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New Holocene pollen records from the Brazilian Caatinga

Abstract

We present two pollen diagrams from the semi-arid Caatinga of the Catimbau National Park, in Pernambuco and from a Mauritia palm forest in the Caatinga/Cerrado ecotone of southern Piauí, NE Brazil, spanning the last 10,000 cal. yrs BP and the last 1,750 cal yrs BP, respectively. These two records contain a signature of the local vegetation and permit the correlation of the pollen signal with regional climatic changes. The Catimbau record shows Zizyphus sp., a typical Caatinga taxon, in all three pollen zones indicating regional Caatinga vegetation and the predominance of local arboreal taxa adapted to high humidity from 10,000 to ca. 6,000 cal. yrs BP with a gradual tendency towards drier conditions revealed by a deposition hiatus between 6,000 to ca. 2,000 cal. yrs BP. This abrupt loss of sediments in both localities is interpreted as a consequence of the establishment of modern semi-arid climates. The subsequent return of humidity is signaled by increased sedimentation rates and 14C date inversions in agreement with high precipitation, revealed by σ18O ratios in speleothems from NE Brazil. Modern sediments deposited in the last 500 years reflect local conditions with the maintenance of humidity by geological faulting and surfacing water tables.

Key words
paleoclimatology; palynology; Pernambuco; Piauí; caatinga vegetation

INTRODUCTION

The Brazilian Caatinga appeared for the first time in the international scientific literature with the seminal study Flora Brasiliensis by Karl Friedrich von Martius in 1817, followed by various contributions on the physical and floristic characteristics of this semi-arid tropical ecosystem (Andrade-Lima 1953ANDRADE-LIMA D. 1953. Notas sobre a dispersão de algumas espécies vegetais no Brasil. In: Anais Soc Biol Pernambuco, p. 25-49., 1977ANDRADE-LIMA D. 1977. Preservation of the flora of Northeastern Brazil. In: Prance GT and Elias TS (Eds), Extinction is forever. New York: The New York Botanic Garden., Rizzini 1963RIZZINI CT. 1963. Nota prévia sobre a divisão fitogeográfica do Brasil. Rev Bras Geog 25(1): 3-64., Rizzini and Mattos Filho 1992RIZZINI CT and MATTOS FILHO A. 1992. Contribuição ao conhecimento das floras do Nordeste de Minas Gerais e da Bahia Mediterrânea. Série Estudos e Contribuições, Rio de Janeiro: Jardim Botânico - IBAMA., Barbosa et al. 2006BARBOSA MRV, SOTHERS C, GAMARRA-ROJAS CFL and MESQUITA AC. 2006. Checklist das plantas do nordeste brasileiro: Angiospermas e Gymnospermas. Brasília: Ministério de Ciência e Tecnologia, 156 p.). Until recently, the Late Quaternary history of this vegetation had not been available due to a lack of palynological studies, which require organic-rich and unoxidized sediments. These were later found in the Icatu River Valley, in the mid-São Francisco River, state of Bahia, by De Oliveira et al. (1999)DE OLIVEIRA PE, BARRETO AMF and SUGUIO K. 1999. Late Pleistocene/Holocene climatic and vegetational history of the Brazilian Caatinga: the fossil dunes of the middle São Francisco River. Palaeogeogr Palaeoclimatol Palaeoecol 152: 319-337. and revealing continuous sedimentation in the last 11,000 years. The authors observed the predominance of rainforest taxa during the Pleistocene/Holocene transition, indicating a humid phase in the Early Holocene, with a gradual loss of humidity. According to the Icatu pollen record, it became clear that rainforest as well as palm forest (buritizal) decreased gradually in abundance in that valley until the mid-Holocene and was followed by the establishment of semi-arid climate at ca. 4,200 yrs BP.

Among other studies that contribute to the understanding of Holocene climates within the Caatinga is that of Behling et al. (2000)BEHLING H, ARZ HW, PÄTZOLD J and WEFER G. 2000. Late Quaternary vegetational and climate dynamics in northeastern Brazil, inferences from marine core GeoB 3104-1. Quat Sci Rev 19: 981-994., who analyzed the pollen signal in marine sediments deposited at the Jaguaribe River delta, in the continental platform, 90 km off the coast of Ceará. These authors show that the terrestrial signal started to decrease after 8,500 yrs BP, thus suggesting the establishment of semi-arid conditions. However, it is noteworthy the return of humid climates after ca. 3,200 yrs BP in high elevation regions of the semi-arid Caatinga domain of Ceará, Piauí and Paraíba (Pessenda et al. 2010PESSENDA LCR, GOUVEIA SEM, RIBEIRO AS, DE OLIVEIRA PE and ARAVENA R. 2010. Late Pleistocene and Holocene vegetation changes in northeastern Brazil determined from carbon isotopes and charcoal records in soils. Palaeogeogr Palaeoclimatol Palaeoecol 297: 597-608.) and in Serra do Maranguape, Ceará (Montade et al. 2014MONTADE V, LEDRU M-P, BURTE, J, MARTINS ESPR, VEROLA CF, COSTA IR and SILVA FHM. 2014. Stability of a Neotropical microrefugium during climatic instability. J Biogeogr. http://wileyonlinelibrary.com/journal/jbi. 1:12.). In fact, the modern vegetation pattern within the Caatinga is predominantly xerophytic in the lowlands in contrast to the conspicuous presence of tropical forests containing Amazonian and Atlantic taxa in elevations higher than 1,000 meters, known as “Brejos de altitude”, maintained by orographic rains which create unusual high rainfall patterns under lower temperatures within the semi-arid domain (Sales et al. 1998SALES MF, MAYO SJ and RODAL MJN. 1998. Plantas vasculares das florestas serranas de Pernambuco: Um checklist da flora ameaçada dos brejos de altitude, Pernambuco, Brasil, Recife: Universidade Federal Rural de Pernambuco.).

