Cal Yr Research Articles

THE COMPLEMENTARY USE OF CHARCOAL NUMBER AND MORPHOLOGY TO RECONSTRUCT FIRE HISTORY IN A LATE HOLOCENE PEAT SEQUENCE FROM NW ROMANIA

Fires influence basic ecosystem processes, including the distribution, the structure and the composition of vegetation, as well as the carbon cycle and climate at the global scale. Long-term knowledge (i.e., centuries or millennia) of fire regime history and forest fire ecology and dynamic in local environments is necessary for sustainable ecosystem management and biodiversity conservation strategies. Charcoal is a widely used proxy for reconstructing fire regime history and vegetation burning. Charcoal analysis is based on the accumulation of charred particles in depositional environments such as lakes and bogs, during and shortly after the occurrence of fire events. Ombrotrophic peat bogs are sensitive to local environmental changes and, given that the deposition of allochthonous material is exclusively atmospheric, they are ideal archives for reconstructing charcoal fluxes resulting from biomass burning. This study quantifies charcoal abundance (number) in a peat sequence extracted from Tăul Mare ombrotrophic peat bog (Văratec Massif, Lăpuş Mts, north-western Romania) aiming to reconstruct local fire history over the last 3000 years and to explore potential drivers. As a novelty, observations concerning the morphology of charred fragments are added to provide additional information on the type of material burnt (woody vegetation or herbs), fire severity and charcoal source area, thus strengthening the interpretation of the charcoal record. Results showed moderate fire activity between 3000 and 2300 cal yr BP, which slightly decreased between 2300 and 700 cal yr BP and varied considerably throughout the last 700 years. Several major fire episodes were further identified around 2500, 1700, 1300, 900 and 500 cal yr BP. Of these, the first four overlapped two phases of progressive landscape opening and extension of pastoral activities, while the latter was unprecedented in the entire history of the bog and was likely associated with the development of mining activities in the area. This study provides the first complementary use of charcoal morphologies in fire history reconstruction in Romania and adds a valuable perspective on the extent of past human impact on the mid-elevation mountain landscape.

Multidisciplinary Study of the Rybachya Core in the North Caspian Sea during the Holocene

Mollusk fauna is an important component of the Caspian Sea ecosystem alongside ostracods and diatoms. These faunal proxies are essential indicators of hydrological shifts reflecting global and regional climate changes. Adding lithological, geochemical, and geochronological (radiocarbon) data, we revealed paleogeographic events of different scales recorded in the sequence of the Rybachya core from the North Caspian Sea. Here, we present the reconstruction of Mangyshlak paleovalley sediments during the Holocene multi-stage Neocaspian transgression, reflecting global and regional climate changes varying in scale and direction. The determined age of paleovalley-fill sediments, 8070 ± 110 cal yr BP and 7020 ± 140 cal yr BP, suggests that sedimentation processes with extended warming and humidification started later and lasted longer than was assumed earlier. Biological proxies indicate quasi-cyclic variability and shifts from brackish to freshwater conditions throughout the studied interval. Rybachya core was obtained from the early Khvalynian deposits. The Mangyshlak flow formed the depression and eroded the late Khvalynian deposits, which we did not observe in the core structure. It possibly collapsed into paleodepression and acted as a host material for the freshwater lentic faunal association. During the Holocene, we detected a transition from a tranquil water regime to a more dynamic one during the paleovalley gradual filling, followed by marine conditions typical for the modern Caspian Sea.

Kill dates from re-exposed black mosses constrain past glacier advances in the northern Antarctic Peninsula

AbstractGlaciers are receding in the northern Antarctic Peninsula and exposing previously entombed soils and plants. We used 39 black (dead) mosses collected from rapidly retreating ice margins at four sites along the Antarctic Peninsula to determine the kill dates using radiocarbon measurements and to constrain the timing of past glacier advances over the last 1500 yr. We established strict new criteria for sample collection to promote robust estimates of plant death. We found distinct phases of ice advance during ca. 1300, 800, and 200 calibrated years before 1950 (cal yr B.P.). We report estimates of the rate of glacier advance at ca. 800 cal yr B.P. at Gamage and Bonaparte Points (southern Anvers Island) of 2.0 and 0.3 m/yr, respectively. Although the range of kill dates is relatively narrow within a region, suggesting multiple glaciers advanced simultaneously, the rates of local advances can vary by almost an order of magnitude and are much less than retreat rates. Our kill dates coincide with evidence for glacier advances from other studies in the northern Antarctic Peninsula at ca. 1300, 800, and 200 cal yr B.P. and for penguin colony abandonment at several sites in the region ranging from 450 to 0 cal yr B.P. The combination of our new terrestrial evidence for glacier advances with other lines of evidence shows the regional synchroneity of glacial dynamics and cryosphere-biosphere connections during rapid climate shifts and the sensitivity of terrestrial ecosystems to climate cooling.

