Climatic Episodes Research Articles

Eruption dynamics of pleistocene maars and tuff rings from the Azrou-Timahdite district (Middle Atlas, northern Morocco) and its relevance to environmental changes and ground water table characteristics

The small (≈500 km2) Azrou-Timahdite basaltic area (Middle Atlas Magmatic Province, Northern Morocco) lies on a Lias (200-180 Ma) karst plateau of medium altitude (between 1,750 and 1,950 m). This area includes 23 small-sized Early Pleistocene (2.5–0.8 Ma) scoria cones and 30 Middle Pleistocene (around 0.6–0.5 Ma) hydrovolcanic edifices. The Pleistocene was a period of strong climatic instability in North Africa: three peaks of aridity would have occurred near 2.8 Ma, 1.7 Ma and 1.0 Ma (DeMenocal, 2004), but the period between 500 and 650 ka would belong to a predominantly wet stage (Jimenez et al., 2010). The scoria cones of the Azrou-Timahdite area would therefore formed when the climate was dry and the hydrovolcanic edifices when it was wet. The hydrovolcanic edifices of the Azrou-Timahdite area are peculiarly interesting because they display an exceptional diversity in terms of morphologies and ejecta deposits which can be only explained by interaction of magma with variable amounts of water, sometimes even during a single eruptive event. The karst regions like the Middle Atlas Plateau are very sensitive to fluctuations in rainfall and during a wet climatic episode the deep karst is permanently saturated with water while the epikarst has degrees of saturation that vary with the topography. Our study suggests that the diversity of hydrovolcanic dynamics in the Azrou-Timahdite area could be linked not only to the degree of saturation of the epikarst but also to the thickness of the transmission zone separating the deep water-saturated karst and the epikarst which also depends on the topographic position of the eruptive sites.

Radiocarbon chronology and environmental context of Last Glacial Maximum human occupation in Switzerland

Central Europe during the Last Glacial Maximum (LGM) was dominated by polar desert and steppe-tundra biomes. Despite this, a human presence during this time period is evident at several locations across the region, including in Switzerland, less than 50 km from the Alpine ice sheet margin. It has been hypothesised that such human activity may have been restricted to brief periods of climatic warming within the LGM, but chronological information from many of these sites are currently too poorly resolved to corroborate this. Here we present a revised chronology of LGM human occupation in Switzerland. AMS radiocarbon dating of cut-marked reindeer (Rangifer tarandus) bones from the sites of Kastelhöhle-Nord and Y-Höhle indicates human occupation of Switzerland was most likely restricted to between 23,400 and 22,800 cal. BP. This timeframe corresponds to Greenland Interstadial 2, a brief warming phase, supporting the hypothesis that human presence was facilitated by favourable climatic episodes. Carbon, nitrogen and sulphur stable isotope analysis of the fauna provides palaeoenvironmental information for this time period. These findings contribute to our understanding of human activity in ice-marginal environments and have implications for understanding cultural connections across central Europe during the LGM.

Buffered, Incomplete, and Shredded: The Challenges of Reading an Imperfect Stratigraphic Record

AbstractClimate, tectonics, and life influence the flux and caliber of sediment transported across Earth's surface. These environmental conditions can leave behind imprints in the Earth's sedimentary archive, but signals of climate, tectonic, and biologic change are not always present in the stratigraphic record. Deterministic and stochastic surface dynamics collectively act as a stratigraphic filter, impeding the burial and preservation of environmental signals in sedimentary deposits. Such impediments form a central challenge to accurately reconstructing environmental conditions through Earth's history. Emergent and self‐organized length and timescales in landscapes, which are themselves influenced by regional environmental conditions, define spatial and temporal sedimentation patterns in basins and fundamentally control the likelihood of environmental signal preservation in sedimentary deposits. Properly characterizing these scales provides a key avenue for incorporating the known “imperfections” of the stratigraphic record into paleoenvironmental reconstructions. These insights are necessary for answering both basic and applied science questions, including our ability to reconstruct the Earth system response to prior episodes of climate, tectonic, or land cover change.

