The southern Brazilian tropical forest during the penultimate Pleistocene glaciation and its termination

To describe the composition of the penultimate glacial Brazilian Atlantic forest, we analyzed pollen, charcoal and diatoms deposited in the section from 871 to 1400 cm of core CO14 drilled in the Colônia basin in southeastern Brazil. The landscape was characterized by a cool grassland with three conifer genera: Araucaria, Podocarpus and Ephedra. Total arboreal pollen frequency did not change during the transition from glacial to interglacial conditions. Changes in Podocarpus frequency and concentration showed out‐of‐phase responses with austral summer insolation at an orbital scale while, at a millennial scale, both northern and southern hemisphere ice volume controlled the interplay between positions of the Inter‐Tropical Convergence Zone and South Tropical Front (STF), which in turn defined the latitudinal distribution of rainfall. The disappearance of Podocarpus and the decrease of Araucaria observed between ~167 and 160 ka were related to a dry interval which was not observed elsewhere. During Termination II a progressive decrease in conifer pollen taxa was in phase with a southward shift in the STF and increase in Atlantic sea surface temperatures. Our results show that southern hemisphere conifer distribution is strongly linked to austral summer insolation and winter precipitation and will be threatened by the southward expansion of the summer rainfall boundary.


Introduction
On glacial to interglacial time scales, defining the impact of tropical latitudes on high-latitude climates through changes in greenhouse gases is a key to future climate projections (Palaeosens Project Members, 2012).The rate of melting of polar ice and the reorganization of air masses and ocean currents that has taken place in only a few decades challenges all previous millennial-or century-scale scenarios.The last glacial ended with an out-of-phase change in the volume of ice and in the climate in Greenland and in the Antarctic that enhanced a southward shift of the Inter-Tropical Convergence Zone (ITCZ) due to large scale ocean-atmosphere reorganization (e.g.Schneider et al., 2014).Two brief climate reversals, called Heinrich events H1 and H0 (the Younger Dryas) lasting respectively 1000 and 1500 years, were observed within the polar deglaciation, both of which characterized a polar to tropics effect that started in the Northern Hemisphere when the release of sea ice led to wetter climate conditions at the southern edge of the Neotropics (Ledru et al., 2002;Stríkis et al., 2018).Nevertheless, little is still known about the influence of the glacial epochs on the Tropics due to the scarcity of continental tropical records spanning several cold-warm intervals on both orbital and millennial scales.The concentration of deuterium in the Vostok ice core in Antarctica evidenced the redistribution of moisture from the Tropics to the Pole at obliquity scale (Vimeux et al., 2001) and neotropical speleothem records clearly revealed Milankovitch precessional forcing on the monsoon system (Cruz et al., 2005;Burns et al., 2019) related to the expansion of tropical rainforest (Ledru et al., 2009).
The American continent is continuous nearly from pole to pole and thus provides an excellent laboratory for examination of the connections between high and low latitudes in both hemispheres, more specifically the climatic teleconnections in the Southern Hemisphere (Markgraf, 2001;Shulmeister et al., 2006).Since the mid-Pleistocene, the expansion and regression phases of ice volume have been orbitally paced by a 100 000-year cycle that, in turn, has affected the tropical hydrological cycle in the high Andes (Hanselman et al., 2011;Torres et al., 2013;Rodbell et al., 2022) as well as in the lowlands (Kern et al., 2023).However, differences in the expression of the glacial epochs and more particularly between the last glacial, Marine Isotopic Stage (MIS) 2-4, and the penultimate glacial, MIS 6, suggest the influence of other forcings on climate and vegetation at millennial scale (Zheng et al., 2013).Continuous melting of ice and smooth transition phases during MIS 6 suggest a more stable ice cover and less climate variability with lower temperatures than in the last glacial (Obrochta et al., 2014).MIS 6 was characterized by lower temperatures than the last glacial at Lake Titicaca in the high Andes (Hanselman et al., 2011) and in Australasian forests (Kershaw et al., 2007;Ryan et al., 2012).The high-resolution pollen record of Fuquene in the Colombian Andes revealed several shifts in the upper forest limit during MIS 6 that were attributed to short-term climate cycles (Bogotá et al., 2016) that are also clearly visible in a Peruvian speleothem (Burns et al., 2019).However, these millennial-scale events in MIS 6 were of lower amplitude and intensity than those in the last glacial.In the Southern Hemisphere, they are associated with an increase in monsoon activity related to shifts in the ITCZ (Bogotá et al., 2016;Burns et al., 2019).In addition, a strong teleconnection between the eastern Atlantic Ocean and the Agulhas leakage (Caley et al., 2012;Hou et al., 2020) forced the accumulation of warm waters in the southern Atlantic Ocean inducing out-of-phase sea surface temperature (SST) minima with the Northern Hemisphere (Santos et al., 2017).In the southwestern Atlantic Ocean (24°S), MIS 6 is divided into three sub-intervals with marked SST variability between 185 and 160 ka (Santos et al., 2017) in agreement with the Peruvian speleothem record (Burns et al., 2019).However, marine records in the southern Pacific showed that the amplitude and strength of the climatic signal during the glacials was differently expressed depending on the latitude and position of the sub-tropical front (Pahnke et al., 2003).
Multi-proxy analyses of sediment cores collected in the Colônia basin in southeastern Brazil revealed the importance of monsoon activity in driving floristic changes of the Atlantic rainforest during the last glacial (Ledru et al., 2009;Rodríguez-Zorro et al., 2020).Here, to evaluate how changes in ice volume affected the floristic composition of a southern tropical forest, we performed a highresolution pollen and diatom analysis of a section of core CO14 that covers the penultimate glacial and the transition to the last interglacial [Termination II (TII)].