Other paleoclimatic analyses within the Caatinga region, derived from geochemical and geological data, support unstable climates during the Holocene, with a wetter early phase, followed by dryer conditions at ca. 4,000 yrs BP, intercalated with a strongly rainy period ca. 2,000 yrs BP (Cruz et al. 2009CRUZ FW, VUILLE M, BURNS SJ, WANG X and CHENG H. 2009. Orbitally driven east–west antiphasing of South American precipitation. Nat Geosci 2(3): 210-214., Novello et al. 2012NOVELLO VF et al. 2012. Multidecadal climate variability in Brazil’s Nordeste during the last 3000 years based on speleothem isotope records. Geophys Res Letters 39: 148-158., Nace et al. 2014NACE TE, BAKER PA, DWYER GS, SILVA CG, RIGSBY CA, BURNS SJ, GIOSAN L, OTTO-BLESNER B, LIU Z and ZHU J. 2014. The role of North Brazil Current transport in the paleoclimate of the Brazilian Nordeste margin and paleoceanography of the western tropical Atlantic during the late Quaternary. Palaeogeogr Palaeoclimatol Palaeoecol 415: 3-13., Mendes 2016MENDES VR. 2016. Registro sedimentar quaternário na Bacia do Rio Parnaíba, Piauí: um estudo multi-indicadores voltado à investigação de mudanças climáticas. IGc/USP, 100 p.).

Despite the recent advances in our knowledge of the vegetation and climatic dynamics, the Caatinga ecosystem remains the least known in the literature in terms of its vegetational and climate evolution. In this present contribution, we provide two new Holocene pollen records from the semi-arid region of central Pernambuco and southern Piauí, both located in an area with the lowest precipitation levels in this ecosystem, known in Brazil as Sertão or Polígono da Seca (Drought Polygon), in order to contribute to the understanding of the vegetational, climate and ecological processes during the Holocene.

STUDY SITES

Pollen analyses were conducted in two localities in the Caatinga domain: Vale do Catimbau, Pernambuco and Bom Jesus, Piaui, shown on Figure 1.

Figure 1
(a) Location map of Catimbau (1) and Bom Jesus (2) sites in relation to important paleoclimatic studies, showing the vegetational distribution of NE Brazil, drawn by Q GIS 2.18 Las Palmas software. Satellite images for both sites are in (b) and (c), respectively and reveal the position of the sampled sites in the environment. Ombrothermic diagrams show mean monthly values of temperature and precipitation and annual precipitation (Pann) and temperature (Tann), for both sites (d) and (e) respectively, calculated for the last 45 years (data from the National Institute of Meteorology, available at: www.inmet.gov. br/portal). Paleocological studies discussed in the present work are: 3 – Parnaíba River (Mendes 2016); 4 – PARNA (Pessenda et al. 2010); 5 – Serra do Maranguape (Montade et al. 2014); 6 – FLONA (Pessenda et al. 2010); 7 – Rio Grande do Norte (Cruz et al. 2009); 8 – REBIO (Pessenda et al. 2010); 9 – Icatu River (De Oliveira et al. 1999); 10 – Diva de Maura and Torrinha Caves (Novello et al. 2012); 11 – GeoB 3104-1 (Behling et al. 2000).

In the first, sediments were collected from a peatbog 0.5 km long x 0.12 km wide in the Vale do Catimbau National Park, Arcoverde municipality, Pernambuco (8º29’26”S; 37º11’20”W), at 740 m elevation. The climate is semi-arid, with a well-defined wet season between February and August, mean annual precipitation of 700 mm, and mean annual temperature of 22.9 ºC. The geological setting of the Vale do Catimbau region is controlled by the Jatobá Basin, of Silurian-Devonian age (CPRM 1964CPRM. 1964. BRASIL – Estudo hidrogeológico do Brejo de São José – Arcoverde. Pernambuco. Recife, 22 p. Brasil, SUDENE, Hidrogeologia, 2.), containing the Tacaratu Formation, composed of sandstones and conglomerates. The sedimentary rocks establish an important deep aquifer in a large section of northeastern Brazil. Geological faults in the Catimbau region (Gomes 1995GOMES HA. 1995. Geologia e Recursos Minerais do Estado de Pernambuco. Brasília: CPRM/DIEDIG.), especially the São José Mountain range are responsible for surfacing waters conducive to peatbog formation (Nascimento 2008NASCIMENTO LRDS. 2008. Dinâmica vegetacional e climática holocênica da Caatinga, na região do Parque Nacional do Catimbau, Buíque - PE. Universidade Federal de Pernambuco.). The modern vegetation cover in Vale do Catimbau includes typical Caatinga genera such as the arboreal and herbaceous Astronium, Cassia, Ceiba, Cereus, Croton, Jatropha, Manihot and Tabebuia. Nearby islands of Cerrado contain the Krameria, Hymenaea, Senna, Guapira and Tocoyena and in some humid areas, rainforest elements such as Mauritia, Sauvagesia and Justicia are common. In some areas Orbignya (Attalea) palms (babaçu) is predominant (Sales et al. 1998SALES MF, MAYO SJ and RODAL MJN. 1998. Plantas vasculares das florestas serranas de Pernambuco: Um checklist da flora ameaçada dos brejos de altitude, Pernambuco, Brasil, Recife: Universidade Federal Rural de Pernambuco.), especially around the peatbog sampled for the present pollen study.