Consumption Change Detection for Urban Planning: Monitoring and Segmenting Water Customers During Drought

AbstractDemand management is a powerful way for water utilities to address the challenges of population growth and climate change. Although active conservation efforts have been studied extensively, recent evidence suggests households respond to many external events beyond a utility's control, including political responses to extreme climatic episodes and corresponding mass media coverage. Despite their importance, these external factors are difficult to analyze in a controlled setting, and few tools exist to evaluate their influence on customers. Here, we present a consumption change detection (CCD) method that offers new insights into how climate‐related mass media and policy events affect conservation by pinpointing the timing and magnitude of customer‐level water use shifts. We use CCD to monitor and segment the responses of residential water customers to policy and media events in Costa Mesa, California, during the severe 2012–2016 drought. Our results show consumption reductions among 75% of customers. Of these, 80% reduced water use before mandatory restrictions were imposed, coincident with intensifying state policy responses and spikes in media coverage that affected all customer types during 2014. Analysis of standardized drought consumption trajectories indicates that 16% of conserving customers increased consumption in 2015–2016. Conservation and rebound were both more likely among affluent and educated customers, suggesting that CCD can identify engaged and informed water savers who make suitable targets for water‐efficient retrofit incentive schemes. This study demonstrates CCD's potential as a novel demand analysis tool in an interconnected world where external social, political, and climatic stressors can exert an important influence on customer behavior.

Human behavioral responses to the 8.2 ka BP climatic event: Archaeological evidence from the Zhongshandong Cave Site in Bubing basin, Guangxi, southern China

As one of the most pronounced climatic episodes during the Holocene, the impact of the 8.2 ka BP cooling event was felt throughout the Northern Hemisphere. However, human behavioral responses to this climatic episode has only recently begun to be documented in different areas of the world. Southern China is one region where these human behavioral responses have yet to be clearly identified. Here, we present a recent discovery of stone artifacts from the Zhongshandong (ZSD) Cave Site, which is located in Bubing Basin, Guangxi Zhuang Autonomous Region, southern China. The cultural deposits within ZSD have been tentatively dated to the 8.2 ka BP cooling event. The ZSD Cave is a narrow, low ceiling cave about 60 m in length. Sixty-one stone artifacts were surface collected in the extremely dark terminal chamber in the back of the cave. One stone artifact was found in situ in the same area of the cave. The overlying stalagmite was U-series dated to 8130 ± 430 years BP and charcoal found below the artifact was AMS dated to 8242 ± 54 years BP. The stone artifact assemblage is comprised of cores, flakes, choppers, and scrapers produced on locally available river cobbles, an artifact collection normally assigned to the eastern Asian Early Paleolithic. Charcoal fragments are abundant in the cultural layer, implying that fire was possibly used for lighting and/or warmth. Interestingly, given the dimensions of the inner chamber and the fact that the cultural deposits sit about 60 m inside the cave, this would not be considered a typical area that would be suitable for long term human occupation. Although other possibilities may exist, one possible explanation may be that, due to the cold winter and/or harsh environment during the 8.2 ka BP climatic event, these hunter-gatherers were forced deeper inside the cave to set up their temporary campsite. This is a hypothesis that needs further testing.

Biochronology of Late Triassic Metoposauridae (Amphibia, Temnospondyli) and the Carnian pluvial episode