Anthropogenic activity and millennial climate variability affect Holocene mercury deposition of an alpine wetland near the largest mercury mine in China

Mercury (Hg) is a potentially toxic element that can be transported globally through the atmosphere, once deposited in the environment, has strong bioaccumulation and extreme toxicity in food webs, especially in wetland ecosystems. Anthropogenic Hg emissions have enhanced Hg deposition by 3–5 times since the industrial revolution, and the mining and smelting of Hg ore are important emission sources. However, the dynamics in Hg deposition around the largest Hg mine in China before the industrial revolution and their driving forces remain poorly explored. Here we reconstruct the atmospheric Hg depositional fluxes (named here Hg influx (Hginflux)) during the Holocene using a 450-cm alpine wetland sediment core taken from the Jiulongchi wetland, which is only 65 km to the Wanshan Mercury Mine. Our record shows an abrupt rapid increase in Hg concentration since 2500 cal yr BP, suggesting that Hg mining in southwest China may have started before the establishment of the Qin dynasty. Two major Hginflux peaks were found during the periods 10,000–6000 and 6000 - 3800 cal yr BP, with an increase in Hg deposition by a factor of 4–8. These two peaks are also found in other terrestrial archives from several sites across the Northern Hemisphere. We speculate that critical millennial-scale climate changes, i.e., the Holocene Climatic Optimum (HCO) and the Mid-Holocene Transition (MHT), were the potential triggers of these two Hginflux peaks. This study highlights the importance of climatic variability and local Hg mining in controlling atmospheric Hg deposition during the Holocene.

AMS 14C ages determination of the late Holocene Pilas, Mula and Cabeza de Vaca monogenetic volcanoes, Nicaragua

Here we present six new 14C ages using the accelerator mass spectrometry (AMS) technique for five samples of paleosol and one charcoal collected from the central part of the Maribios volcanic mountain range, located in the northwestern part of Nicaragua. This region is part of the Nicaraguan active volcanic arc characterized by the occurrence of a historic eruption that gave rise to the “birth” of the Cerro Negro volcano in 1850 CE. The young relief and the new 14C ages obtained in this work reveal that three other Holocene eruptions had recently occurred before the growth of the Cerro Negro volcano in this region. These volcanic events were independently established from an emission vent with simultaneous Strombolian explosions to dominantly effusive eruptions, forming extensive lava flows and associated scoria cones of the Cabeza de Vaca, Mula, and Pilas monogenetic volcanoes. AMS radiocarbon dating from charcoal and paleosols underlying these deposits yielded maximum ages of 1050 ± 30 years BP for Cabeza de Vaca volcano, 860 ± 30 yrs BP for Mula volcano, and 520 ± 15 yrs BP for Pilas volcano. These results of AMS 14C analyses provide reliable age ranges of 990–1025 cal yr AD for Cabeza de Vaca volcano, 1166–1220 cal yrs AD for Mula volcano, and 1410–1424 cal yrs AD for Pilas volcano.