The second site, at Bom Jesus, Piaui, is located at a Caatinga/Cerrado ecotone, thus reflecting a floristic mosaic composed of species belonging to those ecosystems. Organic-rich sediments, forming a superficial peatbog underlain by mineral sediments, were collected in a location named Veredas, (9º13’40.59”S and 44º28’0.92”W), part of an extensive Mauritia flexuosa palm forest. The sampling location is located within an ephemeral drainage system under a semi-arid climate with a wet season from October to April, mean annual precipitation of 1,100 mm and mean annual temperature of 26.5ºC, at 270 m elevation (EMBRAPA 2016EMBRAPA. 2016. Empresa Brasileira de Pesquisa Agropecuária: https://www.cnpm.embrapa.br/projetos/bdclima/balanco/index/index_pe.html. Accessed in 01.11.2016.
https://www.cnpm.embrapa.br/projetos/bdc...
). The Bom Jesus Mauritia flexuosa palm forests (buritizais) are located in humid areas where the surfacing water table creates waterlogged soils colonized by Amazonian and/or Atlantic arboreal taxa such as Mauritiella aculeata, Acacia, Anadenanthera, Commiphora, Dalbergia, Piptadenia, Poeppigia, Copernicia, Geoffroea, Licania as well as Costus herbs (Andrade-Lima 1981ANDRADE-LIMA D. 1981. The Caatingas dominium. Rev Brasil Bot 4: 149-163.).

MATERIALS AND METHODS

At the Vale do Catimbau peatbog, a peat sediment column of 161,5 cm was retrieved with a Russian sampler (Belokopytov and Beresnevich 1955BELOKOPYTOV IE and BERESNEVICH VV. 1955. Giktorf’s peat borers. Torfânaâ promyslennost’ 8: 9-10.) in the northern portion of that basin in order to avoid sampling of disturbed sediments previously collected at the center of the bog by Nascimento (2008)NASCIMENTO LRDS. 2008. Dinâmica vegetacional e climática holocênica da Caatinga, na região do Parque Nacional do Catimbau, Buíque - PE. Universidade Federal de Pernambuco.. At the Bom Jesus site, a 155 cm sediment sequence was obtained with a vibrocore sampler (Martin et al. 1995MARTIN L, FLEXOR JM and SUGUIO K. 1995. Vibro-testemunhador leve: construção, utilização e potencialidades. Revista do Instituto Geológico 16(1/2): 59-66.) in a palm swamp characterized by clayey/organic sediments.

After the opening of the tubes under laboratory conditions, sediments were described and subsampled. A total of 32 samples of one cm3 were collected along the Catimbau core in various depth intervals (10 cm, 5 cm and 2.5 cm), while in the Bom Jesus sequence, were collected a total of 12 samples, within 10 cm depth intervals. All of them were chemically processed according to the Quaternary Palynology protocol described in Colinvaux et al. (1999)COLINVAUX P, DE OLIVEIRA PE and PATIÑO JEM. 1999. Amazon Pollen manual and atlas, Amsterdam: Harwood Academic Publishers.: addition of Lycopodium clavatum (exotic marker) spores, followed by HF (hydrofluoric acid) treatment for silicates removal and acetolysis reaction for the destruction of organic matter in the samples as well as within the pollen. Residues were mounted on glycerine and pollen/spores and other palynomorphs were counted under light microscopy. Counts proceeded until a minimum of about 300 pollen grains or 100 to 200 grains for samples with low palynomorph preservation. Pollen sums were calculated based on all pollen taxa present and belonging to the different categories such as arboreal, shrub, terrestrial and aquatic herbaceous pollen grains. Percentage and concentration values of all taxa were calculated by TILIA, TILIAGRAPH software (Grimm and Troostheide 1994GRIMM EC and TROOSTHEIDE CD. 1994. Tilia 2.00, program for plotting palynological diagrams, Springfield: Illinois State Museum.), and pollen zones were established by means of a similarity dendrogram by CONISS (Grimm 1987GRIMM EC. 1987. CONISS: a Fortran 77 program for stratigraphically constrained cluster analysis by the method of the incremental sum of squares. Comput Geosci 13: 13-35.). Accelerated Mass Spectrometry (AMS) radiocarbon dating of selected samples was carried out by Beta Analytics Laboratory, Miami, Florida. All the calibrations were done with the software CALIB 7.1 (Stuiver et al. 2017STUIVER M, REIMER PJ and REIMER RW. 2017. CALIB 7.1 [www program] at http://calib.org, accessed 2016-9-14.
http://calib.org,...
), using the calibration curve ShCal13 (Hogg et al. 2013HOGG AG et al. 2013. SHCal13 Southern Hemisphere calibration, 0–50,000 years cal BP. Radiocarbon 55(2): 1-15.) and the age-depth models curves were done by Oxcal 4.3 (Ramsey 2008RAMSEY CB. 2008. Deposition models for chronological records. Quat Sci Rev 27(1-2): 42-60.).

