Multiproxy study of anthropogenic and climatic changes in the last two millennia from a small mire in central Poland

The Żabieniec kettle hole is the first peatland in central Poland analyzed quantitatively with four biotic proxies (plant macrofossils, pollen, testate amoebae and chironomids) to reconstruct the past environmental change. Palaeoecological data were supported by historical and archaeological records. We focused on autogenic vegetation change and human impact in relation to climatic effects. The aims of our study were (a) to describe the development history of the mire during the last 2,000 years, (b) to date and reconstruct the anthropogenic land-use changes and (c) to discuss a possible climatic signal in the peat archive. The combination of proxies revealed dramatic shifts that took place in the peatland since the Roman Period. Żabieniec was a very wet telmatic habitat until ca. AD 600. Then, the water table declined, and the site transformed into a Sphagnum-dominated mire. This dry shift took place mainly during the Early Medieval Period. Human impact was gradually increasing, and it was particularly emphasized by deforestation since AD 1250 (beginning of the Late Medieval Period). Consequently, surface run-off and aeolian transport from the exposed soils caused the eutrophication of the mire. Furthermore, chironomids and testate amoebae reveal the beginning of a wet shift ca. AD 1350. Openness considerably increased in the Late Medieval and the Modern Periods. The highest water table during the last 1,000 years was recorded between AD 1500 and 1800. This wet event is connected with deforestation, but it could be also associated with the Little Ice Age. Our study shows plant succession in the Żabieniec peatland, which can be explained with the recent landscape transformation. However, such changes are also possibly linked with the major climatic episodes during the last two millennia, such as the Medieval Warm Period and the Little Ice Age. Guest editors: K. Buczkó, J. Korponai, J. Padisák & S. W. Starratt Palaeolimnological Proxies as Tools of Environmental Reconstruction in Fresh Water     

Climatic changes during the past 1300 years as deduced from the sediments of Lake Nakatsuna, central Japan

Limnological features and sediment characteristics were studied in Lake Nakatsuna, a mesotrophic lake in central Japan. The lake is dimictic, and is anoxic in the hypolimnion during thermal stratification from May to September. In an attempt to reconstruct paleoclimatic changes around the lake, a sediment core taken from the lake center spanning the past 1300 years was analyzed for its organic and inorganic contents. Climatic influences were examined on the variation of total organic carbon (TOC), total nitrogen (TN), and sand contents. Short- and long-term fluctuations in TOC, TN, and sand contents are evident, and variation in atmospheric temperature appears to be important for their long-term variability. The sediment record from AD 900 to 1200 indicates hot summers and warm winters with less snow accumulation, whereas the record from AD 1200 to 1950 is characterized by high variation of temperature, with three cool phases from AD 1300 to 1470, 1700 to 1760, and 1850 to 1950. The warm period from AD 900 to 1200 corresponds well to the Medieval Warm Period, and the second and third cool phases are related to the Little Ice Age. Received: February 16, 2001 / Accepted: June 7, 2001     

南海永暑礁微型软体动物对晚全新世快速气候变化的响应

近2000年来的地球环境变化日益受到人们的关注,许多替代指标被用来指示快速的气候变化。本文试图通过南海永暑礁泻湖微型软体动物丰度和分异度的研究及其与北半球温度异常的对比,来阐述微型软体动物对快速气候变化的响应。研究表明,软体动物丰度变化的三个高值和三个低值较好地对应于北半球温度异常,显示了微型软体动物丰度对快速气候变化的灵敏反应。尤其重要的是“小冰期”和“中世纪暖期”被证明在南海也发生过。这表明快速的气候变化事件也会影响到热带海区。研究还证实另一次温暖的气候事件发生在大约 850A.D.—680A.D.之间。文中对软体动物分异度与气候变化的关系也作了探讨,并表明软体动物丰度和分异度是指示气候变化的有用指标。     

Times of Plenty, Times of Less: Last-Millennium Societal Disruption in the Pacific Basin

During the last millennium in the Pacific Basin (islands and continental rim) there was a marked contrast between ‘times of plenty’ and ‘times of less’ for its human societies. This contrast is attributable to climate and sea-level variations, notably the Medieval Warm Period (a.d. 700–1250) and the Little Ice Age (a.d. 1350–1800) separated by a time of rapid cooling and sea-level fall called the ‘a.d. 1300 Event.’ Outlines of the times of plenty during the Medieval Warm Period and the times of less during the Little Ice Age are given, supported by a number of examples. These confirm a general picture of societal collapse as a result of the a.d. 1300 Event. Well-dated human responses to the a.d. 1300 Event (establishment of fortified settlements, end of ocean voyaging) allow links to potential nonhuman causes to be strengthened. Although more data referring to both (natural) changes and their human effects are needed, a conclusion involving environmental determinism is inescapable.     

