Diatoms, total organic carbon, and total nitrogen of sediment core Dethlingen, Germany

To provide insights into the long-term evolution of aquatic ecosystems without human interference, we here evaluate a decadal- to centennial-scale-resolution diatom record spanning about 12 ka of the Holsteinian interglacial (Marine Isotope Stage 11c). Using a partially varved sediment core from the Dethlingen palaeolake (northern Germany), which has previously been studied for palynological and microfacies signals, we document the co-evolution of the aquatic and surrounding terrestrial environment. The diatom record is dominated by the genera Stephanodiscus, Aulacoseira, Ulnaria and Fragilaria. Based on the diatom assemblages and physical sediment properties, the evolution of the Dethlingen palaeolake can be subdivided into three major phases. During the oldest phase (lasting ~1900 varve years), the lake was ~10-15 m deep and characterized by anoxic bottom-water conditions and a high nutrient content. The following ~5600 years exhibited water depths >20 m, maximum diatom and Pediastrum productivity, and a peak in allochtonous nutrient input. During this phase, water-column mixing became more vigorous, resulting in a breakdown of anoxia. The youngest lake phase (~4000-5000 years) was characterized by decreasing water depth, turbulent water conditions and decreased nutrient loading. Based on our palaeolimnological data, we conclude that the evolution of the Dethlingen palaeolake during the Holsteinian interglacial responded closely to (i) changes within the catchment area (as documented by vegetation and sedimentation) related to the transition from closed forests growing on nutrient-rich soils (mesocratic forest phase) to open forests developing on poor soils (oligocratic forest phase), and (ii) short-term climate variability as reflected in centennial-scale climate perturbations.

Aboveground community and species-specific plant biomass from the Jena Experiment (Main Experiment, year 2007)

This data set contains aboveground community biomass (Sown plant community, Weed plant community, Dead plant material, and Unidentified plant material; all measured in biomass as dry weight) and species-specific biomass from the sown species of the main experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained by bi-annual weeding and mowing. Aboveground community biomass was harvested twice in 2007 just prior to mowing (during peak standing biomass in early June and in late August) on all experimental plots of the main experiment. This was done by clipping the vegetation at 3 cm above ground in four (May) or three (August) rectangles of 0.2 x 0.5 m per large plot. The location of these rectangles was assigned prior to each harvest by random selection of coordinates within the core area of the plots (i.e. the central 10 x 15 m). The positions of the rectangles within plots were identical for all plots. The harvested biomass was sorted into categories: individual species for the sown plant species, weed plant species (species not sown at the particular plot), detached dead plant material (i.e., dead plant material in the data file), and remaining plant material that could not be assigned to any category (i.e., unidentified plant material in the data file). All biomass was dried to constant weight (70°C, >= 48 h) and weighed. Sown plant community biomass was calculated as the sum of the biomass of the individual sown species. The data for individual samples and the mean over samples for the biomass measures on the community level are given. Overall, analyses of the community biomass data have identified species richness as well as functional group composition as important drivers of a positive biodiversity-productivity relationship.

Aboveground community and species-specific plant biomass from the Jena Experiment (Main Experiment, year 2006)

This data set contains aboveground community biomass (Sown plant community, Weed plant community, Dead plant material, and Unidentified plant material; all measured in biomass as dry weight) and species-specific biomass from the sown species of the main experiment plots of a large grassland biodiversity experiment (the Jena Experiment; see further details below). In the main experiment, 82 grassland plots of 20 x 20 m were established from a pool of 60 species belonging to four functional groups (grasses, legumes, tall and small herbs). In May 2002, varying numbers of plant species from this species pool were sown into the plots to create a gradient of plant species richness (1, 2, 4, 8, 16 and 60 species) and functional richness (1, 2, 3, 4 functional groups). Plots were maintained by bi-annual weeding and mowing. Aboveground community biomass was harvested twice in 2006 just prior to mowing (during peak standing biomass in early June and in late August) on all experimental plots of the main experiment. This was done by clipping the vegetation at 3 cm above ground in four rectangles of 0.2 x 0.5 m per large plot. The location of these rectangles was assigned prior to each harvest by random selection of coordinates within the core area of the plots (i.e. the central 10 x 15 m). The positions of the rectangles within plots were identical for all plots. The harvested biomass was sorted into categories: individual species for the sown plant species, weed plant species (species not sown at the particular plot), detached dead plant material (i.e., dead plant material in the data file), and remaining plant material that could not be assigned to any category (i.e., unidentified plant material in the data file). All biomass was dried to constant weight (70°C, >= 48 h) and weighed. Sown plant community biomass was calculated as the sum of the biomass of the individual sown species. The data for individual samples and the mean over samples for the biomass measures on the community level are given. Overall, analyses of the community biomass data have identified species richness as well as functional group composition as important drivers of a positive biodiversity-productivity relationship.