RESULTS

Lithology, radiocarbon dating and sedimentation rates are presented for both sites, followed by separate palynological results.

Peatbog sediments from Catimbau are composed of very dark sandy organic sediments with fine sand laminations at 122.5 cm and from 135 and 140 cm, while the Bom Jesus sequence showed the intercalation of clays and sands (Table I). Radiocarbon ages for the Catimbau sequence vary from 10,322 cal yrs BP to 152 cal yrs BP with dating inversion at around 1,800 cal yrs BP. The Bom Jesus sequence reached 1,749 cal yrs BP at the bottom depth of 100 cm depth, with inversions at ca. 1,700 cal yrs BP, at 154 cm depth (Table II).

TABLE I
Lithology of the Vale do Catimbau peat and Bom Jesus sequence.
TABLE II
Radiocarbon ages for the Catimbau and Bom Jesus samples. Calibrations were calculated by software CALIB 7.1 (Stuiver et al. 2017), ranges of 95,4% (2?). Final calibrated ages were obtained from the median probability provided of the end calibration.

The litology and radiocarbon dating results indicate very slow sedimentation rates varying from 0.009 to 0.233 cm year-1, at Catimbau, as shown on Figure 2, although a significant deposition of 30 cm occurred between the inverted dates of 1,880 and 1,830 cal. yrs BP. The rapid deposition at ca. 1,800 cal. yrs BP at the Catimbau site is probably associated with a humid episode, with torrential rains that could have altered the horizontally layering of the sediments. A hiatus in sedimentation is clear between 6,440 and 1,778 cal. yrs BP in the Catimbau peat core, which appears to bear a correlation to the Mid-Holocene drying climates observed for the Caatinga ecosystem at ca. 4,500 cal. yrs BP. An age model based on previous analyses at the Catimbau site by Nascimento (2008)NASCIMENTO LRDS. 2008. Dinâmica vegetacional e climática holocênica da Caatinga, na região do Parque Nacional do Catimbau, Buíque - PE. Universidade Federal de Pernambuco.) shows similar results, i.e. low sedimentation rates at ca. 2,000 yrs BP followed by oscillating values. It is very likely that due to poor radiocarbon control the author was not able to detect the hiatus. On the other hand, deposition at the Bom Jesus site, also presented on Figure 2, reveals age inversions thus not allowing a thorough interpretation of its pollen data.

Figure 2
Oxcal 4.3 (Ramsey 2008) calibrated age-depth models for the Vale do Catimbau and Bom Jesus peat sequences. The Catimbau data (this study) is given as a continuous line whereas the dotted line represents the age-depth models applied to Nascimento’s data (2008).

Palynological analyses- Vale do Catimbau

Figure 3 and 4 show percentage and concentration pollen diagrams for different palynomorph categories, respectively. Percentage and concentration values for each taxon, given between parentheses, refer to the evolution of its representation from bottom to top of each pollen zone. In the palynomorph diagrams, aquatic herbs, pteridophytic and algal spores provide a clear signature of waterlogged conditions for the entire Catimbau deposition. These, in turn, are determined by geological fault lines allowing the surfacing of the underground water table.

Figure 3
Percentage pollen diagram of the Vale do Catimbau peat sequence, of selected taxa and sum of categories. Dotted line in the lithology column marks a sedimentary hiatus.
Figure 4
Concentration pollen diagram of the Vale do Catimbau peat sequence of plant categories (x 1000). Dotted line at the lithology column marks a sedimentary hiatus.

CA-1 (160 – 111 cm; 10,330 cal. yrs BP – ca. 6,000 cal. yrs BP (extrapolated age) is characterized by fluctuating arboreal elements, both in percentage and concentration values, at the end of this zone. Maximum value of these components occurs at ca. 6,600 cal yrs BP. The most significant taxa, followed by their percent representation from bottom, middle to top of this zone, are represented by Arecaceae (5% - 4%), Byrsonima (4.6%- 5.4% to 0%), Casearia (1.5% - 4.5% to 1.2%), Cecropia (1% - 6% to 1.2%), Melastomataceae (1.5% - 15% to 1.2%), Myrtaceae (0.7%- 2.5% to 2%), Piptadenia (0.5% - 1.7% to 0%) and others. Orbignya (Attalea) palm pollen appeared in the record at an extrapolated age of ca. 9,000 cal. yrs BP represented by less than 6% of the total pollen sum, whereas Ziziphus, a xerophytic Caatinga indicator, fluctuated in this zone with values under 2%. Concentration values, i.e. number of grains per cubic centimeter of sediment (g/cc), of each taxa, follows the same trend observed in the percentage profile. These values shows a clear preponderance of humid adapted taxa in the Early Holocene, gradually decreasing in representation towards the Mid Holocene: Arecaceae (15724 -1010 gr/cc), Myrtaceae (1,429 – 2,511 to 167), Cecropia (2,859 – 5,718 to 502), Melastomataceae (2,654 – 10,191 to 606), Moraceae (2,534 – 326 to 502), Ziziphus (619 to 167). Pollen grains belonging to Orbignya (Attalea) are represented by 9,911 g/cc and are possibly a consequence of human influence on the local landscape.

