Lateglacial climate development in NW Romania — Comparative results from three quantitative pollen-based methods

This paper provides quantitative reconstructions of the Lateglacial changes in four climate parameters from two fine-resolution pollen profiles in the Gutaiului Mountains, NW Romania. Climate estimates are based on two modern analogue techniques (with and without considering vegetation types) and weighted averaging partial least squares regression (WA-PLS), giving evidence for several climatic fluctuations during the period from > 14,700 to 11,500 cal. yr BP. The comparative results of the two modern analogue techniques show consistent trends of climate changes that are also coherent at both sites, but these results appear to largely disagree compared with climate reconstruction provided by WA-PLS.The modern analogue techniques revealed four intervals with low temperatures: prior to 14,700 cal. yr BP, between 13,950 and 13,800; 13,400 and 13,200; and 12,700 and 11,700 cal. yr BP. The temperature declines were more pronounced for winter than for summer, suggesting an intensification of seasonality, which together with a drop in precipitation indicates an increase in continentality. The Younger Dryas is the most pronounced cooling phase with winter temperatures ~ 14–16 °C colder than modern conditions, annual and summer temperatures ~ 2–5 °C and ~ 2 °C, respectively below present ones. Precipitation was ~ 400–500 mm, half that of present. During the Bølling and Allerød, summer temperatures were close to modern values (13 to 17 °C), whereas winter (− 6 to − 12 °C) and annual temperatures (0.5 to 6 °C) as well as precipitation were (550 to 700 mm) lower, indicating more continental conditions compared to the present-day climate.     

A 36,000-yr vegetation history from the Peloncillo Mountains, southeastern Arizona, USA

A 36,200 cal yr B.P. vegetation history was developed from macrofossils and pollen from 55 packrat middens from 1287 to 1442 m elevation in the Peloncillo Mountains of southeasternmost Arizona, USA. Today, these elevations are dominated by semidesert grassland with a mixture of Chihuahuan and Sonoran Desert shrubs, including an eastern disjunct population of jojoba (Simmondsia chinensis). From 36,200 to 15,410 cal yr B.P., rocky areas just above large, pluvial lakes that occupied what are now dry playas supported Pinus edulis, Juniperus osteosperma, Juniperus cf. coahuilensis, Quercus cf. turbinella and a rich understory of summer-flowering C₄ annuals and grasses, indicating abundant summer rains and mild winters. After  15,410 cal yr B.P., P. edulis declined in abundance and disappeared briefly at 13,925 cal yr B.P., coincident with expansion of more xeric species and paleohydrological evidence for regional aridity during the Bølling–Allerød warm interval. P. edulis rebounded briefly during the Younger Dryas at 12,405 cal yr B.P. before disappearing along with other mesic woodland species sometime after 12,100 cal yr B.P. The few middens dating from the early to middle Holocene (10,000–4000 yr B.P.) indicate wetter conditions than today at 7790 cal yr B.P. followed by a general drying trend. The 35 middens from the late Holocene detail the sequential arrival of desertscrub species as vegetation became more modern in character.     

A Holocene environmental record from the southern Yangtze River delta, eastern China

The Holocene sedimentary record of core ZX-1, recovered west of mid-Holocene Chenier ridges on the monsoon-controlled Southern Yangtze delta, eastern China, consists of lagoon, salt marsh, upper tidal flat, and limnic facies, reflecting low-energy depositional environments. Holocene deposits mainly originated from the surrounding Tai Lake drainage basin. The temporal variation of most geochemical element percentages corresponds with the climatic phases inferred from the pollen record, i.e., the relatively low values of SiO₂, Na₂O, CaO and high values of Al₂O₃, K₂O, MgO, Fe₂O₃, FeO, FeO + Fe₂O₃ and TiO₂ generally concur with the warm and humid climate, and vice versa. Three geochemical indices − Al₂O₃/Na₂O, K₂O/Na₂O, and CaO/K₂O − are found to be sensitive to past precipitation in the monsoon-controlled southern Yangtze River delta. Based on fine sediment analysis of core ZX-1, the samples deposited under a dry climate with a mean annual precipitation (MAP) < 500–900 mm tend to have Al₂O₃/Na₂O values less than 12.2, and the samples deposited under a moist climate with an MAP 1000–1800 mm mostly have Al₂O₃/Na₂O values higher than 12.2. Similarly, the K₂O/Na₂O boundary value is 2.0. However, for CaO/K₂O, the dry climate sediments likely show values higher than 0.9, and those wet climate ones generally have values less than 0.9. This geochemical response suggests the potential application of these indices in the interpretation of palaeoclimate variation of monsoon-controlled eastern China.