Late holocene environments in Las Tablas de Daimiel (south central Iberian peninsula,Spain)

The use of a high resolution pollen record in combination with geochemical data from sediments composed mainly of layers of charophytes alternating with layers of vegetal remains plus some detrital beds permits the reconstruction of the environmental evolution of the last 3000 years in an inland wetland of the Mediterranean domain, thus introducing a new climatic dataset for the Late Holocene. Hydrological fluctuations, reflected in the relationship between emerged and aquatic vegetation and inorganic and organic C and N changes, can be related to aridity or humid phases, while relations among arboreal taxa (Quercus and Pinus) and Artemisia are used as temperature indicators. Five climatic periods have been identified: a Subatlantic Cold Period (<150 b.c.), cold and arid; the Roman Warm Period (150 b.c.–a.d. 270), warmer and wetter; the Dark Ages (a.d. 270–a.d. 950), colder and drier; the Medieval Warm Period (a.d. 950–a.d. 1400), warmer and wetter; and the Little Ice Age (>a.d. 1400) indicated by a cooling and drying trend. Despite the lack of any direct evidence of human action, there are some episodes related to deforestation during the Reconquista (Middle Ages) that mask the real climatic signal.     

3800 Years of Quantitative Precipitation Reconstruction from the Northwest Yucatan Peninsula

Precipitation over the last 3800 years has been reconstructed using modern pollen calibration and precipitation data. A transfer function was then performed via the linear method of partial least squares. By calculating precipitation anomalies, it is estimated that precipitation deficits were greater than surpluses, reaching 21% and <9%, respectively. The period from 50 BC to 800 AD was the driest of the record. The drought related to the abandonment of the Maya Preclassic period featured a 21% reduction in precipitation, while the drought of the Maya collapse (800 to 860 AD) featured a reduction of 18%. The Medieval Climatic Anomaly was a period of positive phases (3.8–7.6%). The Little Ice Age was a period of climatic variability, with reductions in precipitation but without deficits.     

滇中阳宗海流域过去1200年以来的环境变化

根据滇中阳宗海78 cm沉积岩芯的花粉/炭屑分析,重建了阳宗海流域过去1200年的植被演替、气候变化和森林火灾史。岩芯年代框架的建立基于底部一个植物残体的AMS14C测年和上部的210Pb测年。结果表明:1)阳宗海流域过去1200年的植被变化经历了4个阶段:暖干期(780—1630 AD)的植被以松栎混交林为主,草本植物少;凉湿期(1630—1860 AD)的植被仍以松栎混交林为主,但比重有所减少并存在明显波动,草本植物显著增加;冷干期(1860—1950 AD)和随后的暖干期(1950 AD之后)受人类活动干扰强烈,人类活动可能已成为影响植被的主导性因素。2) 1200年以来,阳宗海流域气候变化存在明显的暖期(780—1630 AD)和冷期(1630—1950 AD),分别对应了中世纪暖期和小冰期,且水热条件配置呈现暖干-冷湿的模式,与滇西天才湖、洱海和青藏高原东部等邻近区域较为同步。整个暖期气温波动不大,仅在最暖的12世纪中期到15世纪中期温度表现出较大的波动,小冰期存在两个气候波动阶段,分别是1630—1860 AD凉湿期和1860—1950 AD的冷干期。阳宗海流域气候变化的主...     

