Rapa Nui (Easter Island) Rano Raraku crater lake basin: Geochemical characterization and implications for the Ahu-Moai Period

Rano Raraku, the crater lake constrained by basaltic tuff that served as the primary quarry used to construct the moai statues on Rapa Nui (Easter Island), has experienced fluctuations in lake level over the past centuries. As one of the only freshwater sources on the island, understanding the present and past geochemical characteristics of the lake water is critical to understand if the lake could have been a viable freshwater source for Rapa Nui. At the time of sampling in September 2017, the maximum lake depth was ~1 m. The lake level has substantially declined in the subsequent years, with the lake drying almost completely in January 2018. The lake is currently characterized by highly anoxic conditions, with a predominance of ammonium ions on nitrates, a high concentration of organic carbon in the water-sediment interface and reducing conditions of the lake, as evidenced by Mn/Fe and Cr/V ratios. Our estimates of past salinity inferred from the chloride mass balance indicates that it was unlikely that Rano Raraku provided a viable freshwater source for early Rapa Nui people. The installation of an outlet pipe around 1950 that was active until the late 1970s, as well as grazing of horses on the lake margins appear to have significantly impacted the geochemical conditions of Rano Raraku sediments and lake water in recent decades. Such impacts are distinct from natural environmental changes and highlight the need to consider the sensitivity of the lake geochemistry to human activities

Late Holocene records of fire and human presence in New Zealand

New Zealand, and the South Island in particular, can be considered an excellent test site for the study of the early impact of humans on the environment for two main reasons: the Polynesian settlement occurred only about 700-800 y BP and resulted in abrupt and huge landscape modifications. Burning forest for land clearance impacted dramatically on an ecosystem that was not adapted to fire, changing the composition of the vegetation as documented by sedimentary charcoal and pollen records. Although charcoal data give incontrovertible evidence of some unprecedented fire events right after the arrival of the Maori, its significance as a tracer for local and anthropogenic fire events has been questioned, stressing the need for new markers to confirm and complete the information about human presence and its effective impact. In the present work, faecal sterols and polycyclic aromatic hydrocarbons (PAHs) were individuated as suitable molecular markers and analyzed by GC-MS in a sediment core from Lake Kirkpatrick, located in the Lake Wakatipu catchment at 570 m a.s.l. in the South Island of New Zealand. Coprostanol accounts for about 60% of total sterol content in human faeces, being much less relevant in animal dejections. Together with its degradation product epi-coprostanol, it is well conserved in sedimentary archives and can be highly useful in paleoenvironmental reconstructions of human settlements. PAHs are produced in relevant amounts by combustion in conditions of oxygen depletion, and diagnostic ratios (DR) between specific molecules can be used for inferring fuel and sources. The charcoal record for Lake Kirkpatrick shows major fire episodes around AD 1350, confirmed by corresponding high levels of PAHs ascribable to biomass burning (as further evidenced by DR) at c. AD 1350. Moreover, the same trend is observed also in the fluxes of coprostanol and epi-coprostanol, whose sum results in two peaks at c. AD 1346 and 1351. This finding confirms not only the massive presence of humans in the area and the large use of fire at the time, but also complements and refines the reconstructions enabled by charcoal analysis

Lake sediment fecal and biomass burning biomarkers provide direct evidence for prehistoric human-lit fires in New Zealand

Deforestation associated with the initial settlement of New Zealand is a dramatic example of how humans can alter landscapes through fire. However, evidence linking early human presence and land-cover change is inferential in most continental sites. We employed a multi-proxy approach to reconstruct anthropogenic land use in New Zealand’s South Island over the last millennium using fecal and plant sterols as indicators of human activity and monosaccharide anhydrides, polycyclic aromatic hydrocarbons, charcoal and pollen as tracers of fire and vegetation change in lake-sediment cores. Our data provide a direct record of local human presence in Lake Kirkpatrick and Lake Diamond watersheds at the time of deforestation and a new and stronger case of human agency linked with forest clearance. The first detection of human presence matches charcoal and biomarker evidence for initial burning at c. AD 1350. Sterols decreased shortly after to values suggesting the sporadic presence of people and then rose to unprecedented levels after the European settlement. Our results confirm that initial human arrival in New Zealand was associated with brief and intense burning activities. Testing our approach in a context of well-established fire history provides a new tool for understanding cause-effect relationships in more complex continental reconstructions

