Late Glacial and Holocene environmental and climatic changes from a limnological transect through Colombia, northern South America

We present a synthesis of the palaeolimnological and palaeoclimatic reconstructions of four sites in Colombia. The record from Lake El Caimito, the westernmost site on the Pacific Coast, dates from the Late Holocene and shows lacustrine sedimentation frequently interrupted by fluvial pulses. These pulses probably reflect periods of increased precipitation related to La Niña phases. East of El Caimito site is the Patía swamp, situated between the Western and Central Andean Cordilleras. The Patía records the dynamics of forest expansion/reduction and changes in water levels. Although the climatic signal of the Patia core is difficult to reconstruct, there is a clear increase in humidity in the Mid-Holocene. The Fúquene Lake record, on the Eastern Andean Cordillera, records dry and cold conditions during the Late Pleistocene, very humid conditions for the early Mid-Holocene, and dry conditions during the mid-Late Holocene. Las Margaritas site, on the eastern savannas, records dry conditions during the Early Holocene and overall humid conditions for the Mid- and Late Holocene. Climate conditions from the Fuquene and Las Margaritas sites seem to reflect the Holocene movements of the Intertropical Convergence Zone (ITCZ); the latter site being more affected by humidity coming from the Amazon region.     

Palaeoenvironmental studies in NW Iberia (Cantabrian range): Vegetation history and synthetic approach of the last deglaciation phases in the western Mediterranean

At the north-western limit of the Mediterranean basin, in the Mediterranean-Oceanic transition zone, the multidisciplinary study of two palaeolakes: Villaseca and La Mata (Province of Leon), provides data on the last deglaciation. The juxtaglacial lakes were formed during a deglaciation phase of the last cold stage (Weichselian/Würm) estimated, from the regional and Pyrenean chronological data, between circa 48 ka and 32 ka (ka: 1000 years ago). Their drainage occurred circa 17 ka and 15 ka respectively, during the definitive glacial retreat phases. These results provide evidence for a glacial maximum extension preceding the global Last Glacial Maximum (LGM) and an early deglaciation. Comparisons with the Pyrenean data show that in the most important glacial basins of the Pyrenean-Cantabrian range, glaciers were still present at middle elevation circa 18-20 ka. The final deglaciation did not happen until around 16 ka.During the period 48-13.3 ka, along the Pyrenean-Cantabrian range, three stages can be distinguished in the deglacial processes. Between circa 48 and 32 ka, the deglacial retreats were contemporaneous with D-O events 12 to 6. Between circa 32 ka and 18 ka, major sedimentary modifications were rare. Two of them are synchronous with D-O 4 and 3. A glacial readvance also occurred during this period along the Pyrenean-Cantabrian range. Between 18 and 17 ka, major sedimentary changes and an increase in the δ¹⁸O records of the NGRIP ice-core record are synchronous. Between 15 and 13.3 ka, glacial retreats and sedimentary changes are synchronous with the climatic improvement observed from the end of the Oldest Dryas to the end of the Bölling-Alleröd period.These correspondencies suggest relationships between the deglacial processes in the western Mediterranean and the palaeoenvironmental events in the North Atlantic region during the last Glacial-Interglacial transition. During the Full Glacial period, the pollen data indicates dominant steppic environments. The Oldest Dryas was not a constant cooling phase and from around 15.5 ka, the pollen data indicates a slight warming. During the Holocene, until circa 2040 cal BP, mixed oak forests developed and pine was a prominent component of the Cantabrian landscape. Then the forests were destroyed due to mining, agriculture and fire, and this favoured the extension of heathland.     