During the Late Triassic, metoposaurids were one of the last significant families of temnospondyl amphibians, and they have long been used in the correlation of Late Triassic tetrapod assemblages. Their fossil record extends across much of Late Triassic Pangea, including important metoposaurid fossils from the USA, Canada, Portugal, Germany, Poland, Morocco, India and Madagascar. Six genera of metoposarids are recognized: 1) Adamanian-Apachean Apachesaurus , endemic to the western USA, 2) Otischalkian Arganasaurus and Dutuitosaurus , endemic to Morocco, 3) Otischalkian-Revueltian Koskinonodon , endemic to the western USA, 4) Panthasaurus from the Otischalkian of India, and 5) Otischalkian-Adamanian Metoposaurus , known from the western USA, eastern Canada, Portugal, Italy, Germany, and Poland. Of the metoposaurid genera, only Metoposaurus has a broad enough palaeogeographic distribution and relatively restricted temporal range to be of biochronological value; its biochron identifies the Otischalkian–Adamanian (middle–late Carnian). The oldest metoposaurids are of middle Carnian age, the age of the Carnian pluvial episode of global climate. The middle Carnian broad palaeogeographic distribution, diversity and cosmopolitanism of the metoposaurids, followed by reduced diversity and relative endemism, likely indicates that climate changes were an important factor in their evolution.

Mid Holocene Sea-Level Changes in and around Dhaka City, Bangladesh

Bengal basin, the largest fluvio-deltaic sedimentary system on Earth, is located in Bangladesh and three eastern states of India. Sediment accumulates in the basin from the Ganges, Brahmaputra, and Meghna (GBM) river systems and is dispersed into the Bay of Bengal, forming the largest submarine fan in the world. The present-day geomorphology is dominated by the extensive Holocene GBM floodplain and delta. The initiation of the modern GBM delta at the onset of the Pleistocene glacial maximum and its evolution to the present configuration are intricately related to Holocene fluvio-dynamic processes, eustatic sea-level changes, and tectonic movements. Quaternary System in Bengal basin has varieties of depositional environment. Sediment characteristics of different geomorphic units are different. Late Quaternary monsoon climatic episodes played the vital role in creating the present morphology of the Madhupur surfaces. During the Holocene, the central part of the basin experienced cyclic transgression and regression phase in several times. This was the evidence by mangrove pollens. The presence of mangrove pollen specially Phoenix paludosa, Avicennia sp, Phoenix sylvestris, Prosopis grandis, Sonneratiopollis sp found in Chatbari, Dubadia and Mirertek area of Dhaka city along with radiocarbon dating indicated that marine influence occurred during Mid Holocene time. Two phases of transgression and regression have been recorded during mid Holocene time. First transgression was noticed around 6500 cal BP and then a subsequent regression of the bay had been observed around 5500-3500 cal BP. This was again followed by another transgression episode around 3500-1500 cal BP. and then a regression during between 1500 cal BP onwards.

Late Ordovician obliquity-forced glacio-eustasy recorded in the Yangtze Block, South China

A high-precision time framework is critical for improving our understanding of three major events: the Late Ordovician mass extinction, the Hirnantian glaciation, and the Hirnantian isotopic carbon excursion (HICE). In the present study, we conducted detailed cyclostratigraphic analysis of a high-resolution (1–2-cm intervals) anhysteretic remanent magnetization series obtained from the Wanhe section in South China, covering the lower Katian through Hirnantian. Power spectra and derived average spectral misfit results show that the section records the ensemble of Milankovitch cycles with 405-kyr (long-eccentricity), 93–125-kyr (short-eccentricity), 33.8-kyr (main obliquity), and 17–22-kyr (precession) periods. The obliquity period of 33.8 ± 0.46 kyr indicates a precession constant k of 57.19 ± 0.53 arcsec/yr, a length of day of 22.37 ± 0.12 h, and an Earth–Moon distance of 375,330 ± 722 km (vs. 384,000 km today) during the Late Ordovician (445 Ma). The ratios of obliquity band power to total power reveal periodicities of 1.32 Myr for the s4–s3 term and 173.4 kyr for the s3–s6 term. Aided by the highly fluctuating magnetic susceptibility (MS), we recognized a series of 1.32-Myr obliquity-forced glacio-eustatic cycles with three intervals of sea-level rise and climate warming trend characterized by high MS values and two episodes of sea-level fall and climate cooling trend before the Hirnantian. The 405-kyr and subsequent 33.8-kyr calibrations produce an ~7.36-Myr floating astronomical time scale (FATS) for the studied succession, indicating that the estimated durations for the Hirnantian Stage, the worldwide Hirnantian glaciation, and the first and second phases of the Late Ordovician mass extinction were ~1225 kyr, ~830 kyr, ~440 kyr, and ~540 kyr, respectively. This work provides a reliable high-resolution time framework for further investigation of the major geological events occurred in the Late Ordovician, and improves our knowledge of Solar System behaviour and Earth–Moon history during that period.

