# Unexpected wet and warm conditions during glacial periods in the Central North Atlantic as recorded by paleosols from Flores Island (Western Azores)

Laura Loiodice, Francisco Hevia-Cruz, Anthony Hildenbrand, Nathan D Sheldon

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## To cite this version:

Laura Loiodice, Francisco Hevia-Cruz, Anthony Hildenbrand, Nathan D Sheldon. Unexpected wet and warm conditions during glacial periods in the Central North Atlantic as recorded by paleosols from Flores Island (Western Azores). Palaeogeography, Palaeoclimatology, Palaeoecology, 2025, 676, pp.113157. 10.1016/j.palaeo.2025.113157. hal-05343586

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Submitted on 3 Nov 2025

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# Unexpected wet and warm conditions during glacial periods in the Central North Atlantic as recorded by paleosols from Flores Island (Western Azores)

Laura Loiodice<sup>a</sup>, Francisco Hevia-Cruz<sup>a,b,c,*</sup>, Anthony Hildenbrand<sup>a</sup>, Nathan D. Sheldon<sup>d</sup>

## ARTICLE INFO

Editor Name: Dr. Howard Falcon-Lang

**Keywords:**

Paleoclimate

Paleosols

Volcanic islands

Azores Archipelago

K-Ar geochronology

Geochemistry

## ABSTRACT

Rapid climate change is increasingly expected to trigger major disturbances of regional temperatures and precipitation, but the atmospheric effects of globally colder climatic episodes remain poorly documented, especially in oceanic areas. In the Central North Atlantic, the Azores Archipelago lies under the influence of major regional climatic drivers and comprises groups of volcanic islands that recorded successive paleoclimatic conditions during most of the Pleistocene. We reconstructed the Mean Annual Precipitation and Air Temperature of Flores Island, in the westernmost extreme of the archipelago, through paleoclimatic proxies based on paleosols geochemistry. K-Ar geochronology of volcanic units "bracketing" paleosols revealed two episodes of significant weathering during glacial periods (~550 ka and 630-670 ka), contrasting with the Central and Eastern Azores where paleosols formed during interglacial peaks. Mild/wet conditions prevailed in Flores (21.5 °C; 1340 mm yr⁻¹), hotter/drier than current conditions (17 °C; 1716 mm yr⁻¹), and wetter/warmer than those reached in other Azores islands. This is consistent with modern regional climatic gradients (wetter/hotter to the west). Ages between Flores and other Azores islands do not overlap, suggesting (1) persistent warm/wet conditions in Flores due to its northern position, closer to the westerlies' trend; or (2) unexpected regional warm/wet conditions around 550 ka and 650 ka, i.e., even during two globally-cold main glacial periods. Further studies in the Azores and at broader scales (e.g., the Canary Islands) are needed to improve regional paleoclimatic reconstructions, and to shed light on the interactions between global climatic forcing and their impacts in the Atlantic throughout the Quaternary.

## 1. Introduction

Over the last decades, extensive research efforts have been spent to study the causes of Quaternary climatic cycles and their impacts on the Earth system. Major glacial-interglacial transitions, especially, represent critical periods during which global temperatures and sea level increased drastically within only a few millenia (e.g., *Hearty and Neumann, 2001*; *Bard, 2002*). These changes likely triggered a number of regional disturbances such as storms and hurricanes, and favored chemical and physical degradation of emerged lands through mass wasting events, riverine incision, and rock weathering, among other processes (Hildenbrand et al., 2008a; Boulesteix et al., 2013; Dixon et al., 2016; Gayer et al., 2019; Hevia-Cruz et al., 2024a, 2024b). Major glacial-interglacial paleoclimatic transitions thus have gained increasing

attention in recent times, as they may represent analogs to the present climatic trajectory and may provide decisive information on the expected environmental impacts of upcoming global warming.

While global Quaternary paleoclimate has been extensively and systematically studied through proxies such as δ¹⁸O in oceanic sediment cores, or δD in ice cores, paleosols provide a valuable terrestrial complement to these archives. Soils record local climatic and environmental conditions during their formation and are especially sensitive to atmospheric parameters such as temperature and precipitation. As fossil soils, paleosols can record more local climatic and environmental signals during their formation, offering insights into land-atmosphere interactions that may be poorly captured by marine or glacial records, particularly in volcanic or oceanic island settings. Thus, volcanic paleosols represent a valuable, yet under-explored, natural record of past

<footnote><sup>a</sup> Géosciences Paris-Saclay, CNRS, Université Paris-Saclay, Orsay, France.</footnote>

<footnote><sup>b</sup> Laboratoire des Sciences du Climat et de l'Environnement, IPSL, CEA, CNRS, Université Paris-Saclay, Saint-Aubin, France.</footnote>

<footnote><sup>c</sup> Departamento de Ciencias de la Tierra, Universidad de Concepción, Concepción, Chile.</footnote>

<footnote><sup>d</sup> Department of Earth and Environmental Sciences, University of Michigan, USA.</footnote>

<footnote>* Corresponding author at: Géosciences Paris-Saclay, CNRS, Université Paris-Saclay, Orsay, France.
*E-mail addresses:* francisco.hevia-cruz@universite-paris-saclay.fr, fheviac@ug.uchile.cl (F. Hevia-Cruz).</footnote>
<figure><img src="image_5.png" /><figcaption>**Fig. 1.** (A) Location of the Azores Archipelago (red rectangle) and present climatic setting in the Central Atlantic. H: Azores High-pressure system; L: Icelandic Low-pressure system. The orange and blue lines represent isobaric curves, and the black arrows represent the main oceanic currents of the North Atlantic Gyre. Modified after Hevia-Cruz et al. (2024b). (B) Location of main islands in the Azores, including São Miguel (Eastern Azores), Terceira, Pico, Faial, São Jorge islands (Central Azores), and Flores (Western Azores). NA: North American lithospheric plate; EU: Eurasian lithospheric plate; NU: Nubia lithospheric plate; FZ: Fracture zone (white dashed line); MAR: Mid-Atlantic Ridge. The black dashed lines are the approximate limits between lithospheric plates. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

climate changes. Several studies determined that soil formation processes are directly linked to atmospheric conditions that are recorded by their geochemistry, allowing the development of paleoclimatic proxies based on paleosols' geochemistry (e.g., Sheldon et al., 2002; Sheldon, 2003; Sheldon, 2006; Sheldon and Tabor, 2009; Tabor and Myers, 2015).