Holocene climatic variation history is reconstructed for the southern Yangtze delta. From 8000 to 7000 yr BP, regional climate demonstrated frequent fluctuations, with warm and wet periods (8000–7700; 7500–7200 yr BP) alternating with cool and less humid periods (7700–7500; 7200–7000 yr BP). From 7000 to 6000 yr BP, the climate was relatively warm and humid. Since then, it had turned cool and dry, climaxing in an intense cold event around 4000 yr BP. After the cold event, it became warm and humid until around 2500 yr BP.     

Late Quaternary environmental and climate history of Rauer Group, East Antarctica

The Rauer Group is an archipelago in Prydz Bay, East Antarctica. The ice-free islands and the surrounding shallow marine areas provide valuable archives for the reconstruction of the late Pleistocene and Holocene environmental and climatic history of the region. Two sediment records from two marine inlets of Rauer Group have been studied for their sedimentological, geochemical, and biological characteristics. Radiocarbon ages from one of the inlets indicate ice-free conditions within the last glacial cycle, probably during the second half of Marine Isotope Stage 3. Subsequent ice sheet coverage of Rauer Group during the Last Glacial Maxiumum (LGM) can be inferred from a till layer recovered in one of the basins. The inlets became ice-free prior to 11,200 cal yr BP, when biogenic sedimentation started. Deglacial processes in the catchments, however, influenced the inlets until ~ 9200 cal yr BP as evidenced by the input of minerogenic material. Marine productivity under relatively open water conditions indicates an early Holocene climate optimum until 8200 cal yr BP, which is followed by a cooler period with increased sea ice. Warmer conditions are inferred for the mid Holocene, when both basins experienced an input of freshwater between ~ 5700-3500 cal yr BP, probably due to ice-sheet melting and increased precipitation on the islands. Neoglacial cooling in the late Holocene since c. 3500 cal yr BP is reflected by an increase in sea ice in both inlets.     

Late marine isotope stage 3 palaeoclimate for East Asia: A data–model comparison

Climate prediction under impact of anthropological greenhouse-gas emission is impossible to validate, but it can be inferred from past climate and modeling. In East Asia, a general warm–wet period at late Marine Isotope Stage 3, ca. 30–40 ky BP has been identified based upon extensive geological records; this provides an arid/humid reference for possible future warming caused by human activities. Based upon syntheses of geological evidence and the AGCM + SSiB modeling, this paper presents climate simulations focused on 35 ky BP, using forcing of insolation, glaciation and land surface conditions for East Asia. Results of the simulation can be compared with geological records and show that (1) the climate patterns of 35 ky BP were warm–wet conditions in northern China, but with warm–dry conditions in southern China compared to today; (2) mean annual temperatures were higher in most mid-low latitude areas, mainly contributed to by increased winter temperatures, suggesting that insolation has generated significant climate effects through the coupling in atmospheric circulation with land surface patterns; (3) Quaternary ice sheets in the Northern Hemisphere played an important role in temperature decrease at the mid-high-latitudes, and also enhanced the south–north temperature gradients, which in turn, increased moisture transport from low to high latitudes and increased monsoonal precipitation over the Tibetan Plateau; and (4) Vegetation changes in East Asia resulted from an increased temperature in the low latitudes, extended rain-belt northwards into China, and an enlarged area of increased precipitation inland.     

A rapid and non leaky way for preparation of the sharp intracellular recording microelectrodes

To fill microelectrodes using backfilling method needs excessive time approximately 4–6  h. It is often difficult to fill microelectrodes without damage or leakage. A main problem is bubble formation in microelectrodes which has an impact on the electrical properties of the electrode and thus it influences the quality of the recording. Based on Archimede's principle there is a force within a solution which pushes insoluble material with a lower specific gravity upward and outside of the solution. Centrifugation can increase the force to eliminate the bubbles.

We designed a microelectrode holder to protect microelectrode sensitive tips from mechanical damage due to the gravity tensions; it can help to eliminate the bubbles easily and simultaneously in 10  min or less.