Complexity in crisis: The volcanic cold pulse of the 1690s and the consequences of Scotland's failure to cope

Recent work has linked historical crises, both regional and local, with palaeoclimatic estimates of global and hemispheric climate change. Such studies tend to underemphasize the spatiotemporal and socioeconomical disparity of human suffering and adaptive capacity as well as the complexities of past climate change. We focus herein on the effects in Scotland of a severely cold climate episode in the 1690s, associated with major tropical volcanic events including a large unidentified tropical eruption in 1695. A tree-ring based summer temperature reconstruction from the northern Cairngorms region identifies the 1690s as the coldest decade in Scotland for the last 750 years. Archival sources meanwhile reveal the 1690s as likely the worst era of crop failure, food shortage, and mortality ever documented in Scottish history. The connection appears simple - volcanic cooling triggered famine - but the drivers towards famine are far more complex. Although the unusual coldness of the 1690s was near-hemispheric in scale, it had a differential impact across north-western Europe. Within Scotland, both lowlands and highlands experienced dire conditions, but distinct factors exacerbated the suffering in each region. We integrate historical and palaeoclimatic records to explore the influence of the volcanic cold pulse of the 1690s and its consequences in Scotland. We find that while cooling temperatures characterized the regional to larger-scale climate, vulnerability and response potential were diverse and shaped by local circumstances. The Scottish crisis of the 1690s, in the context of the kingdom's failing economy, influenced investors from all parts of society, including the nobility and entire communities, to fund the ill-fated expedition to colonize Darien in modern-day Panama. The climate crisis and the colony's collapse hindered Scotland's already sluggish economy, motivating unification with England soon after.

Análisis estadístico de las dataciones radiocarbónicas de la Motilla del Azuer (Daimiel, Ciudad Real)

Las 70 dataciones radiocarbónicas, de las 80 realizadas en la Motilla del Azuer, incluidas en este trabajo proceden en su mayoría de muestras vegetales de vida corta y de restos humanos y faunísticos. Se pretende realizar diversos análisis estadísticos de las citadas dataciones como suma de probabilidades y análisis bayesianos (a partir de los programas Calib, BCal y OxCal), a fin de definir mejor la secuencia de ocupación del yacimiento y obtener un marco cronológico más detallado para situar en el tiempo los cambios ambientales y socioeconómicos que tuvieron lugar a lo largo de la ocu- pación del asentamiento. Los resultados muestran una primera ocupación calcolítica del yacimiento de escasa entidad separada de la fundación de la fortificación de la Edad del Bronce por un hiatus bien definido. La ocupación de la Motilla del Azuer desde el Bronce Antiguo hasta un momento avanzado del Bronce Tardío es continua y viene marcada por diversas fases de reconstrucción y ampliación de la fortificación que afectan también al pozo y a las estructuras hidráulicas situadas en el patio oriental del recinto fortificado. Del análisis de estos datos se desprende que la periodización publicada para la Motilla del Azuer es válida y muestra, en un marco de progresiva y fuerte jerarquización social, que la sucesión de diferentes episodios climáticos fue un factor crucial en el desarrollo de un sistema de asentamiento específico en La Mancha durante la Edad del Bronce.