The Azores Archipelago, located in the Central North Atlantic region, is particularly sensitive to climate changes due to its position influenced by regional climatic drivers such as the North Atlantic Oscillation atmospheric system and the oceanic North Atlantic Gyre (Fig. 1A). Several of these volcanic islands (São Miguel, Pico, Faial, São Jorge, Terceira, Flores) preserve many paleosols, allowing the reconstruction of the paleoclimate at the scale of the whole archipelago. In addition, the relatively synchronous volcanic activity of these islands (e.g., Hildenbrand et al., 2008b, Hildenbrand et al., 2012, Hildenbrand et al., 2014, Hildenbrand et al., 2018, Hildenbrand et al., 2024; Costa et al., 2014, 2015; Sibrant et al., 2015; Marques et al., 2018; Hevia-Cruz et al., 2024a, 2024b) potentially allows studying paleosols and the paleoclimate over the past 1 Myr, covering 10 glacial-interglacial cycles.

Paleoclimatic reconstructions in the North Atlantic region have traditionally relied on marine sediment cores (e.g., Martrat et al., 2007; Rodrigues et al., 2017) or atmospheric modeling studies (e.g., Martin-Garcia, 2019), which provide valuable regional-scale signals but limited resolution of local terrestrial conditions. Terrestrial archives in oceanic islands are rare, but recent studies in the Central and Eastern Azores using paleosol major element geochemistry have revealed that such records can capture past atmospheric conditions (Hevia-Cruz et al., 2024a, 2024b). These studies provide valuable insights into the spatial and temporal evolution of the atmospheric conditions in the Central to Eastern Azores islands at key glacial-interglacial transitions (terminations IX, V, IV and II at 800 ka, 425 ka, 335 ka, and 130 ka, respectively; Hevia-Cruz et al., 2024a, 2024b). However, no equivalent record exists for the Western Azores, despite their unique position with respect to dominant climatic gradients and oceanic currents. In this study, we address this gap by targeting Flores Island to reconstruct local paleoclimate between ~450 and 800 ka, a period that includes three major glacial-interglacial transitions. Through well-dated paleosols and established geochemical proxies, our aim is to constrain the spatial and temporal variability of climatic conditions across the Azores Archipelago and to assess the role of regional drivers during the Middle to Late Pleistocene.

## 2. Geological and climatic background

The Azores Archipelago is located in the Central North Atlantic along

the Azores Triple Junction between the North American, the Eurasian, and the Nubia lithospheric plates (Fig. 1B). It extends ca. 600 km from Flores (the westernmost island, 39°N 31°W) to São Miguel (the easternmost island, 37°N 25°W) in a WNW-ESE direction trend (Fig. 1). The eastern branch of this triple junction comprises the Terceira Rift and a series of extensive structures making up the present diffuse Eurasia-Nubia plate boundary (Marques et al., 2013; Hildenbrand et al., 2014). Current volcano-tectonic activity along these active structures produces recurrent earthquakes, affecting most Azores islands (from Faial to São Miguel). Flores and Corvo, on the west flank of the Mid-Atlantic Ridge, sit on the North American plate, in a tectonically inactive zone. Flores is a small volcanic island of 142 km², that was volcanically active during the last 2 Myr (Azevedo and Ferreira, 2006; Hildenbrand et al., 2018, 2024). The island is highly asymmetrical and comprises successive volcanic units separated by major scars, interpreted as the remnants of repeated westward flank collapses (Hildenbrand et al., 2018, 2024).

The Azores archipelago is subject to the influence of multiple regional climatic drivers, such as the North Atlantic eastern gyre, and more specifically by the Azores Current, which brings warm water from the Gulf Stream to the south (Fig. 1A). Reorganization of the North Atlantic circulation during reductions/additions of ice volume during major paleoclimatic changes influences the intensity of the northward flow in the North Atlantic, impacting the positions of the Artic Front and the subtropical front during the Quaternary (Martin-Garcia, 2019). Another important climatic driver is the atmospheric pressure system, particularly the Azores High-pressure, which is centered directly over the Azores Archipelago (Fig. 1A). Variations between the Azores High-pressure and the Icelandic Low-pressure systems at sea level define the North Atlantic Oscillation (Wanner et al., 2001, and references therein). The present climate in Flores Island is relatively cool and humid, with a mean annual air temperature (MAAT) and mean annual precipitation (MAP) of 17 °C and 1716 mm yr⁻¹, respectively (AEMET, and IMP, 2012).

Given Flores' volcanic history, tectonic stability, and position within key climatic gradients, it offers an exceptional opportunity to investigate the terrestrial paleoclimate using well-preserved paleosols intercalated in volcanic sequences. The following section outlines the fieldwork strategy and analytical methods employed to characterize these paleosols and their climatic significance.

## 3. Methods

To reconstruct the paleoclimate of Flores Island, we conducted a multi-technique approach combining field-based observations, targeted
<figure><img src="image_6.png" /><figcaption>**Fig. 2.** (A) Flores Island with the location of the studied paleosol profiles (colored circles), and the distribution of modern mean annual precipitation, and mean annual air temperature. (B) Field photography showing the horizon characterization of a paleosol exposed in the northern field site (green circle in A), the holes of the samples collected for geochemical analyses, and the geochronological constraints providing the mean age and the maximum formation time (m.f.t.) of the profile. The right column was modified after Tabor and Myers (2015). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

sampling of paleosol profiles, geochronological analyses of bracketing volcanic units, and geochemical characterization of soil horizons. This integrated methodology allows the precise dating of paleosols and the reconstruction of past mean annual temperature and precipitation using established weathering indices.

### 3.1. Fieldwork and sampling strategy

A fieldwork campaign was conducted in 2023 across Flores Island, in the Western Azores (Fig. 1B). Relatively young paleosols (< 1 Myr) were identified in order to complement previous work on the Azores (Hevia-Cruz et al., 2024a, 2024b). Based on previously published ages that allowed for tight geochronological control (Hildenbrand et al., 2018, and references therein), three sites were selected in the North, West, and South parts of the island (Fig. 2A) to reflect the overall inland climate state and to assess local variations. The western paleosols are intercalated within a volcanic succession previously dated between ~690 ka and ~560 ka (Hildenbrand et al., 2018). This period of paleosol formation has not been recognized in the eastern and central Azores, and thus complements the regional time-series of Hevia-Cruz et al. (2024a, 2024b). Part of the western succession has been exposed recently by ongoing movement along an active slump structure (< 0.37 Ma) and is accessible through a steep sinous pathway allowing a direct stratigraphic control. The northern and southern paleosols were sampled along volcanic successions previously dated around 750 ka and over the old part of the island (> 1 Ma, which mostly crops out at the base of coastal cliffs; Hildenbrand et al., 2018, 2024), respectively. They both occur on relatively flat surfaces at low altitudes (10–100 m a.s.l.), with no evidence of tectonic activity, but have been reasonably well-exposed by riverine incision.

