Vegetation and climate dynamics in southern South America: The microfossil record of Laguna Potrok Aike, Santa Cruz, Argentina

doi:10.1016/j.revpalbo.2007.05.001

Review of Palaeobotany and Palynology

Volume 146, Issues 1–4, September 2007, Pages 234-246

https://doi.org/10.1016/j.revpalbo.2007.05.001 Get rights and content

Abstract

Pollen and diatom assemblages of the sediment record from Laguna Potrok Aike provide new data about the vegetation and climate history since 16,100 cal BP of the drylands in the Patagonian Steppe, some 80 km east of the Andes on the southernmost Argentinean mainland. In combination with formerly published geochemical sediment proxies it is shown that during the Late Glacial the steppe was cold, wind speeds were low and available moisture was high. Pollen, diatoms and geochemical parameters record increasing temperatures and decreasing moisture availability resulting in falling lake levels in the steppe culminating in the lowest lake levels around 7640 cal BP. Contemporaneously, Andean Forest established in the mountains and probably wind speeds increased. Between 6000 and 2300 cal BP the pollen record points to cyclic seasonality fluctuations in the steppe and the Andes. After 2300 cal BP the research area became increasingly humid and the Andean Forest underwent changes in floristic composition. Sheep breeders arrived in the 19th century, and in the 20th century conditions in the steppe area became drier.

Introduction

The level of knowledge on the Quaternary climate history of the northern and southern hemisphere is still uneven. In the northern hemisphere the information on climate history, climate dynamics and its mechanisms are based on a large number of records from different proxies. In the southern hemisphere research not enough data are available to develop a consistent picture of climate change. Climate reconstructions for southern South America are based on macro-and microfossil analyses of cores from marine and terrestrial sediments (e.g. Heusser, 1995, Markgraf et al., 2003, Huber and Markgraf, 2003, Bianchi and Gersonde, 2004, Mancini et al., 2005), dendrochronology (e.g. Villalba et al., 1998, Villalba et al., 2003) and glaciological data (e.g. Clapperton et al., 1995, Hulton et al., 2002). However, an accurate climate reconstruction is often hampered by insufficient time control and the scarcity of terrestrial research sites in the huge and complex area of southern South America. Most of the investigated sites on the southern South American mainland are located in the Andes. Adequate sites with high resolution are rare in the semi-arid eastern part of Patagonia (Latin American Pollen Data Base, site inventory). Recently, it was shown that palaeoenvironmental reconstructions from the Patagonian Steppe east of the Andes add valuable information to the understanding of Holocene climate change in this area (Mancini et al., 2005). In this paper we present a study of sediments obtained from the maar lake Laguna Potrok Aike (Fig. 1), located in the Patagonian Steppe area of the South Argentinean mainland covering the last 16,100 calibrated years before present (cal BP). The aim of this paper is to present a well dated reconstruction of vegetation and climate history for the southern South American mainland. We therefore integrate a new pollen and diatom record into the palaeoenvironmental reconstruction of previously discussed geochemical sediment parameters including Ca, Fe, Mn, N, Ti, total carbon and total inorganic carbon, water content and the sedimentation rate (Haberzettl et al., 2007) from Laguna Potrok Aike, Santa Cruz province, southern Argentina.

Section snippets

Geographical setting

The circular maar lake Laguna Potrok Aike (51°58′ S, 70°23′ W, Fig. 1) is located on the southernmost Argentinean mainland and has a maximum diameter of 3470 m (Zolitschka et al., 2006). The catchment area is about 200 km² and reaches south into the Chilean part of the Pali Aike Volcanic Field. Water runoff occurs episodically through a few canyons. During our field studies in the summer of 2002 the lake level was at 112 m a.s.l. and the maximum water depth was approximately 100 m. Our

Vegetation setting

The strong precipitation gradient determines the distribution of vegetation units in southern Patagonia. Five major vegetation zones are distinguishable for southern South America (Hueck and Seibert, 1981, Moore, 1983, Roig, 1998): Magellanic moorland and evergreen Magellanic rain forest west of the Andes and deciduous Nothofagus forest near the tree line in the Andes as well as at lower elevations east of the Andes where annual precipitation is in excess of 400 mm. Above the tree line Andean

Modern algae and Diatom assemblages in Laguna Potrok Aike

Since 1996 water samples were collected near the western shore to identify the algae and diatom flora of Laguna Potrok Aike in austral summers. The samples show that the algae ssemblages varied in the different years and several new diatom species and assemblages with often more or less unknown ecology have been found (Maidana, 1999, Maidana and Round, 1999). In 1996 and 1997 the dominant species were Navicula gregaria, Fragilaria capucina var. vaucheria, Cocconeis placentula var. lineata,