Study area
The Colônia basin is a circular structure with a diameter of 3.6 km located in the district of Parelheiros, south of the city of São Paulo, in Brazil (23°52′03″S, 46°42′27″W) (Figure 1) (Riccomini et al., 1991(Riccomini et al., , 2011)).Topographical relief is relatively low with elevations ranging between 715 and 900 m asl and there is a circular ridge rising to ~125 m above the bottom of the basin (Riccomini et al., 1991(Riccomini et al., , 2011)).The age of the structure is estimated at between 11.2 and 5.3 Ma (Simon et al., 2020).A seismic survey revealed organic-rich sediments deposited above a layer of rocks at a depth of ~450 m (Prado et al., 2019).
Mean annual precipitation at Parelheiros is 1600 mm, with a 2-month dry season in July and August.Mean annual temperature is 20°C, with a mean of ~17°C in winter (INMET, 2019;DAEE, 2020;Rodríguez-Zorro et al., 2020).A small river, the Vargem Grande, runs through the basin exiting through a single outlet in the eastern ridge of the structure (Riccomini et al., 2011).Modern climate conditions at Colônia show that an increase/decrease in moisture is driven by changes in the amplitude and intensity of the summer monsoon associated with a southward/northward shift of the convergence zones (ITCZ and South Atlantic Convergence Zone) (Marengo et al., 2020).Farther south, between 27 and 35°S, in southern and southwestern Brazil, the climate shows a gradual change in the peak wet season from austral summer to spring and late winter while in the southeastern region of southern Brazil the peak wet season is observed during austral winter, a climate pattern characteristic of cold air penetration associated with extratropical moisture.Today, the influence of the South American Summer Monsoon (SASM) is observed on the coast until 25°S (Grimm et al., 2000;Orrison et al., 2022).

Coring and lithology
In 2014, a 1400-cm sediment core (CO14) was collected from a swamp located in the Colônia basin using a D-section Russian corer.The core reached a depth of 14 m and is described in Ledru et al. (2015).Between a depth of 14 and 9 m, the sediments are silt-clay, with compacted organic peat containing plant fibers in the top 9 m of the core.The core is stored in a cold chamber at ISEM-Montpellier, France.

Chronology and geochemical analyses
The chronological framework of core CO14 spans a period of 180 ka based on 22 radiocarbon dates, optically stimulated luminescence (OSL) and paleomagnetism, and the mean annual air temperature (MAAT) curve was fitted to the benthic δ 18 O LR04 stack using three changes in temperature as tie points (see details in Rodríguez-Zorro et al., 2020).
Details on X-ray fluorescence (XRF) analyses, mean annual air temperature (MAAT) based on the analysis of branched glycerol dialkyl glycerol tetraethers (brGDGTs) performed on 92 samples, and microcharcoal analyses are given in Rodríguez-Zorro et al. (2020).

