High‐Arctic climate conditions for the last 7000 years inferred from multi‐proxy analysis of the Bliss Lake record,North Greenland

The Arctic is more vulnerable to climate change than are mid latitudes. Therefore, palaeolimnological studies from the High Arctic are important in providing insights into the dynamics of the climate system. Here we present a multi‐proxy study from one of the world's northernmost lakes: Bliss Lake, Peary Land, Greenland. The early Holocene (10 850–10 480 cal. a BP) is characterized by increased erosion and gradually more marine conditions. Full marine conditions developed from 10 480 cal. a BP until the lake was isolated at 7220 cal. a BP. From its marine isolation at 7220 cal. a BP Bliss Lake becomes a lacustrine environment. Evidence from geochemical proxies (δ¹³C and total organic carbon) suggests that warmer conditions prevailed between 7220 and 6500 cal. a BP, corresponding to the Holocene thermal maximum, and from 3300 until 910 cal. a BP. From 850 to 500 cal. a BP colder climate conditions persisted. The transition from warmer to colder climate conditions taking place around 850 cal. a BP may be associated with the transition from the Medieval Warm Period to the Little Ice Age. Copyright © 2011 John Wiley & Sons, Ltd.     

Glacier response in the European Alps to Heinrich Event 1 cooling: the Gschnitz stadial

The Gschnitz stadial was a period of regionally extensive glacier advance in the European Alps that lies temporally between the breakdown of the Last Glacial Maximum piedmont lobes and the beginning of the Bølling warm interval. Moraines of the Gschnitz stadial are found in medium to small catchments, are steep‐walled and blocky, and reflect a snowline lowering of 650–700 m in comparison to the Little Ice Age reference snowline. ¹⁰Be surface exposure dating of boulders from the moraine at the type locality at Trins (Gschnitz valley, Tyrol, Austria) shows that it stabilised no later than 15 400 ± 1400 yr ago. The overall morphological situation and the long reaction time of the glacier suggest that the climatic downturn lasted about 500 ± 300 yr, indicating that the Gschnitz cold period began approximately 15 900 ± 1400 yr ago, if not somewhat earlier. This is consistent with published radiocarbon dates that imply that the stadial occurred sometime between 15 400 ¹⁴C yr BP (18 020–19 100 cal. yr) and 13 250 ¹⁴C yr BP (15 360–16 015 cal. yr). A palaeoclimatic interpretation of the Gschnitz glacier based on a simple glacier flow model and statistical glacier‐climate models shows that precipitation was about one‐third of modern‐day precipitation and summer temperatures were about 10 K lower than today. In comparison, during the Younger Dryas, precipitation in this area was only about 10% less and T_s (summer temperature) was only 3.5–4 K lower than modern values. Based on the age of the moraine and the cold and dry climate at that time, we suggest that the Gschnitz stadial was the response of Alpine glaciers to cooling of the North Atlantic Ocean associated with Heinrich Event 1. Copyright © 2005 John Wiley & Sons, Ltd.     

Paleomagnetic correlations between scandinavian ice-sheet fluctuations and greenland dansgaard-oeschger events, 45,000-25,000 yr B.P.

Two paleomagnetic excursions, the Skjong correlated with the Laschamp (about 41,000 GISP2 yr B.P.) and the Valderhaug correlated with the Mono Lake (about 34,000 GISP2 yr B.P.), have been identified in stratigraphic superposition in laminated clay deposited in ice-dammed lakes in three large caves in western Norway. During both periods the margin of the Scandinavian Ice Sheet advanced and reached the continental shelf beyond the outermost coastline. The mild, 4000-yr-long Ålesund interstade, when the coast and probably much of the hinterland were ice-free, separated the two glacial advances. The two paleomagnetic excursions have also been indirectly identified as increased fluxes of ³⁶Cl and ¹⁰Be in the GRIP ice core, Greenland. This article presents a correlation between ice-margin fluctuations of the Scandinavian Ice Sheet and the stratigraphy of GRIP/GISP cores, using the paleomagnetic excursions and the ³⁶Cl and ¹⁰Be peaks and thus circumventing the application of different dates or time scales. Some of the fluctuations of the Scandinavian Ice Sheet were of the “Allerød/Younger Dryas type” in the sense that its margin retreated during mild interstades on Greenland and readvanced during cold stades. However, some fluctuations were apparently not in phase with the Greenland climate.     