The Extratropical Northern Hemisphere Temperature Reconstruction during the Last Millennium Based on a Novel Method

Large-scale climate history of the past millennium reconstructed solely from tree-ring data is prone to underestimate the amplitude of low-frequency variability. In this paper, we aimed at solving this problem by utilizing a novel method termed “MDVM”, which was a combination of the ensemble empirical mode decomposition (EEMD) and variance matching techniques. We compiled a set of 211 tree-ring records from the extratropical Northern Hemisphere (30–90°N) in an effort to develop a new reconstruction of the annual mean temperature by the MDVM method. Among these dataset, a number of 126 records were screened out to reconstruct temperature variability longer than decadal scale for the period 850–2000 AD. The MDVM reconstruction depicted significant low-frequency variability in the past millennium with evident Medieval Warm Period (MWP) over the interval 950–1150 AD and pronounced Little Ice Age (LIA) cumulating in 1450–1850 AD. In the context of 1150-year reconstruction, the accelerating warming in 20^th century was likely unprecedented, and the coldest decades appeared in the 1640s, 1600s and 1580s, whereas the warmest decades occurred in the 1990s, 1940s and 1930s. Additionally, the MDVM reconstruction covaried broadly with changes in natural radiative forcing, and especially showed distinct footprints of multiple volcanic eruptions in the last millennium. Comparisons of our results with previous reconstructions and model simulations showed the efficiency of the MDVM method on capturing low-frequency variability, particularly much colder signals of the LIA relative to the reference period. Our results demonstrated that the MDVM method has advantages in studying large-scale and low-frequency climate signals using pure tree-ring data.     

The Medieval Climate Anomaly and Little Ice Age in Chesapeake Bay and the North Atlantic Ocean

A new 2400-year paleoclimate reconstruction from Chesapeake Bay (CB) (eastern US) was compared to other paleoclimate records in the North Atlantic region to evaluate climate variability during the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). Using Mg/Ca ratios from ostracodes and oxygen isotopes from benthic foraminifera as proxies for temperature and precipitation-driven estuarine hydrography, results show that warmest temperatures in CB reached 16-17 °C between 600 and 950 CE (Common Era), centuries before the classic European Medieval Warm Period (950-1100 CE) and peak warming in the Nordic Seas (1000-1400 CE). A series of centennial warm/cool cycles began about 1000 CE with temperature minima of ~ 8 to 9 °C about 1150, 1350, and 1650-1800 CE, and intervening warm periods (14-15 °C) centered at 1200, 1400, 1500 and 1600 CE. Precipitation variability in the eastern US included multiple dry intervals from 600 to 1200 CE, which contrasts with wet medieval conditions in the Caribbean. The eastern US experienced a wet LIA between 1650 and 1800 CE when the Caribbean was relatively dry. Comparison of the CB record with other records shows that the MCA and LIA were characterized by regionally asynchronous warming and complex spatial patterns of precipitation, possibly related to ocean-atmosphere processes.     

A late Holocene climate record from a stalagmite, Cold Air Cave, Northern Province, South Africa

Stable isotope analyses of a uranium-series-dated stalagmite from South Africa provide a record of climate changes for the periods 4400–4000 years and 800 years ago to recent, interrupted by a prolonged growth hiatus. Generally enriched stable oxygen isotope values, interpreted here to indicate more humid conditions, occurred around 800 years ago. Subsequently a marked depletion in oxygen and carbon isotope values occurred about 600 years ago, reflecting, we believe, shifts toward drier, cooler conditions as the regional indication of the Little Ice Age. This period with depleted, yet oscillating isotope values, is replaced by a period with enriched isotopes until recent times. The record is notable for sharp shifts in isotopic values, on the scale of decades, which reflect rapid oscillations in local climate conditions.     

The North Atlantic Oscillation forcing through the last 2000 years: Spatial variability as revealed by high-resolution marine diatom records from N and SW Europe