CA-2 (110 – 57 cm; 1,714 – 956 cal. yrs BP). The position of sample 110 cm within the contact between reworked and non-reworked layers, as suggested by radiocarbon age inversion, did not allow it to be included in the Ecozone CA-1. It is noteworthy that the CONISS dendrogram separates this sample depth from all previous samples due to reduced similarity between them. CA-2 is subdivided into two sections: a reworked zone from 110 cm to 80 cm interval with date inversion, and a non-disturbed sequence from 79 to 57 cm (1,778 cal. yrs BP to 956 cal. yrs BP). The latter is characterized by the presence of Copaifera (0.75% - 4%), together with Arecaceae (5% to 2%), Simarouba (10% to 9%), Celtis (4%) in synchrony with a steady increase in Cecropia (3% to 7%), Melastomataceae (3% to 4%) and Piptadenia (<1% to 7%) while Ziziphus continued its local representation until present conditions fluctuating within 1% of the pollen sum. Another change in this zone is marked by high Spathiphyllum concentration values, a terrestrial herb found presently at the site in very moist rocky habitats next to the peatbog. In contrast to Spathiphyllum, other herbaceous groups such as Poaceae (Gramineae) and Asteraceae (Compositae) are found in smaller percentage and concentration values. Orbignya (Attalea) palm returns to the Catimbau record at 1,778 cal. yrs BP (80 cm).

Concentration values within this zone, from its beginning to its end, of arboreal taxa is mostly represented by non-Orbignya Arecaceae pollen (1,300 – 6,094), Melastomataceae (741 – 13,421), Cecropia (743 – 22,713), Ziziphus (663 – 1032), Orbignya (743 – 1327). Myrtaceae, which was already in decline in the previous zone, was found in only one sample with 261 g/cc. The herbaceous component is well-represented by Asteraceae (2,590 – 11,356) and Poaceae (7,433 – 29,940) whereas aquatic associations are defined mainly by Borreria (371 – 1,032), Cyperaceae (743 – 2,617) and ferns by Cyathea (1,486 – 3,097) and trilete spores (1,672 – 6,694).

CA-3 (56 – 0 cm; 956 cal. yrs BP – Present). The pollen content of zone CA-3 is represented by Arecaceae, fluctuating between 0.7% to 3%, Casearia (2.4% to 0.7% and 0.5%), Celtis (2% - 13.4% to 0.3%), Melastomataceae (12% to 9%), Orbignya (Attalea) in steady levels around 2.5 % and Piptadenia (2% - 0.2%). Successional elements are represented by Cecropia (5% to 29% and 16%) and Piper (2% - 4.4% to 16%). The presence of nearby Caatinga vegetation is given by Ziziphus, which continued to appear in steady low percentages (around 0.3%) as it did in the previous zone. Concentration values for selected arboreal taxa are given as follows: Arecaceae (1,250 – 10,221), Cecropia (4,385 – 51,106), Myrtaceae (1,000 – 350), Melastomataceae (10,215 – 28,805), Orbignya (2.088 – 9,911). Herbs are represented by Asteraceae (4,176 – 10,619 to 5,575), Poaceae (13,990 – 9,724 to 31,592) and aquatic plants by Cyperaceae (5,220 – 16,106 to 6,504) and ferns by Cyathea (30,486 – 1,351).

Palynological analyses - Bom Jesus

The percentage diagram of the botanical elements of the Bom Jesus (PI) Mauritia palm swamp is presented in two intervals, containing age inversions in its lower section (155-100 cm) and modern, undisturbed deposition ranging from 40 cm to 0 cm (Figure 5). Due to the low resolution of this record, coupled with the fact that it represents a reworked sedimentary record, CONISS zonation was not determined. Pollen percentage and concentration values given below for each taxon represent their overall distribution range within each sedimentary interval as follows:

Figure 5
Percentage pollen diagram of the Bom Jesus sediment sequence.

Interval 155 -100 cm (1,250 – 1,750 yrs cal BP) is represented by the predominance of Mauritia (70% - 80%) and its associated taxon Mauritiella (24% - 36%), followed by other arboreal elements typically found in humid soils such as Crecropia (15% - 22%) and Melastomataceae (14 % - 20%). Herbaceous layer indicators are Poaceae (17% - 50%), Asteraceae (6% - 15%), Hyptis (14% -18%). Aquatic herbs belong to Borreria (10% - 25%) and Cyperaceae (11% - 32%), whereas fern representatives are Cyathea (50% -80%), Pleopeltis (7% - 12%) and Anetium (3% - 4%).