At each site, we targeted paleosol profiles without evidence of post-burial diagenetic alteration or evidence of mixing processes from multiple sources, such as erosive contacts, heterogeneous textures, or signs of bioturbation, none of which were identified in our profiles (see Supplementary Table A.1 for full descriptions). We selected paleosols that were intercalated between well-preserved lava flows in order to constrain their formation timing through K-Ar dating precisely (Fig. 2B). The volcanic unit underlying the paleosol provides a maximum age while the volcanic unit overlying the paleosol provides a minimum age. Consequently, the mean between the age of both volcanic units is the paleosol mean age (Fig. 2B). The maximum paleosol

formation time (m.f.t.) is considered as the difference between the maximum age plus its uncertainty minus the minimum age minus its uncertainty (Hevia-Cruz et al., 2024a, 2024b).

For paleosols, the surface of the outcrop was first quarried to remove surficial weathering and to avoid the incorporation of present features (active soil, vegetation, surficial contamination). Field observations allowed us to recognize the main physical characteristics of each paleosol: horizon geometry, number of horizons, thickness, and colour. According to these characteristics, all paleosols were classified using the USDA soil taxonomy (Soil Survey Staff, 2014). A volume of ca. 0.5 to 1 l of each horizon was sampled (5 to 8 samples per paleosol) in plastic bags. Altogether, 40 samples along six paleosol profiles were sampled for geochemical analyses. One profile (FLO23D1-9) is exposed in a creek in the northern part of the island intercalated between two lava flows (FLO23D, FLO23E), three of them outcrop in a scarp in the western part of Flores (FLO23Q1-7, FLO23S1-8, FLO23U1-4) along a volcanic succession previously dated between ~690 ka and ~630 ka (Hildenbrand et al., 2018), and two in the southern part of the island (FLO23L1-4, FLO23M1-4; Fig. 2A) separated by a lava flow (FLO23M). The sample name of the lava flows FLO23D and FLO23M were maintained to reflect its genetic relationship with the paleosol profiles FLO23D1-9 and FLO23M1-4, respectively, as they developed directly on these volcanic units. In addition, a total of nine lava flows were selected for K-Ar dating to complement previously published geochronological data and to bracket as tightly as possible the paleosols age and mean formation times. These include six new lava flow samples and three others collected during previous fieldwork (samples FLO15E, FLO15H, FLO15O).

### 3.2. K-Ar geochronology

To date the eruption age of volcanic units we analyzed the groundmass of lava flows, which was the last phase to solidify, thus avoiding the incorporation of Ar excess from pre-eruptive crystals (Gillot et al., 2006). The core of massive lava flows was sampled in the field to select the fresh groundmass and avoid any sign of weathering. Thin-sections observation of lava samples allowed us to determine their petrophysical characteristics, such as the rock freshness, abundance of crystals, and lava texture. The samples were then sawed, crushed and sieved at the 125–250 µm fraction. They were washed with 10 % diluted nitric acid in an ultrasonic bath, rinsed with demineralized water, and dried
out overnight. The groundmass was extracted by means of magnetic separation and the systematic use of heavy liquids in a narrow density range (2.95–3.00).

The lava flow samples were dated at GEOPS Laboratory (Orsay, France) with the unspiked K–Ar Cassignol-Gillot technique (Gillot and Cornette, 1986; Gillot et al., 2006), which is specifically appropriate for low-K basalts and has been widely used in volcanic settings, including the Azores Archipelago (e.g., Hildenbrand et al., 2008b, Hildenbrand et al., 2012, Hildenbrand et al., 2014, Hildenbrand et al., 2018, Hildenbrand et al., 2024; Costa et al., 2014, 2015; Sibrant et al., 2015; Marques et al., 2018; Ricci et al., 2020; Hevia-Cruz et al., 2024a, 2024b). The K content and Ar isotopic composition of the samples were measured by flame photometry and mass spectrometry, respectively. The relative uncertainty on each age determination is obtained as the quadratic sum of three sources of uncertainty: the K-content uncertainty (~1 %), uncertainty of the calibration of $^{40}$Ar signals (~1 %), and the uncertainty on the correction of the atmospheric contamination (whose variation between sample ages is negligible). For each sample, at least two individual analyses were made, which overlap in their range of uncertainties, and the mean age was obtained by weighting the ages with the amount of $^{40}$Ar*. K content was measured with an Agilent 240 AA flame spectrophotometer by atomic absorption. Calibration of the instrument was achieved through the analysis of standards with different K concentrations ranging from 1 to 2 ppm. The uncertainty of the K measurement is less than 1 % as shown by sample reproducibility and periodic measurement of standards (MDO-G and BCR-2) under the same conditions. Ar isotope measurements were performed using a magnetic sector mass spectrometer, with simultaneous acquisition of $^{36}$Ar and $^{40}$Ar (Gillot and Cornette, 1986). After calibration of the Ar signal and sample measurements, atmospheric Ar contamination was measured from pure air under the same pressure conditions as the samples by means of adjustable volumes (see details in Gillot et al., 2006). Frequent measurements of the HD-B1 biotite standard with a recommended age of 24.18 ± 0.09 Ma (Schwarz and Trieloff, 2007) allowed us to monitor any potential drift of the air pipette used for mass spectrometer daily calibration of Ar signals.

### 3.3. Paleosol geochemistry

All of the samples from the six studied paleosol profiles were dried for at least three days at 60 °C. The coarser samples were first crushed with an agate pestle and mortar, and then all samples were powdered in a Retsch PM-200 planetary agate mill. Major element analyses were made by an iCapPRO ICP-OES (SARM Laboratory, France) after alkaline fusion with metaborate lithium (LiBO$_{2}$). One duplicate and one standard (BCR-2) were analyzed to ensure reproductibility. Relative errors reported for each element by the SARM Laboratory are included in the Supplementary Materials.

The variation of chemical elements along paleosol profiles relative to the parent material is a function of soil composition, bulk density, and volume changes during weathering or leaching, among other processes. In this work it is expressed as the mass transfer function ($\tau_{j,w}$) of a mobile element j in a weathered system w added to (or removed from) an un- weathered parental rock p, relative to an immobile element i initially present in p, defined by an open-chemical-system transport function (Brimhall and Dietrich, 1987) as:

$$ \tau_{j,w} = \frac{C_{j,w} \times C_{i,p}}{C_{j,p} \times C_{i,w}} - 1 $$

where $C_{j,p}$ and $C_{j,w}$ are the concentrations of the mobile element j in the parent material p and the weathered sample w, respectively, while $C_{i,p}$ and $C_{i,w}$ are the concentrations of the immobile element i in p and w, respectively, with all concentrations expressed as wt%. Negative $\tau_{j,w}$ values represent elemental loss and positive $\tau_{j,w}$ values represent elemental gain, with respect to the immobile element i.

