Holocene Paleoenvironmental Reconstruction at 47° S (Patagonia, Argentina) from Sedimentary Sequences (Fens and Lagoon) and Archaeological Sites: A Regional Synthesis

Abstract

At 47° S in Argentine Patagonia, the interaction between the Southern Westerly Winds (SWW) and the Andean barrier generates a steep climatic gradient, providing an ideal setting to evaluate Holocene vegetation responses. This study focuses on the extra-Andean sector, where new pollen records from La Tapera (LTap) and Cisne 7 provide insights into steppe vegetation dynamics under dry conditions. These sequences are contrasted with previously studied records further west (LF, ZB, CMN1, CMN2, and COCU) to assess west–east gradients in vegetation change and moisture availability throughout the Holocene. Western records indicate that the Early Holocene was dominated by grass–dwarf-shrub steppe under arid conditions, followed by increased humidity around 7600 cal yr BP that promoted the development of forest–steppe ecotonal environments. The Middle Holocene was characterised by aridity, reflected in shrub dominance and reduced forest signals, whereas the Late Holocene included a humid pulse between ~1750 and 1000 cal yr BP, followed by renewed aridity over the last millennium. In contrast, eastern records show persistent shrub–dwarf-shrub steppes since ~4700 cal yr BP, with vegetation changes expressed mainly as shifts in the relative dominance of shrubs and dwarf–shrubs rather than floristic replacements. Archaeological sites corroborated and complemented the continuous records, strengthening the reconstruction of environmental variability across different temporal windows. Overall, this west–east comparison highlights the differential sensitivity of ecosystems to SWW fluctuations, reinforcing their role as an important forcing of hydrological balance and vegetation dynamics in mid-latitude Patagonia.

1. Introduction

Patagonia, located at the southernmost tip of South America, constitutes a region of immense relevance for paleoenvironmental studies because of its unique physiographic, climatic, and geographic configuration ([1,2,3,4,5,6], among others). This vast territory lies under the direct influence of the Southern Westerly Winds (SWW), a fundamental component of global atmospheric circulation that regulates precipitation and ocean circulation between 30° and 60° S latitude [7,8,9]. The interaction between the SWW and the Andes generates a pronounced west–east precipitation gradient, reflected in vegetation zonation ranging from humid temperate forests in the west to semi-arid and arid steppes toward the east. This environmental sensitivity to past climate variability makes Patagonia a natural reference system for investigating long-term climate and vegetation dynamics at Quaternary timescales [10,11,12].

The reconstruction of past plant communities has been achieved through diverse paleoecological methods ([5,13,14,15,16], among others), among which pollen analysis stands out as a key proxy. Understanding the relationship between modern pollen and vegetation is essential for interpreting fossil records, enabling the reconstruction of spatio-temporal vegetation patterns and paleoclimatic changes ([17,18,19,20,21,22], among others). Other proxies—such as carbon and nitrogen isotopes, plant macrofossils, charcoal, and stratigraphic characterization—complement this perspective, providing a more robust framework for assessing paleoenvironmental variability [16,19,20,21,22,23,24].

Numerous paleoecological studies have documented terrestrial ecosystem dynamics in Patagonia since the Late Glacial–Early Holocene transition, covering both Andean and extra-Andean areas ([4,13,14,22,24,25,26,27,28], among others). In Argentine Patagonia, research has focused particularly on Santa Cruz Province, including the basins of Lago San Martín, Lago Pueyrredón, and Lago Argentino, as well as the Deseado Massif [19,20,21,22,24,29,30,31,32]. These studies have provided paleoenvironmental models for the Late Quaternary. Vegetation patterns and responses during the Holocene across Patagonia have been linked primarily to variations in the intensity and latitudinal position of the SWW and, consequently, to precipitation regimes [10,12,33,34]. For instance, in the western sector of the Lago San Martín basin (49° S), extremely arid conditions prevailed between 18,500 and 16,000 cal yr BP, characterized by dwarf-shrub steppes. Subsequently, between 16,000 and 12,800 cal yr BP, greater moisture availability favored the expansion of Nothofagus forests and a transition from dwarf-shrub to grass–dwarf-shrub steppe, likely associated with SWW intensification [22]. Up to 9600 cal yr BP, grass steppe persisted in the Mallín Ciprés (MC) area; after that, Nothofagus forests expanded and consolidated around 9000 cal yr BP. Other sequences from the same basin, with basal ages of 11,500 cal yr BP (La Tercera, LT) and 10,200 cal yr BP (Mallín Ñire, MÑ), have also been analysed. LT reflects a dwarf-shrub environment under arid conditions until 9500 cal yr BP, followed by grass-steppe development linked to increased humidity around 9000 cal yr BP [23,29]. In contrast, MÑ records grass steppe with dwarf shrubs under arid conditions between 10,200 and 9000 cal yr BP [21]. Collectively, Mallín Paisano Desconocido (from 6650 cal yr BP), LT, and MÑ reveal alternating arid and humid phases during the Holocene [18,21,29].

At 50° S, vegetation changes since the Late Glacial–Early Holocene transition have been reconstructed from continuous sedimentary sequences and archaeological sites ([5,23,35,36,37,38,39,40], among others). Following glacier retreat, grass steppe was established, and between 9500 and 9000 cal yr BP, more humid conditions promoted the expansion of Nothofagus forests [5,6,38]. During the Middle Holocene, closed-canopy Nothofagus forests developed in areas such as Cerro Frías and Península Avellaneda, associated with increased humidity and stronger SWW influence [5,9,38]. In contrast, more eastern areas of the basin recorded grass–shrub steppe at Río Bote and forest–steppe ecotone vegetation at Chorrillo Malo 2 [36,38]. The Late Holocene is marked by high climatic variability: initially, forest replacement by grass–shrub steppe indicates declining humidity [5,39], followed by forest resurgence between 2500 and 2000 cal yr BP. In the last 400 cal yr BP, drier and colder conditions led to forest retraction and steppe expansion [24], with changes in recent centuries strongly influenced by anthropogenic factors, including European colonization [6,37].