Oxygen isotope and palaeotemperature records from six Greenland ice‐core stations: Camp Century,Dye‐3, GRIP,GISP2, Renland and NorthGRIP

Oxygen isotope variations spanning the last glacial cycle and the Holocene derived from ice‐core records for six sites in Greenland (Camp Century, Dye‐3, GRIP, GISP2, Renland and NorthGRIP) show strong similarities. This suggests that the dominant influence on oxygen isotope variations reflected in the ice‐sheet records was regional climatic change. Differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios. Palaeotemperature estimates have been obtained from the records using three approaches: (i) inferences based on the measured relationship between mean annual δ¹⁸O of snow and of mean annual surface temperature over Greenland; (ii) modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile, or (iii) by using Monte Carlo simulation techniques. The third of these approaches was adopted to reconstruct Holocene temperature variations for the Dye 3 and GRIP temperature profiles, which yields remarkably compatible results. A new record of Holocene isotope variations obtained from the NorthGRIP ice‐core matches the GRIP short‐term isotope record, and also shows similar long‐term trends to the Dye‐3 and GRIP inverted temperature data. The NorthGRIP isotope record reflects: (i) a generally stronger isotopic signal than is found in the GRIP record; (ii) several short‐lived temperature fluctuations during the first 1500 yr of the Holocene; (iii) a marked cold event at ca. 8.2 ka (the ‘8.2 ka event’); (iv) optimum temperatures for the Holocene between ca. 8.6 and 4.3 ka, a signal that is 0.6‰ stronger than for the GRIP profile; (v) a clear signal for the Little Ice Age; and (vi) a clear signal of climate warming during the last century. These data suggest that the NorthGRIP stable isotope record responded in a sensitive manner to temperature fluctuations during the Holocene. Copyright © 2001 John Wiley & Sons, Ltd.     

Is There Evidence for Solar Forcing of Climate in the GISP2 Oxygen Isotope Record?

Changes in solar constant over an 11 yr cycle suggest a certain, but limited, degree of solar forcing of climate. The high-resolution climate (oxygen isotope) record of the Greenland GISP2 (Greenland Ice Sheet Project 2) ice core has been analyzed for solar (and volcanic) influences. The atmospheric¹⁴C record is used as a proxy of solar change and compared to the oxygen isotope profile in the GISP2 ice core. An annual oxygen isotope profile is derived from centimeter-scale isotope measurements available for the post-A.D. 818 interval. Associated extreme summer and winter isotope ratios were found to yield similar climate information over the last millennium. The detailed record of volcanic aerosols, converted to optical depth and volcanic explosivity change, was also compared to the isotope record and the oxygen isotope response calibrated to short-term volcanic influences on climate. This calibration shows that century-scale volcanic modulation of the GISP2 oxygen isotope record can be neglected in our analysis of solar forcing. The timing, estimated order of temperature change, and phase lag of several maxima in¹⁴C and minima in¹⁸O are suggestive of a solar component to the forcing of Greenland climate over the current millennium. The fractional climate response of the cold interval associated with the Maunder sunspot minimum (and¹⁴C maximum), as well as the Medieval Warm Period and Little Ice Age temperature trend of the past millennium, are compatible with solar climate forcing, with an order of magnitude of solar constant change of 0.3%. Even though solar forcing of climate for the current millennium is a reasonable hypothesis, for the rest of the Holocene the century-scale events are more frequent in the oxygen isotope record than in the¹⁴C record and a significant correlation is absent. For this interval, oceanic/atmospheric circulation forcing of climate may dominate. Solar forcing during the surprisingly strong 1470 yr climate cycle of the 11,000–75,000 yr B.P. interval is rather hypothetical.     