Relationships between the weathering degree of soils and climatic conditions (air temperatures, precipitation) were established in earlier work (Sheldon et al., 2002; Sheldon, 2006) using geochemical analysis of 126 North American soils from the national survey of soil bulk chemical composition (Marbut, 1935). These “climofunctions” have been successfully applied to make paleoclimatic reconstructions in volcanic settings with different paleosol pedotypes (e.g., Sheldon, 2003, 2006; De la Horra et al., 2012; Orr et al., 2021), including recent work elsewhere in the Azores (Hevia-Cruz et al., 2024a, 2024b). Paleosol weathering indexes were expressed as the Chemical Index of Alteration Minus Potash (CIA-K = $[Al_2O_3]/(Al_2O_3 + CaO + Na_2O)] \times 100$; Maynard, 1992) and the Clayeyness Index (C = Al/Si; Retallack, 2001) based on whole-rock geochemistry of B horizons (corresponding to the weathered zone with clay accumulation, Fig. 2B). The geochemistry of B horizons is the result of processes that are in equilibrium with atmospheric conditions due to their long formation time, which limits the transfer function error compared to A to C horizons (Sheldon and Tabor, 2009; Tabor and Myers, 2015). Using these weathering indexes allowed us to reconstruct MAP and MAAT as follows:

$$ \text{MAP} = 221.1 \times e^{(0.0197 \times \text{CIA-K})} $$

with R$^2$ = 0.72, and a standard error of ±182 mm yr$^{-1}$ (Sheldon et al., 2002) and root mean square predictive error (RMSPE) of ±299 mm yr$^{-1}$ (Lukens et al., 2019).

$$ \text{MAAT} = 46.9 \times C + 4 $$

with R$^2$ = 0.96, and a total error of 2.0 °C (Sheldon, 2006; Sheldon and Tabor, 2009).

While the Clayeyness (and the CIA-K) index may be influenced by parent material, its use is justified in this study due to the relatively homogeneous mafic volcanic substrates across the sampled paleosols. This index has been validated for paleotemperature reconstructions in both continental and volcanic contexts (Sheldon, 2006; De la Horra et al., 2012), and its restriction to B horizons further reduces variability from early or late-stage diagenetic processes.

## 4. Results

All data used in this work, including detailed paleosol descriptions, geochemical analyses, and geochronological data, are available at the Mendeley Data repository by Loiodice et al. (2025) and is also included in Apendix A.

### 4.1. Field data

All paleosols are classified as Inceptisols (i.e., soils with weakly developed horizons, limited profile differentiation, and minimal leaching, typically forming under a range of environmental conditions), based upon their degree of development, horzonation, and lack of other features diagnostic to other types of soils (e.g., no gilgai microrelief as in Vertisols); each is developed on volcanic parent material including mafic lava flows and strombolian tephra fallout deposits. Paleosol thicknesses vary between 50 cm and 120 cm.

In the northern sector (Fig. 2A), a ~ 90 cm thick paleosol FLO23D1–9 was formed on the brecciated upper part of a laminated lava flow (FLO23D) and sealed by another lava flow (FLO23E). Nine samples were collected from the top of the B horizon (zone of accumulation of clays and other weathering products) to the horizon R (fresh parental rock) at the base of the profile (unweathered parental rock FLO23D9). The southern ~80 cm thick paleosol FLO23M1–4 (Fig. 2A) is developed between two lava flows (FLO23M at the base and a laminated lava flow too weathered to be dated at the top), for which three horizons were recognized (B, $B_C$, $C_R$; with $B_C$ a transitional layer between B and C horizons, and $C_R$ the parental rock partially weathered, both showing mixed features). Its base is not exposed, and the lowermost sample
<table><caption>**Table 1**
New geochronological ages obtained on lava flow samples from Flores Island. Sampling sites are shown in Fig. 2A.</caption><thead><tr><th>Sample</th><th>UTM E</th><th>UTM N</th><th>K%</th><th><sup>40</sup>Ar*%</th><th><sup>40</sup>Ar* × 10<sup>12</sup> [at/g]</th><th>Age [ka]</th><th>σ1 [ka]</th></tr></thead><tbody><tr><td rowspan="3">FLO23D</td><td rowspan="3">652,285</td><td rowspan="3">4,375,635</td><td rowspan="3">1.480</td><td>11.4 %</td><td>0.847</td><td>548</td><td>9</td></tr><tr><td>11.2 %</td><td>0.831</td><td>537</td><td>9</td></tr><tr><td>Mean</td><td>0.845</td><td>543</td><td>9</td></tr><tr><td rowspan="3">FLO23E</td><td rowspan="3">652,285</td><td rowspan="3">4,375,635</td><td rowspan="3">1.462</td><td>13.8 %</td><td>0.845</td><td>553</td><td>9</td></tr><tr><td>13.1 %</td><td>0.861</td><td>564</td><td>9</td></tr><tr><td>Mean</td><td>0.861</td><td>558</td><td>9</td></tr><tr><td rowspan="3">FLO15H</td><td rowspan="3">657,579</td><td rowspan="3">4,361,049</td><td rowspan="3">3.925</td><td>46.3 %</td><td>2.614</td><td>637</td><td>9</td></tr><tr><td>61.9 %</td><td>2.553</td><td>623</td><td>9</td></tr><tr><td>Mean</td><td>2.553</td><td>629</td><td>9</td></tr><tr><td rowspan="3">FLO23M</td><td rowspan="3">657,422</td><td rowspan="3">4,360,503</td><td rowspan="3">2.330</td><td>27.2 %</td><td>1.545</td><td>635</td><td>9</td></tr><tr><td>25.1 %</td><td>1.550</td><td>637</td><td>9</td></tr><tr><td>Mean</td><td>1.550</td><td>636</td><td>9</td></tr><tr><td rowspan="3">FLO15E</td><td rowspan="3">657,521</td><td rowspan="3">4,360,555</td><td rowspan="3">1.953</td><td>19.5 %</td><td>1.323</td><td>649</td><td>10</td></tr><tr><td>22.6 %</td><td>1.328</td><td>651</td><td>10</td></tr><tr><td>Mean</td><td>1.328</td><td>650</td><td>10</td></tr><tr><td rowspan="3">FLO23V</td><td rowspan="3">650,327</td><td rowspan="3">4,368,713</td><td rowspan="3">1.752</td><td>21.0 %</td><td>1.201</td><td>656</td><td>10</td></tr><tr><td>21.8 %</td><td>1.205</td><td>658</td><td>10</td></tr><tr><td>Mean</td><td>1.205</td><td>657</td><td>10</td></tr><tr><td rowspan="3">FLO23T</td><td rowspan="3">650,326</td><td rowspan="3">4,368,690</td><td rowspan="3">2.037</td><td>34.4 %</td><td>1.428</td><td>671</td><td>10</td></tr><tr><td>34.2 %</td><td>1.423</td><td>668</td><td>10</td></tr><tr><td>Mean</td><td>1.423</td><td>670</td><td>10</td></tr><tr><td rowspan="3">FLO23R</td><td rowspan="3">650,376</td><td rowspan="3">4,368,697</td><td rowspan="3">1.887</td><td>33.4 %</td><td>1.315</td><td>667</td><td>10</td></tr><tr><td>31.4 %</td><td>1.325</td><td>672</td><td>10</td></tr><tr><td>Mean</td><td>1.315</td><td>670</td><td>10</td></tr><tr><td rowspan="3">FLO15O</td><td rowspan="3">650,332</td><td rowspan="3">4,368,655</td><td rowspan="3">1.859</td><td>12.8 %</td><td>1.319</td><td>679</td><td>11</td></tr><tr><td>13.0 %</td><td>1.289</td><td>664</td><td>11</td></tr><tr><td>Mean</td><td>1.289</td><td>671</td><td>11</td></tr></tbody></table>