Reconstruction of landscape and climate of the largest drainage basin in the Ladakh Range, NW Trans Himalaya during the last 7000 years

Landform geomorphology and glacial lake deposits in the largest drainage basin of the Ladakh Range i.e. Chang La-Tangtse basin were studied to infer their palaeoclimatic significance. The grain size, mineral magnetism, percentage loss on ignition (%LOI) and organic carbon stable isotope (δ13C) data in combination with total organic carbon (TOC) supported by AMS 14C (calibrated) dates of a 190 cm long section from the Chang La-Tsoltak palaeolake provides a climatic record since the last ∼ 7075 cal yr BP. The χlf, χARM, and SIRM values suggest that the catchment-derived palaeolake sediments predominantly contain magnetically “soft” minerals like magnetite and maghemite. The δ13C values range between −21 and −24 ‰ with an average of –22 ‰ which suggests a mixed C3-C4 plant signature and water stressed ecosystem. The relatively small variations in the δ13C values of organic matter in the entire lake profile suggest a stable climatic condition. The prominent effect of westerlies is seen between 7075 and 6040 cal yr BP with huge detrital influx at the lake bottom indicating a glacial advancement in the region. The affect of Mid-Holocene warm period is evident at 6040 cal yr BP with the advent of ISM. Paradigm shifts in the proxy values are observed at 5710, 4890, 3435, and 2800 cal yr BP. The influence of westerlies gradually reduces at 2800 cal yr BP. The landscape evolution and the climatic variations in the Trans-Himalaya are primarily governed by westerlies and do not correspond to the Indian monsoon variability records, particularly during the Mid-Holocene Thermal Maxima. Several other regions of the Ladakh Range also record similar climatic variations, indicating that the palaeolake sediments also reflect regional climate variations.

Inconsistent patterns of Holocene rainfall changes at the East Asian monsoon margin compared to the core monsoon region

Documenting spatiotemporal patterns of the Holocene Optimum (HO) at the climatically sensitive East Asian monsoon (EAM) margin are essential for understanding monsoon climate dynamics. However, the timing of the onset of the HO at the EAM margin is still debated and progress has been partly hindered by age uncertainties in different proxy records. To avoid the bias of these chronological uncertainties, we compared moisture variations from the marginal EAM region reconstructed from dust and aluminum (Al) flux records with tree pollen percentages in a dated lake sediment core that tracked moisture changes in the region around the lake. We show a delay (∼1500 years) of HO initiation in the core EAM region in northeastern China compared to the monsoon margin. Synthesizing pollen records with reliable chronologies show a synchronous HO occurrence at ∼8000-7000 cal yr BP at the monsoon margin, which is likely attributed to the shrinkage of the Northern Hemisphere ice sheet. Therefore, although the monsoon margin has always been considered a climate-sensitive area, it might be sensitive to different forcing factors from the core monsoon region.

Charcoal in Kunlun Mountains loess: Implications for environment change and human activity during the middle Holocene

Loess sediment charcoal records are used in paleoecological analyses to reconstruct fire history and human activities. The Tarim Basin is bordered to the south by the Kunlun Mountains, where eolian silt or loess is extensive and has continued to be deposited in modern times. In this study, we conducted multiple analyses of a 720 cm–thick loess section (KLA) at 3,516 m elevation in the Kunlun Mountains to reconstruct the middle Holocene vegetation history in northern China. Our palynological, charcoal, and grain-size data reveal a slightly drying trend with notable moisture fluctuations in the Kunlun highland since ∼4.9 kyr (1 kyr = 1,000 cal yr BP). At approximately 4.1, 2.0, and 1.0 kyr, the climate became more arid; the intervals of 4.0–3.2, 2.4–1.9 and 0.7–0.5 kyr were relatively wet periods. Some sand activity phases in the southern margin of the Taklimakan Desert are recorded around 4.0–3.5, 2.5–2.3, and 1.2–0.7 kyr. Stronger human activities commenced at approximately 2.0 kyr. On the basis of sedimentary charcoal concentrations and regional paleoclimatic and archaeological records, we propose that micro charcoal (<50 μm) originated from the Tarim Basin, reflecting human activity in the basin. Macro charcoal (>50 μm) is suitable for reconstructing Kunlun highland fire events. We suggest that increased anthropogenic activities such as agriculture, construction, and wars played an important role in land degradation and abandonment of ancient cities in the southern Tarim Basin. Our results provide new insights into the role of humans in the ecological evolution of inland arid areas in China during the middle Holocene.