Pollen and diatom analyses
A total of 264 pollen samples were collected at 2-cm intervals from the bottom section of core CO14, between 1400 and 871 cm.The pollen samples were prepared using a 0.5 cm 3 sample volume and two tablets of Lycopodium clavatum L (n = 3862, 9666 ± 671 spores per tablet), and treated with 40% HF, 15% HCl, 10% KOH and density flotation ZnCl 2 using the protocol established by Faegri & Iversen (1989).Pollen and spore residues were mounted in glycerol for microscope analysis.Pollen counts reached a total of at least 300 terrestrial pollen grains, not including aquatic, waterlevel-related taxa or spores.Pollen and spores were identified based on published atlases (Lorscheitter et al., 1998(Lorscheitter et al., , 1999;;Colinvaux et al., 1999;Leal et al., 2011;Lorente et al., 2017), and the pollen reference collection of the Geosciences Institute at the Universidade Estadual de Campinas (UNICAMP) (Fernandez et al., 2021).The pollen taxa and their associated ecological assignments are described in Camejo et al. (2022).The pollen diagram and the stratigraphically constrained classification of spectra (CONISS) were generated in Psimpoll (Bennett, 1996(Bennett, , 2009)).
Thirty-two 0.5-cm 3 subsamples taken at ~10-cm intervals were prepared for diatom analysis following the procedure described by Battarbee (1986), using heated 30% hydrogen peroxide (H 2 O 2 ) and 37% HCl to remove organic matter.Permanent slides were mounted in Naphrax (RI = 1.74).Diatoms were counted and identified at a magnification of 1000×.A minimum of 400 valves were counted per slide (Battarbee et al., 2001) at an efficiency count of at least 90% (Pappas & Stoermer, 1996).Species abundances are expressed as percentages of the total diatom counts in each subsample.Diatom frustules were identified to the species level whenever possible, and grouped according to their life form (habitat).The ratio of plankton to benthic diatoms (P/B ratio) was used as a proxy for lake level, although it is known to indicate trophic changes mainly in disturbed environments (Fontana et al., 2014).Biostratigraphic diagrams were produced using R 3.1.3(R Core Team 2022) and the 'vegan' (Oksanen et al., 2019) and 'Rioja' (Juggins 2017) packages.Only taxa showing relative abundances ≥2% are illustrated.

Results
Our section of the core representing a depth of 1400-871 cm is dated to between 181 and 128 ka, thus almost covering MIS 6 and TII between 135 and 128 ka.Sample resolution is 100

Diatoms
The diatom analyses showed two contrasting sections (Figure 3; Supporting Information Fig. S1); the lacustrine part of core CO14 with 12 samples containing diatoms dated between 180 and 153 ka, and a section lacking diatoms from 151 to 128 ka, in agreement with the disappearance of the lacustrine sediment.Thirty diatom species were identified in the bottom part of core CO14.Although the diatom assemblage is dominated primarily by Pseudostaurosira crateri Marquardt & C.E. Wetzel, a benthic (pennate) taxon, it is composed mostly of unknown species (Marquardt et al., 2021a(Marquardt et al., , 2021b) ) and ecological interpretations were based on modern 'analog' species and modern ecological information (Bradbury et al., 1994;Mackay et al., 2005).

Pollen analyses
Pollen content A total of 132 taxa were identified (Fig. S2a-d) representing 72 plant families, one alga, 10 ferns, three gymnosperms and 58 angiosperms.The 14 pollen taxa shown in the summary diagrams (Figure 2 and S3) were selected based on their proportion in the pollen counts and their ecological significance as defined in modern pollen rain studies (Montade et al., 2019;Portes et al., 2020) and botanical surveys (Garcia & Pirani, 2005;Marçon, 2009;Garcia et al., 2014;Scheer & Mocochinski, 2016).Gymnosperms are represented by three genera, Araucaria, Podocarpus and Ephedra, all associated with low temperatures.Podocarpus and Araucaria are generally associated with cold and wet climate conditions (Quiroga et al., 2016) while Ephedra is associated with cold and dry conditions (Marchant et al., 2002).Araucaria requires a minimum of 1400 mm mean annual precipitation and mean annual temperatures below 18°C and below 10°C in winter (Backes, 2009).The plant assemblage Poaceae, Asteraceae and Myrsine characterizes high-elevation grasslands (Portes et al., 2020;Safford, 2007).The taxon Acaena/Polylepis represents the herb Acaena and the tree Polylepis.Polylepis is strictly restricted to the Andes at elevations between 1800 and 3500 m asl (Kessler, 1955) and has never been recorded in modern vegetation in southern Brazil.Acaena is mainly observed in high-elevation grasslands with two species recorded in the State of São Paulo, Acaena eupatoria Cham.& Schltdl.and Acaena fruscescens Bitter (Flora do Brasil, 2022).Thus, the Acaena/Polylepis pollen type was attributed to Acaena and associated with cold and dry climate conditions.Acaena is a low pollen producer with shortdistance dispersal (Salgado-Labouriau, 1979).Ephedra is restricted to the southernmost region of Brazil and farther south (Flora do Brasil, 2022).Tree ferns of the Atlantic forest, Dicksonia, Lophosoria (Dicksoniaceae) and Cyathea (Cyatheaceae), are associated with moist regional climatic conditions (Montade et al., 2019).
Taxa related to edaphic water levels, Echinodorus, Cyperaceae, Eriocaulon, Juncus and Utricularia, characterize bog habitats while the aquatic taxon Myriophyllum, the lycophyte Isoetes and the alga Botryococcus are associated with a shallow lake.