All ages were acquired in groundmass separates and are reported at 1σ confidence level. Decay constants and isotopic ratios from Steiger and Jäger (1977). Reported K values are the average of at least two independent measurements of distinct sample aliquots. Projection Zone 25S (WGS 84).

corresponds to a relatively weathered $C_R$ horizon. Four horizons were recognized on the underlying ~120 cm thick paleosol FLO23L1-4 (B, $B_C$, $C_B$, $C_R$; with $C_B$ a transition between C and B horizons, with C-dominated features), formed on the brecciated upper part of a lava flow and covered by the lava flow FLO23M that underlies the paleosol FLO23M1-4. In the western part of the island (Fig. 2A), the ~50 cm thick paleosol FLO23U1-4 is bracketed by two lava flows that were sampled for geochronology (FLO23V over the paleosol and FLO23T under it), whose identified horizons are from $C_R$ at the base to B at the top. Lower in the same stratigraphic sequence, the ~1 m thick paleosol profile FLO23S1-8 is formed on a lava flow, showing a well-developed profile from $R_C$ to B horizons, and is covered by a thin unsampled paleosol. It is under the lava flow FLO23V and over FLO23R. Finally, FLO23Q1-7 is a paleosol developed on a tephra fallout deposit, whose horizons are from $C_R$ to $B_C$. It is bracketed by the lava flows FLO23R and FLO15O at the top and the bottom, respectively. Detailed locations and descriptions of paleosol profiles, and their temporal constraints, are in Supplementary Table A.1 and visually supported by Supplementary Figs. A.2-A.7.

## 4.2. New K-Ar ages

The nine new K-Ar ages here obtained range between 671 ± 11 ka and 543 ± 9 ka (Table 1). They are fully consistent with previous ages acquired with the same analytical approach (Hildenbrand et al., 2018) and with the general spatial age distribution of Flores Island. These new ages allowed us to constrain the six paleosol ages tightly, and indicate clustering of two main groups of paeosols with ages around 550 ka and in the range 620-670 ka (Table 1). The paleosols' m.f.t. are shorter than 50 kyr, and the one of profile FLO23D1-9 is particularly short (3 kyr) because the underlying lava flow (FLO23D) has a lower mean age than the overlying lava flow (FLO23E). Thus, the 3 kyr period corresponds to the time gap comprised between the errors of both mean ages (Table 1; Supplementary Table A.1).

## 4.3. Paleosol geochemistry

The compositions of the parental rocks of the six profiles correspond to two basalts (FLO23Q7 and FLO23U4 in the west part of the island), three basanites (FLO23L4, FLO23D9, and FLO23S8, in the south, north and west parts of the island, respectively), and one picrobasalt (FLO23M4 in the south of the island). Together, they form an alkaline series (Supplementary Fig. A.1), although samples FLO23M4 and FLO23U4 are relatively weathered and do not correspond to fresh volcanic rocks (LOI > 10%; Supplementary Table A.2). The full geochemical data are reported in Supplementary Table A.2.

### 4.3.1. Compositional variations with profile depth

The paleosol profiles show vertical variations in geochemistry relative to the parent material with depth (Fig. 3; Supplementary Tables A.2, A.3). The relative standard deviations between duplicates show minimal offsets (0.5-2.2 %), while relative offsets of the standard BCR-2 to recommended values (Jochum et al., 2016) are lower than 5 % (except for $P_2O_5$), indicating that the compositional variations reflect sample to sample differences rather than analytical ones. The elemental composition of paleosol profiles shows significant variations from 74 % gain to 94 % loss relative to the parent material. Most profiles are depleted in Ca, Mg, Na, and K in their uppermost horizon(s), whereas Fe and Al remain relatively constant or even show slight gains towards the upper B horizons (Fig. 3A). This trend is less evident for the paleosols FLO23M1-4 and FLO23U1-4 as the lowermost parts of both profiles are relatively weathered compared with the parental rock of the other profiles (LOI > 10%; Supplementary Tables A.2, A.3). Ti/Al ratios, which typically reflect provenance (Sheldon and Tabor, 2009), vary from 0.17 to 0.3, with a mean of ~0.25 (Fig. 3B, Supplementary Table A.3). These modest variations are within analytical uncertainty and are here considered as functionally constant. In contrast, weathering indexes, reflecting weathering intensity, vary substantially with depth (Fig. 3B, Supplementary Table A.3). Most paleosol profiles show a sharp to a progressive up-profile increase of CIA-K from 53 to 70 % to 96 %,
<figure><img src="image_7.png" /><figcaption>**Fig. 3.** A) Graphics showing elemental variations over depth relative to the parent material, expressed as Tau values considering Ti as an immobile element. The colour code is the same for the six paleosol profiles, as indicated in the graphic of the profile FLO23L. B) Ti/Al ratio and CIA-K indexes along the paleosol profiles of the different study sites.</figcaption></figure>

reflecting substantially higher weathering intensity near the paleosols' surfaces, except for the two profiles with relatively weathered parental rocks (FLO23M1–4 and FLO23U1–4), which show nearly constant high-weathering degrees. Overall, the southern paleosols (FLO23M1–4 and FLO23L1–4) reach higher weathering degrees, with a mean CIA-K index of 97.3 in B horizons, while the other paleosols range between 85 and 94 (Supplementary Table A.3).