The undisturbed interval containing the upper 40 cm of deposition (520 yrs cal. BP) is characterized by Mauritia (60% - 80%), Mauritiella (20% - 40%), other Arecaceae (2% - 24%), Astronium (3% - 18%), Cecropia (20% - 27%), Lythraceae (7% -15%), Melastomataceae (8% - 21%), Meliaceae (6% - 12%), Mimosaceae (2% - 12%), Myrtaceae (9% - 20%) and Sapotaceae (3% - 8%). Among the herbs, the pollen spectra contain Asteraceae (11% -17%), Hyptis (8% - 18%) and Poaceae (20% - 30%). The aquatic herb component is given primarily by Borreria (10% - 15%) and Cyperaceae (15% - 20%) and ferns by Cyathea (65% - 77%), Pleopeltis (4% - 18%) and Anetium (4% - 12%).

DISCUSSION

The Catimbau vegetation during the Holocene can be thought of as a local oasis-like ecosystem within a semi-arid domain maintained by tectonics. Underlain Silurian-Devonian sedimentary rocks function as a source of ground water in a deep aquifer (CPRM 1964CPRM. 1964. BRASIL – Estudo hidrogeológico do Brejo de São José – Arcoverde. Pernambuco. Recife, 22 p. Brasil, SUDENE, Hidrogeologia, 2.) which surfaced possibly due to Mesozoic/Cenozoic geological faulting (Gomes 1995GOMES HA. 1995. Geologia e Recursos Minerais do Estado de Pernambuco. Brasília: CPRM/DIEDIG., Nascimento 2008NASCIMENTO LRDS. 2008. Dinâmica vegetacional e climática holocênica da Caatinga, na região do Parque Nacional do Catimbau, Buíque - PE. Universidade Federal de Pernambuco.). This geological feature might explain the overall abundance and a prolific representation of Spathiphyllum along the Catimbau record. This herbaceous taxon, restricted to humid rocks and soils (Croat 1988CROAT TB. 1988. Ecology and Life Forms of Araceae. Aroideana 11: 4-55.) within semi-arid regions, remained stable in the Catimbau site despite regional climatic fluctuations during the Holocene.

The occurrence of Cecropia in this period is significant. This arboreal taxon, known for its invasive habits and predominance in secondary vegetation, cannot survive in semi-arid climates and can therefore be used as an indicator of successional events under humid climates or in moist soils maintained by edaphic factors (Lorenzi 1998LORENZI H. 1998. Árvores brasileiras: manual de identificação e cultivo de plantas arbóreas nativas do Brasil. 2ª ed., Nova Odessa, SP: Editora Plantarum, 352 p.). Humid signals in both sites are given also by the presence of Borreria and Cyperaceae, in association with pteridophytic and algal spores. Borreria, although commonly found in terrestrial settings, has macrophytic species adapted to soils under prolonged flooding such as B. eryngioides, B. quadrifaria (Pott and Pott 1994POTT A and POTT VJ. 1994. Plantas do Pantanal. Empresa Brasileira de Pesquisa Agropecuária, Centro de Pesquisa Agropecuária do Pantanal. Corumbá, MS: EMBRAPA – SPI, 320 p.), B. saponariifolia and B. capitata (Lorenzi 2000LORENZI H. 2000. Plantas daninhas do Brasil: terrestres, aquáticas, parasitas e tóxicas. 3ª ed., Nova Odessa, SP: Instituto Plantarum, 608 p.). Likewise, Cyperaceae is a large family comprising ca 4,500 species found mainly in waterlogged conditions (Souza and Lorenzi 2005SOUZA VC and LORENZI H. 2005. Botânica Sistemática: guia ilustrado para identificação das famílias de Angiospermas da flora brasileira, baseado em APG II. Nova Odessa, SP: Instituto Plantarum, 640 p.).

Unlike the Late Pleistocene/Holocene and Early Holocene humid phase displayed by the Icatu record in the Bahian semi-arid Caatinga (De Oliveira et al. 1999DE OLIVEIRA PE, BARRETO AMF and SUGUIO K. 1999. Late Pleistocene/Holocene climatic and vegetational history of the Brazilian Caatinga: the fossil dunes of the middle São Francisco River. Palaeogeogr Palaeoclimatol Palaeoecol 152: 319-337.), the pollen signal at Catimbau is of very local and not of regional amplitude. This restricted signal is controlled by a peatbog surrounded by a rocky amphitheater, where its abundant pollen signature, maintained by local trees and herbs, masks regional anemophilous sources. However, it is noteworthy the presence of Ziziphus, very likely to be Z. joazeiro, a well-known evergreen tree species of the xerophyhtic Caatinga of the Sertão region in NE Brazil, thus suggesting nearby semi-arid vegetation around this humid site, throughout the Holocene.