The Tagus pro-delta (Portuguese Margin) and the Skagerrak (NE of the North Sea) are two marine systems controlled by atmospheric changes, which at present are mainly determined by fluctuations of the North Atlantic Oscillation (NAO). On the basis of diatom records from marine sediment cores, environmental changes (primary productivity and salinity) are reconstructed for the last 2000 years for both regions. These sites are investigated focusing on the regional response to changing NAO forcing.Both studied sites are characterized by sedimentation rates in the order of 0.12 cm/year and 0.47 cm/year for the most recent deposits off the Tagus pro-delta, allowing high-resolution paleoceanographic reconstructions (8.3 and 2.1 years represented per sample). The last 2000 years are a period covering in Europe the historical climatic periods known as the Dark Ages (DA), the Medieval Warm Period (MWP) and the Little Ice Age (LIA). In the Skagerrak, the cold periods of the DA and LIA are marked by diatom dissolution stages, whereas at the Tagus pro-delta, the DA were associated with increased diatom production and possible upwelling and the onset of the LIA corresponded to enhanced flow of the Tagus River. During the MWP, better diatom preservation in the Skagerrak, related to stronger advection of salty Atlantic waters, is paralleled by dominant upwelling conditions at the Tagus pro-delta. The two most intense upwelling periods at the Tagus pro-delta, at ∼ AD 600 and ∼ AD 900, correspond to a dissolution stage and a slight change in salinity in the Skagerrak, respectively.Although the comparison of the two study sites suggests a common forcing such as the NAO, the different inferred behaviors for each main climatic period in each region demonstrate that the NAO by its own is not sufficient to explain the climatic variability at a regional scale.     

Tree ring imprints of long-term changes in climate in western Himalaya,India

Tree-ring analyses from semi-arid to arid regions in western Himalaya show immense potential for developing millennia long climate records. Millennium and longer ring-width chronologies of Himalayan pencil juniper (Juniperus polycarpos), Himalayan pencil cedar (Cedrus deodara) and Chilgoza pine (Pinus gerardiana) have been developed from different sites in western Himalaya. Studies conducted so far on various conifer species indicate strong precipitation signatures in ring-width measurement series. The paucity of weather records from stations close to tree-ring sampling sites poses difficulty in calibrating tree-ring data against climate data especially precipitation for its strong spatial variability in mountain regions. However, for the existence of strong coherence in temperature, even in data from distant stations, more robust temperature reconstructions representing regional and hemispheric signatures have been developed. Tree-ring records from the region indicate multi-century warm and cool anomalies consistent with the Medieval Warm Period and Little Ice Age anomalies. Significant relationships noted between mean premonsoon temperature over the western Himalaya and ENSO features endorse utility of climate records from western Himalayan region in understanding long-term climate variability and attribution of anthropogenic impact.     

Past and future demographic dynamics of alpine species: limited genetic consequences despite dramatic range contraction in a plant from the Spanish Sierra Nevada

Anthropogenic global climate change is expected to cause severe range contractions among alpine plants. Alpine areas in the Mediterranean region are of special concern because of the high abundance of endemic species with narrow ranges. This study combined species distribution models, population structure analyses and Bayesian skyline plots to trace the past and future distribution and diversity of Linaria glacialis, an endangered narrow endemic species that inhabits summits of Sierra Nevada (Spain). The results showed that: (i) the habitat of this alpine‐Mediterranean species in Sierra Nevada suffered little changes during glacial and interglacial stages of late Quaternary; (ii) climatic oscillations in the last millennium (Medieval Warm Period and Little Ice Age) moderately affected the demographic trends of L. glacialis; (iii) future warming conditions will cause severe range contractions; and (iv) genetic diversity will not diminish at the same pace as the distribution range. As a consequence of the low population structure of this species, genetic impoverishment in the alpine zones of Sierra Nevada should be limited during range contraction. We conclude that maintenance of large effective population sizes via high mutation rates and high levels of gene flow may promote the resilience of alpine plant species when confronted with global warming.     

Late holocene environmental changes in the Southwestern Chukchi Sea inferred from diatom analysis

The environmental changes in the southern part of the Chukchi Sea over the last 2300 years (two warmings during the ~262 BC–630 AD and ~630–1300 periods AD and 1 cooling ~1300–1840 AD) were inferred from changes in the content of diatoms in sediments (per gram), the ratio of dominant species, and the ecological structure of diatom assemblages. The sediment age was determined based on the recent ²¹⁰Pb sedimentation rates at the sampling point (0.43 mm/yr) and radiocarbon dating of mollusk shells. The environmental changes in the southern Chukchi Sea that were inferred from the diatom analysis correlate with global climate changes, viz., the warming events of the early (Roman) and the middle (Medieval) Subatlantic and the cooling of the late (Little Ice Age) Subatlantic.     