A 21 000 cal years paleoclimatic record from Caçó Lake,northern Brazil: evidence from sedimentary and pollen analyses

Sedimentological studies including seismic profiles, mineralogy and organic geochemistry on two cores from the center and margin of Caçó Lake, Maranhão State, northern Brazil, revealed variable climatic and environmental conditions during the last 21 cal kyr BP. Between 21 and 17 cal kyr BP, during the Late Glacial Maximum, regional climate was predominantly dry, interrupted by short humid phases, as reflected by a succession of very thin layers of sand and organic matter. The Late Pleistocene climate was relatively wet as is suggested by rapid lake-level rise and forest expansion. The Late Pleistocene humid climate differed significantly from present conditions. We suggest that Late Glacial humid conditions were the consequence of intensification of the Inter-Tropical Convergence Zone or shifts of its position, resulting in Antarctic cold-front occurrences. The abrupt climatic changes during this period were marked by siderite deposition into Caçó Lake, which appears to be related to regional hydrologic changes linked to global/Northern Hemisphere events. The Holocene was characterized by lower moisture availability and a distinct dry period until 7 cal kyr BP, in response to South American insolation conditions.     

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.     

Sea ice seasonality during the Holocene, Adélie Land, East Antarctica

Thin sections of laminated cores from different Antarctic coastal areas have demonstrated the potential of diatom species to document climate change at the seasonal scale. Here we present the relative abundances of four diatom species and species groups (Fragilariopsis curta group as a proxy for yearly sea ice cover, F. kerguelensis as a proxy for summer sea-surface temperature, Chaetoceros Hyalochaete resting spores as a proxy for spring sea ice melting and the Thalassiosira antarctica group as a proxy for autumn sea ice formation) in core MD03-2601 retrieved off Adélie Land on the Antarctic continental shelf. These abundances were compared to surface temperatures and sea ice cover modelled over the last 9000 years. Both the marine records and the simulated climate demonstrated a cooler Early Holocene (9000–7700 years BP), a warmer Mid-Holocene (7700–4000 years BP) and a colder Late Holocene (4000–1000 years BP). Yearly sea ice cover followed an inverse pattern to temperatures with less sea ice during the Mid-Holocene Hypsithermal than during the Late Holocene Neoglacial. However, diatom census counts and model output indicate that sea ice spring melting happened earlier in the season, as expected, but that autumn sea ice formation also occurred earlier in the season during the Hypsithermal than during the colder Neoglacial, thereby following seasonal changes in local insolation.     

Late glacial and Holocene environmental changes inferred from sediments in Lake Myklevatnet,Nordfjord, western Norway

Late Glacial and Holocene environmental changes were reconstructed using physical, chemical and biological proxies in Lake Myklevatnet, Allmenningen, (5º13′17″E, 61º55′13″N) located at the northern side of Nordfjorden at the coast of western Norway. Myklevatnet (123 m a.s.l.) lies above the Late Glacial marine limit and contains sediments back to approximately 14,300 years before a.d. 2000 (b2k). Because the lake is located ~48 km beyond the margin of the Younger Dryas (YD) fjord and valley glaciers further inland, and did not receive glacier meltwater from local glaciers during the YD, the lake record provides supplementary information to Lake Kråkenes that received glacial meltwater from a local YD glacier. Lake Myklevatnet has a small catchment and is sensitive to Late Glacial and Holocene climate and environmental changes in the coastal region of western Norway. The age-depth relationship was inferred from a radiocarbon- and tephra-based smoothing-spline model with correlated ages from oxygen isotope maxima and minima in the Late Glacial sequence of the NGRIP ice core (in years b2k) to refine the basal chronology in the Myklevatnet record. The results indicate a two-step YD warming, colder early YD temperatures than in the later part of the YD, and considerably more climate and environmental variability during the late Holocene in western Norway than recorded previously in the oxygen isotopes from Greenland ice cores. The Myklevatnet record is also compared with other Late Glacial and Holocene terrestrial and marine proxy reconstructions in the North Atlantic realm.     

