Abstract
Abstract. High-altitude peatlands of the Andes still remain relatively unexploited although they offer an excellent opportunity for well-dated palaeoenvironmental records. To improve knowledge about climatic and environmental changes in the western Andes of southern Peru, we present a high-resolution record of the Cerro Llamoca peatland for the last 8600 years. The 10.5 m long core consists of peat and intercalated sediment layers and was examined for all kinds of microfossils. We chose homogeneous peat sections for pollen analysis at decadal to centennial resolution. The inorganic geochemistry was analysed in 2 mm resolution (corresponding >2 years) using an ITRAX X-ray fluorescence core scanner. We interpret phases of relatively high abundances of Poaceae pollen in our record as an expansion of Andean grasslands during humid phases. Drier conditions are indicated by a significant decrease of Poaceae pollen and higher abundances of Asteraceae pollen. The results are substantiated by changes in arsenic contents and manganese/iron ratios, which turned out to be applicable proxies for in situ palaeoredox conditions. The mid-Holocene period of 8.6–5.6 ka is characterised by a series of episodic dry spells alternating with spells that are more humid. After a pronounced dry period at 4.6–4.2 ka, conditions generally shifted towards a more humid climate. We stress a humid/relatively stable interval between 1.8 and 1.2 ka, which coincides with the florescence of the Nasca culture in the Andean foothills. An abrupt turn to a sustained dry period occurs at 1.2 ka, which is contemporaneous with the demise of the Nasca/Wari society in the Palpa lowlands. Markedly drier conditions prevail until 0.75 ka, providing evidence of the presence of a Medieval Climate Anomaly. Moister but hydrologically highly variable conditions prevailed again after 0.75 ka, which allowed re-expansion of tussock grasses in the highlands, increased discharge into the Andean foreland and resettling of the lowlands during this so-called late Intermediate Period (LIP). On a supraregional scale, our findings can ideally be linked to and proved by the archaeological chronology of the Nasca–Palpa region as well as other high-resolution marine and terrestrial palaeoenvironmental records. Our findings show that hydrological fluctuations, triggered by the changing intensity of the monsoonal tropical summer rains emerging from the Amazon Basin in the north-east, have controlled the climate in the study area.
Highlights
There is clear evidence that marked, global-scale climatic changes during the Holocene induced significant and complex environmental responses in the central Andes, which repeatedly led to abrupt changes in temperature, precipitation and the periodicity of circulation regimes (Jansen et al, 2007; Bird et al, 2011a)
To supplement and specify the current knowledge about climatic and environmental changes in the western Andes of southern Peru, we present a new record from the Cerro Llamoca peatland (CLP) for the last 8.6 ka
In spring-water samples of the 2009 and 2010 campaigns we measured As contents of 140–270 μg L−1 at the head of the peatland; the small stream leaving the peatland’s main branch further down only contained 4–6 μg L−1 (Schittek; unpublished data), which clearly shows that CLP is a sink for As
Summary
There is clear evidence that marked, global-scale climatic changes during the Holocene induced significant and complex environmental responses in the central Andes, which repeatedly led to abrupt changes in temperature, precipitation and the periodicity of circulation regimes (Jansen et al, 2007; Bird et al, 2011a). This region is characterised by distinct gradients of several climatic parameters over short distances and is sensitive to the effects of environmental change. Considerable efforts have been made to decipher the palaeoenvironmental history of the central Andes, many aspects of the timing, magnitude and origin of past climate changes remain poorly defined (Grosjean et al, 2001; Latorre et al, 2003; Gayo et al, 2012)
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