Chilean records have offered important insights. High-resolution paleoenvironmental sequences from the Chacabuco and Cochrane valleys offer robust evidence of postglacial vegetation and climate dynamics [4,14,28]. The Lago Augusta and Lago Edita records show transitions from steppe–shrub assemblages to the expansion and persistence of Nothofagus-dominated forests, and the development of new chronologies at these sites has enabled the quantification of vegetation change rates using ROC analyses [4]. Complementary evidence from Laguna Maldonado and Laguna Anónima points to changes in forest structure and fire regimes along the forest–steppe ecotone, underscoring the role of climatic variability in shaping these ecosystems [28]. Collectively, these geographically strategic records highlight the sensitivity of central-western Patagonia to variations in the Southern Westerly Winds and provide a solid basis for assessing Holocene paleoenvironmental changes at 47° S. At the same latitude, in the Lago Pueyrredón basin, early paleoenvironmental inferences were based on pollen analyses from archaeological sites; however, the discontinuous nature of these records limited both the information obtained and their spatio-temporal resolution [31,32,41,42]. Subsequent studies at 47° S in the same basin [19,20] produced continuous records that generated new contributions to reconstruct the environmental evolution of the Holocene in the area. Here, the integration of data from multiple sites—both continuous sedimentary (lakes and fens) and archaeological (caves and rock shelters)—helped to overcome the limitations of relying on a single type of record and enabled a more comprehensive understanding of the paleoenvironment [16,31,32,43,44]. In this regard, continuous sequences in the Lago Pueyrredón area, such as Los Flamencos (LF) since 7600 cal yr BP and Mallín Zorro Bayo (ZB) for the last 3000 years, have produced continuous records that allowed more detailed reconstructions of vegetation dynamics [19,20]. However, in steppe zones at different latitudes, where continuous natural deposits are scarce, archaeological sites have been critical sources of paleoenvironmental information [31,35,36,43,45]. For example, refs. [31,41,42] indicated that the Milodón Norte 1 and 2 caves (CMN1, CMN2) and Cerro Cuadrado (COCU) provided paleoenvironmental data for specific temporal windows, allowing for the analysis of interactions between human populations and their environment. Nevertheless, Marcos [31] highlighted the importance of considering pollen preservation, which can be conditioned by taphonomic factors (oxidation, pH, abrasion) and anthropogenic factors (hearths), potentially affecting the reliability of environmental reconstructions. Other studies in the area have shown that paleogeographic changes—such as the retraction of lakes Pueyrredón, Posadas, and Salitroso—generated new routes and greater availability of floral resources, facilitating the mobility of human groups [41,42]. In this respect, research in the Lago Pueyrredón basin illustrates the value of an interdisciplinary approach that integrates evidence from multiple disciplines. This synergy has provided a more comprehensive understanding of environmental change and human–environment interactions throughout the Holocene, offering a key framework for contextualizing human occupation, reconstructing vegetation dynamics, and interpreting anthropogenic impacts [19,20,31,32,41,42]. In summary, the interdisciplinary approach has made it possible to overcome the limitations of isolated records—such as temporal discontinuities or representation biases—and to establish a more robust regional environmental framework for understanding the complex interactions between climatic drivers and human populations in the past.

This study reconstructs the environmental history of the La Tapera fens sequence (47° S), located in the extra-Andean sector of Argentine Patagonia. This record is compared with previously studied sequences situated farther west (Los Flamencos and Zorro Bayo). The information is integrated with archaeological sequences in order to clarify how ecosystems in contrasting hydrological settings responded to Holocene variability along the analysed west–east gradient. The combination of continuous records (lakes, fens) with archaeological data (which provide temporal windows) helps overcome the limitations of individual datasets and contributes to a more comprehensive regional reconstruction of past ecosystems. We hypothesize that plant communities in extra-Andean ecosystems exhibited more buffered and delayed responses to Holocene moisture variability compared to Andean environments, reflecting their greater adaptation to arid conditions and reduced dependence on short-term hydrological changes.

2. Materials and Methods

2.1. Environmental Setting and Vegetation Patterns at 47° S in Southern Patagonia

The Andes form an orographic barrier that generates a pronounced west–east precipitation gradient, with humid conditions in the west and arid conditions in the east, a contrast that is clearly reflected in regional vegetation patterns [46]. In the western sector, near the Chilean border, open forests of Nothofagus pumilio dominate slopes and valleys, while the eastern basin is characterized by shrubs, dwarf-shrub steppes interspersed with cushion plants [47], illustrating the vegetation gradient that is typical of Patagonia.