Late Quaternary millennial-scale variability in pelagic aragonite preservation off Somalia

In order to better understand Late Quaternary pelagic aragonite preservation in the western Arabian Sea we have investigated a high-resolution sediment core 905 off Somalia. Pteropod preservation is enhanced in times of reduced monsoon-driven productivity, indicated by low amounts of C_org and low barium to aluminium (Ba/Al) ratios. All periods corresponding to Heinrich events in the North Atlantic are represented by maxima in shell preservation of the common pteropod Limacina inflata (LDX values < 2, except for H5-equivalent with a poorer shell preservation, LDX > 2.66). Good shell preservation is also found during stadials at 52.1–53.2, 36, 33.2, and 31.9 ka. Relative abundance of pteropods and their fragments in the coarse fraction reaches maxima during Marine Isotope Stage (MIS) 5.2, during time-equivalents of Heinrich events 4–6 and in stadials at  53,  42.5, and 41.4 ka.On longer time scales, the pteropod abundance corresponds to the ‘Indo-Pacific carbonate preservation type’ with poor preservation during interglacials and better preservation during glacials. Late MIS 5 to early MIS 4 sections (84.1–64.8 ka) and the Late Holocene interval (6.5–0 ka) of core 905 contain only traces of pteropods. The early Holocene (9.2–6.5 ka) part is characterized by low pteropod amounts. Between 64.8 and 43.4 ka strong fluctuations occur and an intermediate average relative pteropod abundance is revealed. Between 43.4 and 9.2 ka the highest amounts in relative pteropod abundance in core 905 are observed. Besides the regional monsoonal influence on deepwater chemistry, changes in deepwater circulation occurring on glacial/interglacial and stadial/interstadial time scales might have affected pteropod preservation. However, it remains elusive whether 1) deep water formation in the Arabian Sea, 2) inflow of Glacial North Atlantic Intermediate Water or 3) change in water mass properties of the Circumpolar Deep Water (which is the water mass currently bathing this site) contributed to the observed pteropod preservation pattern.     

Late Quaternary (Weichselian) alluvial history and neotectonic control on fluvial landscape development in the southern Körös plain,Hungary

Four drill cores and a clay pit section have been examined in the southern part of the Körös plain to understand the history and controls on alluvial sedimentation for the last ~ 40 ka. Four facies groups were identified, such as channel, channel margin, floodplain and floodbasin with seven distinctive facies. Magnetic susceptibility and mineralogy have further characterized the sedimentary facies indicating shifts in humidity conditions, variations in sediment flux and pedogenesis. Detailed pollen analysis of a 7.5 m thick clayey succession indicated climatic variability within the MIS 3 period. The spatial distribution of the different facies allowed outlining alluvial architecture of the study area. Three depositional units composed of various facies were identified based on OSL and radiocarbon data. These packages correspond to three major phases of channel activity: (F-I) pre-LGM period (> 30 ka to 24 ka), (F-II) post-LGM interstadial (18–16 ka), and (F-III) Late Glacial < 15 ka to ~ 10 ka). The pre-LGM and post-LGM “interstadial” phases are characterized by meandering river patterns, while the Late Glacial fluvial activity is characterized by a braided system in the area. Higher sediment supply feeding this braided river was probably caused by neotectonic uplift of the southern margin of the basin, documented by a significant stratigraphic gap between 25 and 14 ka.     

A Holocene sequence of vegetation change at Lake Eteza, coastal KwaZulu-Natal, South Africa