Late-Holocene sedimentation and sodium carbonate deposition in hypersaline, alkaline Nasikie Engida, southern Kenya Rift Valley

Continental rift systems are often characterized by geothermal activity and associated discharge of hot groundwater, which can substantially impact the water, solute and sediment budgets of rift-valley lakes. Hot-spring inflow can result in complex lake hydro- and geochemistry, but also buffers against the desiccation of closed-basin lakes in dry climate regimes. Consequently, hydrothermally fed lakes can potentially provide continuous sedimentary records from regions where other types of paleoenvironmental archives are lacking. This is illustrated by Nasikie Engida, a shallow hypersaline and alkaline (soda) lake in the semiarid Rift Valley of southern Kenya. Here, inflow of hot-spring water has maintained a shallow but permanent water body and continuous deposition of sediments through past climate episodes when many other lakes in the eastern (Gregory) branch of the East African Rift System stood dry. We present the first data on late-Holocene sedimentation in this remarkable lacustrine system, typified by authigenic nahcolite [NaH(CO3)] formation during part of its recorded history. Our data include measurements of bulk-sediment and mineralogical composition, clastic-mineral grain size and magnetic susceptibility. Analytical issues related to the large amount of salts within the sediments, both as crystals and in solution in the pore water, are discussed. We also present exploratory time series of the stable-isotope composition of bulk organic matter and authigenic nahcolite. Core lithostratigraphy and preliminary radiocarbon dating indicate that Nasikie Engida has accumulated finely laminated sediments continuously since ca. 2850 cal year BP, which is remarkable given its current maximum depth of only 1.6 m. Synsedimentary nahcolite appears abruptly ~ 2260 cal year BP and since then has been deposited regularly, in the form of distinct pure layers up to several cm thick. Its formation has been enabled by high pCO2, supplied principally from geothermal sources, accumulating in a high-density brine. Although Nasikie Engida has likely been saline over the entire time span covered by the studied sediment sequence, variation in nahcolite deposition and bulk-sediment composition suggests multi-decadal to centennial oscillations in water-column stability and stream inflow driven by variation in climatic moisture balance. Further analyses of this paleoenvironmental archive may thus produce the first continuous climate-proxy record from a vast dry region of equatorial East Africa. Moreover, Nasikie Engida’s extraordinary setting makes it a unique modern analogue for the interpretation of ancient nahcolite-bearing salt-lake deposits.

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

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.

Warm Deep Water Variability During the Last Millennium in the CESM–LME: Pre-Industrial Scenario versus Late 20th Century Changes

Water transformation around Antarctica is recognized to significantly impact the climate. It is where the linkage between the upper and lower limbs of the Meridional Overturning Circulation (MOC) takes place by means of dense water formation, which may be affected by rapid climate change. Simulation results from the Community Earth System Model Last Millennium Ensemble (CESM–LME) are used to investigate the Weddell Sea Warm Deep Water (WDW) evolution during the Last Millennium (LM). The WDW is the primary heat source for the Weddell Sea (WS) and accounts for 71% of the Weddell Sea Bottom Water (WSBW), which is the regional variety of the Antarctic Bottom Water (AABW)—one of the densest water masses in the ocean bearing directly on the cold deep limb of the MOC. Earth System Models (ESMs) are known to misrepresent the deep layers of the ocean (below 2000 m), hence we aim at the upper component of the deep meridional overturning cell, i.e., the WDW. Salinity and temperature results from the CESM–LME from a transect crossing the WS are evaluated with the Optimum Multiparameter Analysis (OMP) water masses decomposition scheme. It is shown that, after a long–term cooling over the LM, a warming trend takes place at the surface waters in the WS during the 20th century, which is coherent with a global expression. The subsurface layers and. mainly. the WDW domain are subject to the same long–term cooling trend, which is decelerated after 1850 (instead of becoming warmer like the surface waters), probably due interactions with sea ice–insulated ambient waters. The evolution of this anomalous temperature pattern for the WS is clear throughout the three major LM climatic episodes: the Medieval Climate Anomaly (MCA), Little Ice Age (LIA) and late 20th century warming. Along with the continuous decline of WDW core temperatures, heat content in the water mass also decreases by 18.86%. OMP results indicate shoaling and shrinking of the WDW during the LM, with a ~6% decrease in its cross–sectional area. Although the AABW cannot be directly assessed from CESM–LME results, changes in the WDW structure and WS dynamics have the potential to influence the deep/bottom water formation processes and the global MOC.

