AD 550–600 Collapse at Teotihuacan

2017 ◽  
Author(s):  
Matthew S. Lachniet ◽  
Juan Pablo Bernal-Uruchurtu
Keyword(s):  
Rainfall Variability ◽  
Spring Discharge ◽  
Domestic Water ◽  
The Past ◽  
Sequence Of Events ◽  
Order Of Magnitude ◽  
Population Sizes ◽  
Sierra Madre Del Sur ◽  
Rainfall Variations ◽  
Monsoon Strength

We analyze a 2400-year rainfall reconstruction from an ultra-high-resolution absolutely-dated stalagmite (JX-6) from southwestern Mexico (Lachniet et al., 2012). Oxygen isotope variations correlate strongly to rainfall amount in the Mexico City area since 1870 CE, and for the wider southwestern Mexico region since 1948, allowing us to quantitatively reconstruct rainfall variability for the Basin of Mexico and Sierra Madre del Sur for the past 2400 years. Because oxygen isotopes integrate rainfall variations over broad geographic regions, our data suggest substantial variations in Mesoamerican monsoon strength over the past two millennia. As a result of low age uncertainties (≤ 11 yr), our stalagmite paleoclimate reconstruction allows us to place robust ages on past rainfall variations with a resolution an order of magnitude more precise than archeological dates associated with societal change. We relate our new rainfall reconstruction to the sequence of events at Teotihuacan (Millon, 1967; Cowgill, 2015a) and to other pre-Colombian civilizations in Mesoamerica. We observe a centuries long drying trend that culminated in peak drought conditions in ca. 750 CE related to a weakening monsoon, which may have been a stressor on Mesoamerican societies. Teotihuacan is an ideal location to test for links between climate change and society, because it was located in a semi-arid highland valley with limited permanent water sources, which relied upon spring fed irrigation to ensure a reliable maize harvest (Sanders, 1977). The city of Teotihuacan was one of the largest Mesoamerican cities, which apparently reached population sizes of 80,000 to 100,000 inhabitants by AD 300 (Cowgill, 1997; 2015a). Following the “Great Fire”, which dates approximately to AD 550, population decreased to lower levels and many buildings were abandoned (Cowgill, 2015). Because of the apparent reliance on rainwater capture (Linn é, 2003) and spring-fed agriculture in the Teotihuacan valley to ensure food security and drinking water, food production and domestic water supplies should have been sensitive to rainfall variations that recharge the surficial aquifer that sustained spring discharge prior recent groundwater extraction.

scholarly journals Rainfall variations in central Indo-Pacific over the past 2,700 y

2019 ◽  
Vol 116 (35) ◽  
pp. 17201-17206 ◽  
Author(s):  
Liangcheng Tan ◽  
Chuan-Chou Shen ◽  
Ludvig Löwemark ◽  
Sakonvan Chawchai ◽  
R. Lawrence Edwards ◽  
...  
Keyword(s):  
Rainfall Variability ◽  
Walker Circulation ◽  
Warm Period ◽  
Tropical Rainfall ◽  
The Past ◽  
Decadal Scale ◽  
Continuous Record ◽  
Southern Central ◽  
Drying Trend ◽  
Rainfall Variations

Tropical rainfall variability is closely linked to meridional shifts of the Intertropical Convergence Zone (ITCZ) and zonal movements of the Walker circulation. The characteristics and mechanisms of tropical rainfall variations on centennial to decadal scales are, however, still unclear. Here, we reconstruct a replicated stalagmite-based 2,700-y-long, continuous record of rainfall for the deeply convective northern central Indo-Pacific (NCIP) region. Our record reveals decreasing rainfall in the NCIP over the past 2,700 y, similar to other records from the northern tropics. Notable centennial- to decadal-scale dry climate episodes occurred in both the NCIP and the southern central Indo-Pacific (SCIP) during the 20th century [Current Warm Period (CWP)] and the Medieval Warm Period (MWP), resembling enhanced El Niño-like conditions. Further, we developed a 2,000-y-long ITCZ shift index record that supports an overall southward ITCZ shift in the central Indo-Pacific and indicates southward mean ITCZ positions during the early MWP and the CWP. As a result, the drying trend since the 20th century in the northern tropics is similar to that observed during the past warm period, suggesting that a possible anthropogenic forcing of rainfall remains indistinguishable from natural variability.

Quantifying recent lake level changes in Patagonia (Argentina and Chile): Back to the future?