Palynological and sedimentological data from a core extracted from Lake Eteza shed new light on the Holocene vegetation and climate history in KwaZulu-Natal and can be linked to regional and global climate change. A 2072 cm core with nineteen radiocarbon dates and chronological extrapolation to the bottom of the sequence suggests that sedimentation started ca. 10 200 cal yrs BP. Between ca. 10 200 and 6800 cal yrs BP pollen indicators point to a change from intermediately humid conditions to comparatively drier grassy environments. This is in good agreement with Sea Surface Temperature (SST) fluctuations from a core in the Mozambique Channel which influence precipitation in coastal KwaZulu-Natal, and the beginning of the Holocene Thermal Maximum ca. 10 500 cal yrs BP. The lower section of the core corresponds to gradually increasing Holocene sea levels along the coast and development of freshwater or estuarine conditions at Lake Eteza. The middle Holocene (ca. 6800-3600 cal yrs BP), when the sea level reached its highest stand and SST peak, indicate humid climatic conditions that favoured an increase of forest trees, e.g. Podocarpus, and undergrowth plants like Issoglossa. As a consequence of higher precipitation and increase of the water table, conditions were favourable for the spread of mangrove, swamp and possibly riverine forest. During the late Holocene after ca. 3600 cal yrs BP a decrease of Podocarpus and other trees as well as an increase of Chenopodiaceae/Amaranthaceae, grasses and Phoenix coincide with a return to lower sea levels and drier conditions. The decrease of all trees including Phoenix at ca. 700 cal yrs BP, accompanied by rapid sedimentation rates, possibly reflect forest clearing and upland erosion induced by activities of Iron Age settlers. A dry period at the globally recognized onset of the Little Ice Age might have contributed to these changes. Late Iron Age settlers have probably already introduced Zea mays, which was detected in the profile since ca. 210 BP. The appearance of neophytes like Pinus, Casuarina and pollen of Ambrosia-type in the youngest sediments indicates increased disturbance of European settlements and land use since ca. 100 cal yrs BP.     

New geochronological, paleoclimatological, and archaeological data from the Narmada Valley hominin locality, central India

The oldest known fossil hominin in southern Asia was recovered from Hathnora in the Narmada Basin, central India in the early 1980's. Its age and taxonomic affinities, however, have remained uncertain. Current estimates place its maximum age at >236 ka, but not likely older than the early middle Pleistocene. The calvaria, however, could be considerably younger. We report recent fieldwork at Hathnora and associated Quaternary type-sections that has provided new geological and archaeological insights. The portion of the exposed ‘Boulder Conglomerate’ within the Surajkund Formation, which forms a relict terrace and has yielded the hominin fossils, contains reworked and stylistically mixed lithic artifacts and temporally mixed fauna. Three mammalian teeth stratigraphically associated with the hominin calvaria were dated by standard electron spin resonance (ESR). Assuming an early uranium uptake (EU) model for the teeth, two samples collected from the reworked surface deposit averaged 49 ± 1 ka (83 ± 2 ka, assuming linear uptake [LU]; 196 ± 7 ka assuming recent uptake [RU]). Another sample recovered from freshly exposed, crossbedded gravels averaged 93 ± 5 ka (EU), 162 ± 8 ka (LU) or 407 ± 21 ka (RU). While linear uptake models usually provide the most accurate ages for this environment and time range, the EU ages represent the minimum possible age for fossils in the deposit. Regardless, the fossils are clearly reworked and temporally mixed. Therefore, the current data constrains the minimum possible age for the calvaria to 49 ± 1 ka, although it could have been reworked and deposited into the Hathnora deposit any time after 160 ka (given the LU uptake ages) or earlier (given the RU ages). At Hathnora, carbonaceous clay, bivalve shells, and a bovid tooth recovered from layers belonging to the overlying Baneta Formation have yielded ¹⁴C ages of 35.66 ± 2.54 cal ky BP, 24.28 ± 0.39 cal ky BP, and 13.15 ± 0.34 ky BP, respectively. Additional surveys yielded numerous lithics and fossils on the surface and within the stratigraphic sequence. At the foot of the Vindhyan Hills 2 km from the river, we recovered a typologically Early Acheulean assemblage comprised of asymmetrical bifaces, large cleavers with minimal working, trihedral picks, and flake tools in fresh condition. These tools may be the oldest Acheulean in the Narmada Valley. Several lithics recovered from the Dhansi Formation may represent the first unequivocal evidence for an early Pleistocene hominin presence in India. In situ invertebrate and vertebrate fossils, pollen, and spores indicate a warm, humid climate during the late middle Pleistocene. High uranium concentrations in the mammalian teeth indicate exposure to saline water, suggesting highly evaporative conditions in the past. Late Pleistocene sediment dated between 24.28 ± 0.39 cal ky BP and 13.15 ± 340 ky BP has yielded pollen and spores indicating cool, dry climatic conditions corresponding to Oxygen Isotope Stage 2 (OIS 2). An early Holocene palynological assemblage from the type locality at Baneta shows evidence for relatively dry conditions and a deciduous forest within the region. The Dhansi Formation provisionally replaces the Pilikarar Formation as the oldest Quaternary formation within the central Narmada Basin. The Baneta Formation, previously dated at 70 ka to 128 ka, correlates with the late Pleistocene and early Holocene. Our results highlight the need for further Quaternary geological and paleoanthropological research within the Narmada Basin, especially because dam construction threatens these deposits.     