Plants growing near the cargo packing station, and seed occurrence in cargo and luggage destined for Gough and Marion Island and the Antarctic

Globalization has resulted in unprecedented movements of people, goods, and alien species across the planet. Although the impacts of biological invasions are widely appreciated, a bias exists in research effort to post-dispersal processes because of the difficulties of measuring propagule pressure. The Antarctic provides an ideal model system in which to investigate propagule movements because of the region's isolation and small number of entry routes. Here we investigated the logistics operations of the South African National Antarctic Programme (SANAP) and quantified the initial dispersal of alien species into the region. we found that over 1400 seeds from 99 taxa are transported into the Antarctic each field season in association with SANAP passenger luggage and cargo. The first ever assessment of propagule drop-off indicated that 30-50% of these propagules will enter the recipient environment. Many of the taxa include cosmopolitan weeds and known aliens in the Antarctic, indicating that logistics operations form part of a globally self-perpetuating cycle moving alien species between areas of human disturbance. in addition, propagules of some taxa native to the Antarctic region were also found, suggesting that human movements may be facilitating intra-regional homogenization. Several relatively simple changes in biosecurity policy that could significantly reduce the threat of introduction of nonnative species are suggested.

Pollen profiles from 8 sediment cores from the Degersee, Southern Germany

The discovery of a neolithic pile field in the shallow water near the eastern shore of the Degersee confirmed earlier palynological and sedimentological studies stating that early man was active in the region since more than 6000 years. The already available off-site data were freshly assessed, completed by additional data from old and new cores and the interpretations revised. A common time scale for the off-site data and the on-site data was obtained by AMS dating of terrestrial macro remains of the neolithic section of off-site core De_I+De_H. The ages can thus be parallelled with AMS ages of construction timber on-site. Pollen analyses from all cores provide a further time scale. The continuously and densely sampled pollen profile of the profundal zone embracing the entire Late glacial and Holocene serves as a reference. From the Boreal onwards the relative ages are transformed by AMS ages and varve counts into calibrated and absolute. A transect cored close to the neolithic pile field across the lake marl-platform demonstrates its geological architecture in the shallow water since the Lateglacial. Studies of the microfabric of thin sections of drilled cores and of box cores from the excavations demonstrate that neolithic settlements now at 2-3,5 m water depth had been erected on lake marl freshly fallen dry, thus indicating earlier lake levels dropped by 1.5-2 m. The neolithic section of the highly resolved off-site profile in the lake=s profundal zone has laminated and calcareous zones alternating with massive ones. Assemblages of diatoms and concentrations of trace elements changing simultaneously characterise the calcareous sections as deposits of low lake levels that lasted between some 40 and more than 300 years. The ages of discovered lake shore dwellings fall into calcareous segments with low lake levels. From the end of the Upper Atlantic period (F VII) appear Secondary Forest Cycles in the beech forest, a man-made sequence of repeated vegetational development with an identical pattern: With a decrease of beech pollen appear pollen of grasses, herbs and cultural indicators. These are suppressed by the light demanding hazel and birch, those again by ash, and finally by the shade demanding beech forming a new pollen peak. Seven main Forest Cycles are identified In the upper Neolithic period each comprising some 250, 450 or 800 years. They are subdivided into subcycles that can be broken down by very dense sampling in even shorter cycles of decadal length. Farming settlers have caused minor patchy clearances of the beech-mixed-forest with the use of fire. The phases of clearance coincide with peaks of charcoal and low stands of the lake levels. The Secondary Forest Cycles and the continuous occurrence of charcoal prove a continued occupation of the region. Together with the repeated restoration of the beech climax forest they point to pulsating occupation probably associated with dynamic demography. The synchronism of the many palynological, sedimentological and archaeological data point to an external forcing as the climate that affects comprehensively all these proxies. The fluctuations of the activity of the sun as manifested in the residual d14C go largely along with the proxies. The initial clearances at the begin of the forest cycles are linked to low lake levels and negative values of d14C that point to dry and warm phases of a more continental climate type. The subcycles exist independent from climatic changes, indicating that early man acted largely independent from external forces.