The Pueyrredón–Posadas–Salitroso lacustrine system, located in the northwest of Santa Cruz Province, Argentina (Figure 1A), is a remnant of a paleolake formed by the melting of a major ice mass during the Late Pleistocene–Early Holocene [41,42]. The Lago Pueyrredón basin is characterized by a glacially eroded landscape within a periglacial setting, containing lakes as well as extensive glacial and glaciofluvial deposits [48,49,50]. Average annual precipitation reaches ~500 mm at the Chilean border, decreases to ~300 mm in the Lago Pueyrredón area, and further declines eastward to ~200 mm. Mean annual temperatures range between 5 °C and 6 °C, with winter averages of 0–1 °C and summer averages of ~11 °C (Figure 1C,D) [51]. The basin’s vegetation corresponds to a shrub–grass steppe [49], locally dominated by species such as Mulinum spinosum, Berberis heterophylla, and Nardophyllum. The pollen–vegetation model of [31] identifies a community composition dominated by M. spinosum and B. heterophylla, with Nardophyllum spp., Schinus polygamus, and grasses such as Festuca pallescens and Stipa spp. Pollen data distinguish three shrub–steppe types: (1) open shrub steppe, dominated by M. spinosum and B. heterophylla, with Asteraceae subf. Asteroideae, Caryophyllaceae, and Poaceae (Stipa sp., F. pallescens, F. argentina); (2) shrub steppe, with M. spinosum and Asteraceae subf. Asteroideae accompanied by S. polygamus, Colliguaja integerrima, and B. heterophylla; and (3) dwarf-shrub steppe, dominated by M. spinosum, Asteraceae subf. Asteroideae, Amaranthaceae subf. Chenopodioideae and Nassauvia darwinii, with S. polygamus, Ephedra frustillata, Chuquiraga sp., and Poaceae (Figure 1B). Although all pollen assemblages represent shrub steppe environments, variations in taxon proportions define each community and reflect edaphic factors such as slope aspect and gradient [31].

Within the basin and adjacent areas are the sedimentary sequences and archaeological sites described below: Los Flamencos (LF) is a small, shallow, oligotrophic lake (47°22′ S, 71°43′ W; 483 m a.s.l.) with clay–silt sediments and carbonates, reaching a maximum depth of 40 cm. Zorro Bayo (ZB) is located on the western shore of Lago Pueyrredón (47°25′55″ S, 72°07′7″ W), in a low-lying wet meadow that forms fens of high ecological value for the present-day ecosystem. Along the west–east transect, ZB and LF are separated by 21 km, while the archaeological sites CMN1, CMN2, and COCU are located approximately 8 km northeast of LF and 23 km from ZB, in a sector surrounded by rocky slopes. Vegetation corresponds to a shrub steppe dominated by M. spinosum and B. heterophylla, and annual precipitation does not exceed 300 mm (Figure 1B,C) [51]. Together, these sites represent a wide range of geomorphological and ecological settings, providing an integrated framework for paleoenvironmental and archaeological research in the basin.

To the east, approximately 65 km from ZB, lies Parque Nacional Patagonia (PNP), where the vegetation changes its physiognomy and is characterised by a dwarf-shrub steppe, including Nassauvia lagascae, Nassauvia lagascae var. globosa, Nassauvia pygmaea and Azorella lycopodioides; low shrubs such as Nardophyllum obtusifolium, Nardophyllum bryoides, species of the genus Mulguraea, Ephedra frustillata, Senecio filaginoides, Senecio magellanicus, Mulinum hallei, and Acaena platyacantha, accompanied by scattered grasses and herbaceous plants. On saline soils, specialised plant communities develop, such as Lepidophyllum cuppresiforme and various Chenopodiaceae (e.g., Atriplex spp.). Transitional zones between steppes are characterised by taller shrublands (1.5–2 m) dominated by Anarthrophyllum rigidum, Berberis heterophylla, Lycium chilense, Mulguraea, and Prosopis denudans [17]. The climate is cold–temperate and arid, with annual precipitation generally below 200 mm, concentrated in the winter months and strongly influenced by the Andean rain shadow. Persistent, high-intensity westerly winds increase evapotranspiration, shaping vegetation structure and distribution. Mean annual temperatures range from 9 °C to 10 °C (Figure 1C,D), with frequent frosts throughout the year [46,51]. In depressions and river valleys, wetlands—highly productive environments—develop, creating sharp ecological contrasts with the surrounding arid landscapes. These wetlands serve as biodiversity refuges and constitute key sites for paleoenvironmental research. This high plateau region experiences pronounced seasonality and frequent frosts; its vegetation is dominated by dwarf-shrub steppe interspersed with fens, making it an exceptional setting for paleoenvironmental research. Within PNP, the La Tapera fen (LTap, 47°24′ S; 71°12′ W) was cored using a Russian corer, yielding a 140-cm-long sediment sequence. Located 40 km southeast of MLTap, the Cisne 7 archaeological site lies near Bajo Caracoles (Figure 1B).

2.2. Pollen Analysis

To integrate paleoenvironmental information from all previously analysed sites in the Lago Pueyrredón area and assess how vegetation changed during the Holocene, available pollen data were compiled from the archaeological sites CMN1, CMN2, and COCU, as well as from the continuous sequences LF and ZB. Additionally, to compare paleoenvironmental data along a longitudinal gradient, the sequences from fens La Tapera (LTap) and the archaeological site Cisne 7 were incorporated. These sites are east of Lago Pueyrredón, within Parque Nacional Patagonia, and near Bajo Caracoles, respectively. Fossil sediment samples from fens La Tapera and Cisne 7 were processed for palynological analysis following a standard protocol. Between 0.8 and 1 g of fossil sediment from LTap and 6–10 g of sediment from Cisne 7 were used for pollen extraction. Three tablets of Lycopodium clavatum spores (BATCH No. 177.445, x = 18,584) were added to each sample before pollen extraction as an exotic marker, allowing for the estimation of pollen concentration and ensuring representative pollen counts. Chemical treatments included hot 10% KOH to remove clays and humic acids, 10% HCl to dissolve carbonates, and a heavy liquid solution of ZnCl₂ (specific gravity δ = 2) to separate the mineral fraction via flotation. Subsequently, HF was applied to dissolve silicates, and acetolysis was performed to eliminate unwanted organic matter. These procedures follow established methodologies [52,53,54]. Finally, the residues were mounted on slides and analysed under a light microscope by counting at least 300 grains of pollen. Pollen and spore identification and counting were performed by comparison with the comprehensive reference collection at the Laboratory of Paleoecology and Palynology (UNMdP).