The Holocene and Upper Pleistocene pollen sequence of Carihuela Cave, southern Spain

A new pollen sequence (ca. 15,700-1250 yr BP) is presented for three stratigraphical sections of Carihuela Cave (Granada, southeastern Spain), thus completing a record that covers from the last Interglacial to late Holocene. The Late Glacial is characterized by open landscapes with junipers and early colonisation of Quercus, while the Holocene is depicted by mixed oak forests, with a diversity of broad-leaf trees and scrub, which decrease after ca. 5470 yr BP synchronously with the expansion of xerophytes and occurrence of indicators of anthropogenic disturbance. The whole pollen record of Carihuela fits into the general trends described for reference pollen sites of southern Europe, including Padul in the province of Granada, and other sequences from Mediterranean Spain, through which the heterogeneity of environmental change increases from mid to late Holocene. We conclude that, in contrast with other regions of Spain, deciduous Quercus-dominated forests are very old in eastern Andalusia, thus conflicting with floristic phytosociological models of vegetation change that imply that monospecific Q. ilex/rotundifolia woodlands are the potential mature forest in the region. Dating results suggest that the last Neanderthals of Carihuela lived between ca. 28,440 and 21,430 yr BP, which agrees with the postulation that southern Spain was the latest refugium for this human species in Europe.     

Fluvial response to late Quaternary climate change in NE Queensland, Australia

Samples of alluvial and colluvial deposits from the coastal plain and coastal valleys north and south of Cairns (17°S) have been dated using optically stimulated luminescence (OSL) protocols, with additional thermoluminescence (TL) and Radiocarbon assays. Coarse fanglomerates from elevated coastal terraces date back to 81 ka, but most are clustered in oxygen isotope stage three (OIS3, 64-28 ka), indicating high-energy conditions during this period. Extensive fans and terraces of finer calibre sediments are widely represented grading from coarse gravels and cobbles in proximal zones fine sand and silt in distal areas. Dates show that vertical accumulation of 10-15 m of sediment occurred between ∼ 28 and 14 ka (OIS2), after which the fans were dissected and Holocene deposits become fragmentary. A number of deposits indicating hillslope instability were successfully dated and these fall mainly into OIS3 and post 12 ka. These results are interpreted as catchment responses to Late Pleistocene climate and vegetation changes, documented elsewhere from local pollen and ocean drilling sites. Correlation with these records and with evidence for regional climate change from the Austral-Asian region is good and indicates that these changes were sufficient to transform fluvial activity and slope processes.     

Early Holocene environmental change in the Kreekrak area (Zeeland, SW-Netherlands): A multi-proxy analysis