The tests were performed for 2000, 4000, and 8000  rpm centrifugation each one for 3, 6 and 12  min duration respectively, it was found that the bubbles were completely eliminated at 8000  rpm for 6–12  min and there were no significant differences for resistance, and the number of leaky or damaged electrodes between the two methods.

In the new design of devices, the materials used and the design of the holder are simple and the approach is applicable to many laboratories worldwide.     

Holocene vegetation–fire–climate linkages in northern Yellowstone National Park,USA

Yellowstone National Park has been an important location for paleoecologic studies that focus on the use of charcoal data to reconstruct past fire activity and on the role of climate variations in shaping past vegetation and fire regimes. One hypothesis, which has been explored in other parts of the western U.S., is the idea that present-day summer-dry and summer-wet precipitation regimes were intensified during the early Holocene as a result of greater-than-present summer insolation and its effect on atmospheric circulation patterns. In Yellowstone, this hypothesis was previously examined at two sites, one in summer-wet and one in summer-dry precipitation regions. The records showed variation in both fire and vegetation history that supported the hypothesis. We present a fire and vegetation history from Blacktail Pond, located in Pseudotsuga parkland in the transitional region. The Blacktail Pond data indicate the following ecological history: prior to 12,000 cal yr BP, the site supported tundra vegetation and fire episodes were infrequent. Between 12,000 and 11,000 cal yr BP, Picea–Pinus parkland was established and fire activity increased; these changes are consistent with increasing temperature, as a result of rising summer insolation. From 11,000 to 7600 cal yr BP, the presence of a closed forest of Pinus and some Picea is attributed to high levels of winter moisture, but high fire activity indicates that summers were drier than at present. After 7600 cal yr BP, the presence of forest and steppe vegetation in combination with high fire activity suggest that middle-Holocene conditions were warm and dry. The decrease in Picea and Betula in the last 4000 cal yr indicates continued drying in the late Holocene, although fire-episode frequency was relatively high until 2000 cal yr BP. The pollen data at Blacktail Pond and other low-elevation sites in the northern Rocky Mountains suggest a widespread vegetation response in summer-wet regions to effectively wetter conditions in the early Holocene and decreased moisture in the middle and late Holocene. In contrast, the more-variable fire history among the three sites implies either that (1) summer moisture stress and fire conditions are related to year-round moisture balance and not well predicted by the hypothesis, (2) the transitional area between summer-wet and summer-dry precipitation regimes experienced complicated shifts in effective moisture through time, and/or (3) fire-episode data have a limited source area that makes it difficult to separate local influences from regional climate changes in understanding long-term variations in fire-episode frequency.     

Temporal and spatial variability of the oxygen isotopic composition of massive corals from the South China Sea: Influence of the Asian monsoon

Coral colonies of Porites lutea and P. lobata were collected from areas to the east and south offshore of Hainan Island, South China Sea. Oxygen isotope ratios, ¹⁸O/¹⁶O, were analyzed along the major axis of growth at a resolution of 25–28 samples within an annual band from three colonies, giving data series lengths of 15, 20 and 30 years. Coral δ¹⁸O correlates well with sea surface temperature (SST) throughout most years, particularly when the Asian winter monsoon prevails over the region. Due to the same seasonal phases of SST and sea surface salinity (SSS), it is estimated that most of the seasonal features of coral δ¹⁸O are controlled by changes in SST with a significant contribution of SSS. This indicates the importance of temperature, as determined by the Asian winter monsoon, as a control on seasonal coral δ¹⁸O variations in the South China Sea. Given the fact that annual SSS maxima show minor inter-annual changes, the inter-annual change of annual coral δ¹⁸O maximum mainly reflects the SST induced by the winter monsoon. While the coral δ¹⁸O is mainly controlled by SST, deviations of the δ¹⁸O from SST correlate statistically with sea surface salinity, particularly for summer extreme events when SST reaches its annual maximum with minor inter-annual change. Therefore, we suggest that the inter-annual variation of the annual coral δ¹⁸O minima is mainly controlled by seawater composition. Seawater composition analysis indicates that its δ¹⁸O and salinity are simultaneously affected by freshwater inputs primarily from precipitation, which is mainly supplied by the Asian summer monsoon. Thus seasonal alternations of the winter and summer monsoon mainly control the coral δ¹⁸O, thereby allowing reconstruction of these monsoonal variables. The three coral records consistently reveal clear inter-decadal trends in δ¹⁸O — a gradual increase from 1968 to 1987, and a subsequent decrease from 1987 to 2003. These inter-decadal trends are roughly consistent with salinity changes — but not with temperature and precipitation, suggesting that seawater composition controlled by freshwater inputs from distant source areas, rather than from local precipitation, is responsible for the trends in seawater composition and coral δ¹⁸O over the last 30 years. Comparison of the three coral records indicates that spatial variations in coral δ¹⁸O coincide with variations in seawater salinity and local precipitation, but not with temperature. This confirms the dominant role of seawater composition, mainly controlled by monsoonal precipitation, on the spatial variability of coral δ¹⁸O in the South China Sea.     