The Medieval Warm Period and the Little Ice Age from a sediment record of Lake Ebinur,northwest China

Ma, L., Wu, J., Yu, H., Zeng, H. & Abuduwaili, J. 2011: The Medieval Warm Period and the Little Ice Age from a sediment record of Lake Ebinur, northwest China. Boreas, Vol. 40, pp. 518–524. 10.1111/j.1502‐3885.2010.00200.x. ISSN 0300‐9483. Lake Ebinur, Xinjiang, northwest China, is a closed‐basin, shallow lake that responds rapidly to changes in the ratio of precipitation to evaporation (P/E). A sediment record spanning the last 1500 years was obtained from the lake. We used δ¹⁸O and δ¹³C in bulk carbonate, and δ¹³C of organic matter in the lake sediments to infer environmental changes in the Ebinur region during the Medieval Warm Period (MWP) and the Little Ice Age (LIA). Decreased δ¹⁸O values of carbonate largely reflect an enhanced P/E ratio within the basin and a higher lake level. Bulk carbonates with higher δ¹³C values are deposited during periods when lake‐water pH is high, while lower δ¹³C values reflect a lower pH in the water column. δ¹³C in organic matter is associated with the amount of precipitation. The results indicate that the Ebinur region experienced a dry MWP and a wet LIA, although the MWP and LIA were warm and cold periods, respectively, as expected. Furthermore, the MWP and LIA were hydrologically complex and cannot be characterized as uniformly wet or dry. Peak wet periods are recorded in the sediment core around AD 1000, 1400 and 1700, and a dry event also occurred in the period of temperature change within the LIA (cold to warm around AD 1500). A comparison of the Lake Ebinur data with proxy records for the strength of the Siberian High and climate proxy indicators suggests that precipitation in the Ebinur region was a consequence, in part, of an enhanced Siberian High during the LIA.     

Holocene hydrological variability of Lake Ladoga,northwest Russia,as inferred from diatom oxygen isotopes

This article presents a new comprehensive assessment of the Holocene hydrological variability of Lake Ladoga, northwest Russia. The reconstruction is based on oxygen isotopes of lacustrine diatom silica (δ¹⁸O_diatom) preserved in sediment core Co 1309, and is complemented by a diatom assemblage analysis and a survey of modern isotope hydrology. The data indicate that Lake Ladoga has existed as a freshwater reservoir since at least 10.8 cal. ka BP. The δ¹⁸O_diatom values range from +29.8 to +35.0‰, and relatively higher δ¹⁸O_diatom values around +34.7‰ between c. 7.1 and 5.7 cal. ka BP are considered to reflect the Holocene Thermal Maximum. A continuous depletion in δ¹⁸O_diatom since c. 6.1 cal. ka BP accelerates after c. 4 cal. ka BP, indicating Middle to Late Holocene cooling that culminates during the interval 0.8–0.2 cal. ka BP, corresponding to the Little Ice Age. Lake‐level rises result in lower δ¹⁸O_diatom values, whereas lower lake levels cause higher δ¹⁸O_diatom values. The diatom isotope record gives an indication for a rather early opening of the Neva River outflow at c. 4.4–4.0 cal. ka BP. Generally, overall high δ¹⁸O_diatom values around +33.5‰ characterize a persistent evaporative lake system throughout the Holocene. As the Lake Ladoga δ¹⁸O_diatom record is roughly in line with the 60°N summer insolation, a linkage to broader‐scale climate change is likely.     