Summer monsoon precipitation variations in central China over the past 750 years derived from a high-resolution absolute-dated stalagmite

A 2–3-year resolution record of stalagmite oxygen isotope variations from the south flank of the Qinling Mountains, central China, has revealed the Asian summer monsoon (ASM) precipitation variations in the investigated area over the past 750 years. The summer monsoon precipitation gradually increased since 1249 AD, reaching its highest values in the period 1535–1685 AD, and then decreased with substantial decadal- to centennial-scale fluctuations. The monsoon precipitation increased again between 1920 and 1970 AD. Three intervals of high monsoon precipitation were identified: 1535–1685 AD, 1755–1835 AD, and 1920–1970 AD. Three intervals of low precipitation were inferred in 1249–1325 AD, 1390–1420 AD, and 1890–1915 AD. The δ¹⁸O composition and lithological features of the stalagmite coincidently indicate a wetter climate during the Little Ice Age (LIA), which is also confirmed by climate records from Chinese historical documents within this area. A comparison with other high-resolution speleothem records indicates regional differences in monsoon precipitation variability from the south to the north of central China in the last 750 years on decadal- to centennial-scale. Power spectrum analysis of the δ¹⁸O record shows significant 117.8-, 34.6-, 14-, 10.3-, and ~ 6-year periodicities. These periodicities are widely observed in the climate records from ASM-controlled areas of China and are consistent with the Gleissburg periodicity, Brϋckner periodicity, sunspot periodicity of solar activity, and El Nińo–Southern Oscillation (ENSO) periodicity. These correlations suggest that both solar activity and ENSO periodicity may have had important influences on ASM precipitation in China over the past 750 years.     

A 215-yr coral δ18O time series from Palau records dynamics of the West Pacific Warm Pool following the end of the Little Ice Age

The West Pacific Warm Pool (WPWP) is a critical region of the global climate system that is closely linked with the El Niño-Southern Oscillation (ENSO). We have generated two monthly resolved coral δ¹⁸O (δ¹⁸O_CRL) records from a key region of the WPWP, the Republic of Palau (7′N, 135′E). The isotopic time series span the years 1793–2008 and 1899–2008. During the period of overlap, the two records are well correlated at interannual and annual periods. Multiple lines of evidence demonstrate a strong ENSO signal in Palau δ¹⁸O_CRL. Our records are consistent with previous investigations of twentieth-century tropical Pacific climate variability. We identify a regionally coherent bi-decadal cycle in the WPWP following the termination of the Little Ice Age. The Palau δ¹⁸O_CRL records show long-term trends towards warming/freshening, suggesting a century scale increase in the strength of the hydrologic cycle associated with the WPWP. Our study represents an important addition to the network of tropical paleo-archives.     

X-ray microdensitometry applied to subfossil tree-rings: growth characteristics of ancient pines from the southern boreal forest zone in Finland at intra-annual to centennial time-scales

A collection of subfossil wood of Pinus sylvestris (Scots pine) was exposed to X-ray densitometry. The collection of 64 samples from the southern boreal forest zone was dendrochronologically cross-dated to a.d. 673-1788. Growth characteristics were determined by performing density profiles including the following parameters: minimum density, earlywood and latewood boundary density, maximum density, earlywood width, earlywood density, latewood width, latewood density, annual ring width and annual ring density. Seven out of the nine parameters were found to contain non-climatic growth trends and six were found to be heteroscedastic in their variance. Tree-specific records were indexed, to remove the non-climatic growth trends and stabilize the variance, and combined into nine parameter-specific tree-ring chronologies. Growth characteristics of the pines changed in parallel with the generally agreed climatic cooling from the Medieval Warm Period to the Little Ice Age: pine tree-rings showed decreasing maximum densities from the period a.d. 975-1150 to a.d. 1450–1625. A concomitant change in the intra-annual growth characteristics was detected between these periods. The findings indicate that not only the trees growing near the species’ distributional limits are sensitive to large-scale climatic variations but also the trees growing in habitats remote from the timberline have noticeably responded to past climate changes.     