2021 ◽  
Author(s):  
Daniel Ariztegui ◽  
Clément Pollier ◽  
Andrés Bilmes
Keyword(s):  
Water Level ◽  
Lake Level ◽  
Satellite Images ◽  
Meteorological Data ◽  
Tierra Del Fuego ◽  
Water Level Fluctuations ◽  
Lake Levels ◽  
The Past ◽  
Rainfall Variations ◽  
The Impact

<p>Lake levels in hydrologically closed-basins are very sensitive to climatically and/or anthropogenically triggered environmental changes. Their record through time can provide valuable information to forecast changes that can have substantial economical and societal impact.</p><p>Increasing precipitation in eastern Patagonia (Argentina) have been documented following years with strong El Niño (cold) events using historical and meteorological data. Quantifying changes in modern lake levels allow determining the impact of rainfall variations while contributing to anticipate the evolution of lacustrine systems over the next decades with expected fluctuations in ENSO frequencies. Laguna Carrilaufquen Grande is located in the intermontane Maquinchao Basin, Argentina. Its dimension fluctuates greatly, from 20 to 55 km<sup>2</sup> water surface area and an average water depth of 3 m. Several well-preserved gravelly beach ridges witness rainfall variations that can be compared to meteorological data and satellite images covering the last ~50 years. Our results show that in 2016 lake level was the lowest of the past 44 years whereas the maximum lake level was recorded in 1985 (+11.8 m above the current lake level) in a position 1.6 km to the east of the present shoreline. A five-years moving average rainfall record of the area was calculated smoothing the extreme annual events and correlated to the determined lake level fluctuations. The annual variation of lake levels was up to 1.2 m (e.g. 2014) whereas decadal variations related to humid-arid periods for the interval 2002 to 2016 were up to 9.4 m. These data are consistent with those from other monitored lakes and, thus, our approach opens up new perspectives to understand the historical water level fluctuations of lakes with non-available monitoring data.</p><p> </p><p>Laguna de los Cisnes in the Chilean section of the island of Tierra del Fuego, is a closed-lake presently divided into two sections of 2.2 and 11.9 km<sup>2</sup>, respectively. These two water bodies were united in the past forming a single larger lake. The lake level was  ca. 4 m higher than today as shown by clear shorelines and the outcropping of large Ca-rich microbialites. Historical data, aerial photographs and satellite images indicate that the most recent changes in lake level are the result of a massive decrease of water input during the last half of the 20<sup>th</sup> century triggered by an indiscriminate use of the incoming water for agricultural purposes. The spectacular outcropping of living and fossil microbialites is not only interesting from a scientific point of view but has also initiated the development of the site as a local touristic attraction. However, if the use of the incoming water for agriculture in the catchment remains unregulated the lake water level might drop dangerously and eventually the lake might fully desiccate.</p><p>These two examples illustrate how recent changes in lake level can be used to anticipate the near future of lakes. They show that ongoing climate changes along with the growing demand of natural resources have already started to impact lacustrine systems and this is likely to increase in the decades to come.</p>

Ore textures: problems and opportunities

1991 ◽  
Vol 55 (380) ◽  
pp. 303-315 ◽  
Author(s):  
Paul B. Barton
Keyword(s):  
Spatial Relations ◽  
Ore Deposits ◽  
Chemical Processes ◽  
Process Models ◽  
Textural Features ◽  
The Past ◽  
Geological Processes ◽  
Sequence Of Events ◽  
Definition Of ◽  
Scientific Endeavour

AbstractOver the past several decades, thinking about chemical processes in rocks had been dominated by experimental and theoretical treatments of mineral equilibrium, which is the state from which the time variable has been excluded. But, to an extent exceeding that of any of our sister sciences, we in geology are concerned with the behaviour of things as a function of time; thus equilibrium is but one of several interesting boundary conditions. Textures, (defined as the spatial relations within and among minerals and fluids, regardless of scale or origin) provide a means to sort out and identify successive states. In fact, it is the pattern of evolution of those states that enables us to deduce the processes. We may well draw the analogy with thermodynamics and kinetics, respectively:equilibrium textures and phase assemblages, via thermodynamic analysis → definition of conditions of equilibration,whereaskinetics, as displayed in disequilibrium textures → sequence of events and processes of mineralization.The interpretation of textures is one of the most difficult yet important aspects of the study of rocks and ores, and there are few areas of scientific endeavour that are more subject to misinterpretation. Although the difficulties are many, the opportunites for new understanding are also abundant. Textural interpretations have many facets: some are well established and accepted; some that are accepted may be wrong; others are recognised to be speculative and controversial; and we trust that still other textural features remain to be described and interpreted. This paper will deal principally with low-temperature, epigenetic ore deposits, and will emphasise silica and sphalerite; but extension to other materials is not unreasonable.Ore and gangue minerals react internally, or with their environment, at widely ranging rates, ranging from the almost inert pyrite, arsenopyrite, well-crystallised quartz, and tourmaline to the notoriously fickle copper/iron and copper/silver sulfides. Arrested or incomplete reactions may be identifed by textural criteria and, when appropriately quantified, can provide guides to the duration of geological processes.In recent years so much emphasis has been placed on isotopes, fluids, chemistry, and deposit and process models that the textural features have been ignored. In part this oversight occurs because we have grown accustomed to using superposition, cross-cutting, pseudomorphism, mutual intergrowths, exsolution and so on as off-the-shelf tools, to be grasped and applied without evaluation or even description. Surely science must build on previous work without constant and exhaustive reassessment, but for mineral textures a little reassessment may yield substantial benefit.