Lake carbonate-δ18O records from the Yukon Territory,Canada: Little Ice Age moisture variability and patterns

A 1000-yr history of climate change in the central Yukon Territory, Canada, is inferred from sediment composition and isotope geochemistry from small, groundwater fed, Seven Mile Lake. Recent observations of lake-water δ¹⁸O, lake level, river discharge, and climate variations, suggest that changes in regional effective moisture (precipitation minus evaporation) are reflected by the lake’s hydrologic balance. The observations indicate that the lake is currently ¹⁸O-enriched by summer evaporation and that during years of increased precipitation, when groundwater inflow rates to the lake increase, lake-water δ¹⁸O values decrease. Past lake-water δ¹⁸O values are inferred from oxygen isotope ratios of fine-grained sedimentary endogenic carbonate. Variations in carbonate δ¹⁸O, supplemented by those in carbonate and organic δ¹³C, C/N ratios, and organic carbon, carbonate and biogenic silica accumulation rates, document changes in effective moisture at decadal time scales during the early Little Ice Age period to present. Results indicate that between ～AD 1000 and 1600, effective moisture was higher than today. A shift to more arid climate conditions occurred after ～AD 1650. The 19th and 20th centuries have been the driest of the past millennium. Temporal variations correspond with inferred shifts in summer evaporation from Marcella Lake δ¹⁸O, a similarly small, stratified, alkaline lake located ～250 km to the southwest, suggesting that the combined reconstructions accurately document the regional paleoclimate of the east-central interior. Comparison with regional glacial activity suggests differing regional moisture patterns during early and late Little Ice Age advances.     

Monsoonal changes inferred from the Middle to Late Holocene sediments off Landfall Island,North Andaman

In this paper, sediment texture, clay mineral composition, and δ ¹⁸O data on Globigerinoides ruber of a sediment core collected from a water depth of 250 m near Landfall Island, Bay of Bengal, is presented to understand paleoenvironmental shifts during the Mid–Late Holocene period. From the sediment core, five organic carbon-rich samples were radiocarbon dated and the reservoir-corrected ages range from 6,078 to 1,658 years BP. The marine sediment core is represented dominantly by clayey silt with incursions of coarser components that occur around 6,000, 5,400, and 3,400 years BP. The sedimentation of the coarser detritus is due to strengthened southwest monsoon (SWM) since 6,500 to 5,400 years BP. Clay minerals are represented by smectite, illite, kaolinite, and chlorite in varying amounts. High kaolinite content and K/C ratio indicate intense SWM and strong bedrock weathering from the hinterland (~6,500–5,400 years BP). Incidence of smectite (48.82 to 25.09 %) and chlorite/illite (C/I) ratio (0.56 to 0.28) indicate an overall weakened southwest monsoon since 6,000 to 2,000 years BP with a brief incursion of extremely reduced SWM around 4,400 to 4,200 years BP. This is corroborated with the oxygen isotope on G. ruber that reveals a significant shift in the isotopic values ~4,300 years BP (?3.39?‰), indicating weakening in SWM. Subsequently, fluctuations in the intensity of SWM are observed since 2,000 years to present.     

The last Welsh Ice Cap: Part 1 – Modelling its evolution,sensitivity and associated climate

A high‐resolution, three‐dimensional, thermomechanical ice‐flow model is used to investigate the glaciodynamics of the Last Glacial Maximum Welsh Ice Cap – a large, independent ice centre of the British–Irish Ice Sheet. The model uses higher‐order physics to solve longitudinal stresses, and is coupled to climate via a distributed, positive degree‐day mass‐balance scheme. A suite of model experiments driven by the GISP2 δ¹⁸O curve was initiated from a climatic optimum at 38.3 ka BP through to the Devensian/Holocene boundary to identify an icecap configuration compatible with available empirical evidence. An enhanced cooling from present of 11.85°C and strong precipitation suppression are required between 27.4 and 23.5 ka BP for the modelled icecap to attain well‐established empirical limits, a scenario probably associated with Heinrich Event‐2 and the potential collapse of thermohaline circulation in the North Atlantic. The experiments indicate ice‐dispersal centres located in North and Mid Wales, the latter being essential for forcing ice southwards of the Brecon Beacons during the Last Glacial Maximum. Deglaciation of the Welsh Ice Cap was relatively rapid, occurring within one millennium. Dynamic stability is governed largely by the dominance and vigour with which fast‐flowing outlet glaciers drain the icecap interior, which in turn are linked to variations in the climatic forcing. The distribution of permanently cold‐based ice across the uplands and summits indicates the probable preservation of relict landscapes in these areas throughout the full glacial cycle.     

