Holocene environmental changes in the highlands of the southern Peruvian Andes (14° S) and their impact on pre-Columbian cultures

Abstract

Abstract. Within palaeoenvironmental studies, high-altitude peatlands of the Andes still remain relatively unexploited, although they offer an excellent opportunity for high-resolution chronologies, on account of their high accumulation rates and abundant carbon for dating. Especially in the central Andes, additional high-quality proxy records are still needed due to the lack of continuous and well-dated records, which show a significant variability on sub-centennial to decadal precision scales. To widen the current knowledge on climatic and environmental changes in the western Andes of southern Peru, we present a new, high-resolution 8600 year-long record from Cerro Llamoca peatland, a high-altitude Juncaceous cushion peatland in the headwaters of Río Viscas, a tributary to Río Grande de Nasca. A 10.5 m core of peat with intercalated sediment layers was examined for all kinds of microfossils, including fossil charred particles. We chose homogeneous peat sections for pollen analysis at a high temporal resolution. The inorganic geochemistry was analysed in 2 mm resolution using an ITRAX X-ray fluorescence (XRF) core scanner. We interpret the increase 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 as applicable proxies for in situ palaeo-redox conditions. The mid-Holocene period of 8.6–5.6 ka is characterized 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 1.8–1.2 ka, which coincides with the florescence of the Nasca culture in the Andean foreland. An abrupt turnover to a sustained dry period occurs at 1.2 ka, which coincides with the collapse of the Nasca/Wari society in the Palpa lowlands. Markedly drier conditions prevail until 0.75 ka, providing evidence for the presence of a Medieval Climate Anomaly. Moister but hydrologically highly variable conditions prevailed again after 0.75 ka, which allowed the re-expansion of tussock grasses in the highlands, increased discharge into the Andean foreland and the re-occupation of the settlements in the lowlands during this so-called Late Intermediate Period. On a supraregional scale, our findings can ideally be linked to and proofed 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.

Cloud dynamic contribution to high-elevation peatland growth during the Holocene (Escalerani, Central Andes, Bolivia)

“…yr BP and a drier phase between 4600 and 4200 cal. yr BP (Schittek et al, 2015). The record at Nevado Coropuna, also in southern Peru, at 4400 m a.s.l., showed a similar trend, with the driest episode between 5200 and 3000 cal.…”

“…The progressive enhancement of SASM during the Holocene occurred in response to the increasing insolation during the precession cycle (Bernal et al, 2016; Bustamante et al, 2016; Vuille et al, 2012). In northeastern Peru, high-resolution speleothem and pollen records show that the increase in wetter conditions was interrupted by a series of dry spells throughout the mid-Holocene (Bustamante et al, 2016; Schittek et al, 2015). At Escalerani, the strongest decrease in precipitation was observed between 4700 and 3500 cal.…”

Ecotypic differentiation under farmers' selection: Molecular insights into the domestication of Pachyrhizus Rich. ex DC. (Fabaceae) in the Peruvian Andes

“…Lomas have played a major role in the history of pre‐Columbian cultures (Engel, ; Fehren‐Schmitz et al., ), and archeological records indicate they were focal points for the early onset of yam bean agriculture in the Peruvian Andes. However, these lowland populations probably disappeared as desertification progressed on the coast of Peru starting ~AD 500, forcing settlements to relocate into the middle and upper valleys of the Andean foothills (Fehren‐Schmitz et al., ; Schittek et al., ). Roots discovered in the Casma River valley and dated from ~AD 1500 (Ugent et al., ) indicate that Pachyrhizus cultivation was briefly resumed on the Peruvian coast during the Late Intermediate Period as climatic conditions improved and Chimú‐Inca resettled coastal lowlands for the last time (Fehren‐Schmitz et al., ; Mächtle & Eitel, ).…”

Multi‐Centennial‐Scale Variations of South American Summer Monsoon Intensity in the Southern Central Andes (24–27°S) During the Late Holocene

“…Especially in the arid west, the number of available paleoclimate archives is still considerably small. In this respect, high‐Andean cushion peatlands can be valuable (paleo‐)environmental recorders, especially due to their high accumulation rates that allow for chronologies up to sub‐decadal resolution (e.g., Engel et al, ; Kock, Schittek, Mächtle, et al, ; Schittek et al, ). Further, these peatlands are very sensitive towards climatic changes and offer comparability across climatic gradients and (Schittek, ; Schittek et al, ).…”