(Table 1) Age determination of sediment cores CH07-98-22 and KNR140-2-59

Western subtropical North Atlantic oceanic and atmospheric circulations connect tropical and subpolar climates. Variations in these circulations can generate regional climate anomalies that are not reflected in Northern Hemisphere averages. Assessing the significance of anthropogenic climate change at regional scales requires proxy records that allow recent trends to be interpreted in the context of long-term regional variability. We present reconstructions of Gulf Stream sea surface temperature (SST) and hydrographic variability during the past two millennia based on the magnesium/calcium ratio and oxygen isotopic composition of planktic foraminifera preserved in two western subtropical North Atlantic sediment cores. Reconstructed SST suggests low-frequency variability of ~1°C during an interval that includes the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). A warm interval near 1250 A.D. is distinct from regional and hemispheric temperature, possibly reflecting regional variations in ocean-atmosphere heat flux associated with changes in atmospheric circulation (e.g., the North Atlantic Oscillation) or the Atlantic Meridional Overturning Circulation. Seawater d18O, which is marked by a fresher MCA and a more saline LIA, covaries with meridional migrations of the Atlantic Intertropical Convergence Zone. The northward advection of tropical salinity anomalies by mean surface currents provides a plausible mechanism linking Carolina Slope and tropical Atlantic hydrology.

Deuterium isotope ratios of Victoria Lower Glacier Ice Core

The Little Ice Age (LIA) is one of the most prominent climate shifts in the past 5000 yrs. It has been suggested that the LIA might be the most recent of the Dansgaard-Oeschger events, which are better known as abrupt, large scale climate oscillations during the last glacial period. If the case, then according to Broecker (2000a, 2000b) Antarctica should have warmed during the LIA, when the Northern Hemisphere was cold. Here we present new data from the Ross Sea, Antarctica, that indicates surface temperatures were ~2 °C colder during the LIA, with colder sea surface temperatures in the Southern Ocean and/or increased sea-ice extent, stronger katabatic winds, and decreased snow accumulation. Whilst we find there was large spatial and temporal variability, overall Antarctica was cooler and stormier during the LIA. Although temperatures have warmed since the termination of the LIA, atmospheric circulation strength has remained at the same, elevated level. We conclude, that the LIA was either caused by alternative forcings, or that the sea-saw mechanism operates differently during warm periods.

Talos Dome Ice Core Deuterium Data

During the 1996 Programma Nazionale di Ricerche in Antartide-International Trans-Antarctic Scientific Expedition traverse, two firn cores were retrieved from the Talos Dome area (East Antarctica) at elevations of 2316 m (TD, 89 m long) and 2246 m (ST556, 19 m long). Cores were dated by using seasonal variations in non-sea-salt (nss) SO42- concentrations coupled with the recognition of tritium marker level (1965-1966) and nss SO42- spikes due to the most important volcanic events in the past (Pinatubo 1991, Agung 1963, Krakatoa 1883, Tambora 1815, Kuwae 1452, Unknown 1259). The number of annual layers recognized in the TD and ST556 cores was 779 and 97, respectively. The dD record obtained from the TD core has been compared with other East Antarctic isotope ice core records (Dome C EPICA, South Pole, Taylor Dome). These records suggest cooler climate conditions between the middle of 16th and the beginning of 19th centuries, which might be related to the Little Ice Age (LIA) cold period. Because of the high degree of geographical variability, the strongest LIA cooling was not temporally synchronous over East Antarctica, and the analyzed records do not provide a coherent picture for East Antarctica. The accumulation rate record presented for the TD core shows a decrease during part of the LIA followed by an increment of about 11% in accumulation during the 20th century. At the ST556 site, the accumulation rate observed during the 20th century was quite stable.

Spatial and temporal variability in midge (Nematocera) assemblages in shallow Finnish lakes (60−70 °N) : community-based modelling of past environmental change