Climate variability and glacial processes in eastern Iceland during the past 700 years based on varved lake sediments

Striberger, J., Björck, S., Ingólfsson, Ó., Kjær, K. H., Snowball, I. & Uvo, C. B. 2010: Climate variability and glacial processes in eastern Iceland during the past 700 years based on varved lake sediments. Boreas, 10.1111/j.1502‐3885.2010.00153.x. ISSN 0300‐9483. Properties of varved sediments from Lake Lögurinn in eastern Iceland and their link to climate and glacial processes of Eyjabakkajökull, an outlet glacier of the Vatnajökull icecap, were examined. A varve chronology, which covers the period AD 1262–2005, was constructed from visual observations, high‐resolution images, X‐ray density and geochemical properties determined from X‐radiography and X‐ray fluorescence scanning. Independent dating provided by ¹³⁷Cs analysis and eight historical tephras verify the varve chronology. The thickness of dark‐coloured seasonal laminae, formed mainly of coarser suspended matter from the non‐glacial river Grímsá, is positively correlated (r=0.70) with winter precipitation, and our 743‐year‐long varve series indicates that precipitation was higher and more varied during the later part of the Little Ice Age. Light‐coloured laminae thickness, controlled mainly by the amount of finer suspended matter from the glacial river Jökulsáí Fljótsdal, increased significantly during the AD 1972 surge of Eyjabakkajökull. As a consequence of the surge, the ice‐dammed Lake Háöldulón formed and recurrently drained and delivered significant amounts of rock flour to Lake Lögurinn. Based on these observations, and the recurring cyclic pattern of periods of thicker light‐coloured laminae in the sediment record, we suggest that Eyjabakkajökull has surged repeatedly during the past 743 years, but with an increased frequency during the later part of the Little Ice Age.     

Multi-proxy record of Holocene glacial history of the Spearhead and Fitzsimmons ranges,southern Coast Mountains,British Columbia

Evidence from glacier forefields and lakes is used to reconstruct Holocene glacier fluctuations in the Spearhead and Fitzsimmons ranges in southwest British Columbia. Radiocarbon ages on detrital wood and trees killed by advancing ice and changes in sediment delivery to downstream proglacial lakes indicate that glaciers expanded from minimum extents in the early Holocene to their maximum extents about two to three centuries ago during the Little Ice Age. The data indicate that glaciers advanced 8630–8020, 6950–6750, 3580–2990, and probably 4530–4090 cal yr BP, and repeatedly during the past millennium. Little Ice Age moraines dated using dendrochronology and lichenometry date to early in the 18th century and in the 1830s and 1890s. Limitations inherent in lacustrine and terrestrial-based methods of documenting Holocene glacier fluctuations are minimized by using the two records together.     

Glacier variations in Breheimen,southern Norway: dating Little Ice Age moraine sequences at seven low‐altitude glaciers

Moraine sequences in front of seven relatively low‐altitude glaciers in the Breheimen region of central southern Norway are described and dated using a ‘multi‐proxy’ approach to moraine stratigraphy. Lichenometric dating, based on the Rhizocarpon subgenus, is used to construct a composite moraine chronology, which indicates eight phases of synchronous moraine formation: AD 1793–1799, 1807–1813, 1845–1852, 1859–1862, 1879–1885, 1897–1898, 1906–1908 and 1931–1933. Although the existence of a few cases of older moraines, possibly dating from earlier in the eighteenth or late in the seventeenth centuries cannot be ruled out by lichenometry, Schmidt hammer R‐values from boulders on outermost moraine ridges suggest an absence of Holocene moraines older than the Little Ice Age. Twenty‐three radiocarbon dates from buried soils and peat associated with outermost moraines at three glaciers—Tverreggibreen, Storegrovbreen and Greinbreen—also indicate that the ‘Little Ice Age’ glacier maximum was the Neoglacial maximum at most if not all glaciers. Several maximum age estimates for the Little Ice Age glacier maximum range between the fifteenth and seventeenth centuries, with the youngest from a buried soil being AD 1693. A pre‐Little Ice Age maximum cannot be ruled out at Greinbreen, however, where the age of buried peat suggests the outermost moraine dates from AD 981–1399 (at variance with the lichenometric evidence). Glaciofluvial stratigraphy at Tverreggibreen provides evidence for minor glacier advances about AD 655–963 and AD 1277–1396, respectively. Copyright © 2003 John Wiley & Sons, Ltd.     