The tendency towards drying of the landscape after the Mid-Holocene shown regionally by the Icatu pollen record (De Oliveira et al. 1999DE OLIVEIRA PE, BARRETO AMF and SUGUIO K. 1999. Late Pleistocene/Holocene climatic and vegetational history of the Brazilian Caatinga: the fossil dunes of the middle São Francisco River. Palaeogeogr Palaeoclimatol Palaeoecol 152: 319-337.) and by δ18O ratios in cave speleothems for NE Brazil (Wang et al. 2004WANG X, AULER AS, EDWARDS RL, CHENG H, CRISTALLI PS, SMART PL, RICHARDS DA and SHEN C-C. 2004. Wet periods in northeastern Brazil over the past 210 kyr linked to distant climate anomalies. Nature 432(7018): 740-743., Cruz et al. 2009CRUZ FW, VUILLE M, BURNS SJ, WANG X and CHENG H. 2009. Orbitally driven east–west antiphasing of South American precipitation. Nat Geosci 2(3): 210-214., Nace et al. 2014NACE TE, BAKER PA, DWYER GS, SILVA CG, RIGSBY CA, BURNS SJ, GIOSAN L, OTTO-BLESNER B, LIU Z and ZHU J. 2014. The role of North Brazil Current transport in the paleoclimate of the Brazilian Nordeste margin and paleoceanography of the western tropical Atlantic during the late Quaternary. Palaeogeogr Palaeoclimatol Palaeoecol 415: 3-13., Mendes 2016MENDES VR. 2016. Registro sedimentar quaternário na Bacia do Rio Parnaíba, Piauí: um estudo multi-indicadores voltado à investigação de mudanças climáticas. IGc/USP, 100 p.), is possibly represented in the Catimbau record by the lack of sediment deposition after ca. 6,400 and prior to ca. 1,800 cal yrs BP. This was likely to be a consequence of lowering water tables under a regional and strong semi-arid climatic phase. However, it is possible that humid conditions, concomitantly with sediment deposition, persisted during the Mid-Holocene in the climatically closed system of Catimbau, shown by the presence of various moist-adapted taxa either side of the hiatus (ca. 6,400 yrs to 1714 cal. yrs BP). This sedimentation hiatus is possibly correlated to a phase of generalized drying of that portion of NE Brazil as suggested by the Syntrace Climatic Model (Nace et al. 2014NACE TE, BAKER PA, DWYER GS, SILVA CG, RIGSBY CA, BURNS SJ, GIOSAN L, OTTO-BLESNER B, LIU Z and ZHU J. 2014. The role of North Brazil Current transport in the paleoclimate of the Brazilian Nordeste margin and paleoceanography of the western tropical Atlantic during the late Quaternary. Palaeogeogr Palaeoclimatol Palaeoecol 415: 3-13.) and by the isotopic data from cave speleothems in State of Rio Grande do Norte (Cruz et al. 2009CRUZ FW, VUILLE M, BURNS SJ, WANG X and CHENG H. 2009. Orbitally driven east–west antiphasing of South American precipitation. Nat Geosci 2(3): 210-214.). In both studies, there is a clear tendency toward arid phases, reaching a peak at ca. 4,000 cal. yrs BP. Under this context the surfacing water table (Costa Filho and Demétrio 2005COSTA FILHO WD and DEMÉTRIO JGA. 2005. Comportamento das bacias sedimentares da região semi-árida do Nordeste brasileiro. Hidrogeologia da Bacia do Jatobá: Sistema Aquífero Tacaratu/Inajá. In: Costa Filho WD, Demétrio JGA, Feitosa ED and Filho JM (Eds), Recife: UFPE/CPRM/FINEP.) at the Catimbau site had been lowered.

This Mid-Holocene climatic phase is possibly correlated with the return of a moist phase in the Early Holocene as detected by Novello et al. (2012)NOVELLO VF et al. 2012. Multidecadal climate variability in Brazil’s Nordeste during the last 3000 years based on speleothem isotope records. Geophys Res Letters 39: 148-158., Nace et al. (2014)NACE TE, BAKER PA, DWYER GS, SILVA CG, RIGSBY CA, BURNS SJ, GIOSAN L, OTTO-BLESNER B, LIU Z and ZHU J. 2014. The role of North Brazil Current transport in the paleoclimate of the Brazilian Nordeste margin and paleoceanography of the western tropical Atlantic during the late Quaternary. Palaeogeogr Palaeoclimatol Palaeoecol 415: 3-13., Mendes (2016)MENDES VR. 2016. Registro sedimentar quaternário na Bacia do Rio Parnaíba, Piauí: um estudo multi-indicadores voltado à investigação de mudanças climáticas. IGc/USP, 100 p.. It is possible that the same climatic episode had occurred at Bom Jesus, which could explain the inverted ages as well as the high mineral content (sandy sediments) of its sequence, as well as loss of older deposits.

The increase of Spathiphyllum sp. and sedimentation rates between 2,000 and 1,500 cal yrs BP at Catimbau and Bom Jesus and the date inversions in both sites are suggestive of sediment transport and reworking under intense high energy precipitation. Such storm conditions have been reported for the same time period by Mendes (2016)MENDES VR. 2016. Registro sedimentar quaternário na Bacia do Rio Parnaíba, Piauí: um estudo multi-indicadores voltado à investigação de mudanças climáticas. IGc/USP, 100 p. and Viana et al. (2014)VIANA JCC, SIFEDDINE A, TURCQ B, ALBUQUERQUE ALS, MOREIRA LS, GOMES DF and CORDEIRO RC. 2014. A late Holocene paleoclimate reconstruction from Boqueirão Lake sediments, northeastern Brazil. Palaeogeogr Palaeoclimatol Palaeoecol 415: 117-126..