FROM AGGREGATE METHODS TO MICROSIMULATION: ASSESSING THE BENEFITS OF MICROSCOPIC ACTIVITY-BASED MODELS OF TRAVEL DEMAND

Two competing approaches to travel demand modeling exist today. The more traditional “4step” travel demand models rely on aggregate demographic data at a traffic analysis zone (TAZ) level. Activity-based microsimulation methods employ more robust behavioral theory while focusing on individuals and households. While the vast majority of U.S. metropolitan planning organizations (MPOs) continue to rely on traditional models, many modelers believe that activity-based approaches promise greater predictive capability, more accurate forecasts, and more realistic sensitivity to policy changes. Little work has examined in detail the benefits of activity-based models, relative to more traditional approaches. In order to better understand the tradeoffs between these two methodologies, this paper examines model results produced by both, in an Austin, Texas application. Three scenarios are examined here: a base scenario, a scenario with expanded capacity along two key freeways, and a centralized-employment scenario. Results of the analysis reveal several differences in model performance and accuracy, in terms of replicating travel survey and traffic count data. Such distinctions largely emerge through differing mode

Broad-Scale Surface and Atmospheric Conditions during Large Fires in South-Central Chile

The unprecedented size of the 2017 wildfires that burned nearly 600,000 hectares of central Chile highlight a need to better understand the climatic conditions under which large fires develop. Here we evaluate synoptic atmospheric conditions at the surface and free troposphere associated with anomalously high (active) versus low (inactive) months of area burned in south-central Chile (ca. 32–41° S) from the Chilean Forest Service (CONAF) record of area burned from 1984–2018. Active fire months are correlated with warm surface temperatures, dry conditions, and the presence of a circumpolar assemblage of high-pressure systems located ca. 40°–60° S. Additionally, warm surface temperatures associated with active fire months are linked to reduced strength of cool, onshore westerly winds and an increase in warm, downslope Andean Cordillera easterly winds. Episodic warm downslope winds and easterly wind anomalies superimposed on long-term warming and drying trends will continue to create conditions that promote large fires in south-central Chile. Identifying the mechanisms responsible for easterly wind anomalies and determining whether this trend is strengthening due to synoptic-scale climatic changes such as the poleward shift in Southern Hemisphere westerly winds will be critical for anticipating future large fire activity in south-central Chile

Insight into the carbonaceous fraction of three cultural layers of different age from the area of Verona (NE Italy)

Cultural layers are deposits resulting from settlement and human activity on natural soil in the past. Materials from past domestic activities that become buried into the soil can be used to reconstruct human impact in a specific area in the past. For instance, humans have used fire for millennia, and charcoal in soils and sediments is applied as evidence of anthropic activity. In this context, assessing the abundance and degradation level of charcoal fragments can clarify anthropic activities in cultural deposits. In European towns, cultural layers with similar characteristics, have been defined as urban "Dark Earth" (UDE) but their age, formation and composition often differ significantly across sites.This study examined three archaeological sites in Verona, Italy, where UDE layers with similar characteristics have been identified. The primary aim of this research is to understand the anthropogenic influence on the development of UDE layers, by characterizing their geochemistry and the carbonaceous materials. To pursue this goal, we provide a micromorphological description of the sites, evaluate UDE features and the abundance of charred material and characterize the amorphous/crystalline degree through jr-Raman spectroscopy. Bulk material was described in terms of amounts of total organic carbon (TOC), recalcitrant organic carbon (ROC), total inorganic carbon (TIC), and trace element concentration. Radiocarbon dating of charred and humin fractions was performed to clarify the dynamics underlying UDE origin. We investigate the relationship between the different variables analyzed in the UDE layers at each site. Results show that a diverse array of human activities including metal tool and/or ceramic manufacturing were related to the formation of UDE layers. The investigation of carbonaceous fractions highlight differences in soil organic carbon and charred material, both of which are correlated with human influence

Use of organic biomarkers for the Late Holocene reconstruction of fire and human presence in New Zealand