The representative pollen categories for each sequence or archaeological site were Grass, Herbs, Dwarf-shrubs, Shrubs, Forest, Ecotone, and Human Impact. Each category is made up of the following pollen variables: CMN1: Grasses (Poaceae, Cyperaceae); Herbs (Iridaceae, Ranunculaceae, Acaena, Senecio, Apiaceae, Caryophyllaceae); Dwarf-shrubs (Nassauvia, Empetrum); Shrubs (Mulinum, Asteraceae subf. Asteroideae, Schinus, Lycium, Colliguaja, Berberis); Forest (Nothofagus, Podocarpus); Human Impact (Rumex, Brassicaceae). LF: Grasses (Poaceae, Cyperaceae); Herbs (Caryophyllaceae, Plantago, Rosaceae, Geraniaceae, Mutisieae, Iridaceae, Valeriana, Solanaceae, Gilia, Apiaceae); Dwarf-shrubs (Amaranthaceae subf. Chenopodioideae, Nassauvia); Shrubs (Mulinum, Asteraceae subf. Asteroideae, Berberis, Colliguaja, Euphorbiaceae, Ericaceae, Schinus); Ecotone (Escallonia, Maytenus, Fuchsia, Osmorhiza, Blechnum, L. magellanicum); Forest (Nothofagus, Podocarpus); Human Impact (Brassicaceae, Asteraceae subf. Cichorioideae). ZB: Grasses (Poaceae, Cyperaceae); Herbs (Caryophyllaceae, Mutisieae, Rosaceae, Ranunculaceae, Malvaceae, Iridaceae, Boraginaceae, Phacelia, Liliaceae, Rubiaceae, Valeriana, Onagraceae, Gilia, Armeria, Azorella); Dwarf-shrubs (Nassauvia, Amaranthaceae subf. Chenopodioideae, Ephedra); Shrubs (Mulinum, Berberis, Asteraceae subf. Asteroideae, Colliguaja); Ecotone (Escallonia, Maytenus, Blechnum, L. magellanicum); Forest (Nothofagus, Podocarpus); Human Impact (Rumex). COCU: Grasses (Poaceae); Herbs (Caryophyllaceae, Malvaceae, Gilia, Phacelia, Ranunculaceae, Euphorbiaceae, Apiaceae); Dwarf-shrubs (Nassauvia, Amaranthaceae subf. Chenopodioideae, Ephedra); Shrubs (Mulinum, Berberis, Asteraceae subf. Asteroideae, Colliguaja, Schinus); Forest (Nothofagus, Podocarpus); Human Impact (Rumex). CMN2: Grasses (Poaceae); Herbs (Adesmia, Gilia, Caryophyllaceae, Ranunculus, Malvaceae, Euphorbia, Acaena, Mutisieae, Phacelia); Dwarf-shrubs (Nassauvia, Amaranthaceae subf. Chenopodioideae); Shrubs (Mulinum, Asteraceae subf. Asteroideae, Schinus, Berberis, Colliguaja, Lycium); Forest (Nothofagus, Podocarpus); Human Impact (Rumex, Asteraceae subf. Cichorioideae).

For Parque Nacional Patagonia and Bajo Caracoles sites, categories were grouped as follows: MLTap and Cisne 7: Grasses (Poaceae, Cyperaceae); Herbs (Caryophyllaceae, Polygala, Malvaceae, Fabaceae, Boraginaceae, Geraniaceae, Caesalpinoideae, Rosaceae); Dwarf-shrubs (Amaranthaceae subf. Chenopodioideae, Ephedra, Empetrum, Nassauvia, Cactaceae); Shrubs (Mulguraea tridens, Mulinum, Schinus, Colliguaja, Berberis, Asteraceae subf. Asteroideae); Forest (Nothofagus, Podocarpus); Human Impact (Brassicaceae).

The summarized pollen diagrams were plotted using the TILIAGRAPH program TGView 2.0.2 [55]. Furthermore, for continuous lake and fens sequences, and in accordance with the prevailing vegetation, forest–ecotone vs. shrub indices (LF, ZB) and shrub vs. dwarf-shrubs indices (MLTap) were calculated to represent the main patterns of Holocene vegetation associated with moisture variability along the west–east gradient at 47° S. These indices synthesise pollen assemblages into variables that reflect vegetation composition. Ecological groups defined for each sequence were: (1) forest–steppe, (2) shrubs, and (3) dwarf-shrubs. For each pollen spectrum sample, the relative percentages of the pollen types in each group were summed. Indices were calculated as follows:

Forest–ecotone vs. shrubs index: Σ (% forest–ecotone)/Σ (% shrubs)

Shrubs vs. dwarf-shrubs index: Σ (% shrubs)/Σ (% dwarf-shrubs)

Values were normalized between 0 and 1 to facilitate comparisons. Forest–ecotone dominance indicates wetter periods, shrub dominance semi-arid periods, and dwarf-shrubs dominance arid periods. Archaeological sites were excluded from index calculations, as they represent temporal windows.

2.3. Chronological Data

Table 1. Radiocarbon ages of CMN1, LF, ZB, COCU, CMN2, MLTap, Cisne 7, and calibrations in accordance with [57].