Late Holocene lake-level fluctuations in Walker Lake, Nevada, USA

Walker Lake, a hydrologically closed, saline, and alkaline lake, is situated along the western margin of the Great Basin in Nevada of the western United States. Analyses of the magnetic susceptibility (χ), total inorganic carbon (TIC), and oxygen isotopic composition (δ¹⁸O) of carbonate sediments including ostracode shells (Limnocythere ceriotuberosa) from Walker Lake allow us to extend the sediment record of lake-level fluctuations back to 2700 years B.P. There are approximately five major stages over the course of the late Holocene hydrologic evolution in Walker Lake: an early lowstand (> 2400 years B.P.), a lake-filling period ( 2400 to  1000 years B.P.), a lake-level lowering period during the Medieval Warm Period (MWP) ( 1000 to  600 years B.P.), a relatively wet period ( 600 to  100 years B.P.), and the anthropogenically induced lake-level lowering period (< 100 years B.P.). The most pronounced lowstand of Walker Lake occurred at  2400 years B.P., as indicated by the relatively high values of δ¹⁸O. This is generally in agreement with the previous lower resolution paleoclimate results from Walker Lake, but contrasts with the sediment records from adjacent Pyramid Lake and Siesta Lake. The pronounced lowstand suggests that the Walker River that fills Walker Lake may have partially diverted into the Carson Sink through the Adrian paleochannel between 2700 to 1400 years B.P.     

Diatom response to the Holocene climatic optimum on the North Icelandic shelf

A diatom record from core MD992275 on the North Icelandic shelf reveals palaeoclimatic and palaeoceanographic changes during the time interval 9000 to 5600 cal. year BP. The study period includes the Holocene Climate Optimum (HCO), as widely known in the North Atlantic region. A comparison with data for the last 2000 years and with the present-day surface sediment diatom assemblages shows that there was considerably stronger influence of Atlantic water masses in the area during the HCO than in the late Holocene and today. The results of cluster analysis and principal component analysis divide the studied period into three intervals, each characterised by a specific diatom assemblage. The assemblages indicate changes in the interaction of the relatively warm Irminger Current (IC) and the cold East Greenland Current (EGC) and East Icelandic Current (EIC). The North Icelandic shelf was strongly affected by the IC during the interval 8000–6800 cal. year BP, which may be the warmest period of the Holocene. During the intervals 9000–8000 and 6800–5600 cal. year BP, the influence of the IC was relatively weak and that of the EGC and EIC increased correspondingly. The well-known 8200 cal. year BP cooling event, shown in many records from the North Atlantic, is reflected by a relatively strong influence of the EGC and EIC between about 8300 and 8100 cal. year BP in our record. However, the diatom assemblages show that the inferred circulation change did not bring the strength of the IC down to the levels seen at present and during the last two millennia.     

Late and postglacial vegetation and fire history in Southern Patagonia and Tierra del Fuego