scholarly journals China's water sustainability in the 21st century: a climate-informed water risk assessment covering multi-sector water demands

2014 ◽  
Vol 18 (5) ◽  
pp. 1653-1662 ◽  
Author(s):  
X. Chen ◽  
D. Naresh ◽  
L. Upmanu ◽  
Z. Hao ◽  
L. Dong ◽  
...  
Keyword(s):  
Water Stress ◽  
Risk Measures ◽  
Rainfall Variability ◽  
Political Process ◽  
Temporal Distribution ◽  
High Water ◽  
Annual Rainfall ◽  
Water Sustainability ◽  
Domestic Water ◽  
Water Demands

Abstract. China is facing a water resources crisis with growing concerns as to the reliable supply of water for agricultural, industrial and domestic needs. High inter-annual rainfall variability and increasing consumptive use across the country exacerbates the situation further and is a constraint on future development. For water sustainability, it is necessary to examine the differences in water demand and supply and their spatio-temporal distribution in order to quantify the dimensions of the water risk. Here, a detailed quantitative assessment of water risk as measured by the spatial distribution of cumulated deficits for China is presented. Considering daily precipitation and temperature variability over fifty years and the current water demands, risk measures are developed to inform county level water deficits that account for both within-year and across-year variations in climate. We choose political rather than watershed boundaries since economic activity and water use are organized by county and the political process is best informed through that unit. As expected, the risk measures highlight North China Plain counties as highly water stressed. Regions with high water stress have high inter-annual variability in rainfall and now have depleted groundwater aquifers. The stress components due to agricultural, industrial and domestic water demands are illustrated separately to assess the vulnerability of particular sectors within the country to provide a basis for targeted policy analysis for reducing water stress.

scholarly journals Freshwater Reservoir Effect Variability in Northern Germany

Radiocarbon ◽  
2013 ◽  
Vol 55 (3) ◽  
pp. 1085-1101 ◽  
Author(s):  
Bente Philippsen ◽  
Jan Heinemeier
Keyword(s):  
Radiocarbon Dating ◽  
Potential Problem ◽  
Northern Germany ◽  
Reservoir Effect ◽  
The Past ◽  
Human Bones ◽  
Age Correction ◽  
Order Of Magnitude ◽  
Freshwater Reservoir ◽  
Reservoir Age

The freshwater reservoir effect is a potential problem when radiocarbon dating fish bones, shells, human bones, or food crusts on pottery from sites near rivers or lakes. The reservoir age in hardwater rivers can be up to several thousand years and may be highly variable. Accurate 14C dating of freshwater-based samples requires knowing the order of magnitude of the reservoir effect and its degree of variability. Measurements on modern riverine materials may not give a single reservoir age correction that can be applied to archaeological samples, but they show the order of magnitude and variability that can also be expected for the past. This knowledge will be applied to the dating of food crusts on pottery from the Mesolithic sites Kayhude at the Alster River and Schlamersdorf at the Trave River, both in Schleswig-Holstein, northern Germany.

The Trianon Peace Treaty of 1920: facts, legends, speculations

2020 ◽  
Author(s):  
Balázs Ablonczy ◽  
Keyword(s):  
Twentieth Century ◽  
Political Culture ◽  
Peace Treaty ◽  
World War ◽  
World War One ◽  
Conspiracy Theories ◽  
The Past ◽  
Sequence Of Events ◽  
Mass Consciousness ◽  
Opinion Polls

The signing of the peace treaty between the winners of World War One and the defeated Austria-Hungary in the Grand Trianon Chateau in the suburbs of Paris in 1920 was one of the most dramatic events in twentieth-century Hungarian history. It left traces in the mass consciousness and political culture of Hungary, and is still a controversial historical topic. According to recent opinion polls, the vast majority of the population believes that the treaty signed in Versailles was unjust. This book explores the mythical nature of this popular conviction, legends born around the signing of this document, and conspiracy theories that are still used to plausibly explain the past. The book is intended for the reader who wants to go beyond a mere reconstruction of the formal sequence of events, who searches for deeper explanations of the non-evident interdependences of the present day with the past, and who does not take “hot” news, journalistic speculations, and gossip at face value.

scholarly journals A Unifying View on Individual Bounds and Heuristic Inaccuracies in Bidirectional Search