Multi- and intralake datasets of fossil midge assemblages in surface sediments of small shallow lakes in Finland were studied to determine the most important environmental factors explaining trends in midge distribution and abundance. The aim was to develop palaeoenvironmental calibration models for the most important environmental variables for the purpose of reconstructing past environmental conditions. The developed models were applied to three high-resolution fossil midge stratigraphies from southern and eastern Finland to interpret environmental variability over the past 2000 years, with special focus on the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA) and recent anthropogenic changes. The midge-based results were compared with physical properties of the sediment, historical evidence and environmental reconstructions based on diatoms (Bacillariophyta), cladocerans (Crustacea: Cladocera) and tree rings. The results showed that the most important environmental factor controlling midge distribution and abundance along a latitudinal gradient in Finland was the mean July air temperature (TJul). However, when the dataset was environmentally screened to include only pristine lakes, water depth at the sampling site became more important. Furthermore, when the dataset was geographically scaled to southern Finland, hypolimnetic oxygen conditions became the dominant environmental factor. The results from an intralake dataset from eastern Finland showed that the most important environmental factors controlling midge distribution within a lake basin were river contribution, water depth and submerged vegetation patterns. In addition, the results of the intralake dataset showed that the fossil midge assemblages represent fauna that lived in close proximity to the sampling sites, thus enabling the exploration of within-lake gradients in midge assemblages. Importantly, this within-lake heterogeneity in midge assemblages may have effects on midge-based temperature estimations, because samples taken from the deepest point of a lake basin may infer considerably colder temperatures than expected, as shown by the present test results. Therefore, it is suggested here that the samples in fossil midge studies involving shallow boreal lakes should be taken from the sublittoral, where the assemblages are most representative of the whole lake fauna. Transfer functions between midge assemblages and the environmental forcing factors that were significantly related with the assemblages, including mean air TJul, water depth, hypolimnetic oxygen, stream flow and distance to littoral vegetation, were developed using weighted averaging (WA) and weighted averaging-partial least squares (WA-PLS) techniques, which outperformed all the other tested numerical approaches. Application of the models in downcore studies showed mostly consistent trends. Based on the present results, which agreed with previous studies and historical evidence, the Medieval Climate Anomaly between ca. 800 and 1300 AD in eastern Finland was characterized by warm temperature conditions and dry summers, but probably humid winters. The Little Ice Age (LIA) prevailed in southern Finland from ca. 1550 to 1850 AD, with the coldest conditions occurring at ca. 1700 AD, whereas in eastern Finland the cold conditions prevailed over a longer time period, from ca. 1300 until 1900 AD. The recent climatic warming was clearly represented in all of the temperature reconstructions. In the terms of long-term climatology, the present results provide support for the concept that the North Atlantic Oscillation (NAO) index has a positive correlation with winter precipitation and annual temperature and a negative correlation with summer precipitation in eastern Finland. In general, the results indicate a relatively warm climate with dry summers but snowy winters during the MCA and a cool climate with rainy summers and dry winters during the LIA. The results of the present reconstructions and the forthcoming applications of the models can be used in assessments of long-term environmental dynamics to refine the understanding of past environmental reference conditions and natural variability required by environmental scientists, ecologists and policy makers to make decisions concerning the presently occurring global, regional and local changes. The developed midge-based models for temperature, hypolimnetic oxygen, water depth, littoral vegetation shift and stream flow, presented in this thesis, are open for scientific use on request.

Sexual reproduction in chydorid cladocerans (Anomopoda, Chydoridae) in southern Finland - implications for paleolimnology

The relationship between sexual reproduction of littoral chydorid cladocerans (Anomopoda, Chydoridae) and environmental factors in aquatic ecosystems has been rarely studied, although the sexual behavior of some planktonic cladocerans is well documented. Ecological monitoring was used to study the relationship between climate-related and non-climatic environmental factors and chydorid sexual reproduction patterns in nine environmentally different lakes that were closely situated to each other in southern Finland. Furthermore, paleolimnological ephippium analysis was used to clarify how current sexual reproduction is reflected in surface sediments of the same nine lakes. Additionally, short sediment cores from two of the lakes were studied with ephippium analysis to examine how recent climate-related and non-climatic environmental changes were reflected in chydorid sexual reproduction. Ephippium analysis uses the subfossil shells of asexual individuals to represent asexual reproduction and the shells of sexual females, i.e. ephippia, to represent sexual reproduction. The relative proportion of ephippia of all chydorid species, i.e. total chydorid ephippia (TCE) indicates the relative proportion of sexual reproduction during the open-water season. This thesis is part of the EPHIPPIUM-project which aims to develop ephippium analysis towards a quantitative climate reconstruction tool. To be able to develop a valid climate model, the influence of the environmental stressors other than climate on contemporary sexual reproduction and its reflection in sediment assemblages must be clarified so they can be eliminated from the model. During contemporary monitoring a few sexual individuals were observed during summer, apparently forced to sexual reproduction by non-climatic local environmental factors, such as crowding or invertebrate predation. Monitoring also revealed that the autumnal chydorid sexual reproduction period was consistent between the different lakes and climate-related factors appeared to act as the main inducers and regulators of autumnal sexual reproduction. However, during autumn, chydorid species and populations among the lakes exhibited a wide variation in the intensity, induction time, and length of autumnal sexual reproduction. These variations apparently act as mechanisms for local adaptations due to the genetic variability provided by sexual reproduction that enhance the ecological flexibility of chydorid species, allowing them to inhabit a wide range of environments. A large variation was also detected in the abundance of parthenogenetic and gamogenetic individuals during the open-water season among the lakes. On the basis of surface sediment samples, the general level of the TCE is ca. 3-4% in southern Finland, reflecting an average proportion of sexual reproduction in this specific climate. The variation in the TCE was much lower than could be expected on the basis of the monitoring results. This suggests that some of the variation detected by monitoring may derive from differences between sampling sites and years smoothed out in the sediment samples, providing an average of the entire lake area and several years. The TCE is always connected to various ecological interactions in lake ecosystems and therefore is always lake-specific. Hypothetically, deterioration of climate conditions can be detected in the TCE as an increase in ephippia of all chydorid species, since a shortening open-water season is reflected in the relative proportions of the two reproduction modes. Such an increase was clearly detected for the time period of the Little Ice Age in a sediment core. The paleolimnological results also indicated that TCE can suddenly increase due to ephippia of one or two species, which suggests that at least some chydorids can somehow increase the production of resting eggs under local environmental stress. Thus, some environmental factors may act as species-specific environmental stressors. The actual mechanism of the increased sexual reproduction seen in sediments has been unknown but the present study suggests that the mechanism is probably the increased intensity of gamogenesis, i.e. that a larger proportion of individuals in autumnal populations reproduce sexually, which results in a larger proportion of ephippia in sediments and a higher TCE. The results of this thesis demonstrate the utility of ephippium analysis as a paleoclimatological method which may also detect paleolimnological changes by identifying species-specific environmental stressors. For a quantitative TCE-based climate reconstruction model, the natural variation in the TCE of surface sediments in different climates must be clarified with more extensive studies. In addition, it is important to recognize the lakes where the TCE is not only a reflection of the length of the open-water season, but is also non-climatically forced. The results of ephippium analysis should always be interpreted in a lake-specific manner and in the context of other paleoecological proxies.