	CODE LAB	DEPTH cm	AGE 14C	CAL YEARS BP	REFERENCES
CMN1					[41,42]
	UGAMS 4019	Layer 4	1950 ± 30	1841
	UGAMS 4022	Layer 5	2530 ± 170	2539
	UGAMS 1654	Layer 7	5160 ± 50	5800
	UGAMS4020	Layer 8	7790 ± 30	8500
LF					[19]
	DAMMS-028033	6	2959 ± 39	3059
	DAMMS-024153	14	3387 ± 29	3583
	DAMMS-024152	22	4225 ± 29	4721
	UGAMS-A26640	31	4771 ± 25	5475
	UGAMS-A26641	41	5350 ± 26	6086
	UGAMS-A26649	51	6081 ± 26	6886
	DAMMS-014679	63	6610 ± 33	7471
ZB					[20]
	DAMS-028827	35	264 ± 25	286
	DAMS-028031	51	843 ± 23	709
	DAMS- 028032	72	1722 ± 24	1580
	DAMS-028826	100	2188 ± 24	2245
	DAMS-014678	120	2845 ± 29	2841
COCU					[20]
	CODE LAB	DEPTH cm	AGE 14C	CAL YEARS BP
	UGAMS-5883	Layer 2	460 ± 20	493
	UGAMS-5884	Layer 3	2080 ± 20	2040
CMN2					[41]
	UGAMS 5881	Layer 4	945 ± 15	1020
	UGAMS 5882	Layer 7	1600 ± 20	1448
MLTap
	DAMS-054065	24	595 ± 15	548	[58]
	DAMS-046908	64	2448 ± 20	2594
	DAMS-046907	108	2550 ± 20	2738
	DAMS-054066	139	4173 ± 26	4681
Cisne 7					New data
	UGAMS 5880	Layer 2	2140 ± 20	2117
	UGAMS 5879	Layer 3	3070 ± 25	3236

presents radiocarbon dates from the analysed fossil sequences and archaeological sites. A Bayesian age–depth model was constructed for the MLTap, LF, ZB sequences using the Bacon package in R [56], based on 13 sections and estimating weighted means and 95% confidence intervals at each sedimentary level. These results provide robust chronological control and facilitate regional comparisons with other records. The LF and ZB sequences were previously published and correspond to [19,20] (Figure 2).

3. Results

3.1. Pollen Analysis

Vegetation responses to climate change during the Holocene were reconstructed from pollen records collected along a latitudinal gradient at 47° S in Argentine Patagonia. Pollen assemblages were grouped into Human Impact, Forest, Ecotone, Shrub, Dwarf-shrub, Herb, and Grass categories. Spatial patterns of vegetation formations were reconstructed for different time periods to assess distributional shifts. Fossil pollen data were interpreted by comparing them with modern pollen assemblages from various vegetation communities. Previous studies along the west–east gradient at 47° S [19,20,31,32,42] have examined pollen–vegetation relationships.

3.1.1. Lago Pueyrredón

The pollen analysis of the different sites in the Lago Pueyrredón basin has revealed vegetation dynamics that reflect changes in climatic and environmental conditions throughout the Holocene. To facilitate interpretation of these trends, the results have been grouped by time period.

During the early Holocene, from 8500 cal yr BP onward, the landscape was characterised by a steppe dominated by grasses (60–70%) and dwarf-shrubs (10%), as recorded at CMN1. Subsequently, from 7600 cal yr BP, a transition towards greater moisture availability is observed, a pattern that persists until 6600 cal yr BP. The Los Flamencos (LF) record evidences this change through increased forest pollen (30–45%) and ecotonal taxa (10%), associated with shrubs (20–45%) and grasses (40–60%). This trend coincides with enriched carbon isotope values (δ¹³C), suggesting the development of a shrubland environment with forest patches.

Between 6600 and 5400 cal yr BP, the LF record indicates a phase of aridity, evidenced by decreasing δ¹³C values and a reduced presence of enriched C₃ species. This change correlates with an increase in shrubs (40–70%) and dwarf-shrubs (5–25%), a decline in forest and ecotone pollen (5%), and an increase in herbs (20–30%). Consistently, the CMN1 site records similar conditions around 5800 cal yr BP. Aridity intensifies between 5400 and 5000 cal yr BP, with a notable increase in dwarf-shrubs (25%) and shrubs (60–75%), and the absence of ecotone pollen at LF. This trend coincides with palaeogeographic changes documented for the region during this period [41,42].

Subsequently, from 5000 to 3550 cal yr BP, arid conditions persist, characterised by shrub dominance (70–80%), dwarf-shrubs (25–10%), and fluctuations in grass values between 20–50% in the pollen record. Although forest pollen increases (20–40%), it is interpreted as long-distance transport, since it is not associated with ecotonal taxa, indicating in situ forest formations. This interpretation is consistent with the lower δ¹³C values recorded in the area (Figure 3a).

A shrub–grass steppe with forest elements (~20%), ecotonal taxa (5–7%), shrubs (25–35%), and grasses (20–25%) is inferred at 3000 cal yr BP. A marked increase in forest elements (~40%) is evident between 1750 and 1000 cal yr BP, accompanied by ecotonal pollen types (5%), moderate shrub values (20–30%), and the absence of dwarf-shrubs, which suggests greater moisture availability during this period. This increase in forest elements and the decrease in dwarf-shrubs are also recorded at CMN1 (1841 cal yr BP), COCU (2040 cal yr BP), and CMN2 (1020 cal yr BP), although without the presence of ecotonal elements. However, the temporal windows provided by the archaeological sites make it difficult to analyse broader patterns, and this information was therefore complemented with continuous sequences (Figure 3b).

In the last 1000 cal yr BP, the Lago Pueyrredón basin (ZB) shows the development of a shrub steppe, with increasing shrubs (~60%) and decreasing forest elements (30–10%) and grasses (20–10%). This aridity trend is reinforced by the COCU record at 493 cal yr BP, which shows increased shrubs (60–70%) and dwarf-shrubs (~15%), together with a reduction in forest elements (<20%). The decrease in forest pollen types at ZB around 500 cal yr BP is consistent with this aridity signal. The pollen results from ZB, together with isotopic data, suggest a vegetation transition from a forest–shrub steppe ecotone (more depleted δ¹³C values) towards a shrub steppe (less depleted δ¹³C values) at the end of the sequence (Figure 3a,b). Details of landscape-scale vegetation changes during the Holocene for the sites presented in this synthesis can be found in [16,19,20,24,31,32,41,42].