Environment change of Sihu Lake in the past 450 years, southern China

In recent years, climate and environment changes since the Little Ice Age have become a focus in modern research. The paper selected the sediment (77 cm) of Sihu Lake, which was located in Guilin, southern China, as the research object and analyzed the karst wetland environmental changes within nearly 450 years. According to the vertical profile of indicators and geochemical elements in sediment core, the regional environmental evolution was divided into four stages. The former two stages were mainly influenced by Little Ice Age (1562–1895). The third stage climate has changed slowly. The fourth stage was mainly affected by human activities and global warming. The factor analysis of geochemical elements indicated that karst wetland regional environmental change was affected by four major factors. In the 53–77 cm stage (1562–1703), F1 (erosion factor), F2 (watershed runoff and diagenesis factor) and F3 (regional background factor) were reduced, indicating that it was in cold and dry stage of Little Ice Age. In the 20–53 cm stage (1703–1895), F1 and F2 increased, indicating that it was in cold and wet stage of Little Ice Age. In the 4–20 cm stage (1895–1987), F1, F2 and F4 (human activity factor) increased slowly, indicating that the climate was affected by global warming and more precipitation. In the 0–4 cm stage (1987–2007), F1 and F2 reduced and F4 increased, indicating the reduced precipitation, rising temperature and more impact of human activities. In addition, it was proposed that the Little Ice Age in Guilin District in southern China started in the 1560s and lasted until the 1895s or so.     

Late Quaternary glaciation in the Nun‐Kun massif,northwestern India

The late Quaternary glacial history of the Nun‐Kun massif, located on the boundary between the Greater Himalaya and the Zanskar range in northwestern India, was reconstructed. On the basis of morphostratigraphy and ¹⁰Be dating of glacial landforms (moraines and glacial trimlines), five glacial stages were recognized and defined, namely: (i) the Achambur glacial stage dated to Marine Oxygen Isotope Stage 3 to 4 (38.7–62.7 ka); (ii) the Tongul glacial stage dated to the early part of the Lateglacial (16.7–17.4 ka); (iii) the Amantick glacial stage dated to the later part of the Lateglacial (14.3 ka, 11.7–12.4 ka); (iv) the Lomp glacial stage dated to the Little Ice Age; and (v) the Tanak glacial stage, which has the youngest moraines, probably dating to the last few decades or so. Present and former equilibrium‐line altitudes (ELAs) were calculated using the standard area accumulation ratio method. The average present‐day ELA of ～4790 m above sea level in the Greater Himalaya is lower than those in the Ladakh and Zanskar ranges, namely 5380 and ～5900 m a.s.l., respectively. The ELA in the Zanskar range is higher than in the Ladakh range, possibly due to the higher peaks in the Ladakh range that are able to more effectively capture and store snow and ice. ELA depressions decrease towards the Ladakh range (i.e. inner Plateau). Peat beds interbedded with aeolian deposits that cap the terminal moraine of Tarangoz Glacier suggest millennial‐time‐scale climate change throughout the Holocene, with soil formation times at c. 1.5, c. 3.4 and c. 5.2 ka, probably coinciding with Holocene abrupt climate change events. Given the style and timing of glaciation in the study area, it is likely that climate in the Nun‐Kun region is linked to Northern Hemisphere climate oscillations with teleconnections via the mid‐latitude westerlies.     