Detailed botanical (microfossil and macroremain), zoological and geochemical analyses (major and trace elements including C, Al, S, Ca, Fe, P, As, Zn, U, Ba and Rare Earth Elements) of organic deposits provide new insights into Early Holocene environmental change in the Kreekrak area (southwestern Netherlands). The age assessment of the record is based on high resolution AMS ¹⁴C wiggle-match dating (WMD). For the first time an AMS ¹⁴C WMD based chronology covering the Late Glacial/Holocene transition and early Preboreal is introduced for a site in The Netherlands.The Kreekrak botanical record reflects the end of the Younger Dryas to early Boreal and can be well correlated with pollen records from other sites in The Netherlands and Belgium. The palaeo-topography showed that the Kreekrak deposits formed in an abandoned channel of the River Schelde. Around ca. 11,490 cal BP, at the end of the Late Glacial/Holocene transition, infilling of the lake started with predominantly organic deposits in slowly running water. As a result of the warmer climate the area became forested with birch and poplar during the Friesland Phase (ca. 11,490-11,365 cal BP). Biological productivity of the lake and its surroundings increased. Aquatic vegetation developed in the lake, while shrubs of willow, reed swamps and grasslands fringed the shores. Precipitation increased, which caused a rise in the lake water table and an increase in the supply of oxic surface (= river) water into the Kreekrak lake. During this period, the Kreekrak lake was fed by inflowing river water, run-off, precipitation and seepage of Fe-rich groundwater. Around ca. 11,435 cal BP the water became stagnant probably as result of a total cut-off of the river channel. Inflow of river water ceased, while the supply of reduced Fe-rich groundwater became dominant. During the Rammelbeek Phase (ca. 11,365-11,250 cal BP), the climate was more continental and the abundance of grasslands and open herbaceous vegetation increased. Biological productivity remained high. In the lake, the supply of Fe-rich groundwater continued, the water level slightly decreased but aquatic vegetation remained present. At the end of the Rammelbeek Phase a sudden reduction in the supply of Fe-rich reduced groundwater caused a lowering of the groundwater level in the area, resulting in the development of a hiatus. Due to this hiatus, the Late Preboreal (11,250-10,710 cal BP) is absent from the record. During the early Boreal (10,710-10,000 cal BP) the landscape became densely forested and accumulation of peat in the former lake resumed due to a slowly rising groundwater level. The Boreal was a relatively stable period with low sedimentation rates.The combination of palaeobotanical and geochemical analyses in the Kreekrak record shows a close interrelation between landscape development and geochemistry. It appears that the environmental development of this area during the Late Glacial/Holocene transition and Early Holocene was largely influenced (directly or indirectly) by major climatic changes that occurred during this period, which determined local phenomena such as the composition and density of the vegetation, occurrence of seepage and river activity. Further research of this type has the potential to develop the application of major- and trace element geochemistry in palaeoenvironmental reconstructions.     

Seasonal and geographic climate variabilities during the Last Glacial Maximum in North America: Applying isotopic analysis and macrophysical climate models

Climate models provide estimates of climatic change over periods of time in the ancient past. Macrophysical climate models (MCM) differ from the more widely used general circulation models (GCM), in that MCMs provide temporally high-resolution (~ 100 years) and site-specific estimations of monthly values of climate variables such as temperature and precipitation. In this paper, seasonal changes in climate variables are modeled for six ¹⁴C-dated fossil localities in North America. Five of these localities represent the time of maximum extent of ice during the most recent glacial episode, the Full Glacial (25 + –15 ka), including one at the peak of the Last Glacial Maximum (17–15 ka). The other locality represents the time as the ice began to recede, the Late Glacial (15–11 ka). Seasonal variations in temperature and precipitation modeled by MCM are herein compared with interpretations of seasonal variation based upon oxygen isotopes from serially sampled hypsodont teeth (mostly Equus and Bison) collected from each of these localities. Additionally, the MCM-modeled seasonal variations are used to predict the expected abundances of different plant functional groups (PFG) during those times, especially C3 and C4 functional groups, using modern relationships. These predictions are compared with carbon isotopic values from the same teeth. The importance of atmospheric pCO² for the relative abundance of plants utilizing the C4 metabolic pathway is discussed, given that glacial episodes are known to have been times of lower atmospheric pCO². Interpretations of seasonal variability and the relative abundance of C3 versus C4 vegetation based upon isotopes from tooth enamel are in broad agreement with predictions using the MCM and the modern distribution of PFGs with climate variables. The influence of pCO² on the distribution of C4 vegetation during glacial times appears to be negligible.     