Pollen zones
Pollen grains are well preserved with concentrations ranging between 359 253 and 55 209 grains cm −3 .The definition of the seven pollen zones (C1 to C7) was based on changes in AP and non-arboreal pollen (NAP) frequencies and CONISS groupings (Figure 2).The diatom analyses are detailed in Fig. S1.

Discussion
Change from a lake to a peat bog Interpretation of the diatoms revealed a significant change in the basin with the progressive evolution from a permanent shallow lake in the penultimate glacial to the formation of a peat bog and the disappearance of the lake at the beginning of the last interglacial (Figure 3 and S1).A dominance of araphid species until 160 ka is consistent with shallow-water conditions (Davydova et al., 2001).Small-celled fragilarioid diatoms are common in depleted nutrient and mineral environments (ombrotrophic conditions), as long as there is enough moisture to survive (Rühland et al., 2009;Hargan et al., 2015).During this low lake period detrital deposition was high (see Si on Figure 3).The associated benthic assemblage suggests that the margins of the lake were colonized by acidophilous and epiphytic taxa, mainly Pinnularia and Eunotia (Hargan et al., 2015;Costa et al., 2017;Paull et al., 2017), indicating oligotrophic (oligotrophic-dystrophic) environments.In addition, the presence of benthic diatom assemblages reflects circumneutral to slightly acidic conditions in the lake (Metzeltin & Lange-Bertalot, 1998;Krammer, 2000;Unkel et al., 2010) and swamp and peat bog formation around the lake (Sterken et al., 2008) with increased turbidity and more particulate matter.The following increase in the epiphytic and acidophilous taxon Gomphonema (Fig. S1) was probably caused by a reduction in light availability beneath the plants when the lake was colonized and gradually became shallower, suggesting a well-developed aquatic vegetation with a small peak in plankton species representing the peat-lake interface.Aulacoseira ambigua is commonly found in lotic and lentic environments in different regions in Brazil (Tremarin et al., 2013;Bicudo et al., 2016) and usually observed in relatively cold (~19.3°C),slightly acid (pH 6) and mesotrophic waters of reservoirs (Bicudo et al., 2016).Finally, the shallow lake was replaced by a swamp.The organic matter derived from the plants mentioned above accumulated in the lake sediment and could be associated with the drop in lake level.A sterile zone with no diatoms is observed at this stage.A plausible hypothesis to explain poor diatom preservation at Colônia is dissolution caused by an undersaturated silica environment and organic acids existing under oxic conditions (Bennett et al., 1991;Gell et al., 1994).This conclusion is corroborated by the parallel mass expansion of Botryococcus (Fig. S2d).Botryococcus pila J.Komárek & P.Marvan characterizes the dystrophic water of small peaty lakes and its high frequency is probably associated with the poor preservation of diatoms, as the oil compounds stored by these algae break up and produce organic acids during decay, which, in turn, triggers the dissolution of siliceous compounds (Komárek & Jankovská, 2001).Finally, the dominance of Botryococcus algae suggests that competition between species was low during its deposition (Tyson 1995), which may have resulted from the lack of nutrients in the environment (Tyson 1995).