Two 17,000-yr-old peat bog records from low-elevation sites in Tierra del Fuego (Harberton, 54°54′S) and southern Patagonia (Río Rubens, 52°4′48″S) and one c. 14,000 cal yr BP record from the upper treeline in Tierra del Fuego (Paso Garibaldi, 54°43′S) were analyzed for pollen, charcoal, and plant macrofossils to reconstruct changes in regional and local vegetation, fire frequency, and bog hydrology, respectively. Past environmental changes in both lowland records and in the upper treeline record are interpreted in terms of variations in effective moisture. During the late-glacial period, effective moisture changes at both low and high-elevation sites were interpreted from comparable shifts between mesic herb-rich grasslands and arid Empetrum heath or shrub-grassland with abundant disturbance indicators. The late-glacial effective moisture changes were primarily driven by temperature changes. During the early Holocene, expansion of open Nothofagus woodlands in the lowlands in present-day areas of dense forest was related to a marked precipitation increase. However, precipitation must have remained highly variable with century-long periods of increased summer drought, as evidenced by repeated intervals when bogs dried out and fire frequency was high. Up-slope shifts of the Nothofagus forest — Andean tundra ecotone at 11,000 and 9000 cal yr BP also appear to reflect precipitation increases. Precipitation variability, however, must not have affected the upper treeline environments as no fires were recorded and the present-day Nothofagus forest had become established after 9000 cal yr BP. Upper treeline apparently was below present from 8000 to 7000 and 2500 to c. 400 cal yr BP. During those times low-elevation environments did not register change which suggests that the upper treeline may have been affected by lower temperatures. After c. 5000 cal yr BP fires became rare in the lowlands, suggesting a shift to an equable precipitation regime with only minor intervals of summer drought. No simultaneous change was recorded at the upper treeline. Thus, for the late-glacial and early Holocene the upper and lower treeline environments apparently responded similarly to primarily moisture changes. Only during the mid- and late Holocene environmental changes at high and low elevations differed, suggesting responses to different climate signals, precipitation in the lowlands and temperature at high elevation.     

Postglacial climate in the St. Lawrence lowlands, southern Québec: pollen and lake-level evidence

Pollen and lake-level data are used to reconstruct past climate changes in the St. Lawrence lowlands, southern Québec. Past lake-level changes are assessed from sedimentological, pollen and macrofossil records from a single shallow-water core from Lac Hertel, which lies in the central part of the studied area. Three low lake-level phases are recognised: prior to 8000, 7600-6600 and 4800-3400 cal. BP. The modern analogue method is applied to pollen data from seven well-dated sites from the St. Lawrence lowlands and adjacent mountain areas, constrained and unconstrained by lake-level changes. The reconstructed climate changes are congruent with the pattern of climate changes known from eastern North America: a dry and cold late-glacial episode due to the presence of pro-glacial lakes and seas; a rapid warming between 12?500 and 11?000 cal. BP possibly caused by increasing summer insolation; a dry period from 10?000 to 6500 cal. BP; a brief cooling between 9000 and 8000 cal. BP, possibly related to a summer cooling of Arctic airmasses; a temperature maximum around 8000 cal. BP; and finally, a progressive decrease in summer temperature and an increase in (winter?) precipitation over the 4500 last years. These results show that it is possible to reveal seasonal patterns in climate by combining pollen and lake-level data.     

Lake Baikal climatic record between 310 and 50 ky BP: Interplay between diatoms, watershed weathering and orbital forcing

The environmental record from Lake Baikal, Russia, from 310 to 50 ky BP (MIS 9a to MIS 3) was interpreted using rock magnetic, UV–Vis spectral, mineralogical, and diatom analyses. The age model was based on a correlation of the diatom and chemical weathering records and the summer insolation curve at 55°N and checked against an age model based on the proxy of relative palaeointensity of the Earth's magnetic field. Peaks in chemical weathering within the watershed, inferred from maximum concentration of magnetic and coloured minerals and mica, the lowest mean Fe oxidation state in silicates and highs in expandable clay minerals correlated with the Northern Hemisphere summer insolation minima at 55°N. Reconstructed changes in weathering intensity are better correlated to insolation patterns than to global ice volume records. We propose a scheme of yet missing palaeoenvironmental interpretation of the diatom assemblage, including also some extinct species. Aulacoseira baicalensis and Aulacoseira skvortzowii were abundant in the early stages of lake flora recovery immediately after deglaciation and during MIS 7e and MIS 5e; periods of more pronounced continental climate and peak chemical weathering. Stephanodiscus formosus var. minor, Cyclotella minuta and Cyclotella ornata dominated in intervals of decreased seasonality and decreased humidity at the end of most interglacial/interstadial diatom zones. Stephanodiscus grandis, Stephanodiscus carconeiformis and Stephanodiscus formosus were ubiquitous between MIS 8 and MIS 5, an interval marked by high seasonality, i.e., large differences between winter and summer insolation, and low humidity revealed by a low hydrolysis of expandable clay minerals in the watershed. Diatom concentrations peaked in the climatic optima of MIS 7e and MIS 5e and in the short periods marked by shifts to warmer conditions in the upper sections of MIS 5: MIS 5c (103–99 ky BP), MIS 5b (90–88 ky BP), and MIS 5a (84–79 ky BP) in which increased humidity resulted in enhanced hydrolysis of clay minerals. No such short similar climatic optimums were found from MIS 9a to MIS 6. Sharp climate deteriorations recorded in the diatom and clay mineral records at 107, 94, and 87 ky BP, however, occurred within 1–2 ky of cold extremes in North Atlantic sea surface temperature emphasizing the strong teleconnections between the two localities.     