Pollen records and age determination of site Bokanjacko Blato

In summary, one may conclude that human influence in the Bokanjac area started in the Eneolithic or Earlier Bronze Age - the third to second millennia Cal. BC. Traces of agriculture are weak or missing in the pollen diagram but grazing is indicated. Chestnut and walnut were introduced by humans to the area in classical times. These findings are in general agreement with the results of earlier studies at coastal sites north-west and south-east of Bokanjacko Blato.

High-resolution multi-proxy record of the last glacial period from Lake Van, eastern Anatolian high plateau, Turkey

Detailed analyses of the Lake Van pollen, Ca/K ratio and stable oxygen isotope record allow the identification of millennial-scale vegetation and environmental changes in eastern Anatolia throughout the last glacial (~75-15 ka BP). The climate within the last glacial was cold and dry, with low arboreal pollen (AP) levels. The driest and coldest period corresponds to Marine Isotope Stage (MIS) 2 (~28-14.5 ka BP) dominated by the highest values of xerophytic steppe vegetation. Our high-resolution multi proxy record shows rapid expansions and contractions of tree populations that reflects variability in temperature and moisture availability. This rapid vegetation and environmental changes can be linked to the stadial-interstadial pattern of the Dansgaard-Oeschger (DO) events as recorded in the Greenland ice cores. Periods of reduced moisture availability were characterized by enhanced xerophytic species and high terrigenous input from the Lake Van catchment area. Furthermore, comparison with the marine realm reveals that the complex atmosphere-ocean interaction can be explained by the strength and position of the westerlies, which is responsible for the supply of humidity in eastern Anatolia. Influenced by diverse topography of the Lake Van catchment, larger DO interstadials (e.g. DO 19, 17-16, 14, 12 and 8) show the highest expansion of temperate species within the last glacial. However, Heinrich events (HE), characterized by highest concentrations of ice-rafted debris (IRD) in marine sediments, are identified in eastern Anatolia by AP values not lower and high steppe components not more abundant than during DO stadials. In addition, this work is a first attempt to establish a continuous microscopic charcoal record over the last glacial in the Near East, which documents an initial immediate response to millennial-scale climate and environmental variability and enables us to shed light on the history of fire activity during the last glacial.

High-resolution multi-proxy record of the last interglacial period from Lake Van, eastern Anatolian high plateau, Turkey

A high-resolution multi-proxy record from Lake Van, eastern Anatolia, derived from a lacustrine sequence cored at the 357 m deep Ahlat Ridge (AR), allows a comprehensive view of paleoclimate and environmental history in the continental Near East during the last interglacial (LI). We combined paleovegetation (pollen), stable oxygen isotope (d18Obulk) and XRF data from the same sedimentary sequence, showing distinct variations during the period from 135 to 110 ka ago leading into and out of full interglacial conditions. The last interglacial plateau, as defined by the presence of thermophilous steppe-forest communities, lasted ca. 13.5 ka, from ~129.1-115.6 ka BP. The detailed palynological sequence at Lake Van documents a vegetation succession with several climatic phases: (I) the Pistacia zone (ca. 131.2-129.1 ka BP) indicates summer dryness and mild winter conditions during the initial warming, (II) the Quercus-Ulmus zone (ca. 129.1-127.2 ka BP) occurred during warm and humid climate conditions with enhanced evaporation, (III) the Carpinus zone (ca. 127.2-124.1 ka BP) suggest increasingly cooler and wetter conditions, and (IV) the expansion of Pinus at ~124.1 ka BP marks the onset of a colder/drier environment that extended into the interval of global ice growth. Pollen data suggest migration of thermophilous trees from refugial areas at the beginning of the last interglacial. Analogous to the current interglacial, the migration documents a time lag between the onset of climatic amelioration and the establishment of an oak steppe-forest, spanning 2.1 ka. Hence, the major difference between the last interglacial compared to the current interglacial (Holocene) is the abundance of Pinus as well as the decrease of deciduous broad-leaved trees, indicating higher continentality during the last interglacial. Finally, our results demonstrate intra-interglacial variability in the low mid-latitudes and suggest a close connection with the high-frequency climate variability recorded in Greenland ice cores.

Pollen record from Kleiner Mochowsee, Germany

A Holocene pollen diagram from Kleiner Mochowsee (northern Niederlausitz, East Germany) shows pine as an important constituent of the woodland south of the Schwielochsee. Oak woodland was widespread since the Atlantic. Betula lost its importance at the end of the Preboreal. Fagus is represented continuously in the pollen record since the Atlantic, Carpinus since the Subboreal. However, the two latter tree species remain without great importance throughout the whole pollen record. The poor sandy soils are furthermore reflected by the low values of Corylus during the Boreal, comparable to other records from Berlin and its surrounding area. The 'classical' elm decline could be shown for the Niederlausitz, radiocarbon dates assume a contemporaneous age for this event with other records from northern Germany. Only small-scaled human impact is indicated in prehistoric times, during the migration period it seems to have ceased completely. Later, in the Medieval, deforestation and tillage can be shown. Secale was cultivated since the early Medieval; an accompanying weed flora appeared at the same time. Cultivation of Fagopyrum and Linum usitatissimum could be shown for the late Medieval times.