Vegetation at Colônia during the penultimate glacial
Two taxa associated with cold and dry climate conditions, Ephedra and Acaena, are no longer observed in the vegetation today (Garcia & Pirani, 2005;Camejo et al., 2022).Two rare taxa are observed today as single isolated trees: Araucaria grows inside the basin and is linked to low temperatures and high moisture levels, and Podocarpus with P. sellowii found in the high-elevation grassland of the state park 'Serra do Mar' near Colônia (Garcia & Pirani, 2005).Two species of Podocarpus, P. sellowii and P. lambertii Klotzsch ex Endl., are observed today in southern Brazil associated with Araucaria, either in high-elevation grassland (P.sellowii) or in the shade provided by the Araucaria forest (P.lambertii).P. sellowii is always observed in riverine or swamp forests where soil moisture content is higher than in the grassland (Ledru et al., 2007;Teixeira & Assis, 2011).Thus, even though we were not able to identify the pollen grains at the species level, we can assume that Podocarpus is associated with moist soil environments.Pollen grains of Podocarpus and Araucaria have low dispersal capacity (Ledru et al., 2007;Montade et al., 2019).Thus, we conclude that the almost unbroken record of their presence during the penultimate glacial implies development of trees in the vicinity of the core site and reflects humid climate conditions.Fluctuations in Podocarpus frequencies (0.3-18%) (Figure 3), more accentuated than for Araucaria, probably due to its larger size and its ability to feed on cloud drippings, were used to detect changes in moisture at the millennial scale.High Poaceae and Asteraceae frequencies together with tree taxa characteristic of high-elevation grassland, Myrsine, Ilex and Symplocos (Fig. S2) (Scheer & Micochinski, 2016;Portes et al., 2020), suggest a landscape of cold grassland with sparse conifers and low-standing tree species.The taxa associated with low temperatures (Araucaria, Podocarpus, Acaena, Ephedra) were not found in a modern pollen rain study of the high-elevation grassland of the State of Rio de Janeiro (Portes et al., 2020) where today's mean temperature is probably too high for their growth.Thus, we infer that, during the glacial epoch, changes in pollen frequencies of the above-mentioned indicators are related rather to moisture variability and seasonal distribution.In addition, Podocarpus pollen frequency and concentration follow the same variability (Fig. S3) showing that there was not an over-representation due to a local tree expansion and rather a regional-scale distribution (Birks & Birks, 1980).
Between 180 and 170 ka, fluctuations in the vegetation cover with four peaks of Podocarpus with high variability in both the pollen concentration and in the frequencies of AP were observed (Figure 3 and S3).The high incoherent/coherent ratio that relates to organic matter (see Rodríguez-Zorro et al., 2020) and the low silica content (Figure 3), for instance mica, which is abundant at the edge of the basin along with quartzites (Riccomini et al., 2011), suggest regular rainfall while the presence of the aquatic taxa Isoetes and Botryococcus suggest the presence of a shallow lake in the basin (Figure 3 and S2).This landscape is similar to the open landscape observed today above the upper forest limit with sparse Podocarpus sellowii in gallery forests, Araucaria angustigolia (Bertol.)Kuntze, and P. lambertii (Garcia & Pirani, 2005;Jeske-Pieruschka et al., 2010;Gonçalves et al., 2016), either in southern Brazil or restricted to high-elevation tropical grasslands, also called paramo-like grassland (Safford, 2001).The relatively low and continuous fire activity observed during this interval suggests remote seasonal burning (Leys et al., 2013) in agreement with the adaptation to burning of the plants that currently grow in the high-elevation grassland (Safford, 2001).Between ~167 and 160 ka, a sharp decrease in both conifer taxa Araucaria and Podocarpus, concomitant with the expansion of Poaceae and Asteraceae, suggest the development of a more open landscape than the one observed in the previous interval.The increase in Myrtaceae and Melastomataceae could represent either an artefact due to local humidity and the presence of a type of gallery forest around the lake or high-elevation species of these two genera, both of which are high pollen producers (Scheer & Mocochinski, 2016;Portes et al., 2020).Fire activity is still evident.Then, between ~155 and 140 ka, we observed a significant decrease in pollen concentration (Figure 2), the continuous presence of Acaena and a decrease in Moraceae/ Urticaceae (Figure 3), which suggest drier and colder climatic conditions.The abrupt decrease in fire activity at ~148 ka also suggests changes in fuel properties (Safford, 2001).Peaks in fire activity are observed at 175 and 150 ka, during the low summer insolation phases, suggesting an open landscape with sparse trees of P. sellowii and frequent burning as observed today above the upper forest limit (Safford, 2001;Scheer and Mocochinski, 2016).Finally, between ~132 and 128 ka, a 2°C increase in temperature (Table 1) and overall lower fire activity are observed (Figure 3).Podocarpus frequencies are low (<3%) and, together with the presence of Araucaria, the regression of Poaceae and the expansion of Asteraceae suggest a significant change in the landscape in phase with the global increase in CO 2 (Shin et al., 2020).The decrease in the aquatic taxon Myriophyllum characterizes the progressive replacement of the lake by a bog (Fig. S2; Rodríguez-Zorro et al., 2020) in agreement with the changes in the lake predicted by diatoms (Figure 3 and S1).The penultimate glacial landscape at Colônia was composed of a grassland with conifers and probably small trees due to the low CO 2 (Shin et al., 2020) and low temperature.The continuous presence of austral conifers but with several oscillations suggest low temperature (MAAT 14.3°C) and a winter rainfall dominant regime different from the summer rainfall dominant regime we know today.Regression of the conifers occurred when the SASM became stronger preventing installation of winter rainfall (Rodríguez-Zorro et al., 2020).Today, high temperature and stronger SASM activity have induced a southward shift of the conifers (Ledru et al., 1994) which will probably become accentuated in the future (Wilson et al., 2021).