Relationship of environmental changes in central Sri Lanka to possible prehistoric land-use and climate changes

A radiocarbon-dated pollen-analysed peat sequence from the Horton Plains (> 2000 m a.s.l.), in central Sri Lanka, together with physical and chemical parameters (organic carbon, mineral magnetics, carbon isotopes and phytoliths), indicates major environmental changes during the last 24,000 years. The results suggest that a mobile life form, i.e. a hunter–forage culture, predominated in an open landscape, associated with xerophytic vegetation, e.g. Chenopodium spp. at  17.5 ka BP. Incipient management of cereal plants and slash-and-burn techniques seem to have prevailed between 17.5 and 13 ka BP, which was indigenous and associated with grazing. Evidence of systematic cereal cultivation in the form of oat and barley pollen grains is found from the late Pleistocene ( 13 ka BP). This is the earliest evidence of farming activities noted in Sri Lanka as well as in south Asia. After 13 ka BP, cereal cultivation was associated with an increase in humidity. With a later abrupt increase in aridity, agricultural land-use decreased from  8 to  3.6 ka BP, when the area appears to have been almost deserted. After a severe middle Holocene arid phase (i.e. 5.4–3.6 ka BP), the agricultural activity with a limited extension was again initiated by  2.9 ka BP. During the next  900 years, cultivation ceased allowing the upper montane rain forest to dominate. Between 0.2 and 0.15 ka BP, new phases of agricultural activities were undertaken and potato cultivation took place lately, between 1950 and 1969 AD.     

An exploration of the controls of pre-instrumental streamflow using multiple tree-ring proxies

Previous studies have used tree-ring chronologies from several species to develop reconstructions of precipitation, temperature, streamflow and glacier mass balance for sites in Banff National Park, Alberta. This study examines the variability in a >300-year summer streamflow reconstruction for the Bow River at Banff in conjunction with changes in the major contributors to streamflow (glacier melt, winter and summer pecipitation). Reconstructed winter mass balance for Peyto Glacier is used as a surrogate for winter precipitation and April–August precipitation is reconstructed for Banff. Streamflow variability correlates most highly with winter precipitation and periods of high flow follow above average snowfall in the previous winter (high winter balance) and in some cases also with above normal summer precipitation. A clear response to changes in summer mass balance at Peyto Glacier (i.e. summer glacier melting) cannot be identified in this summer discharge record. Problems developing physically realistic flow reconstructions for snowmelt dominated rivers from summer sensitive tree-ring chronologies are also discussed.     

Holocene altitudinal shifts in vegetation belts and environmental changes in the Sierra Madre Occidental, Northwestern Mexico, based on modern and fossil pollen data

A modern pollen rain study was performed in a 300 km-long altitudinal transect (~ 28° N latitude) from 300 to 2300 m elevation. The higher elevation modern communities: epithermal oak–pines, pine–oak forest, pine forest, and mixed conifer forest were easy to distinguish from their pollen content. In contrast, lower elevation subtropical communities: thornscrub and tropical deciduous forest were difficult to separate, because they share many pollen taxa. Nevertheless we identify high frequencies of Bursera laxiflora as an important component of the tropical deciduous forest.Additionally, fossil pollen was analyzed at three sites located between 1700 and 1950 m altitude at ~ 28° latitude north in the Sierra Madre Occidental of northwestern Mexico. The sites were in pine–oak (Pinus–Quercus), pine, and mixed-conifer forests respectively. Shifts in the altitudinal distribution of vegetation belts were recorded for the last 12,849 cal yr BP, and climate changes were inferred. The lowest site (pine–oak forest) was surrounded by pine forest between 12,849 and 11,900 cal yr BP, suggesting a cold and relatively dry Younger Dryas period. The early Holocene was also cold but wetter, with mixed conifer forest with Abies (fir) growing at the same site, at 1700 m elevation, 300 m lower than today. After 9200 cal yr BP, a change to warmer/drier conditions caused fir migration to higher elevations and the expansion of Quercus at 1700 m. At 5600 cal yr BP Abies was growing above 1800 m and Picea (spruce) that is absent today, was recorded at 1950 m elevation. Fir and spruce disappeared from the 1950 m site and reached their present distribution (scattered, above 2000 m) after 1000 cal yr BP; we infer an episodic Holocene migration rate to higher elevations for Abies of 23.8 m/1000 cal yr and for Picea of 39.2 m/1000 cal yr. The late Holocene reflects frequent climate oscillations, with variations in the representation of forest trees. A tendency towards an openness of the forest is recorded for the last 2000 yrs, possibly reflecting human activities along with short-term climate change.     