Methods

The sediment record presented here is a composite profile of three cores (PTA 02/4, PTA 03/12 and PTA 03/13) that were taken in 2002 and 2003 (for location see Fig. 1B). A composite profile of 1892 cm length was constructed from overlapping core sequences with the aid of marker horizons and by matching geochemical data (e.g. Ca contents). The age depth model is based on 16 AMS radiocarbon dates (Table 1) performed on different materials and the recalibrated ¹⁴C age of the Mt. Burney tephra (

Results

Based on visual inspection of the pollen record and supported by CONISS cluster analysis (Grimm, 1987, not shown) six pollen assemblage zones (PTA 1–6) were identified (Fig. 2, Fig. 3). In the following pollen and diatoms are presented in a percentage diagram to provide a better comparability with other microfossil records from southern South America. The profiles of pollen concentration of Andean Forest and Patagonian Steppe in Fig. 2 show almost parallel progression. Therefore, fluctuations

Vegetation and climate reconstruction inferred from the microfossil record of Laguna Protrok Aike

Throughout the pollen record Patagonian Steppe elements dominate. Between 16,100 and 13,890 cal BP the Patagonian Steppe was dominated by grasses. High contribution of Poaceae points to a high available moisture level in the steppe area. The higher occurrence of Acaena, Ericaceae, Empetrum and of the pioneer forest taxon Gunnera suggests that the vegetation cover in the steppe was relatively open, probably due to low temperatures. The rare occurrence of wind transported Andean Forest taxa and

Discussion

The pollen and diatom record from Laguna Potrok Aike provides additional information to the previously discussed geochemical proxy data (Haberzettl et al., 2007) concerning paleoclimate change during the late Quaternary in southern South America, and makes a more detailed interpretation of the sediment record possible. Sediment and microfossil data show that moisture availability was high in the lowermost part of the record covering the Late Glacial. The water level of Laguna Potrok Aike was

Conclusions

A microfossil record from the maar lake Laguna Potrok Aike is presented. The vegetation and climate history of the last 16,100 years were reconstructed under the integration of the geochemical proxies. Geochemical and microfossil data suggest that during the Late Glacial wind speeds were low and the climate was cold and humid. The lake level was high in Laguna Potrok Aike. At the transition to the Holocene conditions in the Patagonian Steppe became warmer, drier and wind speeds probably

Acknowledgements

We are grateful to S. Dietrich and A. Tenn for processing the pollen samples and preparing the pollen slides. The authors thank J. Meurers-Balke (Archaeobotany, University of Cologne) for the temporary use of her laboratory. G. Oliva, M. Masco and R. Cofalt (INTA, Río Gallegos) are thanked for discussions and the supply of plant reference material. Logistic support by C. Kennard, J. Moreteau is gratefully acknowledged. The reviewers M. V. Mancini and V. Markgraf are thanked for valuable

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Vegetation and climate dynamics in southern South America: The microfossil record of Laguna Potrok Aike, Santa Cruz, Argentina

Abstract

Introduction

Section snippets

Geographical setting

Vegetation setting

Modern algae and Diatom assemblages in Laguna Potrok Aike

Methods

Results

Vegetation and climate reconstruction inferred from the microfossil record of Laguna Protrok Aike

Discussion

Conclusions

Acknowledgements

Quaternary Science Reviews

Earth and Planetary Science Letters

Quaternary Research

Computers and Geosciences

Quaternary International

Palaeogeography, Palaeoclimatology, Palaeoecology

Quaternary Science Reviews

Quaternary Science Reviews

Quaternary International

Journal of Hydrology

Quaternary Science Reviews

Palaeogeography, Palaeoclimatology, Palaeoecology

Journal of South American Earth Sciences

Crisis and conservation at the end of the world: sheep ranching in Argentine Patagonia

Environmental Conservation

Diatom analysis

Ganaderia ovina sustentable en la Patagonia Austral- Tecnologia de Manejo Extensivo

INTA-UNPA-CAP, Río Gallegos

Klimatische Aspekte der Weidedegradation in Ost-Patagonien

Textbook of Pollen Analysis

Late-glacial and Holocene vegetation history of the Magellanic rain forest in southwestern Patagonia, Chile

Vegetation History and Archaeobotany

Cyclostephanos patagonicus sp. Nov., a new freshwater diatom from Western Patagonia (Argentina)

Diatom Research

Climatically induced lake level changes during the last two millennia as reflected in sediments of Laguna Potrok Aike, southern Patagonia (Santa Cruz, Argentina)

Journal of Paleolimnology

Late glacial and Holocene wet–dry cycles in southern Patagonia: Chronology, sedimentology and geochemistry of a lacustrine record from Laguna Potrok Aike, Argentina

The Holocene

Pollen and Spores of Chile