3.1.2. Parque Nacional Patagonia and Bajo Caracoles

At La Tapera (MLTap), vegetation changes are relatively subtle. Between 4700 and 4000 cal yr BP, a dwarf-shrub steppe (60–70%; Nassauvia, Amaranthaceae subf. Chenopodioideae and Ephedra) prevailed, with low proportions of shrubs (Mulinum, Colliguaja), grasses (Mutisieae, Fabaceae, Geraniaceae), and forest taxa (Nothofagus and Podocarpus), indicating high aridity. From 4000 to 3000 cal yr BP, the vegetation became more heterogeneous, forming a dwarf-shrub–shrub steppe in which dwarf-shrubs such as Nassauvia, Amaranthaceae subf. Chenopodioideae and Ephedra decreased from 60 to 20%, while shrubs such as Mulguraea tridens and Asteraceae subf. Asteroideae increased from 20 to 70%. This interval also shows an increase in grasses (10–30%; Malvaceae, Boraginaceae, Caesalpinoideae, Mutisieae), suggesting semi-arid conditions. A brief local humid pulse around 3000 cal yr BP is reflected by a marked increase in Cyperaceae (50%).

Afterwards, the record indicates a shrub steppe mainly dominated by Asteraceae subf. Asteroideae and Mulguraea tridens (40–60%), together with dwarf-shrubs such as Amaranthaceae and Ephedra (20–30%), grasses (Poaceae, 15–35%), and herbs mainly belonging to Caryophyllaceae (20–30%). Around 1000 cal yr BP, dwarf-shrubs (Nassauvia, Amaranthaceae subf. Chenopodioideae, and Ephedra) increased sharply (up to 60%), while shrubs, herbs, and grasses decreased. Subsequently, this trend reversed, and by approximately 500 cal yr BP it led to the establishment of the present shrub–dwarf-shrub vegetation (Figure 3a). The fen sequence shows a significant increase in Myriophyllum, suggesting higher soil moisture and the possible development of a seasonal water body. The surrounding vegetation, similar to the present-day steppe, is dominated by Mulguraea tridens, Colliguaja, Schinus, Berberis, and Nassauvia [58].

At the Cisne 7 site, two time points are represented (3236 and 2117 cal yr BP), both showing dominance of dwarf-shrubs such as Amaranthaceae subf. Chenopodioideae and Ephedra (40–50%), shrubs including Mulinum, Asteraceae subf. Asteroideae, and Mulguraea tridens (15–20%), and grasses such as Poaceae (20–40%), indicating arid conditions (Figure 3b). Together with other records from the Deseado Massif, these results indicate marked regional vegetation heterogeneity and humidity–aridity oscillations during the Late Holocene.

3.1.3. Indices

The calculated indices suggest alternating wet and dry periods throughout the Holocene. In the LF sequence from the Lago Pueyrredón area, a predominance of forest pollen indicators with ecotonal elements (index values close to 1) was recorded between 7600 and 6500 cal yr BP, followed by shrub-dominated phases (index values ~0–0.2) that persisted until 2800 cal yr BP. Between 6500 and 2800 cal yr BP, although shrubs predominated (index values 0–0.40), fluctuations are evident that reflect intervals of more and less pronounced aridity (Figure 4, LF). Around 3000 cal yr BP, the ZB sequence shows moderate index values (0.4–0.6), suggesting a shrub steppe with forest patches. From 1700 to 1000 cal yr BP, values approach 1, indicating increased moisture and forest taxa. During the last 1000 years, values declined to 0.20–0, evidencing arid conditions with shrub dominance (Figure 4, ZB). Overall, these results highlight an environmental dynamic of alternating moisture and aridity that drove vegetation cover changes.

In LTap, farther east, shrub vs. dwarf-shrub indices indicate dwarf-shrub dominance from 4700 cal yr BP (index values near 0). Between 3500 and 3000 cal yr BP, index values (0.2–0.45) reflect greater coexistence of shrubs and dwarf-shrubs. Around 2500 and 700 cal yr BP, shrubs increase (index values 0.9 and 0.75, respectively), suggesting more semi-arid conditions, interspersed with more arid phases between 2000–1000 cal yr BP and during the last 500 years, when dwarf-shrubs again predominate (index values near 0.2) (Figure 4, LTap). In this environment, vegetation responded to moisture fluctuations not through the incorporation of new community components but through shifts in the relative dominance of existing life forms. In particular, shrubs and dwarf-shrubs alternated in dominance throughout the Holocene according to water availability, interacting with other drivers such as temperature, evapotranspiration, and soil conditions.

4. Discussion

4.1. Contributions of Archaeological Sites to Paleoenvironmental Reconstruction

The archaeological sites in Santa Cruz provide key insights into vegetation change and land use by hunter–gatherer groups across different temporal and spatial scales [16,31,32,38,41,42,43]. In previous studies, pollen data from archaeological sites were interpreted alongside continuous sequences to contextualise human occupation, assess the representativeness of samples, and evaluate pollen preservation [31,32,41,42,43].

The CMN1, CMN2, COCU, and Cisne 7 sequences span different environmental periods. Although they represent temporal windows, the palynological evidence is broadly consistent with that derived from continuous sequences. At CMN1, the Early Holocene is characterised by a grass steppe with dwarf-shrubs, later shifting to a heterogeneous shrub steppe from the Middle Holocene onwards (Figure 3b). Palynological evidence from CMN1 and LF converges in highlighting floristic heterogeneity and woody resources that may have supported diverse human activities [19].

COCU and CMN2 document vegetation for 2000, 1500, 1000, and 500 cal yr BP. Together with CMN1 and the continuous sequence ZB, these records indicate the persistence of shrub steppe over the last 2500 years (Figure 3b). CMN1 and COCU yielded the largest number of pollen samples and displayed good preservation, allowing for more precise inferences of vegetation change [31]. Impact pollen types (Rumex) associated with sheep grazing during the last century were also recorded [59].