The responses of benthic foraminifera to paleoceanographic changes during the last glacial maximum,deglaciation, and the Holocene in the northwestern Pacific

Based on the changes in the species composition, abundance, and species richness of benthic foraminiferal assemblages in sediments of the northwestern Pacific, we reconstructed the paleoenvironment (paleoproductivity and near-bottom water ventilation) during the period of 8000–19000 calendar years ago (ka). A moderate seasonal productivity of the surface water, a relatively high oxygen content of the near-bottom water, and the influence of sea ice occurred during the Last Glacial Maximum in the studied area. An increased primary production and suboxic conditions in the near-bottom water were typical of the cold Heinrich 1 event (17.5–14.7 ka). A further increase in surface-water productivity and a decrease in oxygen content of the near-bottom and pore waters have been reconstructed for the second half of the Bølling/Allerød interstadial (14.7–12.8 ka) and the Pre-Boreal (11.8–9.2 ka). Surface water productivity decreased and oxygen saturation of the near-bottom water increased during the Younger Dryas (12.8–11.8 ka). In the Middle Holocene, the total decrease in productivity led to an increased oxygen content of the near-bottom and pore waters.     

Elevational gradients during the Late-Glacial/Holocene vegetational transition in southern Bulgaria

The Late Glacial and early-Holocene vegetational history of a newly dated pollen and macrofossil diagram from Besbog, a cirque lake at 2250 m just above the forest limit in the Pirin Mountains of southwestern Bulgaria, is compared with a newly dated pollen diagram for the mire Shiroka Polyana at 1400 m in the conifer forest of the nearby Rhodope Mountains in order to investigate the chronology of major changes in the vegetation at different elevations. In the Lake Besbog record the non-arboreal pollen assemblage of the Late Glacial changed abruptly to that of Betula, Quercus and other deciduous types. The date for this change is about 11.6 ka cal b.p. The Quercus assemblage may be composed of pollen blown from intermediate elevations, to which deciduous forest had expanded because of higher summer temperatures related to high summer insolation. At Shiroka Polyana (1400 m) in the modern conifer belt, a similar change did not occur until about 8.8 ka cal b.p. The persistence of the dry steppe or steppe forest in the early Holocene at this lower site can also be attributed to high summer insolation. Thus as atmospheric temperature increased at the end of the Late Glacial, deciduous forests expanded first at intermediate elevations in the Pirin Mountains and only later in the Rhodope Mountains at lower elevations as summer insolation decreased.     

Last glacial–Holocene water structure in the southwestern Okhotsk Sea inferred from radiolarian assemblages

In order to reconstruct paleoceanographic conditions in the southwestern (SW) Okhotsk Sea, radiolarian assemblages were analyzed from 10 surface sediments and 5 sediment cores obtained from various water depths, ranging between 461 and 1348 m. We also measured geochemical components such as biogenic opal, calcium carbonate, total organic carbon, total sulfur and total nitrogen for one sediment core. These data imply that the complicated water structure in the SW Okhotsk Sea changed with time from the last glacial to Holocene. The glacial surface water was characterized by low primary production in the summer and expanded sea-ice coverage in the winter. During this time, the ventilation might have reached deeper than during the Holocene. During the major deglacial period including the melt-water pulses 1A and 1B, the deep-sea oxygen content had declined with less ventilation and/or more oxygen consumption with organic matter supply into the deeper depths. The intermediate layer has been well ventilated and has supplied large amount of organic matter during the last 20 kyrs, especially in the early-mid Holocene, however such condition ceased during 3 to 2 ka. The warm Pacific deep water has been present since 9 ka. The influence of warmer surface water such as the Soya Warm Current (SWC) increased in the coastal area during 7 to 4 ka and since 2 ka till present. Neritic-derived productivity might be extended at 2.2–1.8 ka and since 1.2 ka till present.     