Centennial-scale variability of the Indian Summer Monsoon during the middle to late Holocene and its links with ENSO activity

Relatively little is known about the relationship between the Indian summer monsoon (ISM) and the El Niño-Southern Oscillation (ENSO) on the centennial timescale during the Holocene. We present a well-dated high-resolution X-ray fluorescence (XRF) scanning record from a sediment core from Lake Qionghai on the southeastern Tibetan Plateau, which reveals the impact of ENSO activity on ISM variability. The results indicate a gradual drying of the regional climate on the sub-orbital timescale, which is in broad agreement with ISM changes controlled by Northern Hemisphere summer insolation. Additionally, centennial-scale drought events occurred at around 6230–5740, 4620–4250, 3820–3540, 3210–2440, 2180–1320, and 1000–615 cal yr B.P. and are consistent with enhanced ENSO activity, documenting the occurrence of ENSO-related drought events in the Holocene. Both ISM oscillations and ENSO variability show significant 350-yr, 500-yr, and 800-yr cyclicities, and there is a highly significant negative relationship between the ISM and ENSO at these cyclicities, indicating that a weak ISM was related to increased ENSO intensity, and vice versa. Our findings provide evidence for the modulation of ISM intensity by ENSO variability on the centennial timescale during the Holocene.

Peat sequence diatoms from Kedarnath, Central Himalaya, used to reconstruct mid-late Holocene hydroclimatic conditions

Diatoms preserved in peat can preserve valuable evidence of palaeoenvironmental changes due to their sensitivity to climatic changes and their crucial role in high productivity and nutrient cycling. We present total diatom concentrations and diatom community composition preserved in a high-altitude peat deposit located in the headwaters of the Mandakini River, Central Himalaya, India, to reconstruct the hydroclimatic conditions which prevailed during the mid-late Holocene. Since diatom productivity is associated with water table height/elevation, the high diatom concentrations during ∼5656–5307 cal yr BP, ∼4310–4264 cal yr BP, ∼3515–3024 cal yr BP and ∼ 1679–988 cal yr BP are inferred to have been periods of relatively high water table, denoting improved hydrological conditions. Conversely, low concentrations of diatoms occurred during ∼8077–5866 cal yr BP, ∼5263–4332 cal yr BP, ∼4241–3570 cal yr BP, ∼2970–1715 cal yr BP, and ∼ 697–370 cal yr BP. The temporal changes in the diatom suggest stressed hydrological conditions. The water table fluctuations inferred from diatom concentration variability show a positive correlation with the Indian summer monsoon (ISM) intensity and a negative correlation with the westerlies. The observed low concentrations of diatoms was associated with the relatively dry climatic conditions, which is detrimental to the peat environment and therefore suggests the need for in-situ data monitoring for the Indian peat deposits. As dry conditions can result in the deterioration of peat deposits, which may prove a significant source of atmospheric carbon dioxide in a changing climate, their conservation strategies will help limit carbon emissions.

Geochemistry of Holocene–Late Pleistocene sediments in the Berezovka River valley (Near-Yenisey Siberia)

Despite their great importance, Holocene–Late Pleistocene sediments are poorly studied in the valleys of rivers in the Krasnoyarsk forest-steppe territory. We present the first detailed study of the geochemical composition of the first floodplain terrace sediments in the valley of the Berezovka River, and the continuous accumulation that occurred at the Late Pleistocene-Holocene (from 20833 ± 519 cal yr BP). This is of great fundamental importance and is the basis for further studies on the influence of anthropogenic activities on the natural environment in the Krasnoyarsk agglomeration. The sediments were covered by modern alluvial dark-humus hydrometamorphosed soil. Macromorphological studies and investigation of the humus content have revealed a well-developed process of humus formation and humus accumulation, a gley process. The measured contents of some elements (U, Pr, Rb, V, Bi, Cd, As, Th, Ga, Co, and Sm) exceeded the respective Clarke values for the Earth’s crust. The distribution of most elements and their accumulation in the Middle-Late Holocene (from to 5477–4985 to 1241–803 cal yr BP) in the middle of the sediment profile is explained by the high content of mud and clay minerals. Based on the coefficients of radial migration, we established that most of the studied elements were introduced into the sediments during high water levels and floods. The values of palaeomarkers indicate a change in climatic conditions in the Late Pleistocene and Holocene from dry and cold to more humid and warm, and from arid and cold (in the Early Holocene) to modern climatic conditions, respectively.

A focus on the last 1000 years of natural environmental changes in the tropical rainforests of West and Central Africa. Can we detect anthropogenic disturbances?