### 4.3.2. Paleoclimatic reconstructions

The MAAT and MAP were estimated using the Clayeyness and the CIA-K indexes in B-horizon samples, respectively (Supplementary Table A.4). Our new MAAT reconstructions show a range between 18.7 °C and

24.3 °C, with a mean of 21.5 °C, while MAP reconstructions range between 1157 mm yr⁻¹ and 1537 mm yr⁻¹, with a mean of 1341 mm yr⁻¹. Considering the standard error of the proxies (2 °C and 182 mm yr⁻¹), MAAT and MAP reconstructions do not vary significantly across the whole Island during the two glacial periods studied in this work (~550 ka and ~670–630 ka; Fig. 4, Supplementary Table A.4). On the other hand, a noticeable difference between our reconstructed MAAT and MAP with respect to current conditions is observed (Fig. 4). MAP estimates are lower than the modern conditions in Flores (1716 mm yr⁻¹), while MAAT estimates are significantly higher than the current MAAT (17 °C; AEMET, and IMP, 2012).
<figure><img src="image_8.png" /><figcaption>**Fig. 4.** Comparison of our new paleoclimatic reconstructions (colored squares) in Flores Island and previous reconstructions in the Central and Eastern Azores (Flores, Pico, Faial, São Jorge, and São Miguel islands, colored circles) after Hevia-Cruz et al. (2024a, 2024b), contrasted with a global δ¹⁸O curve (gray line; Lisiecki and Raymo, 2005) and a regional sea surface temperature (SST) reconstruction (green lines; Martrat et al., 2007; Rodrigues et al., 2017). The horizontal blue and green dashed lines correspond to the modern MAP and MAAT in Flores Island at sea level (AEMET, and IMP, 2012). MIS: Marine Isotope Stage; T with Roman numbers represent glaciation terminations. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

<table><caption>**Table 2**
Mean paleosol thicknesses, age, maximum formation time, and minimum formation rate.</caption><thead><tr><th>Samples</th><th>Location</th><th>Thickness [cm]</th><th>Mean age [ka]</th><th>Maximum formation time [kyr]</th><th>Minimum formation rate [mm kyr<sup>-1</sup>]</th></tr></thead><tbody><tr><td>FLO23D1-9</td><td>North</td><td>87</td><td>551</td><td>3</td><td>290</td></tr><tr><td>FLO23M1-4</td><td rowspan="2">South</td><td>80</td><td>633</td><td>25</td><td>32</td></tr><tr><td>FLO23L1-4</td><td>120</td><td>643</td><td>33</td><td>36</td></tr><tr><td>FLO23U1-4</td><td rowspan="3">West</td><td>50</td><td>664</td><td>33</td><td>15</td></tr><tr><td>FLO23S1-8</td><td>100</td><td>670</td><td>20</td><td>50</td></tr><tr><td>FLO23Q1-7</td><td>80</td><td>671</td><td>22</td><td>36</td></tr></tbody></table>

# 5. Discussion

## 5.1. Paleosol formation during glacial stages

Based on our new geochronological analyses, paleosol mean ages and their m.f.t. were tightly constrained, as shown in Table 2. Including the uncertainties on paleosol ages, a group of five paleosols was formed between 633 ka and 671 ka on the West and South parts of Flores Island, and a younger paleosol was formed at 550.5 ± 1.5 ka in the North part of the island (Fig. 4). The maximum formation times are relatively low (< 50 kyr), with variable minimum formation rates between 15 and 290 mm kyr⁻¹. The short maximum formation times and the minimum soil formation rates estimated here agree with the estimates from the Central

and Eastern Azores by Hevia-Cruz et al. (2025), generally formed in less than ~35 kyr at rates between 3 and 180 mm kyr⁻¹. The very well-dated profile FLO23D1-9 shows an exceptionally high weathering rate, which far exceeds those calculated for the Eastern and Central Azores. That could be the result of conditions particularly favorable for soil formation, such as wet/warm conditions, or a particularly vesicular parental rock with high specific surface area. Although FLO23E (558 ± 9 ka) stratigraphically overlies FLO23D (543 ± 9 ka), the two measured ages are undistinguishable within the analytical uncertainties. Each of the two age determinations is the mean of internally consistent replicate measurements, and sample alteration is unlikely given the field selection, petrographic inspection, and groundmass purification procedures. Therefore, these ages are considered reliable and mutually supporting
very fast paleosol formation. The resulting much faster formation of FLO23D1–9 may reflect the capture of the initial, transient stage of intense chemical alteration (e.g., Zehetner et al., 2024; Hevia-Cruz et al., 2025), which tends to stabilize relatively quickly due to the precipitation of secondary mineral phases more resistant to weathering and the depletion of mobile cations from the parent material (e.g., Sowards et al., 2018; Chadwick et al., 2022; Hevia-Cruz et al., 2024a).

The new ages reported here allowed us to tightly constrain the paleosol formation time, as previously achieved for other Azores islands in recent work by Hevia-Cruz et al. (2024a, 2024b). Most volcanic units have overlapped ages within the same stratigraphic sequence, showing short periods of soil formation (3 kyr for minimal duration). All paleosols are formed in less than 50 kyr, consistent with these previous works, allowing us to compare the mean paleosol ages with global climatic curves. In Fig. 4, our data is contrasted with the $\delta^{18}$O data of the LR04 stack from Lisiecki and Raymo (2005) over the past 1 Myr. The clustered group (between 633 ka and 671 ka) was formed between Marine Isotope Stage (MIS) 17 and MIS 15b, near the glacial termination TVII at 621 ka. The younger paleosol (551 ka) was formed near the glacial termination TVI (around 553 ka) between MIS 15a and MIS 13 (Fig. 4).

In contrast with the Eastern and Central Azores, where paleosols were mostly formed during interglacial peaks (Hevia-Cruz et al., 2024a, 2024b), all the paleosols studied in this work were developed near glacial peaks, or in transitions from interglacial to glacial stages.

Although our data do not include the interglacial interval between ~670 and 550 ka, the absence of paleosols from that time may itself reflect a lack of suitable climatic conditions for pedogenesis, reinforcing the idea that soil formation on Flores occurred preferentially during locally warm and wet conditions, despite occurring during globally glacial periods. This contrast with the Central and Eastern Azores may be explained by several hypotheses, such as 1) a sampling bias in the other islands; 2) a different volcanic evolution between distinct islands, or 3) different paleoenvironmental conditions. The first option is unlikely because Hevia-Cruz et al. (2024a, 2024b) studied more than 20 profiles developed on volcanic units covering the past 1.3 Myr and explored other volcanic successions spanning glacial periods, where no paleosols were identified. The second option is also unlikely, because the volcanic activity between islands has been relatively synchronous for the last 1 Myr. Finally, and more probably, paleoenvironmental conditions could have been different between the Western Azores and the rest of the Archipelago. As the Azores Archipelago is oriented in a nearly WNW-ESE direction, climate drivers could have had different impacts depending on island locations. This last possibility is further discussed below.