The penultimate glacial in the southern Tropics
MIS 6 is characterized by the development of a large ice sheet, extensive sea ice cover, low temperature in the South Atlantic, and relatively wet conditions with millennial-scale climate oscillations (Gottschalk et al., 2020).Sea level varied between −60 and −130, with an increase in sea level (-60 m) between 180 and 160 ka followed by a decrease to −140 m at 137 ka (Cawthra et al., 2018).In eastern Brazil (the western part of the South Atlantic), two marine records dating to the penultimate glacial (Figure 1b) reveal strong differences between the two last glacial stages (Santos et al., 2017;Hou et al., 2020).Moreover, reconstruction of the temperature gradient between the two sides of the South Atlantic showed that between 155 and 143 ka, a low E-W Atlantic SST gradient induced colder waters and lower SST offshore Brazil than during the glacial maximum (Hou et al., 2020).The closest marine record to Colônia, core GL-1090 (24.92°S, 42.51°W, 2225 m water depth) (Figures 1b and 4) (Santos et al., 2017) shows several oscillations of SSTs between 185 and 156 ka, from 24 to 27°C, with the lowest SSTs observed at 176, 172 and 160 ka.The lowest SST was observed between 156 and 153 ka and was followed by a progressive warming trend that reached 30°C at the beginning of the interglacial (Figure 4).After 140 ka, the beginning of the progressive warming trend observed in the South Atlantic is attributed to the increased influence of subtropical waters driven by the Agulhas leakage (Martínez-Méndez et al., 2010).
At Colônia, based on Podocarpus frequency (%) and concentration (Cn) (Fig. S3), we observed an out-of-phase relationship between austral summer (i.e.December-January-February) insolation and Podocarpus (Figure 4) with the near disappearance of Podocarpus during the austral summer insolation maximum phases observed at 180, 162 and 139 ka.As the expansion of Podocarpus requires humid conditions, we infer that low austral summer insolation is associated with high moisture rates at the latitude of Colônia during the penultimate glacial.Superimposed on this orbital trend, millennial-scale oscillations of Podocarpus lasting between 200 and 1000 years were observed between 180 and 170 ka and from 160 to ~143 ka (Figure 3 and S3).
The millennial-scale sawtooth pattern observed at Colônia looks similar to the instabilities observed in marine records, e.g.sedimentary molybdenum (Mo) at Cariaco (Gibson & Peterson, 2014), and ice records, e.g.methane and deuterium excess at Epica Dome C (EDC) (Loulergue et al., 2008) (Figure 4).Indeed, ice core methane events are usually linked to an increase in tropical wetlands associated with monsoon processes (Bock et al. 2017) while Antarctic ice deuterium and high moisture rates in the Tropics are interlinked in a feedback process (Vimeux et al., 2001).Between 180 and 160 ka high monsoon variability related to unstable conditions of the ITCZ during a low austral summer insolation phase was observed in the northern Tropics (Gibson & Peterson, 2014) and farther south in the high Peruvian Andes (Burns et al., 2019) (Figures 1a  and 4).Thus, during early MIS 6, changes in moisture at Colônia followed the variability observed at both high (EDC; Jouzel et al., 2007) and low latitudes (Huagapo Cave; Burns et al., 2019), suggesting that the millennial-scale oscillations could be related to successive changes in the intensity and amplitude of the monsoon system and in the sea ice dynamics suggesting ice-volume forcing on the low-latitude hydrological cycle and on the floristic composition of the vegetation.Thus, we infer that penultimate glacial moisture oscillations at Colônia were controlled by the interplay between the position of the South Tropical Front (STF) (Pahnke & Zahn, 2005) and the ITCZ shifts which regulated the amplitude and intensity of the SASM.The conifer expansion suggests that the monsoon was not the dominant rainfall system, probably being restricted to a narrow band near the Equator and rarely reaching the latitude of Colônia.Dominant precipitations were brought by the northward shift of the STF enhancing winter rainfall at the latitude of Colônia (Grimm et al., 2000).Consequently, when the STF was shifted northward or southward from Colônia, drier conditions prevailed and induced a regression of the conifers as observed between ~167 and 160 ka.During this interval, the onset of drier conditions in the northern tropics (Tisserand et al., 2009) was linked to a southward shift of the ITCZ (Mulitza et al., 2008), in agreement with the more humid conditions observed at Huagapo (Burns et al., 2019) (Figure 4).However, the drier conditions observed at Colônia were not observed at EDC or at Huagapo, where the oscillations continued from the previous interval, suggesting that (i) the SASM system was positioned at the latitude of Huagapo but was unable to reach the latitude of Colônia due to a weaker amplitude and intensity than today, and (ii) changes in sea ice forcing and the position of the subtropical front prevented winter rains at Colônia.
The two other drier intervals at Colônia (low concentration of Podocarpus) are observed at 153-152 and 140-137 ka.The first low-Podocarpus event was associated with the lowest SST, the penultimate glacial maximum, observed in both the southwestern Atlantic (Santos et al., 2017) and the southwestern Pacific (Pahnke & Zahn, 2005) suggesting sea ice expansion.At Huagapo, this interval (158-152 ka) is characterized by weaker monsoon activity, in agreement with the Cariaco northward position of the ITCZ (Gibson & Peterson, 2014) while the northward shift of the STF observed in the southwestern Pacific (Pahnke et al., 2003) probably constrained precipitation further north of the latitude of Colônia.The second drier event at 140-137 ka occurred during a low sea level episode (Cawthra et al., 2018), a southwestern Pacific SST decrease and a northward shift of the STF (Pahnke & Zahn, 2005) while no change was observed in the SASM near the Equator (Burns et al., 2019) (Figure 4).TII started at ~145 ka at Colônia and was characterized by an increase in MAAT and in AP taxa, a decrease in cool conifer taxa and low erosive activity (low silica intensity) in the basin (Figure 2 and Table 1).The last Podocarpus and Araucaria expansion of the penultimate glacial, around 137-133 ka, coincides with a low austral summer insolation phase while the STF progressively shifted southward (Pahnke et al., 2003).This southward latitudinal shift in winter precipitation belts was observed at 42°S (New Zealand; Ryan et al., 2012) (Figure 1a) with TII starting at 140 ka, and characterized by a shift from an open environment to the expansion of the conifer Podocarpus during the continuous discharge of Antarctic ice between 140 and 131 ka (Masson-Delmotte et al., 2010).Climate reconstruction showed that meltwater release in the Southern Ocean induced a 2°C cooling at the latitude of Colônia (Swingedouw et al., 2009).Consequently, we infer that the joint effect of a strengthening monsoon and low temperature favored a short expansion of conifers during TII.The southern conifers declined after 133 ka, during the 135-130 ka Heinrich Stade 11, a cold episode induced by meltwater in the North Atlantic (Marino et al., 2015) with strong SASM response (Stríkis et al., 2018) and a progressive increase in temperature (Table 1).
The penultimate glacial high moisture rates observed at Colônia at an orbital scale resulted from a northward shift of the winter precipitation belt linked to Antarctic ice volume and the northward shift of the STF (Pahnke & Zahn, 2005) while millennial-scale shifts of the ITCZ controlled SASM intensity and amplitude across South America (Burns et al., 2019).The progressive disappearance of Araucaria, the development of a dry season, and the progressive dominance of the SASM system in the climate system that characterized the last glacial (MIS 2-4) (Rodríguez-Zorro et al., 2020) differed significantly from MIS 6. Due to the northernmost position of the ITCZ during MIS 6 (Reimi et al., 2019), the amplitude of the southern monsoon boundary never reached the latitude of Colônia and a dominant extratropical circulation is inferred to explain the floristic composition of the forest and its related hydrological cycle.Superimposed on this general feature, the Colônia record shows that climate change at the millennial scale has been a dominant feature of the tropical climate since at least the penultimate glacial.Indeed, a system that integrates sea ice expansion/regression in the Northern Hemisphere, latitudinal migration of the ITCZ and ice expansion in the Southern Hemisphere influenced the strength and amplitude of the monsoon system (Stríkis et al., 2018) and of the winter rainfall belt between the tropics and the sub-tropics (Ledru et al., 1994) relating to latitudinal shifts in rainforest boundaries that strongly influenced tropical forest biodiversity during the Quaternary.