2020 ◽  
Vol 34 (03) ◽  
pp. 2327-2334
Author(s):  
Vidal Alcázar ◽  
Pat Riddle ◽  
Mike Barley
Keyword(s):  
Lower Bound ◽  
Heuristic Search ◽  
Search Algorithm ◽  
Substantial Improvement ◽  
Full Potential ◽  
The Past ◽  
Heuristic Search Algorithms ◽  
Bidirectional Search ◽  
Order Of Magnitude ◽  
The Cost

In the past few years, new very successful bidirectional heuristic search algorithms have been proposed. Their key novelty is a lower bound on the cost of a solution that includes information from the g values in both directions. Kaindl and Kainz (1997) proposed measuring how inaccurate a heuristic is while expanding nodes in the opposite direction, and using this information to raise the f value of the evaluated nodes. However, this comes with a set of disadvantages and remains yet to be exploited to its full potential. Additionally, Sadhukhan (2013) presented BAE∗, a bidirectional best-first search algorithm based on the accumulated heuristic inaccuracy along a path. However, no complete comparison in regards to other bidirectional algorithms has yet been done, neither theoretical nor empirical. In this paper we define individual bounds within the lower-bound framework and show how both Kaindl and Kainz's and Sadhukhan's methods can be generalized thus creating new bounds. This overcomes previous shortcomings and allows newer algorithms to benefit from these techniques as well. Experimental results show a substantial improvement, up to an order of magnitude in the number of necessarily-expanded nodes compared to state-of-the-art near-optimal algorithms in common benchmarks.

scholarly journals An Ion Source for the HVEE 14C Isotope Ratio Mass Spectrometer for Biomedical Applications

Radiocarbon ◽  
1997 ◽  
Vol 40 (1) ◽  
pp. 283-288 ◽  
Author(s):  
Dirk J. W. Mous ◽  
Wim Fokker ◽  
Rein Van Den Broek ◽  
Ron Koopmans ◽  
Christopher Bronk Ramsey ◽  
...  
Keyword(s):  
Biomedical Research ◽  
Biomedical Applications ◽  
Ion Source ◽  
User Friendliness ◽  
The Past ◽  
Widespread Acceptance ◽  
First Results ◽  
Order Of Magnitude ◽  
Isotope Ratio Mass Spectrometer ◽  
Near Future

During the past two decades, accelerator mass spectrometry (AMS) has allowed major developments in many areas of geosciences and archaeology. In the near future, AMS should realize a similar potential in the field of biomedical research, leading ultimately to clinical applications. For such applications, the required instrument differs significantly from that presently used in the field of 14C dating. Whereas the needed accuracy and sensitivity is more than an order of magnitude less demanding than that for present state-of-the-art 14C instrumentation, the widespread acceptance of 14C AMS in biomedical research will require AMS spectrometers that are small, simple to operate and capable of handling CO2 samples. In order to satisfy these demands, HVEE has developed a compact 14C AMS spectrometer dedicated to biomedical research. The instrument consists of a compact accelerator with a footprint of 2.25 × 1.25 m and an ion source that features direct CO2 acceptance and optimal user friendliness. Having previously described the layout and design of the accelerator, we here discuss progress on the accelerator and present the design and first results of the CO2 ion source.

scholarly journals Remote sensing and conservation of isolated indigenous villages in Amazonia

2014 ◽  
Vol 1 (3) ◽  
pp. 140246 ◽  
Author(s):  
Robert S. Walker ◽  
Marcus J. Hamilton ◽  
Aaron A. Groth
Keyword(s):  
Remote Sensing ◽  
Satellite Imagery ◽  
Term Survival ◽  
Surveillance Programme ◽  
Non Invasive ◽  
External Threats ◽  
Indigenous Groups ◽  
Order Of Magnitude ◽  
Population Sizes

The vast forests on the border between Brazil and Peru harbour a number of indigenous groups that have limited contact with the outside world. Accurate estimates of population sizes and village areas are essential to begin assessing the immediate conservation needs of such isolated groups. In contrast to overflights and encounters on the ground, remote sensing with satellite imagery offers a safe, inexpensive, non-invasive and systematic approach to provide demographic and land-use information for isolated peoples. Satellite imagery can also be used to understand the growth of isolated villages over time. There are five isolated villages in the headwaters of the Envira River confirmed by overflights that are visible with recent satellite imagery further confirming their locations and allowing measurement of their cleared gardens, village areas and thatch roofed houses. These isolated villages appear to have population densities that are an order of magnitude higher than averages for other Brazilian indigenous villages. Here, we report on initial results of a remote surveillance programme designed to monitor movements and assess the demographic health of isolated peoples as a means to better mitigate against external threats to their long-term survival.

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