Clay minerals in the sediments as useful paleoclimate proxy: Lake Sentarum case study, West Kalimantan, Indonesia

Lake Sentarum is a flood-plains lake that will dry and flood as climate cycle that is interesting to be studied climate change from the past to near the present. The objective of this study is to reveals paleoclimate conditions by analysing clay minerals that present in the lake sediments. The study investigated clay mineral in lake sediments from 70 cm long core, X-RD analysis was obtained to identify various of clay minerals. The clay minerals of Lake Sentarum comprises of illite, chlorite, and kaolinite. The relative change in abundance of clay minerals indicating climate conditions, besides numbers of chemistry and crystallinity of illite represents weathering mechanism. Our research reveals that climate history of Lake Sentarum from sediments core began cold and arid climate episode. This episode was characterized by low value of illite chemistry and illite crystallinity were 0.37-0.41 and 0.19°Δ2θ-0.2°Δ2θ, respectively, and slight decrease abundance of kaolinite. There was no significant changes until the middle of the sediments core. Significant changes of abundance of kaolinite and illite chemistry occurred in top of the core. The percentage of kaolinite and illite chemistry became the highest value that reflected strong chemical weathering occurred in the watershed with warm and high rainfall climate conditions.

Episódio do clima urbano em São Carlos/SP em situação sazonal de outono em 2014: modelagem da ilha de calor urbana.

Entendido como um dos principais problemas ambientais, o clima urbano resulta das alterações no clima local associadas ao processo de urbanização, sobretudo pelas transformações na ocupação do solo e a retirada da cobertura vegetal e sua substituição por materiais construídos. As ilhas de calor ou bolsões de ar quente que se formam sobre a superfície é um fenômeno recorrente nas cidades e sua identificação, intensidade e representação espacial é fundamental para as análises dos problemas ambientais e urbanos. Deste modo, este artigo apresenta a análise de um episódio do clima urbano em situação sazonal de outono a partir de transectos móveis e procedimentos estatísticos para a modelagem da ilha de calor em função das categorias geográficas em estudo aplicado a São Carlos/SP. A metodologia se mostrou robusta e as diferenças térmicas foram superiores a 5°C de intensidades distribuídas espacialmente em função do padrão construtivo, áreas densamente edificadas e aos locais pouco arborizados.

Sensitivity of grain yields to historical climate variability in India

Fluctuations in temperature and precipitation influence crop productivity across the planet. With episodes of extreme climate becoming increasingly frequent, buffering crop production against these stresses is a critical aspect of climate adaptation. In India, where grain production and diets are closely linked, national food supply is sensitive to the effect of climate variability on monsoon grain production. Here we quantitatively examine the historical (1966–2011) relationship between interannual variations in temperature and rainfall and rainfed yield variability for five monsoon crops—rice and four alternative grains (finger millet, maize, pearl millet, and sorghum). Compared to rice, we find that alternative grains are significantly less sensitive to climate variation and generally experience smaller declines in yield under climate extremes. However, maximizing harvested area allocations to coarse grains (i.e. holding maize production constant) reduced grain production by 12.0 Mtonnes (−17.2%) under drought conditions and 12.8 Mtonnes (−18.0%) during non-drought years (non-drought). Increasing the harvested area allocated to all alternative grains (i.e. including maize) can enhance production by +39.6% (drought) and by +37.0% (non-drought). These alternative grains therefore offer promise for reducing variations in Indian grain production in response to climate shocks, but avoiding grain production shortfalls from increased alternative grains will require yield improvements that do not compromise their superior climate resilience.