After ca. 500 cal yrs BP towards modern times the pollen signal at the Catimbau site is characterized by a gradual decrease in taxa adapted to high levels of humidity such as aquatic herbs and algae. A semi-arid climatic pattern is also present in the Icatu record where a decline in the arboreal component is in synchrony with an increase of charred particles indicating higher natural or anthropogenic fire frequencies. Both dry scenarios are in agreement with the climatic phases given by Novello (2012), derived from isotopic data in cave speleothems in southern Bahia. These climatic scenarios are well supported by concentration values in the Catimbau pollen signal. One example of this trend is given by Myrtaceae which declined from 1,000 to 350 g/cc, however other elements expected to behave the same way such as Cecropia, Melastomataceae, Arecaceae and Orbignya (Attalea), followed a contrary pathway, and instead increased in the local landscape. The first two taxa are well known elements found in disturbed vegetation (Prather 2014PRATHER C. 2014. Divergent responses of leaf herbivory to simulated hurricane effects in a rainforest understory. For Ecol Manag 332: 87-92., Shiels and González 2014SHIELS AB and GONZÁLEZ G. 2014. Understanding the key mechanisms of tropical forest responses to canopy loss and biomass deposition from experimental hurricane effects. Forest Ecol Manag 332: 1-10., Rodríguez-Zorro et al. 2015RODRÍGUEZ-ZORRO PA, ENTERS D, HERMANOWSKI B, COSTA ML and BEHLING H. 2015. Vegetation changes and human impact inferred from an oxbow lake in southwestern Amazonia, Brazil since the 19th century. J South Am Earth Sci 62: 186-194.), whereas the palm family, and particularly Orbignya (Attalea), are important taxa in cultural forests (Balée 2013BALÉE W. 2013. Cultural forests of the Amazon: A historical ecology of people and their landscapes. University of Alabama Press.).

The presence of Orbignya (Attalea) pollen in the Catimbau sediments was already attributed by Nascimento et al.(2009)NASCIMENTO LRDS, DE OLIVEIRA PE and BARRETO AMF. 2009. Evidências Palinológicas do Processo de Ocupação Humana na Região do Parque Nacional do Catimbau, Buíque, Pernambuco. Clio Série Arqueológica UFPE 24: 147-155. to human manipulation of the vegetation at around 5,000 yrs BP. Our study shows the occurrence of the Orbignya (Attalea) pollen type as early as 9,000 cal. yrs BP, decreasing during the Mid-Holocene drying event and returning afterwards. Such distribution therefore might suggest Early Holocene human manipulation at the Catimbau site.

CONCLUSIONS

The pollen analysis carried out at the Catimbau site is indicative of an anomalous island of humidity amidst a semi-arid environment created and maintained by geological features such as the Mesozoic/Cenozoic fault systems that permitted the surfacing of ground water. This in turn has allowed this area to function as a refuge for arboreal and herb elements typically found in moist forest ecosystems such as Cecropia, Cedrela, Simarouba, Piptadenia, Melastomataceae, Myrtaceae, Copaifera as well as the conspicuous modern Orbignya (Attalea) palm.

The low geographical amplitude of the pollen signal obtained in this site, contrary to the Icatu sequence which appears to be in synchrony with regional climatic scenarios of NE Brazil, is still useful in determining the presence of nearby Caatinga by the fluctuating presence of Ziziphus pollen in all three zones of the Catimbau record.

The Mid-Holocene drying climatic signal, widely recognized by the Icatu pollen record and by δ18O ratios in cave speleothems in NE Brazil, is likely to be represented by a long term sedimentation hiatus, lasting from 6,000 to 2,000 cal. yrs BP in the Catimbau.

The return of humid conditions both in the Catimbau and in the Bom Jesus site has left a signature in the sedimentation pattern of both locations, marked by higher sedimentation rates and radiocarbon ages inversions.

After ca. 500 cal yrs BP towards modern times the pollen signal at the Catimbau site demonstrates a gradual decrease in concentration values of taxa adapted to high levels of humidity such as aquatic herbs and algae. Spatiphyllum, for example, decreases from ca. 184,000 g/cc at 950 cal. yrs BP to ca. 78,000 g/cc in the modern surface of the deposit.

By and large, the Holocene records provided by these two new pollen diagrams, although representative of the local vegetation, do show the presence of Ziziphus, an important Caatinga indicator, that appeared to have tolerated a great deal of climatic change since the humid phases of the Early Holocene to the intensification of semi-arid climates since the Mid Holocene. However, such a pattern is very likely to be explained by its tolerance to wide precipitation ranges, varying from 315 mm to 1700 mm/year-1 (Gomes and Fernandes 1985GOMES MAF and FERNANDES AG. 1985. Cobertura vegetal do sertão dos Inhamuns-Ceará. In: Anais do XXXIII Congresso nacional de botânica, Maceió. Brasília: EMBRAPA - DDT, p.165-184.), which is not expected to be found in most elements of the Caatinga flora.

ACKNOWLEGMENTS

Funds for field work and 14C analyses were provided by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) through Edital MCT/CNPq/MEC/CAPES/FNDCT Ação Transversal/FAPs Nº 47/2010 Sistema Nacional de Pesquisa em Biodiversidade - SISBIOTA BRASIL to Dr. Marcelo A. Teixeira de Oliveira. The principal author thanks Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) for a doctoral scholarship Proc. 2015/01782-8.

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Publication Dates

  • Publication in this collection
    Aug 2018

History

  • Received
    9 Mar 2017
  • Accepted
    7 Oct 2017
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