Climatic fluctuations during the LIA and post-LIA in the Kumaun Lesser Himalaya, India: Evidence from a 400 y old stalagmite record

This paper presents the first stable isotope (delta O-18 and delta C-13) data of a similar to 400 years (1590-2006 AD) long annual to decadal-resolution speleothem record collected from the Indian Lesser Himalaya. The data show a variation from -2.7 to -5.9 parts per thousand in delta O-18 and -5.3 to -8.8 parts per thousand in delta C-13. The isotopic analyses indicate that the climate during this period can be divided into two stages: a wet phase during the Little Ice Age (LIA) (1590-1850 AD) and comparatively dry phase during the post-LIA after 1850 AD. However, the record also documents the minor dry events during the LIA and a wet episode after the LIA. Within the age uncertainty, the dry spells during the LIA are linked with the historical drought events in the Indian subcontinent and similar latitudes. The isotopic record is consistent with a number of previous studies in the areas influenced by the Westerlies but appears to be conflicting to the regions, dominated by the Indian Summer Monsoon (ISM). This may be due to the possible changes in the strength of Westerlies in the study area and added by negative anomaly of North Atlantic Oscillation (NAO) during the LIA. (C) 2012 Elsevier Ltd and INQUA. All rights reserved.

Climatic variability in Central Indian Himalaya during the last similar to 1800 years: Evidence from a high resolution speleothem record

Stable isotopes from a U/Th dated aragonite stalagmite from the Central Kumaun Himalaya provide evidence of variation in climatic conditions in the last similar to 1800 years. The delta O-18 and delta C-13 values vary from -4.3 parts per thousand to -7.6 parts per thousand and -3.4 parts per thousand to -9.1 parts per thousand respectively, although the stalagmite was not grown in isotopic equilibrium with cave drip water, a clear palaeoclimatic signal in stalagmite delta O-18 values is evident based on the regional climate data. The stalagmite showed a rapid growth rate during 830-910 AD, most likely the lower part of Medieval Warm Period (MWP), and 1600-1640 AD, the middle part of Little Ice Age (LIA). Two distinct phases of reduced precipitation are marked by a 2 parts per thousand shift in 8180 values towards the end of MWP (similar to 1080-1160 AD) and after its termination from similar to 1210 to 1440 AD. The LIA (similar to 1440-1880 AD) is represented by sub-tropical climate similar to modern conditions, whereas the post-LIA was comparatively drier. The Inter Tropical Convergence Zone (ITCZ) was located over the cave location during wetter/warmer conditions. When it shifted southward, precipitation over the study area decreased. A prominent drop in delta O-18 and delta C-13 values during the post-LIA period may also have been additionally influenced by anthropogenic activity in the area. (C) 2013 Elsevier Ltd and INQUA. All rights reserved.

Transformaciones agropecuarias en Guipúzcoa durante los siglos XVI y XVII

Actas de la XII Reunión Científica de la Fundación Española de Historia Moderna, celebrada en la Universidad de León en 19-21 de junio de 2012.