The vast tropical rainforests of West and Central Africa were impacted by marked climatic deterioration, which mainly developed between 2500 and 2000 cal yr BP. However, the incidence of human intervention in these rainforests appears all the more speculative, although this was the period when the first stages of Bantu migration occurred towards the south. On the scale of the last millennium, which has seen increasing penetration and colonization of these Bantu peoples, one can envisage a priori a more accentuated anthropogenic pressure on the forest landscape. The combined observations of the environmental processes during the last 1000 years, as preserved in sediments from lakes, swamps, flooded forests and even oceanic environments, are presented on the basis of 24 records. The dominant number of sites in the humid forest or wooded savannas recorded only processes of relatively small size and local effects influencing vegetation cover almost simultaneously around 1000 and 500 cal yr BP; nothing is comparable with the devastating effect on a very large scale of the 2600 cal yr BP forest crisis. Conversely, other sites located in more perennial forest or savanna did not reveal any discontinuity. In all the examples of sedimentary archives considered, no out-of-phase or unusual event, possibly linked to human population and its impact, was observed. However, in more recent times, in intensive iron-ore mining/smelting areas, changes in the vegetal cover could be a legacy of charcoal production impacting forest biomass. Nevertheless, despite the clear cultural and socio-political importance of iron, its role in shaping vegetation communities in the Central African forest is generally presumed to be negligible. The oceanic causes of these climatic oscillations are more widely accepted. On a larger scale, the Medieval Warm Period and Little Ice Age are climatic anomalies visible in a number of palaeoenvironmental records worldwide and date to ∼1600–1000 cal yr BP and ∼ 700–100 cal yr BP, respectively. These events are less visible or sometimes not present in some palynological records of tropical Africa, whereas reconstructions from lacustrine records in Atlantic equatorial Africa show overall reductions in lake levels and increases in pollen belonging to light-demanding and pioneer vegetation formations in relation to these two oscillations. To reply to what was more important «the potential influence of human activities on regional climate, or the vulnerability of societies to environmental variability», it appears clearly to date, that the second paradigm is most likely. However, today, the ongoing combined efffects of climate change and human impact, including the decimation of the diversity of seed dispersers necessary to regenerate the rainforests of West and Central Africa, may have irreparable and unforeseen consequences.

Reconstruction of sedimentation conditions in paleo-reservoirs of the northern part of the Sambian Peninsula based on the comprehensive study of the Kulikovo section

A comprehensive analysis of the deposits of the paleo-reservoir represented in the Kulikovo section (the northern part of the Sambian Peninsula) has been carried out. According to results of radiocarbon dating, the deposits formed approximately from 14100 to 12900 cal yr BP. The most detailed data were obtained for the lower part of the section (depth 192–141 cm), comprising the Older Dryas and the first half of the Allerød. Results of a comprehensive lithological, diatom, spore-and-pollen analysis and algo-zoological microfossil analysis allowed us to identify 8 stages of the sedimentation conditions of the paleo-reservoir.

New evidence for Holocene vegetation variations and their drivers in an East Asian sandy land: A perspective from aeolian sand-paleosol deposits

Past vegetation responses to climate change in semi-arid and arid regions are not yet well understood, especially in northeastern China. This study provides new evidence for long-term vegetation changes and their possible driving forces in northeastern China's Songnen sandy lands by employing a multiproxy approach applied to well-dated aeolian sand-paleosol sediments. Pollen analyses and data on total organic carbon (TOC) are used to reconstruct paleovegetation dynamics whereas grain size data are used for interpreting independent paleoclimate changes. Results show that Chenopodiaceae and Ephedra plants dominated in a brief early period that was followed by an abrupt transition to Artemisia and Asteraceae plants with the encroachment of dry steppes between 9000 and 7000 cal yr BP. From 7000 to 3200 cal yr BP, Chenopodiaceae plant dominated the region. During the 3200 to 400 cal yr BP interval Ulmus, Salix, and Tribulus abundance increased while Chenopodiaceae abundance decreased. After 400 cal yr BP, Poaceae plants generally expanded and the regional landscape alternated between dry steppe and steppe. In addition, changes in the regional vegetation exhibit 1000 yr periodic oscillations especially during 9000 to 4500 cal yr BP. By comparing these features with regional climate change, we suggest that regional paleovegetation dynamics were linked to East Asia Summer Monsson (EASM) circulation. These findings reveal a pronounced long-term relationship between vegetation and climate change in semi-arid regions worldwide.