The Polynesian colonization of New Zealand occurred quite recently in history (about 700-800 years BP) and resulted in abrupt and huge landscape modifications, as documented by sedimentary charcoal and pollen records. The native forest was not adapted to fire, thus burning for land clearance impacted dramatically on the ecosystem by modifying the composition of vegetation (McWethy et al., 2014). Therefore, this location can be considered an extraordinary test site for the study of the very first human impacts on the environment. Despite the incontrovertible evidence of some unprecedented fire events right after the arrival of the Māori, reconstructed through charcoal, its significance as a tracer for local and anthropogenic fire events has been questioned, stressing the need for new markers to confirm and complete the information about human presence and its effective impact (Butler, 2008). In the present work, novel organic molecular proxies are proposed for the reconstruction of fire events in association with anthropic activities. Namely, faecal sterols (FeSt), polycyclic aromatic hydrocarbons (PAHs) and monosaccharide anhydrides (MAs) were individuated as suitable molecular markers of human presence and fire activity, respectively. In particular, coprostanol accounts for about 60% of total sterol content in human faeces, being much less relevant in animal dejections (Bull et al., 2002). Together with its degradation product epi-coprostanol, it is well conserved in sedimentary archives and can be highly useful in paleoenvironmental reconstructions of human settlements. PAHs are produced in relevant amounts by combustion in conditions of oxygen depletion, and diagnostic ratios (DR) between specific molecules can be used for inferring fuel and sources (Ravindra et al., 2008). MAs are specific tracers of biomass burning, being generated only by the combustion of cellulose and hemicelluloses above 300° C (Simoneit et al., 1999). The three classes of tracers were analyzed in a sediment core from Lake Kirkpatrick (570 m asl), and FeSt were analyzed also in a core from Lake Diamond (380 m asl). Both lakes are located in the Otago region, in New Zealand South Island. The charcoal record for Lake Kirkpatrick (LK) and Lake Diamond (LD) shows major fire episodes around AD 1350, confirmed for LK by corresponding high levels of PAHs, ascribable to biomass burning (as further evidenced by DR), and MAs, both peaking at c. AD 1350. Moreover, the same trend is observed also in the fluxes of coprostanol and epi-coprostanol, whose sum results in two peaks at c. AD 1346 and 1351, respectively. For LD, a peak in FeSt is observed as well, slightly preceding the increase in fire activity starting around AD 1330. These findings confirm not only an important presence of humans in the area and the large use of fire at the time, but also the validity of selected tracers for complementing and refining the reconstructions enabled by charcoal analysis

Late Holocene human-environment interactions in New Zealand: a biomarker approach

The recent colonization history of New Zealand makes it an excellent test site for investigating the early impact of human activities on natural ecosystems. The arrival of humans around 700-800 yr BP is marked by a neat increase in fire activity and land clearance, as documented by charcoal and pollen records [1]. Here, the validity of biomarkers was tested in a multi-proxy study including three different categories of organic molecular markers. Results were compared with existing paleoecological data. Samples from a small alpine lake in the South Island of New Zealand (Lake Kirkpatrick, Otago), covering a time span of about 800 years (~AD 1153-1961), were analyzed for polycyclic aromatic hydrocarbons (PAHs) as combustion tracers, monosaccharide anhydrides (levoglucosan and its isomers, MAs) as specific markers of biomass burning and fecal sterols (FeSt) for the reconstruction of human/animal presence, organic matter input and chemical conditions of the basin. All tracers peak sharply and abruptly in a brief period centered at about AD 1350, which corresponds to the first increase in fire activity and decline in arboreal species in the South Island. Values decrease to background after ~AD 1400, until the beginning of the 19th century, when a huge increase is registered in FeSt after the European arrival. Results are confirmed also by the FeSt record from Lake Diamond, not far from Lake Kirkpatrick, that is coherent with significant human presence and increased erosion and sedimentation during the 14th century. Such changes are consistent with the so-called “AD 1300 event”, a short period of increased precipitation and erosion observed in many records from Pacific Islands [2]. Whether natural changes affected human settlement and land use or vice-versa is matter of debate [3], and multi-proxy studies look promising in the reconstruction of such complex interactions and feedbacks