Effects of El Niño-related Drought on Freshwater and Brackish-water Fishes in Suriname, South America

Droughts associated with the El Niño-Southern Oscillation (ENSO) affected fishes of brackish-water lagoons, freshwater swamps and a rainforest creek in Suriname, South America. The mean rainfall in the period August to February in 22 El Niño years was 76.6% of the mean rainfall in the same months of non-El Niño years. In the period 1900–1999, three out of four years in which an extreme drought (rainfall less then 60% of the mean value) occurred were El Niño years. The recent 1997/1998 ENSO event caused the second most severe drought in a 100-year record. Drying up of brackish-water lagoons, freshwater swamps and rainforest creeks was observed during El Niño-related droughts. In the lagoons ariid catfish died first, followed by snook, tilapia, mullet and tarpon, respectively. Landings of lagoon fish were positively correlated with rainfall in the period August–February. During the El Niño-related drought we observed failure of reproduction in three species of callichthyid armoured catfish in both coastal freshwater swamps and a rainforest creek in the interior. In the El Niño year 1997/1998, the no flow period of the rainforest creek was extended by four months beyond the long dry season and the dissolved oxygen levels in the dry-season pools dropped to 1.27mg O₂l^–1 (as compared to 4.53mg O₂l^–1 under running water conditions). Other fish species of the rainforest creek also showed decreased reproductive success in the El Niño year. We suggest that the stochastic effects of El Niño-related drought may be an important non-equilibrium component in the ecology of neotropical inland fish communities.     

Vegetation history,human impact and climate change during the last 700 years recorded in annually laminated sediments of Lac Pavin,France

This paper presents a 1.80-m-long varved sediment record documenting the vegetation history by pollen and diatom analysis recovered from Lake Pavin, a volcanic crater lake in the Auvergne (French Massif Central). High-resolution sampling and a varve-based age model allowed the reconstruction of ecosystem responses to both regional climate change and human impact. According to the present varve chronology, the Lake Pavin sequence covers the last 700 years, thus representing the late Subatlantic period (i.e. from the Late Medieval onwards). The pollen record largely reflects intensive human influence (clearing, cultivation and grazing) on the lake surrounding area. The arboreal pollen spectrum of the entire sequence is co-dominated by Fagus and Quercus, except during the 20th century. However, whilst the Quercus record is relative stable, several major fluctuations are discernable in the Fagus curve. An increase in Pinus and Picea shortly before of the turn the 20th Century, indicates afforestation by conifers. The varve counting indicates that the most prominent signal in the Fagus curve occurs during the period between about 1540 and 1670 AD. During this interval, the initial drop in the Fagus curve is estimated to have taken 5–10 years, with the subsequent recovery occurring over a similar period. Since there is no clear evidence of tree population replacement, such rapid signals imply that the fluctuations in the Fagus curve reflect variations in pollen production, being influenced by the cooler temperatures experienced during a cold spell of the Little Ice Age.     

1200 years of fire and vegetation history in the Willamette Valley, Oregon and Washington, reconstructed using high-resolution macroscopic charcoal and pollen analysis

High-resolution macroscopic charcoal and pollen analyses were used to reconstruct the fire and vegetation history of the Willamette Valley for the last 1200 years. Presented in this paper are three new paleoecological reconstructions from Lake Oswego, Porter Lake, and Warner Lake, Oregon, and portions of previous reconstructions from Battle Ground Lake, Washington, and Beaver Lake, Oregon. The reconstructions show that prior to Euro-American settlement vegetation and fire regimes were influenced by a combination of natural and anthropogenic factors. Battle Ground Lake shows a stronger influence from climate, while Lake Oswego, Beaver Lake, Porter Lake, and Warner Lake were more controlled by human activity. However, human-set fires were also modulated by regional climate variability during the Medieval Climate Anomaly and the Little Ice Age. Fire reconstructions from Battle Ground Lake, Lake Oswego, Beaver Lake, and Porter Lake imply that fires were infrequent in the Willamette Valley 200-300 years prior to Euro-American settlement. The decline of Native American populations due to introduced disease may have led to this reduction in fire activity. The prehistoric record from Warner Lake, however, indicates that fires in the foothills of the Cascade Range were more frequent than on the valley floor, at least until ca. AD 1800. The historic portions of the reconstructions indicate that Euro-American land clearance for agriculture and logging produced the most dramatic shifts in vegetation and fire regimes. All five records indicate that few fires in the Willamette Valley have occurred since ca. AD 1930, and fires today are predominantly grass fires.