Reconstruction of environmental and climate changes at Braamhoek wetland,eastern escarpment South Africa,during the last 16,000 years with emphasis on the Pleistocene–Holocene transition

A paleo-environmental record covering the last 16 ka (16,000 cal yrs BP) from the eastern areas of the summer rainfall region in South Africa is presented. This area is until now sparsely investigated due to the lack of well preserved natural archives. For this study, we used a peat section from a wetland situated close to the Drakensberg escarpment, where the high annual rainfall amounts supported a continuous peat accumulation since c. 16 ka. One peat core was analysed in terms of fossil pollen composition, carbon and nitrogen content, isotope composition (δ¹³C, δ¹⁵N) and microscopic charcoal concentration. The greatest degree of temporal resolution was achieved from the late Pleistocene and early Holocene section, where proxy-records indicate relatively dry conditions between ca. 16–13.7 ka, 12.8–10.5 ka, 9.5–8.2 ka, and wet conditions between c. 13.7–12.8 ka and 10.5–9.5 ka. A weak moisture signal is also evident at c. 8.2–7.5 ka. The late Pleistocene to early Holocene period was relatively cool, while conditions became generally warmer after 11–8 ka. The interpretation of the mid- and late-Holocene sequence is limited due to a slow accumulation and low sample resolution, but the available data suggest relatively dry conditions until c. 1.5 ka, followed by more humid conditions until c. 0.5 ka. We suggest that the millennial scale variability within the record can be attributed to shifts in the circulation systems dominating the region, i.e. the latitudinal movements of the inter-tropical convergence zone (ITCZ) and the dynamics of the mid-latitude low pressure belts.     

Foraminiferal assemblages of the Bric della Muda laminites (Nizza Monferrato, Piedmont): Proxies of cyclic palaeoenvironmental changes in the early Messinian of Northwestern Italy

Foraminiferal assemblages in laminites cropping out at the Bric (i.e. Hill) della Muda (Nizza Monferrato, Piedmont, Northwestern Italy) document deep marine conditions during the early Messinian, spanning a time-interval approximating, or slightly wider than the stratigraphic range of Globorotalia nicolae (6.82-6.72 Ma). Fluctuations in abundance of planktonic warm-water oligotrophic taxa and cold-water eutrophic species show a cyclical pattern, very comparable to variations measured in cyclically-bedded formations of the pre-evaporitic Messinian in the Mediterranean area. A subtropical climate with cyclic warmer and cooler episodes, characterized by surface water stratification and vertical mixing in the water column, respectively, is also documented. A depositional depth close to or larger than 1000 m is inferred on the basis of planktonic assemblages yielding also the deep planktonic Hastigerinella digitata and of very high P/(P + B) ratios. Anoxic or strongly dysoxic bottom conditions are indicated by the absence or rareness of benthic foraminifers, which are represented by taxa tolerant of low-oxygen or high organic content (Bolivina pseudoplicata, Chilostomella oolina, Globobulimina affinis). A slight decrease in P/(P + B) ratios, and the presence of rare shallow-water forms in the uppermost layers suggest a mild dysoxia and a probable shallowing, when compared with coeval events in Northern Apennines and Southern Greece sections.     

Late Quaternary diatoms in the sediments of Przedni Staw Lake (Polish Tatra Mountains)

The paper presents a diatom succession in the Late Glacial and Holocene sediments of the Przedni Staw lake in the Pie Stawów Polskich Valley High Tatra Mts. Ten diatom phases are distinguished and presented against a pollen diagram from the analyzed core showing continuous sedimentation from the Oldest Dryas to the Subatlantic period. The diatom flora in the Late Glacial sediments is predominantly littoral — Fragilaria, Navicula, Nitzschia, Diploneis, Pinnularia and Amphora species. The Holocene sediments enclose more abundant planktonic species such as Cyclotella quadriiuncta, Asterionella formosa and Melosira distans.