Snow accumulation time series and their climatic interpretation

EXTRACT (SEE PDF FOR FULL ABSTRACT): Several snow accumulation time series derived from ice cores and extending over 3 to 5 centuries are examined for spatial and temporal climatic information. ... A significant observation is the widespread depression of net snow accumulation during the latter part of the "Little Ice Age". This initially suggests sea surface temperatures were significantly depressed during the same period. However, prior to this, the available core records indicate generally higher than average precipitation rates. This also implies that influences such as shifted storm tracks or a dustier atmosphere may have been involved. Without additional spatial data coverage, these observations should properly be studied using a coupled (global) ocean/atmosphere GCM.

Eastern tropical Pacific corals monitor low latitude climate of the past 400 years

EXTRACT (SEE PDF FOR FULL ABSTRACT): We have measured coral growth band thickness and skeletal stable isotopic composition through a 371-year transect (AD 1583-1954) from a massive specimen of Pavona clavus from the Galápagos Islands. ... We observe a general cooling trend during 1860-1954, corresponding to the end of the Little Ice Age, an interval characterized by general warming at many mid-latitude sites. Variance at sunspot cycle frequencies in growth rate, stable isotopic, and trace element composition implies a direct or indirect link between the solar cycle and climate modulation in the eastern Pacific.

Sea surface temperature and paleo-El Niño events in Santa Barbara Basin, AD 1841-1941

Like pages of a "natural coastal diary", successive layers of anoxic varved sediment in the central Santa Barbara Basin have been used by paleoceanographers to reconstruct aspects of past coastal climate. This report focuses on the end of the "Little Ice Age" (15th to 19th century) and on the beginning of this century, a period known to encompass extreme climate excursions and weather events in the Santa Barbara Basin and other parts of Southern California. El Niño events are known to disrupt Southern California's coastal ecosystems and to cause anomalous weather conditions, but El Niño events in Southern California before 1990 have been largely undocumented.

Recent 2000-year geological records of mud in the inner shelf of the East China Sea and their climatic implications

AXIS(14)C dating and grain-size analysis for Core DD2, located at the north of the Yangtze River-derived mud off the Zhejiang-Fujian coasts in the inner shelf of the East China Sea, provide us a high-resolution grain-size distribution curve varying with depth and time. Data in the upper mud layer of Core DD2 indicate that there are at least 9 abrupt grain-size increasing in recent 2000 years, with each corresponding very well with the low-temperature events in Chinese history, which might result from the periodical strengthening of the East Asian Winter Monsoon (EAWM), including the first-revealed maximum temperature lowering event at around 990 a BP. At the same time, the finer grain size section in Core DD2 agrees well with the Sui-Tang Warming Period (600-1000 a AD) defined previously by Zhu Kezhen, during which the climate had a warm, cold and warm fluctuation, with a dominated cooling period of 750-850 a AD. The Little Ice Age (LIA) can also be identified in the core. It starts around 1450 a AD and was followed by a subsequent cooling events at 1510, 1670 and 1840 a AD. Timing of these cold events revealed here still needs to be further verified owing to some current uncertainty of dating we used in this study.

东北四海龙湾玛珥湖啊1500年来长链烯酮不饱和度温标与古水温重建

The alkenone unsaturation paleothermometer is an important proxy to reconstruct water temperature, and is widely applied to reconstructing sea surface temperature in most oceanographic settings. Recent research indicates that long chain alkenone is preserved in lacustrine sediments, and the alkenone unsaturation has good relationship with mean annual temperature in studied lakes. Thus, the alkenone unsaturation could be used as a temperature proxy to reconstruct temperature in limnic systems. In this study, we analyzed long chain alkenone from the varved sediments in Lake Sihailongwan, northeastern China. Based on the counting varves, we established time scale during the past 1500 years. The distribution pattern in the sediment is similar with the previous study in lacustrine environment. The ratio of C37:4 methyl ketone to the sum of C37 alkenones is high. Based on the published temperature- alkenone unsaturation equation, we reconstructed the mean air temperature and July water temperature during the past 1500 years. Three major cold periods are in AD560-950, AD 1540-1600 and AD1800-1920. Three major warm periods are AD450-550, AD 950-1400 and AD 1600-1800. The Medieval Warm Period was a significant warm periods. However, the traditional “Little Ice Age” was not a persistent cold period, and interrupted by relative longer warm period. The temperature variations in this study show a general similar pattern with the summer temperature reconstruction from Shihua Cave and the winter temperature from historical documents. The temperature variations from long chain alknone record show a good agreement with solar activity (10Be data from ice core and sunspot number from tree rings). It may suggest that solar activity is most important forcing in the studied area.