Late Weichselian and Holocene sedimentary environments and ice rafting in Isfjorden, Spitsbergen

Multi-proxy analyses of two sediment cores from central Isfjorden were used to reconstruct the glacial history in central Spitsbergen during the Late Weichselian and the Holocene, and to relate iceberg rafting and sea-ice rafting to climatic and oceanographic changes in the north Atlantic region. A basal till was deposited beneath an ice stream prior to 12,700 cal. years BP (calendar years before the present). Several tidewater glaciers influenced the sedimentary environment during the Younger Dryas and probably already during the Allerød. The Younger Dryas cooling might be reflected by enhanced sea-ice formation and suspension settling, as well as reduced iceberg rafting. The final deglaciation was dominated by intense iceberg rafting. It terminated around 11,200 cal. years BP. Optimum Holocene climatic and oceanographic conditions with significantly reduced ice rafting occurred between c. 11,200 and 9000 cal. years BP. Ice rafting occurred almost exclusively from icebergs after 10,200 cal. years BP. The icebergs most probably originated from tidewater glaciers on east Spitsbergen, indicating the presence of a strong east–west temperature gradient at this time. An increase of iceberg rafting around 9000 cal. years BP, followed by enhanced sea-ice rafting, reflects the onset of a general cooling in the western Barents Sea–Svalbard region. Comparatively intense rafting from icebergs and sea ice between 9000 and 4000 cal. years BP is related to this cooling. A general reduction in ice rafting after 4000 cal. years BP is most probably the result of the enhanced formation of shore-fast and/or more permanent sea-ice cover, reducing the drift of icebergs and sea ice in the fjord. The results indicate that the palaeoenvironmental conditions on central Spitsbergen to a large degree depended on the oceanographic conditions in the western Barents Sea and west off Spitsbergen. However, climatic trends affecting Greenland and the entire north Atlantic region can also be identified.     

High-resolution sea surface temperature records derived from foraminiferal Mg/Ca ratios during the last 260 ka in the northern South China Sea

High-resolution sea surface temperatures (SST) derived from Mg/Ca ratios of Globeriginoides sacculifer at ODP Site 1144 were reported to reveal the SST changes during the last 260 ka in the northern South China Sea (SCS). The results indicate an average Holocene SST of about 26.7 °C, about 3.6 °C increase from LGM to the Holocene, and higher temperature during MIS 5.5 than the Holocene. These agree well with other foraminifer Mg/Ca and U^k₃₇ SST records in this region. The Mg/Ca records suggest warmer SSTs during MIS 3 in the northern SCS, compared with those in the eastern Pacific. Strong East Asian summer monsoon during MIS 3 indicated by paleoclimate records from nearby continents may account for it. Step-wise increases during terminations are shown in our SST record, and the beginning of deglacial warming occurs at about 19 ka, which precedes the change of oxygen isotopes, suggesting a tropical driven forcing for the SST change in the northern SCS. This is further supported by a robust semi-precessional cycle centering at  9.1 ka in the spectra of the SST record, which is absent in that of the oxygen isotopes. However, tropical driven forcing seems not to be indicated in another Mg/Ca SST record in the northern SCS [Oppo, D.W. and Sun, Y.B., 2005. Amplitude and timing of sea-surface temperature change in the northern South China Sea: Dynamic link to the East Asian monsoon. Geology, 33 (10): 785–788.]. The discrepancy may be caused by different post-deposition dissolutions of foraminifer tests at these two sites. Details about the modification of foraminifer Mg/Ca ratios after burial, however, are not well known in this region, and further studies are needed.     

