Fig 1.
Geographical and geological context.
A) Position of the Monte San Nicola area (red square) within the Caltanissetta sedimentary Basin (Sicily). B) Sapropel clusters O and A (upper Piacenzian) in the badlands close to the “Mandorlo” section. Yellow asterisks indicate the “Nicola bed” (sapropel A5), physical reference for the Piacenzian/Gelasian boundary and our reference zero level for sampling. The tripartite grey band (gb in figure) at the change of slope above the “Nicola bed” contains the MIS 100 –MIS 96 interval. C) Essential stratigraphic information for the “Mandorlo” section. Left: magneto-stratigraphy of section. R: Reunion; M: Matuyama. Right: lithological log. Legend is reported above. Individual sapropel layers of clusters A, B and C are labelled in blue. Purple stars: episodic influxes of left-coiled Neogloboquadrina atlantica, deemed as correlative to MIS 100, 98 and 96 (see [11]). D) Blow-up of the stratigraphic interval of relevance for this study. Left: chronostratigraphic, lithological, and magneto-stratigraphic logs (same as above). Right: the δ18O record for Uvigerina spp, with indication of glacial (blue) and interglacial (red) MISs. Light blue bands indicate glacial intervals. The thin orange line marks the Piacenzian/Gelasian boundary (Plio/Pleistocene as well). Modified from [13].
Fig 2.
Paleoclimatic records for the “Mandorlo” section.
From the top downwards: A) the LR04 benthic δ18O stack of [6]. B) the local δ18O record of Uvigerina spp. [13]. C) purple line: the high-resolution δ18O record for G. ruber reconstructed at the “Mandorlo” section (this study); dashed black line: 65° N summer insolation by [40]. D) the composite PP-MSN alkenone-derived Mediterranean SST record (°C) by [5]; PP = Punta Piccola and MSN = Monte San Nicola. E) the high-resolution alkenone-derived SST (°C) record for “Mandorlo” section (green) reconstructed for this study, based on the age model of [13] and plotted against the obliquity curve by [40] (dashed black line). Thick light gray bands indicate glacial stages (MIS 104, MIS 102, MIS 100). Thin dark gray bands indicate the sapropel layers of cluster A considered for this work (A4, A4/5 and A5).
Fig 3.
Spectral and wavelet analysis of the raw alkenone-derived SST signal.
Bottom left: spectral analysis, revealing the presence of a 47-kyr signal (in the orbital obliquity time domain). Blue and red lines correspond to the 90% and 95% confidence thresholds, respectively. Bottom right: wavelet analysis. The colour scale is indicative of signal power. Red = stronger; blue = weaker. Top: our alkenone-derived SST record.
Fig 4.
Climate variability at the suborbital scale.
From the top downwards: A) the high-resolution alkenone-derived SST (°C) record for the “Mandorlo” section (this study). B) the Relative Sea Level (RSL) curve by [55]. C) the high-resolution δ18O record of Uvigerina spp. by [13]. D) the high-resolution δ18O record for G. ruber (this study). E) the Ice Rafted Debris (IRD) record by [3]. Isotopic values are reported in per mil (‰) relative to the VPDB standard. The dashed green lines mark the position of prominent IRD peaks within MIS 100. Thick light grey bands indicate glacial stages (MIS 104, MIS 102, MIS 100). Thin dark grey bands indicate the sapropel layers of cluster A considered for this work (A4, A4/5 and A5).
Fig 5.
Spectral and wavelet analysis of the IMF3 component of the alkenone-derived SST record.
Bottom left: spectral analysis revealing suborbital cycles on the order of 10.9 and 8.5 kyr. Blue and red lines correspond to the 90% and 95% confidence thresholds, respectively. Bottom right: wavelet analysis showing that the periodicities above are pervasive throughout the study interval, although they grow stronger since the beginning of the Pleistocene (signal power scale is reported on the far right: red = stronger, blue = weaker). Top: the SST IMF3 component spectrum.
Fig 6.
Spectral and wavelet analysis of the IMF2 component of the alkenone-derived SST record.
Bottom left: spectral analysis revealing a second cluster of suborbital periodicities centred on the ~5 kyr band (i.e., 4.5, 5, 7.2 and 8.2 kyr, the 5 kyr period being the most significant). Blue and red lines correspond to the 90% and 95% confidence thresholds, respectively. Bottom right: wavelet analysis showing that said periodicities occur throughout but become stronger during the glacial stages, especially in MIS 100 (the signal power scale is reported on the far right: red = stronger, blue = weaker). Top: the SST IMF2 component spectrum.