Conclusion
The high-resolution pollen analyses of core CO14 collected from the Colônia basin have revealed an open landscape with cold forest taxa during the penultimate glacial and confirmed that fire is a long-term integral part of the ecology of cold tropical grasslands.The successive changes observed in the conifer Podocarpus were related to the reorganization of air masses between the Pole and the Equator in both hemispheres with changes in the boundary conditions of the SASM system through glacial-interglacial cycles.The penultimate glacial at the latitude of Colônia is characterized by a relatively high total AP frequency, with no change during the transition from glacial to interglacial, an orbitally driven variability with conifer expansion  (Laskar et al., 2004), δ 18 O of the speleothem of Huagapo (Burns et al., 2019) that characterizes SASM activity near the Equator, planktic δ 18 O for SST (°C) of the Northern Atlantic Ocean (Hodell et al., 2023), Globigerinoides ruber SST Mg/Ca (°C) at the latitude of Colônia core GL-1090 (Santos et al., 2017), Globigerina bulloides SST Mg/Ca (°C) of the southwestern Pacific core (Pahnke & Zahn, 2005) that characterizes the volume of ice in the Southern Hemisphere and the shift in the STF, and deuterium (a temperature proxy) of the ice at EDC (Jouzel et al., 2007).The vertical dashed lines show the changes in vegetation discussed in the text.[Color figure can be viewed at wileyonlinelibrary.com] during low summer insolation phases and considerable variability at millennial timescales.Between around 170 and 160 ka, an interval that lasted ~10 ka showed no connection with other paleoclimatic records, thereby revealing specific climate behavior in the region of Colônia.During the penultimate glacial period, the climate at Colônia was characterized by a weaker influence of the monsoon and a lower MAAT than during the last glacial period.This pattern resulted from several forcings linked mainly to the positions of the STF and of the ITCZ.The combination of these factors strongly influenced Brazilian Atlantic forest biodiversity allowing the expansion of a paramo-like grassland at lower elevations than today with sparse tree components, many being the same Andean taxa.The expansion of high-elevation grassland to lowlands probably helped connect cold Andean and eastern Brazilian forest/grassland formations and taxa during this glacial stage of the Pleistocene.