Short-term climate changes in the southern Aegean Sea over the last 48,000 years

High-resolution palaeoenvironmental changes, corresponding to a mean time interval of 450 years covering the last 48,000 years, were examined in a core from the Cretan Basin in the southern Aegean Sea. The intensity and duration of the climatic and oceanographic events were determined by examining the compositional changes in the planktonic foraminifera and pollen assemblages, along with the δ¹⁸O signal of Globigerinoides ruber. A reconstruction of sea-surface temperatures was attempted using the Modern Analogue Technique (MAT). In total, 10 stadials and 6 interstadials occurred over the last 48,000 years. These fluctuations in climatic conditions coincide with fluctuations documented in the western and central Mediterranean and seem to be associated with Dansgaard–Oeschger events. Some of these climatic fluctuations are correlated with changes in the vegetation in the surrounding land.

Between 48 and 10 cal kyr BP the most pronounced stadials occurred at 41 cal kyr BP (C69-ST10) and at 13 cal kyr BP (C69-ST4). These events are characterized by: (i) high positive δ¹⁸O values of Globigerinoides ruber, (ii) drops in SST and (iii) increases in aridity. These events may be correlated with the Heinrich H4 event and the Younger Dryas event, respectively. Two other stadials at 23 cal kyr BP (C69-ST6) and at 16 cal kyr BP (C69-ST5) which are characterized by increases in the abundance of the cold plaktonic foraminifera species and increases in aridity may be correlated with the H2 and H1 events, respectively. The dominant planktonic foraminiferal species during the stadials witch are correlated with the Heinrich events were Turborotalita quinqueloba and Globorotalia scitula. The most pronounced interstadials occurred between 39.5 and 38.5 cal kyr BP (C69-IST6) and between 25 and 24 cal kyr BP (C69-IST3) and are characterized by depletion in δ¹⁸O values, increases in SST and increases in humidity. The former event coincides with the formation of the sapropelitic layer S2.

In the Holocene the most pronounced stadial occurred between 8 and 6.5 cal kyr BP (C69-ST2), during the interruption of S1 and is characterized by a reduction in SST and an increase in aridity. The most pronounced interstadials of Holocene occurred during the formation of S1a and S1b between 9 and 8 cal kyr BP (C69-IST1) and between 6.5 and 5.5 cal kyr BP (C69-IST2), respectively. These events are characterized by depletion in δ¹⁸O values, increased SST and an increase in humidity as is indicated by the expansion of temperate evergreen and Mediterranean taxa in the pollen record.     

Late Quaternary stratigraphy and sedimentology of Orphan Basin: Implications for meltwater dispersal in the southern Labrador Sea

Orphan Basin is a deep-water basin on the continental margin off Newfoundland, which throughout the late Quaternary received proglacial sediment from local ice that crossed the continental shelf. Sediment from more distant sources was transported southward in the Labrador Current as proglacial plumes and in icebergs. Five sedimentary facies related to glacial processes are distinguished in cores recovered from Orphan Basin: hemipelagic sediment, nepheloid-layer deposits (layered mud), beds rich in ice-rafted detritus (IRD), sand and mud turbidites, and glaciogenic debris-flow deposits. IRD-rich beds correspond to periods of intensified iceberg calving, and layered mud, turbidites, and glaciogenic debris-flow deposits with glacial meltwater discharge.

In the Late Wisconsinan, eight periods of meltwater discharge and iceberg calving from the Newfoundland ice sheet are interpreted from the sediment facies in Orphan Basin. These discharges coincide with the terminations of the colder periods of the D–O cycles recorded in Greenland ice cores. The oldest minor meltwater event (27.5–28.5 cal ka) corresponds to the first Late Wisconsinan ice advance across the Grand Banks and NE Newfoundland Shelf. The following three meltwater discharges (23–23.5, 23.8–24.5, and 25–27 cal ka) deposited sand turbidites and glaciogenic debris-flow deposits seaward of Trinity Trough, which was occupied by an ice stream at this time, and mud turbidites in the southern part of the basin derived from a mid-shelf ice margin on the Grand Banks. Four periods of meltwater discharge occurred during the deglaciation and are centered at 15, 18.5, 19.75, and 20.75 cal ka. The youngest is correlated to Heinrich event 1. In the literature, the 18.5 and 20.75 cal ka events have been recorded in multiple glacial settings in the North Atlantic, and therefore, are interpreted as large-scale events of meltwater discharge and iceberg calving, but in Orphan Basin the 19.75 cal ka event is also of similar scale.