Further east, Cisne 7 offers palaeoenvironmental snapshots (3236 and 2117 cal yr BP), which, when analysed alongside the continuous sequence LTap, generally support the palaeoenvironmental trends inferred for the region (Figure 3a,b).

4.2. Paleoenvironmental Changes at 47° S in a Regional Context

The results of the sequences analysed in this study provide new data on the palaeoenvironmental dynamics of Patagonia at 47° S during the Holocene. Changes in plant communities are closely linked to shifts in water availability resulting from positive and negative anomalies in the SWW. Taken together, the calculated indices and the pollen records from continuous sequences in the Lago Pueyrredón and Parque Nacional Patagonia areas reveal transitions between forest–ecotone steppe communities, shrub steppes, and dwarf-shrub steppes, suggesting alternating wet and dry periods throughout the Holocene. Although with some discrepancies in synchronicity, this climatic variability is recorded in multiple sequences, both east and west of the Andes.

For example, in the extra-Andean region, lake-level records from Lago Cardiel document a hydrological maximum during the Early Holocene between ~11300 and 8900 cal yr BP, with persistent lake circulation forced by winds, followed by subsequent declines and oscillations. This pattern is interpreted as the result of greater moisture availability in the Early Holocene and more variable conditions during the Late Holocene, associated with changes in the zonal and meridional trajectories of SWW-related storms [13,60,61]. To the west, in Chilean Patagonia, sequences at 47° S also indicate changes in moisture availability. The high-resolution record from the Chacabuco Valley (Lago Edita) shows very humid conditions and the persistence of closed-canopy Nothofagus forests to the present, with millennial-scale alternations of drier and warmer intervals during the Holocene [4]. Similarly, the Laguna La Anónima record documents a closed forest between 8200 and 3800 cal yr BP, followed by a shift to an open forest with patches of grass–shrub steppe during the last 3000 years [28].

According to our results, the pollen record from the CMN1 archaeological site indicates that during the Early Holocene, the vegetation was dominated by a grass steppe with dwarf-shrubs [19,20,31,32]. After 7600 cal yr BP, the presence of shrub communities with forest patches and ecotonal vegetation, together with index values close to 1 in LF, suggests an increase in water availability. This pattern is consistent with eastern records showing a positive SWW anomaly. For instance, on the Chilean side at ~47° S, the Lago Edita record reveals strengthened precipitation, the establishment of closed forests, and moderate fire activity by ~7800 cal yr BP [4]. In the Argentine sector of Lago Pueyrredón, this wet phase was followed by drier conditions—a pattern consistent with declining δ¹³C values, index values between 0 and 0.2, and increased shrubs in LF between 6600 and 5400 cal yr BP. Local aridity, greater environmental heterogeneity, and falling lake levels around 5800 cal yr BP may have favoured greater human mobility by opening new areas and resources [41,42]. Thus, the Middle Holocene was characterised by pronounced environmental complexity.

Multiproxy records from the Cochrane–Pueyrredón basin in Chile indicate the persistence of closed forests between 8500 and 2000 cal yr BP, with a Nothofagus pollen peak between 5500 and 5000 cal yr BP linked to strengthened SWW and neoglacial advances [28]. This increase in Andean moisture contrasts with the aridity recorded east of the Andes. For instance, in the Deseado Massif, the development of a shrub steppe indicates a gradual temperature rise and declining water availability since ~8000 cal yr BP [45]. At Mallín La Primavera (47° S, 68° W), dry conditions are evident after 7700 cal yr BP [30]. The relative decline in Lago Cardiel levels between 8900 and 7400 cal yr BP, followed by subsequent hydrological oscillations in this extra-Andean area, is consistent with this dry phase [13]. Intensification of aridity in the extra-Andean sector is also evident at LTap, where dwarf-shrubs and dry conditions predominate from 4700 cal yr BP onwards.

At 49° S, records from Lago San Martín show, from 8000 cal yr BP onwards, an increase in shrubs and a decline in grasses, together with an expansion of Nothofagus between 8000 and 7500 cal yr BP at La Tercera, suggesting forest expansion in the Andean sector [29]. At Mallín Ñire, Nothofagus and Ericaceae also expanded, generating a broad forest–grass steppe ecotone between 8000 and 6500 cal yr BP, indicative of reduced water availability [21]. Between 6500 and 4000 cal yr BP, an increase in shrub steppe is evident at Mallín Ñire [21], Mallín Paisano Desconocido [18], and Mallín La Tercera [29], pointing to lower moisture availability and reduced fire activity, the latter likely attributable to fuel discontinuity at La Tercera [23,29]. The CPD site shows a shift to drier conditions from 7700 cal yr BP [43]. Further south, at Lago Argentino (50° S), closed forests developed between 8000–7000 and 6000–4000 cal yr BP, probably linked to higher Andean precipitation [5,23,37,39,40]. This regional variability supports the hypothesis of opposing hydrological balances between Andean and extra-Andean environments, driven by SWW intensification at 50° S. Such intensification is associated with high precipitation values in the Andean region and semi-arid conditions in the extra-Andean sector [62]. Thus, greater moisture availability in the cordillera facilitated forest development, while to the east, subsidence effects increased water deficits, promoting xeric communities [23].