Reconstruction holocene environmental changes in North-Western Pacific in relation to paleorecord from Shikotan Island

Results of a paleolimnological investigated of a well-dated lake sediment section from Shikotan Island (Southern Kurils) showed that from ca 8.0 to 5.8 cal ka BP warm and humid period corresponding to middle Holocene optimum took place. Cooling thereafter corresponds to Neoglacial. A reconstructed from ca 0.9 to ca 0.58 cal ka BP warm period can be correlated to a Medieval Warm Period. Cooling after 0.58 cal ka BP can be correlated with the LIA. Marine regression stages were identified at ca 6.2-5.9, 5.5-5.1 and 1.07-0.36 cal ka BP. The general chronology of major climatic events of Holocene in the island is in accordance with the climate records from the North Pacific region. Revealed spatial differences in timing and magnitude of the Late Holocene climatic episodes (LIA, MWP) within region needs further investigations.

Millennial-scale glacial climate variability in Southeastern Alaska follows Dansgaard-Oeschger cyclicity

A stalagmite from Prince of Wales Island grew episodically between ~75,000 and ~11,100 yr BP; interrupted by seven hiatuses. Hiatuses most likely correspond to permafrost development and a temperature drop of up to 5 °C from modern conditions. Intervals of calcite deposition place tight constraints on the timing of mild climatic episodes in Alaska during the last glacial period, when permafrost was absent, allowing water infiltration into the karst system. These periods of calcite deposition are synchronous, within dating uncertainties, with Greenland Interstadials 1, 10, 11, 12c, 14b-14e, 16.1a, 17.2, and 20c.

Reconstruction of Holocene Environmental Changes in North-Western Pacific in Relation to Paleorecord from Shikotan Island

Results of a paleolimnological investigation of a well-dated lake sediment section from Shikotan Island (Southern Kurils) showed that from ca 8.0 to 5.8 cal ka BP a warm and humid period corresponding to middle Holocene optimum took place. Cooling thereafter corresponds to Neoglacial. A reconstructed from ca 0.9 to ca 0.58 cal ka BP warm period can correspond to a Medieval Warm Period. Cooling after 0.58 cal ka BP can be correlated with the LIA. Marine regression stages were identified at ca 6.2–5.9, 5.5–5.1 and 1.07–0.36 cal ka BP. The general chronology of major climatic events of Holocene in the island is in accordance with the climate records from the North Pacific region. Revealed spatial differences in timing and magnitude of the Late Holocene climatic episodes (LIA, MWP) in the region needs further investigations.

The role of Late Pleistocene-Holocene tectono-sedimentary history on the origin of patches of savanna vegetation in the middle Madeira River, southwest of the Amazonian lowlands

Savanna patches are features of the Amazonian landscape that have been long under intense debate, but there are still questions about the main factors that have determined their establishment and evolution within the rainforest matrix. In particular, their geological substrates were poorly documented. The aim of this work is to reconstruct the tectono-sedimentary history of four savanna patches in the middle Madeira River, southwest Amazonia, and discuss its potential control over the development of the savanna communities. The approach consisted in the integration of geomorphological, sedimentological, chronological and floristic data. The results revealed that the savanna substrates are sandy deposits aged between 118.9 and 35.6 ky, overlain by late Pleistocene to Holocene muddier successions <25,700 cal yr BP. Most of the geologically stable and topographically higher terrains of the geomorphological unit T1 is dominated by forests. These intermingle with open habitats formed by renewed sedimentation that were colonized by tree and shrub species of the Amazonian biome. By contrast, the ground of unit T2 subsided to a level that allowed the meandering of the main river. This process resulted in the replacement of the rainforest by open habitats dominated by savannas with lower richness and diversity than in the T1 unit, which were dominated by species with wide distribution in the cerrado biome of Central Brasil. The cerrado species might have expanded into this region during Pleistocene drier climatic episodes, but environmental filters shaped by geological processes determined the floristic contrasts between units T1 and T2. The lack of competition with Amazonian species probably constituted an important factor for the preferential colonization of arboreal and shrubby species from neighboring cerrados on meandering scroll bars, marginal levees and crevasse splays of unit T2.