Prof Christopher Ramsey

Abstract:

The Llanos de Moxos in the Bolivian Amazon, the second largest South American wetland, hosts many endemic species and a rich archaeological record that spans the entire Holocene. Despite its ecological and archaeological importance, very little is known about its Holocene environmental history. A growing body of evidence suggests that neotectonics played an important role in shaping its modern landscape and controlling past flooding dynamics, but the chronology and vertical displacements of past tectonic events are still largely unknown. Here, we present new data from a core taken at Lake Oceano, a large ria lake in the northern part of the Llanos de Moxos. To identify changes in the lithology and environment, we performed a battery of analyses, such as XRF scanning, mineralogy, granulometry, C/N and C and N stable isotopes, and also built an age-depth model using eighteen radiocarbon dates obtained from accelerator mass spectrometry (AMS) determinations. Based on the sedimentology and chemical analyses, we identified three major disturbances in the lake sedimentation that we interpret as positive tectonic events (i.e., tectonic uplifts). The first identified event occurred at approximately 13,400 cal yr BP and led to the formation of the lake by blocking the river course. A second uplift event took place around 10,000 cal yr BP, accompanied by a significant change in the geochemistry of the lake sediments. Furthermore, we have verified a third event at 6000 cal yr BP, previously recognized as responsible for the onset of Lake Rogaguado (aprox. 100 km NE of Lake Oceano), one of the largest lakes in South America. Overall, we show that ria lakes can provide key sedimentary archives to reconstruct the past timing and intensity of tectonic events. We discuss the interplay between tectonics and climate, highlighting the connection between tectonics and the region's flood history, with crucial implications for the interpretation of both archaeological and palaeoecological records throughout the Holocene.

Abstract:

The Casarabe culture (500–1400 ce), spreading over roughly 4,500 km² of the monumental mounds region of the Llanos de Moxos, Bolivia, is one of the clearest examples of urbanism in pre-Columbian (pre-1492 ce) Amazonia. It exhibits a four-tier hierarchical settlement pattern, with hundreds of monumental mounds interconnected by canals and causeways. Despite archaeological evidence indicating that maize was cultivated by this society, it is unknown whether it was the staple crop and which type of agricultural farming system was used to support this urban-scale society. Here, we address this issue by integration of remote sensing, field survey and microbotanical analyses, which shows that the Casarabe culture invested heavily in landscape engineering, constructing a complex system of drainage canals (to drain excess water during the rainy season) and newly documented savannah farm ponds (to retain water in the dry season). Phytolith analyses of 178 samples from 18 soil profiles in drained fields, farm ponds and forested settings record the singular and ubiquitous presence of maize (Zea mays) in pre-Columbian fields and farm ponds, and an absence of evidence for agricultural practices in the forest. Collectively, our findings show how the Casarabe culture managed the savannah landscape for intensive year-round maize monoculture that probably sustained its relatively large population. Our results have implications for how we conceive agricultural systems in Amazonia, and show an example of a Neolithic-like, grain-based agrarian economy in the Amazon.

Abstract:

<jats:title>Abstract</jats:title> <jats:p>A 350 <jats:sup>14</jats:sup>C yr discrepancy was found between dates on postcranial remains and mandibular teeth on what was thought to be the same individual from the Early Neolithic cemetery of Shamanka II, Lake Baikal. Stable nitrogen isotope results suggested a major shift in diet between childhood (when the teeth formed) and adulthood (represented by the postcrania), which could have resulted in different <jats:sup>14</jats:sup>C ages through a freshwater reservoir effect. Subsequent additional dating on the mandible and postcranial elements, however, indicated that the mandible actually belonged to a different individual. More subtle reservoir effects can be seen on the sequentially forming teeth and mandible. The practice by prehistoric hunter-gatherers of Lake Baikal of re-opening graves and removing cranial elements has long been known, but this is the first evidence for the inclusion of a mandible from a separate individual, though whether it was intentional or incidental is uncertain. As well as providing new insights into mid-Holocene mortuary practices in the region, our findings raise a cautionary note for the examination of disturbed graves.</jats:p>

Abstract:

As part of a larger project identifying and directly radiocarbon dating Late Pleistocene megafaunal remains in British Columbia (B.C.), Canada we have confirmed the identity of many newly identified mammoth (Mammuthus sp.) specimens (n=32) from Vancouver Island in Southwestern B.C. We undertook radiocarbon dating on all specimens and were able to obtain dates (due to preservation) on 16 of these remains, including re-dating a previously dated mammoth using newer radiocarbon extraction methods. The mammoth dates span a wide range, from >47,500 to 18,000 radiocarbon years BP (uncalibrated). These later new dates support other lines of evidence for portions of Vancouver Island remaining unglaciated towards the end of Late Pleistocene.

Abstract:

Anthropogenically-driven climate warming and land use change are the main causes of an ongoing decrease in global biodiversity. It is unclear how ecosystems, particularly freshwater habitats, will respond to such continuous and potentially intensifying disruptions. Here we analyse how different components of terrestrial and aquatic ecosystems responded to natural climate change during the Lateglacial. By applying a range of analytical techniques (sedimentology, palaeoecology, geochemistry) to the well-dated sediment archive from Lake Hämelsee (Germany), we show evidence for vegetation development, landscape dynamics and aquatic ecosystem change typical for northwest Europe during the Lateglacial. By particularly focussing on periods of abrupt climate change, we determine the timing and duration of changes in biodiversity in response to external forcing. We show that onsets of changes in biodiversity indicators (e.g. diatom composition, Pediastrum concentrations) lag changes in environmental records (e.g. loss-on-ignition) by a few decades, particularly at the Allerød/Younger Dryas transition. Most biodiversity indicators showed transition times of 10–50 years, whereas environmental records typically showed a 50–100 year long transition. In some cases, transition times observed for the compositional turnover or productivity records were up to 185 years, which could have been the result of the combined effects of direct (e.g. climate) and indirect (e.g. lake stratification) drivers of ecosystem change. Our results show differences in timing and duration of biodiversity responses to external disturbances, suggesting that a multi-decadal view needs to be taken when designing effective conservation management of freshwater ecosystems under current global warming.