Correlation of Swedish glacial varves with the Greenland (GRIP) oxygen isotope record

A mean varve thickness curve has been constructed for a part of the Swedish varve chronology from the northwestern Baltic proper. The mean varve thickness curve has been correlated with the δ¹⁸O record from the GRIP ice-core using the Younger Dryas–Preboreal climate shift. This climate shift was defined by pollen analyses. The Scandinavian ice-sheet responded to a warming at the end of the Younger Dryas, ca. 10995 to 10700 clay-varve yr BP. Warming is recorded as a sequence of increasing mean varve thickness and ice-rafted debris suggesting intense calving of the ice front. The Younger Dryas–Preboreal climatic shift is dated to ca. 10650 clay-varve yr BP, about 40 yr after the final drainage of the Baltic Ice Lake. Both the pollen spectra and a drastic increase in varve thickness reflect this climatic shift. A climate deterioration, correlated with the Preboreal oscillation, is dated to ca. 10440 to 10320 clay-varve yr BP and coincides with the brackish water phase of the Yoldia Sea stage. The ages of the climatic oscillations at the Younger Dryas–Preboreal transition show an 875 yr discrepancy compared with the GRIP record, suggesting a large error in the Swedish varve chronology in the part younger than ca. 10300 clay-varve yr BP. Copyright © 1999 John Wiley & Sons, Ltd.     

Holocene glacial and tree-line variations in the White River Valley and Skolai Pass,Alaska and Yukon Territory

Complex glacier and tree-line fluctuations in the White River valley on the northern flank of the St. Elias and Wrangell Mountains in southern Alaska and Yukon Territory are recognized by detailed moraine maps and drift stratigraphy, and are dated by dendrochronology, lichenometry, ¹⁴C ages, and stratigraphic relations of drift to the eastern (1230 ¹⁴C yr BP) and northern (1980 ¹⁴C yr BP) lobes of the White River Ash. The results show two major intervals of expansion, one concurrent with the well-known and widespread Little Ice Age and the other dated between 2900 and 2100 ¹⁴C yr BP, with a culmination about 2600 and 2800 ¹⁴C yr BP. Here, the ages of Little Ice Age moraines suggest fluctuating glacier expansion between ad 1500 and the early 20th century. Much of the 20th century has experienced glacier recession, but probably it would be premature to declare the Little Ice Age over. The complex moraine systems of the older expansion interval lie immediately downvalley from Little Ice Age moraines, suggesting that the two expansion intervals represent similar events in the Holocene, and hence that the Little Ice Age is not unique. Another very short-lived advance occurred about 1230 to 1050 ¹⁴C yr BP. Spruce immigrated into the valley to a minimum altitude of 3500 ft (1067 m), about 600 ft (183 m) below the current spruce tree line of 4100 ft (1250 m), at least by 8020 ¹⁴C yr BP. Subsequent intervals of high tree line were in accord with glacier recession; in fact, several spruce-wood deposits above current tree line occur bedded between Holocene tills. High deposits of fossil wood range up to 76 m above present tree line and are dated at about 5250, 3600 to 3000, and 2100 to 1230 ¹⁴C yr BP. St. Elias glacial and tree-line fluctuations, which probably are controlled predominantly by summer temperature and by length of the growing and ablation seasons, correlate closely with a detailed Holocene tree-ring curve from California, suggesting a degree of synchronism of Holocene summer-temperature changes between the two areas. This synchronism is strengthened by comparison with the glacier record from British Columbia and Mt. Rainier, Likewise, broad synchronism of Holocene events exists across the Arctic between the St. Elias Mountains and Swedish Lappland. Finally, two sequences from the Southern Hemisphere show similar records, in so far as dating allows. Hence, we believe that a preliminary case can be made for broad synchronism of Holocene climatic fluctuations in several regions, although further data are needed and several areas, particularly Colorado and Baffin Island, show major differences in the regional pattern.     