## 5.2. Climate as the dominant factor controlling soil formation

Soil formation depends on a combination of internal and external factors, including climate, topography, formation time, texture and geochemistry of parental rock, and biological activity (Jenny, 1941). As all paleosols were sampled in subhorizontal lava sequences, topography had probably little impact on soil formation. Profile FLO23D1–9 shows evidence of water infiltration by the presence of a weathered horizon in its lower contact with the fresh volcanic substrate. Water accumulation over this impermeable surface may have allowed the persistent weathering of the lower part of the profile. Nevertheless, this should not have affected the upper part of the profile. Regarding time, the relatively consistent and short soil formation times deduced here suggest that intense weathering occurred rapidly over just a few kyr, consistent with similar durations of pedogenesis for different weathering profiles in the Azores (Hevia-Cruz et al., 2025) and in other volcanic islands (e.g. the Galapagos; Zehetner et al., 2024). In addition, time of formation is not correlated with weathering degree (Fig. 3), as observed in previous studies (Hevia-Cruz et al., 2024a, 2025). While the modern Azores Archipelago has a high proportion of non-indigenous plant species for an island setting (Silva and Smith, 2004), the floral assemblages vary little

across the islands studied here, with four of six recognized natural vegetation zones in common to all the islands (Elias et al., 2016). Stable isotope-based estimates of past vegetation were consistent with the present-day vegetation for the other islands of the Azores (Hevia-Cruz et al., 2024b), so that is also likely the case for Flores. Thus, while specific vegetation assemblages may have expanded or contracted their ranges, biology as soil forming factor is unlikely to have been a primary driver of differences in pedogenesis and the degree of weathering. Furthermore, organic activity is highly dependent on climate, and thus it is not a direct controller of soil formation (White, 2005). Almost all paleosol profiles show a progressive depletion in K, suggesting negligible biological activity, except for FLO23D1–9, for which K accumulation in its uppermost part could be due to either K bioaccumulation or K metasomatism as a result of fluid migration (Sheldon, 2003). It is worth noting that K enrichment occurs only in the upper part of the weathering profile, while the dated sample FLO23D was collected from the unaltered interior of the lava flow, well below the paleosol contact, following standard K–Ar sampling protocols. Therefore, this enrichment does not affect the accuracy of the reported age.

The degree of weathering is also dependent on the geochemistry and texture of parental rocks, as suggested by Hevia-Cruz et al. (2024a). Highly porous and fine-grained parental rocks promote intense weathering due to greater specific surface areas. Nevertheless, the parental rocks of the studied paleosols are relatively homogeneous in terms of texture and composition (Supplementary Fig. A.1; Supplementary Tables A.1–A.3), and probably did not impact significantly the soil formation process either.

Our whole-rock geochemistry results show up-profile depletion of mobile elements such as Na, K, Ca, and Mg compared to immobile elements (Ti, Al, Fe) during soil formation (Fig. 3A), indicating that pedogenic processes such as leaching and hydrolysis reactions are the main drivers of the paleosols’ geochemistry (Sheldon and Tabor, 2009). Along those lines, weathering index profiles show upward increases reaching the maximum degree in B-horizon samples (e.g., CIA-K in Fig. 3B), consistent with horizon identifications in the field. It is also consistent with Al/Si ratio results, as Al tends to accumulate into clay minerals, particularly abundant in B-horizon samples (e.g., Sheldon and Tabor, 2009). In addition, Ti/Al ratio is used as an indicator of provenance, as Ti and Al are both relatively immobile during weathering (Sheldon and Tabor, 2009). Almost all paleosol profiles studied here show relatively constant values, except for FLO23M1–4 whose Ti/Al ratio is reduced in the upper part of the profile. This is probably due to the accumulation of Al in neoformed clay minerals (Chadwick et al., 2003), and thus still reflective of pedogenesis. Profiles FLO23M1–4 and FLO23U1–4 show patterns that do not clearly show an increase in the weathering degree to the top, but this is probably because the rock being considered as their parental material. In both cases, the lowermost sample was relatively weathered compared to the parental rock of the other profiles (LOI > 10 %; Supplementary Table A.2), thus showing minor differences between the lower and upper horizons. Overall, the up-profile increase of weathering indexes, the constant ratio of immobile elements, and the accuracy of horizon identification reveal that there is no major contamination from the incorporation of allochthonous material, and that weathering was the main process controlling soil formation. Consequently, paleoclimate seems to be the main factor controlling soil formation in Flores Island.

## 5.3. Paleoclimatic implications

### 5.3.1. Local paleoclimate in Flores and the Azores Archipelago

Temperature and precipitation potentially increased between ca. 670 and 630 ka (Fig. 4), however, the changes are largely within error for the MAAT and MAP proxies, and the overall climatic regime was fairly consistent. Although more recent studies (e.g., Lukens et al., 2019) suggest that the RMSPE of CIA-K-based MAP estimates may be closer to $\pm 299 \text{ mm yr}^{-1}$ than to the standard error of $\pm 182 \text{ mm yr}^{-1}$ from
<figure><img src="image_9.png" /><figcaption>**Fig. 5.** Boxplots of the MAAT and MAP reconstructions in the different parts of the Azores Archipelago during the Quaternary, including our results in Flores Island (West), and those of Hevia-Cruz et al. (2024a, 2024b) in the Central and Eastern Azores.</figcaption></figure>

Sheldon et al. (2002), we retained the original proxy error as in previous studies of the Azores because our paleosols are derived from a relatively homogeneous volcanic substrate with limited lateral variability across the study sites. Single substrate paleosol paleoproxy studies typically have lower prediction error than global ones (e.g., Sheldon and Tabor, 2009), which is consistent with the findings of Dzombak et al. (2021), who suggest that when lateral variation is constrained, proxy uncertainty can be reduced relative to broad continental-scale estimates. Thus, we suspect that the true uncertainty lies between the two constraints, but regardless, changes in MAP are all within proxy error, so we do not interpret a robust trend in the data. Compared with modern conditions, our MAAT and MAP reconstructions indicate warmer but drier conditions for both periods (Fig. 4).

