Vegetation and climate dynamics of southern Chile during the past 50,000 years: results of ODP Site 1233 pollen analysis

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Abstract

High-resolution pollen data from ODP Site 1233 (41°0.005S, 74°26.992W, 838 m water depth) provide a continuous, chronostratigraphically controlled ∼50,000-yr record of regional changes in vegetation from temperate South America. Deposited ∼38 km west of the transition from northern, summer-green, lowland forest to southern evergreen rain forest, the 135 m core documents the comparatively brief Holocene development of thermophilous vegetation (Lowland Deciduous Beech Forest and Valdivian Evergreen Forest), and the expansion of glacial, subantarctic vegetation (North Patagonian Evergreen Forest-Subantarctic Parkland) during Marine Isotope State (MIS) 2 and 3. Systematic variability in these terrestrial climate proxies that reflect latitudinal movement of the southern westerlies is mirrored in co-eval ocean conditions inferred from radiolaria census data and in Antarctic climate records.

Introduction

Southern hemisphere glacial–interglacial changes in ocean/atmosphere circulation have been reconstructed from marine cores and Antarctic ice cores for the past 30 years. Comparable terrestrial information is sparse, and such South American records are rare. Only three records of glacial–interglacial changes in subtropical and temperate South American environments extend through Marine Isotope State (MIS) 3 (Heusser, 2003). To obtain lengthy, calibrated, directly correlative, high-resolution records of glacial–interglacial changes in the southeast Pacific and in southern South America ODP (Ocean Drilling Program) Site 1233 was drilled ∼35 km from the Chilean Coast, where sedimentation rates exceed 100 cm/yr (Mix et al., 2003). Initial results of pollen analysis of the ∼135 m composite core from this site provide a continuous, high-resolution >50 ka pollen record from southern South America, a regional record of vegetation and climate that extends and expands previously published reconstructions of local vegetation based on sediment cores from mires and small lakes in southern Chile.

Section snippets

Setting

Primary regional climatic controls of the narrow strip of south-central Chile are the longitudinal mountain ranges (low-lying Coast Range and glacier-capped Southern Andes) that bracket a central valley, and the coastal waters offshore (the cool northward flowing Peru–Chile Current (PCC), Chilean Countercurrent, and Chilean Fjord Water (Mix et al., 2003) (Fig. 1a). Due to the low land/ocean ratio and the moderating oceanic influence, climate is highly equable. Between 34°S and 41°S, annual mean

Methods

Our core site (Site 1233, 41°0.005S, 74°26.992W, 838 m water depth) is located ∼38 km west of the Chilean coast near the transition from Lowland Deciduous Beech Forest to Valdivian Evergreen Forest. The site was deliberately located close to shore in order to obtain very high-resolution terrestrial records (Mix et al., 2003). Hemipelagic sediment deposited at the site contains well-preserved biogenic components, including abundant pollen. Like other fine-grained terrigenous components of the

Results and discussion

Two distinctly different assemblages, separated by a transition interval in which components of each overlap, characterize pollen spectra from ODP 1233 (Fig. 3). The lengthy basal assemblage (25–136 mcd) is dominated by alternating peaks in Nothofagus dombeyi type (average 59%) and Gramineae (∼20%) accompanied by fluctuations in lesser amounts of coniferous (Podocarpus nubigena and Pilgerodendron) and myrtaceous pollen. The large decrease in N. dombeyi type at ∼26 mcd identifies the base of the

Conclusions

1. High-resolution pollen data from ODP Site 1233 provide the first, continuous, chronostratigraphically controlled >50 ka vegetational–environmental record from southern Chile. This regional record extends and expands previously published reconstructions of local vegetation based on sediment cores from mires, and small lakes in southern Chile.

2. During the last Full Glacial, the prominence of hyper-humid vegetation (North Patagonian and Subantarctic forests and parkland) implies sustained,

Acknowledgements

This research used samples provided by the Ocean Drilling Program (ODP). ODP is sponsored by the National Science Foundation (NSF) and participating countries under management of Joint Oceanographic Institutions (JOI), Inc. Funding for this work was partially provided by JOIDES. We thank the Shipboard Scientific Party, Captain and crew of the JOIDES Resolution Leg 202, Mysti Weber of COAS, Oregon State University, and Lydia Dupont. We gratefully acknowledge those members of the Scientific Party

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