Drastic desalination of small lakes in East Siberia (Russia) in the early twentieth century: inferred from sedimentological, geochemical and palynological composition of small lakes

Reconstruction of temporal and spatial climate development on a seasonal basis during the last few centuries may help us better understand modern-day interplay between natural and anthropogenic climate variability. The objective of this paper is to reconstruct hydrology and landscape changes of East Siberia during the termination of the Little Ice Age and the subsequent Recent Warming. We analysed sediment samples from the saltwater Sulfatnoe Lake, Bolshoye Alginskoe and freshwater Shuchie Lake using high-resolution X-ray fluorescence spectroscopy at 1-mm scan resolution, Fourier-transform infrared techniques and pollen analyses. The depth–age models of the cores were constructed by ²¹⁰Pb activity using the constant rate of supply model. The lake sediment cover of these lakes began to form from ca. 1870. Three significant periods (1870–1895, 1895–1925 and from 1925 to the present) were defined in hydrology and chemical regime of these lakes for the past 140 years. Lake levels were extremely low and high saturated with salts during the final period of the Little Ice Age. Lake levels began to slowly rise from 1870 to 1895 and vegetation was poor at that period. Intensive desalination of the lakes occurred in 1895–1925, and environment conditions were temperate and favourable for the majority of the taxa of the regional vegetation. Regional precipitation significantly increased and water saturation of the catchments was high from 1925 to the present. The chemical precipitation of carbonate stopped completely in Lake Shichie and reduced considerably in Lake Sulfatnoe and B. Alginskoe. Strong increasing trend of weathering of the lake catchments began in 1970 and still continues.     

The Preboreal climate reversal and a subsequent solar‐forced climate shift

Accurate chronologies are essential for linking palaeoclimate archives. Carbon‐14 wiggle‐match dating was used to produce an accurate chronology for part of an early Holocene peat sequence from the Borchert (The Netherlands). Following the Younger Dryas–Preboreal transition, two climatic shifts could be inferred. Around 11 400 cal. yr BP the expansion of birch (Betula) forest was interrupted by a dry continental phase with dominantly open grassland vegetation, coeval with the PBO (Preboreal Oscillation), as observed in the GRIP ice core. At 11 250 cal. yr BP a sudden shift to a humid climate occurred. This second change appears to be contemporaneous with: (i) a sharp increase of atmospheric ¹⁴C; (ii) a temporary decline of atmospheric CO₂; and (iii) an increase in the GRIP ¹⁰Be flux. The close correspondence with excursions of cosmogenic nuclides points to a decline in solar activity, which may have forced the changes in climate and vegetation at around 11 250 cal. yr BP. Copyright © 2004 John Wiley & Sons, Ltd.     

Compound-specific D/H ratios of the marine lakes of Palau as proxies for West Pacific Warm Pool hydrologic variability

We tested the use of hydrogen isotopic ratios (δD) of lipids in marine lake sediments from the Micronesian Republic of Palau against the instrumental record of the last century to assess their capacity to record past hydrological changes of the Western Pacific Warm Pool. δD values of the algal lipid biomarker dinosterol (δD_Dino) and the more generic palmitic acid (δD_PA) were found to be sensitive indicators of the intensity of regional precipitation, as recorded by the Southern Oscillation Index (SOI). The observed sensitivity is caused by the combined effect of: 1) The amount effect in tropical precipitation; 2) Dilution of the isotopically heavy saline surface waters with light precipitation; 3) A salinity effect on the biosynthetic D/H fractionation between lipid and lake water. Both lake water δD (δD_Lake) and δD_Dino could be expressed as a quadratic function of either precipitation or lake water salinity. δD_Dino values were used to reconstruct past hydrological changes of the region. Long-term variations in the strength and sign of the El Niño - Southern Oscillation (ENSO) since the Little Ice Age (LIA, ～1450–1850 A.D.) and during the early Holocene (～7–9 kyr BP) appeared to dominate decadal variability, and indicate very dry conditions during the LIA. Early Holocene δD_Dino values were on average ～10‰ higher than those of recent centuries, which we interpret as a result of millennial scale hydrologic and water mass changes on a global level. The similar ～35‰ range of δD changes during the early Holocene and last several centuries imply a similar range of decadal-centennial hydrologic variability during those two climate regimes. Our results indicate that a correlation exists between solar irradiance levels and tropical Pacific climate.