Quantitative tree cover reconstruction during the past 2000 years in the central–northern parts of the Daxing'an Mountains, northeast China

Reconstructing the history of tree cover and exploring the relationship between forest growth and environmental factors are of great significance for predicting future vegetation changes and guiding ecosystem restoration and protection. On the basis of pollen data of two lake cores and three peat profiles in the central–northern parts of the Daxing'an Mountains and using multiple methods, we quantitatively reconstructed the tree cover of the past 2000 years. We found that the reconstruction results of the different methods are quite similar. Among all these methods, random forest had the highest prediction accuracy for modern pollen samples. Therefore, the random forest reconstruction results can better reflect changes in regional tree cover, which was approximately 38%–42% during 2000–200 Cal yr BP. It then obviously increased from a low value of approximately 40% to a modern level of approximately 45%. The precipitation and carbon dioxide (CO2) concentration were the main drivers for the tree cover before and after 200 Cal yr BP, respectively. This indicates that environments with elevated CO2 level in the near future will benefit the growth of vegetation in the central–northern parts of the Daxing'an Mountains.

Dating of a large tool assemblage at the Cooper's Ferry site (Idaho, USA) to~15,785 cal yr B.P. extends the age of stemmed points in the Americas.

The timing and character of the Pleistocene peopling of the Americas are measured by the discovery of unequivocal artifacts from well-dated contexts. We report the discovery of a well-dated artifact assemblage containing 14 stemmed projectile points from the Cooper's Ferry site in western North America, dating to ~16,000 years ago. These stemmed points are several thousand years older than Clovis fluted points (~13,000 calyr B.P.) and are ~2300 years older than stemmed points found previously at the site. These points date to the end of Marine Isotope Stage 2 when glaciers had closed off an interior land route into the Americas. This assemblage includes an array of stemmed projectile points that resemble pre-Jomon Late Upper Paleolithic tools from the northwestern Pacific Rim dating to ~20,000 to 19,000 years ago, leading us to hypothesize that some of the first technological traditions in the Americas may have originated in the region.

A multi-approach inventory of the blue carbon stocks of Posidonia oceanica seagrass meadows: Large scale application in Calvi Bay (Corsica, NW Mediterranean)

In Mediterranean, Posidonia oceanica develops a belowground complex structure (‘matte’) able to store large amounts of carbon over thousands of years. The inventory of blue carbon stocks requires the coupling of mapping techniques and in situ sediment sampling to assess the size and the variability of these stocks. This study aims to quantify the organic (Corg) and inorganic (Cinorg) carbon stocks in the P. oceanica matte of the Calvi Bay (Corsica) using sub-bottom profiler imagery and biogeochemical analysis of sediment cores. The matte thicknesses map (average ± SD: 2.2 m ± 0.4 m) coupled with marine benthic habitat cartography allows to estimate matte volume at 12 473 352 m3. The cumulative stocks were assessed at 20.2–50.3 kg Corg m−2 and 26.6–58.7 kg Cinorg m−2 within the first meter of depth on matte (3632 ± 486 cal yr BP). The data contributed to estimate the overall carbon stocks at 389 994 t Corg and 615 558 t Cinorg, offering a new insight of the heterogeneity of blue carbon stocks in seagrass meadows. Variability of carbon storage capacity of matte influenced by substrate is discussed.

Washover deposits related to tsunami and storm surge along the north coast of the Shimokita Peninsula in northern Japan