As mentioned in 5.1, previous works observed pulses of soil formation during interglacial peaks (Hevia-Cruz et al., 2024a, 2024b), both for the Eastern (São Miguel Island) and Central (Pico, Faial, and São Jorge Islands) Azores. There, MAAT reconstructions are consistent with sea surface temperature (SST) reconstructions during warm interglacial periods over the last 1 Myr. Conversely, we observed soil formation occurring exclusively during glacial periods in Flores Island, and our MAAT reconstructions are much higher than previously reconstructed SST (Fig. 4). This suggests that the local conditions in the Western Azores were fairly different than those of the Central and Eastern Azores. We suggest that the westward increase of temperature and precipitation reconstructions can be a consequence of the regional WNW-ESE distribution of the Azores Archipelago (Fig. 1). Hevia-Cruz et al. (2024b) observed higher MAP and MAAT in the central part of the Azores compared to its eastern part. They proposed that the increasing wetter/warmer conditions to the west could be related to the closer position

with respect to the westerlies, which carry warmth and humidity from the equator. This trend is here confirmed, as our MAP and MAAT reconstructions in Flores Island, in the Western Azores, are higher than in the rest of the archipelago (Fig. 5). This is consistent with current conditions in the Azores, especially for precipitation regimes. Modern MAPs are high in Flores (1716 mm yr⁻¹), intermediate in the Central Azores (1110 mm yr⁻¹ and 960 mm yr⁻¹ in Pico and Faial, respectively), and lower in the Eastern Azores (980 mm yr⁻¹ in São Miguel; AEMET and IMP, 2012).

### 5.3.2. Regional paleoclimatic drivers

The interannual climate variations in the Azores region are mainly influenced by atmospheric heat flux changes (Martin-Garcia, 2019), which can be greatly impacted by changes in SST due to the heat capacity of water masses. During interglacial-glacial transitions, the southward migration of the Arctic Front induces polar cold water to expand into lower latitudes. This results in a drop in SST, as observed in the Iberian margin by Martin-Garcia (2019). This might seem contrary to the relatively warm and humid conditions observed in Flores over two glacial periods, as our high MAAT reconstructions contrast with the low SST conditions in the Iberian margin (Fig. 4; Martrat et al., 2007; Rodrigues et al., 2017). Nevertheless, the same processes carrying cold water into the Iberian margin could be responsible for carrying warm water into the Flores Island vicinity. Indeed, it has been suggested that the southward migration of the Arctic Front may also produce a southward migration of the North Atlantic Current, bringing warm water into the Azores region (Fig. 6; Martin-Garcia, 2019). This might have been particularly important for Flores Island, due to its location in the WNW extreme of the Azores, promoting the relatively warm conditions here evidenced for the two glacial periods (Figs. 5, 6). The location of Flores in the northwestern Azores may have favored the persistence of moist westerly air masses even during glacial periods. Hevia-Cruz et al. (2024b) proposed that increased humidity in the Central and Eastern Azores during interglacials could be linked to a southward migration or weakening of the Azores High pressure system. In contrast, Flores may have remained under the influence of these humid oceanic currents even when the Azores High did not shift significantly. This could explain why paleosols in Flores developed during glacial periods, unlike in the rest of the archipelago. However, this does not preclude the formation of paleosols during interglacials in Flores; their apparent absence in our dataset may reflect preservation or exposure biases. Identifying such interglacial paleosols would allow for direct comparisons across climate stages within a single island, providing a unique opportunity to evaluate

<figure><img src="image_10.png" /><figcaption>**Fig. 6.** A) Present-day approximate distribution of the main currents integrating the North Atlantic Gyre, representative of the conditions during interglacial periods. B) Conditions of the North Atlantic oceanic currents during glacial periods, as proposed by Martin-Garcia (2019), with a southward migration of the Arctic Front (A. F.), the North Atlantic Current, and the Azores Current. The red rectangle shows the location of the Azores Archipelago. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>
local environmental thresholds for pedogenesis. It is worth noting that the paleosols studied in Flores are not contemporaneous with those previously identified in the Central and Eastern Azores, which limits direct paleoclimatic comparisons across the archipelago. Future studies targeting volcanic sequences of similar age in the yet-unstudied islands of Terceira and Graciosa (Central Azores) could help determine whether the warm/wet glacial conditions identified in Flores were spatially restricted or part of a broader regional pattern.

## 6. Conclusions

Our precise geochronological constraints allowed us to determine the age and timing of soil formation on Flores Island. All of the studied paleosols were formed during glacial periods, contrary to what was recently observed in the central and eastern parts of the archipelago. Future studies should help to elucidate if these glacial periods were particularly wet/warm at the whole scale of the Azores Archipelago, or if it was restricted to the Western Azores.

The geochemistry of paleosols revealed a climatic control on soil formation processes and allowed us to reconstruct paleoclimatic conditions at the time of their formation. A previously suggested regional trend of increasing temperature and humidity to the west is supported by the data, although the periods covered by the reconstructions are not the same. The two periods of soil formation here studied (~550 ka and 630–670 ka) revealed wet/warm conditions during glacial periods, which had not been observed on other islands of the Azores. In future studies, it would be interesting to target Corvo Island to see if these wet/warm conditions can be observed during other glacial periods or in other parts of the Western Azores. It would also be interesting to study the unexplored islands in the Central Azores (Terceira and Graciosa) to search specifically for paleosols along volcanic sequences of ca. 550 ka and 650 ka, to determine if the warm/wet glacial periods here studied were extended farther to the east. Further perspectives could include other volcanic islands in the Atlantic Region, such as the Canary Islands and Cape Verde, extending our paleoclimatic observations to a broader scale over the North Atlantic Ocean. Extending the scale of our studies would certainly improve our understanding of the Quaternary evolution of climate in the North Atlantic region, and its impact in Western Europe, Eastern North America, and Northwestern Africa.

## CRediT authorship contribution statement

**Laura Loiodice:** Writing – review & editing, Writing – original draft, Visualization, Validation, Methodology, Investigation, Data curation.
**Francisco Hevia-Cruz:** Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Methodology, Investigation, Formal analysis, Data curation, Conceptualization.
**Anthony Hildenbrand:** Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Project administration, Methodology, Investigation, Funding acquisition, Data curation, Conceptualization.
**Nathan D. Sheldon:** Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Methodology, Investigation, Conceptualization.

## Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Acknowledgments

This work was supported by the CNRS-INSU Tellus-SYSTER program 2022-2023. We thank Valerie Godard for thin section preparation. This is LGMT contribution number 201.

# Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.palaeo.2025.113157.

## Data availability

Data are available through Mendeley Data at https://doi.org/10.17632/z749s8v2vt.1 and in Appendix A. Supplementary Materials.

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