The Late Holocene (4200 cal yr BP–present) is characterised by marked paleoenvironmental variability, with small-scale changes generating pronounced heterogeneity in regional vegetation patterns. At Lago Pueyrredón, the LF record shows a reduction in dwarf-shrubs, the expansion of a shrub steppe, and an increase in herbs between 3500 and 3000 cal yr BP, suggesting wetter conditions than in earlier periods, although still comparable to the area’s present-day aridity. At ZB, farther west, a grass–shrub steppe with forest and ecotonal elements is recorded between 2800 and 1000 cal yr BP, interpreted as a wet phase followed by a return to aridity during the last 1000 years. Consistently, index values at ZB indicate a shrub-steppe landscape with forest patches, followed by a humid pulse between 1700 and 1000 cal yr BP (values near 1), interpreted as a forest–ecotone–steppe community. Finally, the last 1000 years show minimum values (0–0.2), reflecting the establishment of arid conditions and shrub dominance—a pattern consistent with the decline of forest pollen in regional records [39,63].

West of the Andes (47° S), Chilean records indicate that after the Middle Holocene wet phase, open forests and forest patches within a grass–shrub steppe developed from 3800 cal yr BP onwards, accompanied by increased fire incidence [28], in line with the environmental heterogeneity observed in the extra-Andean sector. Similarly, at LTap, between 4000 and 3000 cal yr BP, a mildly semi-arid phase characterised by dwarf-shrub–shrub steppes was followed by persistent aridity, interrupted only by a brief humid episode around 3000 cal yr BP. In the Deseado Massif (Los Toldos, La Martita, La Primavera) [30,64], sequences indicate semi-arid conditions comparable to the present, consistent with the west–east humidity–aridity patterns proposed for Patagonia. The variability inferred for the Late Holocene is also evident at Lago Cardiel, where successive lake-level transgressions and regressions occurred between 4500 and 3100 cal yr BP, with humid pulses recorded at 2000, 1450, and 800 cal yr BP [61].

Further south, records between 49° and 50° S indicate the establishment of open forests [5] and the transition from a shrub–grass steppe to a grass steppe, accompanied by a decline in Nothofagus at Paisano Desconocido and La Tercera [18,29]. At Mallín Ñire, the shift from a shrub–grass steppe to a shrub steppe with herbs between 4000 and 1400 cal yr BP reflects a slight increase in humidity and greater environmental heterogeneity, although overall conditions remained dry. During the last 1400 years, a shrub–grass steppe developed at Mallín Ñire, suggesting a transitional environment between forest and steppe [21]. At La Tercera, sustained fuel availability between 2500 and 1500 cal yr BP promoted high fire frequency [23]. Similarly, between 3000 and 2000 cal yr BP, a period of intense fire activity occurred at Lago Argentino (50° S), probably associated with biomass accumulation [23].

Finally, the last millennium shows a trend towards aridity in Lago Pueyrredón, evidenced by an increase in shrubs and dwarf-shrubs and a decline in forest elements at ZB and COCU. In the Deseado Massif, sequences indicate the dominance of shrub–dwarf-shrub steppe under arid conditions [30,38,64], consistent with the LTap record, where dwarf-shrubs increased markedly. Between 500 and 100 cal yr BP, sequences at 49° S suggest a grass steppe transitioning to shrubs around 400 cal yr BP, linked to reduced moisture availability [18]. In recent centuries, the presence of dwarf-shrubs at Mallín Ñire may indicate drier and colder conditions, possibly associated with the Little Ice Age [21]. Likewise, palaeohydric indices calculated from various Patagonian records show low values in eastern environments between 700 and 500 cal yr BP [65]. Consequently, at Lago Argentino (50° S), a shift from humid to dry conditions is documented around 400 cal yr BP, accompanied by a reduction in forest pollen [5,39,40]. Archaeological pollen records at the same latitudes [38] also indicate shrub steppe development under dry conditions. At a broader scale, geochemical indicators [66] and speleothems [67] corroborate reduced water availability associated with weakened SWW.

Specifically for this study, interpretation of the pollen-derived indices suggests pronounced environmental heterogeneity during the Middle and Late Holocene in sequences along the west–east environmental gradient. While in the more western environments (LF, ZB) humid pulses promoted the expansion of forest patches, at more arid eastern sites such as LTap, the response was expressed through changes in the relative dominance of shrubs and dwarf-shrubs. These discrepancies highlight the differential sensitivity of ecosystems to variations in SWW intensity and position across Patagonia [9,10,11,33]. In this sense, although plant communities in the study areas responded to changes in moisture availability, their responses differed depending on the geomorphological characteristics of each site. Such variations may be associated not only with water availability but also with other environmental drivers such as temperature and edaphic conditions, particularly in ecosystems located east of the Andes, like LTap, where vegetation responses are manifested not as floristic replacements but as internal shifts in the dominance of life forms within the community.

5. Conclusions

This study integrates continuous lacustrine and fen records with archaeological pollen sequences distributed along a west–east gradient at 47° S in Argentine Patagonia, providing a robust regional framework for evaluating Holocene climate–vegetation dynamics.

The results suggest that ecosystems closer to the Andes responded to humid pulses through the development of forest–steppe ecotonal environments, whereas extra-Andean environments primarily reflected shifts in the relative dominance of shrubs and dwarf-shrubs. The La Tapera (LTap) sequence is particularly significant, as it shows that vegetation in arid eastern settings did not respond through floristic replacements but through internal shifts in the balance between shrubs and dwarf-shrubs, highlighting the distinctive ecological dynamics of these systems.

In addition, the archaeological sites analysed confirmed and complemented the information provided by the continuous sequences, strengthening the interpretation of vegetation changes and environmental variability across different temporal windows.

Taken together, our results reveal alternating humid and arid phases throughout the Holocene. These findings are consistent with fluctuations in the intensity and position of the Southern Westerly Winds (SWW) previously postulated by other authors, e.g., [9,12], and further supported by other regional records. In this context, the SWW emerge as an important forcing of hydrological balance and vegetation dynamics at 47° S, underscoring both the differential sensitivity of ecosystems across the Patagonian gradient and the complexity of climate–vegetation interactions in this region.