values in different environmental components.
Topsoil (red point) does not lie on the line because it is not involved in the fractionation process occurring in the lake.
Fig 8.
Ce/Ce* (brown) and LREE/HREE (green) mean ratios with standard deviation in the analyzed matrices: Water, SPM (suspended particulate matter), WSI (water-sediment interface), bed sed. (bed sediment), topsoil.
Fig 9.
LREE/HREE and Ce anomaly vs elevation of topsoil samples from the Rano Raraku internal crater.