A decade after the 2011 Tohoku-oki earthquake (Mw 9.0), geological surveys were conducted at multiple sites along the Pacific Coast of the tsunami-inundated Tohoku region in Japan, providing thousands of years of tsunami history. However, the challenges of correlation between historical records and geological tsunami deposits and identifying sources of historical and paleotsunamis have newly surfaced. Particularly the simultaneity and source of the 1611 Keicho tsunami in the Tohoku region and the seventeenth-century tsunami in the Hokkaido region are problematic. To solve such major issues, we conducted a tsunami-deposit survey at Sekinehama on the north coast of Shimokita Peninsula, near the junction of the Japan and Kuril trenches. We performed nondestructive analyses (X-ray computed tomography and micro-X-ray-fluorescence core scanning), grain-size analysis, tephra analysis, and radiocarbon dating of sediments from two coastal outcrops and inland drill cores. We identified five tsunami deposits (TD1–TD5) during the last 6 kyr and correlated them at a 200–400 m distance from the coast. They also correlate with previously identified tsunami deposits around the Shimokita Peninsula. From our study on tsunami deposits, we found other washover deposits in the coastal outcrops that are not represented in the inland cores. These indicate minor washover events related to small tsunamis and infrequent storm surges. The modeled age of the latest tsunami deposit is 500–300 cal yr BP (1450–1650 cal CE). This either correlates with two known tsunamis (the 1611 Keicho tsunami and another seventeenth-century tsunami) or is a previously unknown tsunami that occurred in the fifteenth–seventeenth centuries. If the latest tsunami deposit is to be accurately correlated with tsunami deposits previously identified within a 50-km distance from the study site, we need to consider an unknown fifteenth-century tsunami. Our investigation yields insights regarding the tsunami source in the vicinity of the junction of the Japan and Kuril trenches.

TRACES OF SEISMIC ACTIVITY IN THE LAKE BOTTOM SEDIMENTS OF EASTERN FENNOSCANDIA

This paper presents the results of a study on traces of ancient earthquakes in the lake bottom sediments of eastern Fennoscandia (Kola region and Karelia). Based on the sediment cores from six lake basins located within large active structures of the region, consideration is being given to the most typical features of sedimentation affected by neotectonic movements of the Earth’s crust. The data presented here provide lithological-stratigraphical, paleobotanical and chronometrical evidence for lakes. The paper causes and mechanisms of formation of seismic structures in bottom sediments and their distinction from deformations of another origin. Generalized earthquake history in provided an opportunity to organize the existing information on the time of paleoearthquake manifestations and distinguish three active periods in paleoseismicity. These are Late Glaciation-Early Holocene marked by the most rapid uplift after the retreat of the last ice sheet (13500–8100 cal yr BP), Middle Holocene (6800–6600 cal yr BP), and Late Holocene (3100–200 cal yr BP). The results of this study showed that the number and intensity of seismic events changed at different stages of sedimentation. Since the Younger Dryas, fault zones (or their segments) have been repeatedly activated. Combined with the data on paleoseismicity in adjacent parts of Fennoscandia, our studies indicate an irregular pattern of the Late Pleistocene-Holocene seismic activity in stable areas formerly covered by glaciers. The obtained data make further adjustments to the neogeodynamic and seismic estimates of intraplate areas.

Temporal and geographic extent of the late Holocene dry period in the central Great Basin, USA

We provide evidence from pollen and radiocarbon dating of wet meadow sediments for the presence of multi-centennial drought, termed the Late Holocene Dry Period (LHDP), in the central Great Basin between 3100 and 1800 cal yr BP. We examine four sites along a south to north transect between 39° N and 42° N latitude, spanning the boundary of the anti-phasing dipole pattern of precipitation associated with ENSO. The LHDP conforms to the dipole pattern but contains three different phases, an initial 900-year dry period, followed by 200 years of wetter climate and then another 200 years of extreme drought. The dipole boundary appears to have shifted to a new semi-stable position with each period. Between 3100 and 2200 cal yr BP, the boundary seems to conform to the 40° N parallel across central Nevada, and trending to 42° N in northwest Nevada. Between 2200 and 2000 cal yr BP the boundary shifted south of 40° N, when all sites predominantly record wet conditions. Between 2000 and 1800 cal yr BP the boundary shifts north to ∼41° N, representing the driest phase which was widespread across central Nevada. A review of lake levels, tree-rings, and submerged stumps suggest that the drought between 2000 and 1800 cal yr BP was of greater magnitude than that recorded during the MCA megadrought. We do not yet have sufficient information to establish a cause for megadroughts, however it is important to note that the climate system periodically locks into a pattern with a consistently northward shifted storm track that persists for multiple decades to centuries, bringing persistent drought to the American Southwest. Indigenous human societies adapted to severe droughts through a variety of responses, suggesting a pattern of resilience and mobility in response to recurring climate change across the Great Basin.