AMS radiocarbon dates and pollen analysis of ODP Hole 175-1078C

ODP Site 1078 situated under the coast of Angola provides the first record of the vegetation history for Angola. The upper 11 m of the core covers the past 30 thousand years, which has been analysed palynologically in decadal to centennial resolution. Alkenone sea surface temperature estimates were analysed in centennial resolution. We studied sea surface temperatures and vegetation development during full glacial, deglacial, and interglacial conditions. During the glacial the vegetation in Angola was very open consisting of grass and heath lands, deserts and semi-deserts, which suggests a cool and dry climate. A change to warmer and more humid conditions is indicated by forest expansion starting in step with the earliest temperature rise in Antarctica, 22 thousand years ago. We infer that around the period of Heinrich Event 1, a northward excursion of the Angola Benguela Front and the Congo Air Boundary resulted in cool sea surface temperatures but rain forest remained present in the northern lowlands of Angola. Rain forest and dry forest area increase 15 thousand years ago. During the Holocene, dry forests and Miombo woodlands expanded. Also in Angola globally recognised climate changes at 8 thousand and 4 thousand years ago had an impact on the vegetation. During the past 2 thousand years, savannah vegetation became dominant.

Pollen record and age determination of a sediment profile from Schmiechener See, Germany

Die untersuchten Schluffe und Kiese sind unter kaltzeitlichen Bedingungen in einem See mit Schwimmpflanzengesellschaften abgelagert worden. Zur Sedimentationszeit gab es in der Umgebung des Sees eine tundrenartige Vegetation, die auch Steppenarten enthielt.

Palynology on a profile from the Krusné Hory Mountains

Site details: The raised bog Fláje-Kiefern (50°429N, 13°329 E; 760 m a.s.l.; size ca. 500x500 m) lies in the Krusné Hory Mountains (Erzgebirge), Czech Republic, about 10 km from Georgenfelder Moor in Germany. Hejny and Slavík (1988) described the phytogeographic region of the Krusne Hory Mountains as 'a region of mountain flora and vegetation, with thermophilous species largely missing. In the natural forests, conifers, especially spruce (Picea excelsa) prevail. The deforested areas have been converted into meadows and pastures'. The climate is cool with annual average temperatures of about 5°C and annual precipitation of about 900 mm. The bedrock is Precambrian crystallinicum.

Diatom assamblage in samples from sediment traps across the Pacific Sector of the Southern Ocean

An array of four sediment trap moorings recorded the particulate flux across the Antarctic Circumpolar Current (ACC) at 170 °W, between November 1996 and January 1998, as part of the US JGOFS-Antarctic Environment and Southern Ocean Process Study (AESOPS) program. The trap locations represent sampling within the Polar Frontal Zone, the Antarctic Polar Front, the Antarctic Zone and the Southern Antarctic Zone. Here we report observations from 1000 m below the sea-surface compared to seafloor and surface water distributions. Sub-sample splits from each trap were obtained and total diatom flux and species composition were determined. The diatom fluxes were quantified using both a dilution and a 'spike' method to allow for the rapid repeatability of measurements. Diatom flux was found to be highly seasonal across the ACC particularly at higher latitudes. Marine snow aggregates of intact diatom cells and chains were the major components of the biogenic flux. Siliceous particle size was noted to decrease with increasing latitude, which could be aligned with a shift of the diatom assemblage to small-size species/sea-ice affiliated species. A 'double-structured' diatom flux was recorded at the location of the Antarctic Polar Front trap, with a shift in the diatom assemblage from larger to smaller diatoms in the second flux episode. The sediment trap assemblage shows deviations from the surface water assemblage, while surface sediment samples indicate that significant dissolution occurs after 1000 m and at the sediment-water interface. Estimation of diatom biovolumes across the ACC shows that large diatoms have the potential to greatly impact biogenic fluxes to the ocean interior despite their low fluxes. Small species of the genus Fragilariopsis could potentially export as much Corg as Fragilariopsis kerguelensis near the retreating ice edge. However, their low abundance in the surface sediments also suggests that these diatoms are a shallow export species.