Figure 2 .
Figure 2. Summary pollen diagram showing arboreal pollen and frequencies of 14 selected taxa and microcharcoal concentration through time.The parts shaded in gray represent the 4× exaggeration curves.The dashed horizontal lines represent the pollen zone boundaries.[Color figure can be viewed at wileyonlinelibrary.com]

Figure 3 .
Figure 3. Paleoecological changes in section 871-1400 cm of core CO14 represented by: MAAT (°C), Si intensity and microcharcoal particles (from Rodríguez-Zorro et al., 2020); and the frequency of arboreal pollen of Araucaria, Podocarpus and Acaena/Polylepis pollen (this study).Orbital cycles represent changes in insolation at 23°S latitude(Laskar et al., 2004).The vertical dashed lines show the changes in vegetation discussed in the text.[Color figure can be viewed at wileyonlinelibrary.com]

Figure 4 .
Figure 4. Regional comparison of the expression of MIS 6 between arboreal pollen and Podocarpus frequencies of Colônia (this study), changes in summer (DJF) insolation et 23°S latitude(Laskar et al., 2004), δ 18 O of the speleothem of Huagapo(Burns et al., 2019) that characterizes SASM activity near the Equator, planktic δ 18 O for SST (°C) of the Northern Atlantic Ocean(Hodell et al., 2023), Globigerinoides ruber SST Mg/Ca (°C) at the latitude of Colônia core GL-1090(Santos et al., 2017), Globigerina bulloides SST Mg/Ca (°C) of the southwestern Pacific core(Pahnke & Zahn, 2005) that characterizes the volume of ice in the Southern Hemisphere and the shift in the STF, and deuterium (a temperature proxy) of the ice at EDC(Jouzel et al., 2007).The vertical dashed lines show the changes in vegetation discussed in the text.[Color figure can be viewed at wileyonlinelibrary.com]

Table 1 .
Summary of the geochemical and charcoal results obtained for the studied interval (see Figure 2 for pollen zones) of core CO14 extracted from Rodríguez-Zorro et al. (2020).