Climate changes during the last glacial termination inferred from diatom-based temperatures and pollen in a sediment core from Längsee (Austria)

A sediment core section from Längsee, a small meromictic lake in the southern Alpine lowland (Carinthia, Austria) close to the Würmian ice margin, was investigated by means of diatoms and pollen. The main aims of the study were to reconstruct water temperature as a signal of climate change during the last glacial termination, compare the aquatic and terrestrial response to the changing climate, and place our findings into a climatic frame on the northern hemispheric scale. A calibration data set (ALPS06) of 116 lakes was constructed using data from newly studied lakes and from two previously published data sets and we established a transfer function for predicting summer epilimnetic water temperatures (SEWT). A locally weighted weighted average regression and calibration model (R _jack ²  = 0.89; RSMEP = 1.82°C) was applied to the fossil diatom assemblages in order to reconstruct SEWT. Three major sections were distinguished in the time window of approximately 19–13 cal ka BP, which fitted well with the oxygen isotope curve and the isotope-event stratigraphy from the Greenland ice-core GRIP. The first section was a warming period (SEWT range from 11.6 to 18.0°C; average 15.8°C = ca. 6°C below present) called the Längsee oscillation, which probably correlates with the warmer sub-section (GS-2b) of the Greenland Stadial 2. The subsequent section represents a climate cooling, called the Längsee cold period (SEWT range between 10.6 and 15.9°C; average 12.9°C), which probably corresponds with the sub-section GS-2a of the Greenland Stadial 2, the Heinrich 1 cold event of the North Atlantic, and partially the Gschnitz Stadial in the Alps. The Längsee cold period shows a tri-partition: Two colder phases are separated by a warmer inter-phase. The passive ordination of the core sample scores along maximum water depth indicated that the Längsee cold period was drier than the Längsee oscillation. Strong short-term fluctuations during the Längsee oscillation and the Längsee cold period indicate climate instability. The third section represented climate warming during the Längsee late glacial interstadial (=Greenland Interstadial 1, GI-1) with an average SEWT of 17.5°C. From the minor climatic fluctuations during this interstadial, mainly indicated by pollen, the fluctuation most likely related to the Gerzensee oscillation showed a SEWT decline. During the early immigration and expansion period of shrubs and trees, aquatic and terrestrial records showed distinct discrepancies that might have arose because of time lags in response and differences in sensitivity.     

Luminescence dating of lacustrine sediments from Tangra Yumco (southern Tibetan Plateau) using post‐IR IRSL signals from polymineral grains

Radiocarbon dating of bulk organic matter is the most commonly used method for establishing chronologies of lake sediments for palaeoclimate reconstructions on the Tibetan Plateau. However, this method is likely to be problematic because the dated material often suffers from old carbon contamination. Recently, advances in luminescence‐based chronological techniques have provided new options for dating lacustrine sediments. In the current study, we tested for the first time the applicability of a new post‐IR IRSL (pIRIR) measurement protocol for dating fine‐grained polymineral material from a deep‐lake sediment core from the central part of Tangra Yumco, on the southern Tibetan Plateau. Our results show that: (i) radioactive disequilibria in the uranium decay chain were observed in the studied lake sediments, and thus taken into account for dose rate calculation by using a dynamic modelling approach; (ii) the suitability and robustness of the pIRIR protocol measured at 150°C (pIRIR₁₅₀) for our samples are confirmed by a set of luminescence characteristic tests as well as the agreement with an independent age control; (iii) turbidite deposition partly caused an insufficient resetting of luminescence signals and thus apparent overestimation in luminescence dating; (iv) compared with the luminescence‐based age‐depth model, the ¹⁴C ages of bulk organic matter from the studied core generally yielded an age difference of ～2 ka, which is attributed to hardwater reservoir effects in Tangra Yumco. This study highlights the need for multi‐dating approaches of lake sedimentary archives on the Tibetan Plateau.     

Nanociliates of the order Prostomatida: Their relevance in the microbial food web of a mesotrophic lake

Two nanociliates of the order Prostomatida,Pseudobalanion planctonicum (12–18 µm) andUrotricha furcata (12–21 µm), were found to be the most abundant ciliates in the epilimnion of Piburger See, a small mesotrophic lake. Temperature and food availability were the main factors controlling the sudden increase in abundance, which reached a maximum of 101 cell ml^–1 at the beginning of summer. During their exponential development in numbers and biomass, a strong decrease in chlorophylla and in the abundance of phytoplankton, especiallyRhodomonas, was observed. We assume, therefore, thatPseudobalanion planctonicum andUrotricha furcata together with rotifers, mainlyPolyarthra dolichoptera, are able to reduce the phytoplankton biomass in the upper epilimnion to the same level as found during the clearwater phase. Preliminary results of grazing on bacteria suggest that these nanociliates are omnivorous, although their impact on bacterial assemblages was low (3.1% of the standing stock grazed per day). Feeding on the base of the food web combined with their high abudance at certain times makes them an important link for higher trophic levels. This study constitutes the second report onPseudobalanion as an important component of the microbial food web in lakes.     

Effects of multiple stressors on lakes in south-central Ontario: 15 years of change in lakewater chemistry and sedimentary diatom assemblages

Freshwater ecosystems are increasingly affected by human influences. Since the pre-industrial era, lakes of the Muskoka–Haliburton region of south-central Ontario have had increases in shoreline residential development and acid deposition. Previous research on 54 of these lakes, using sediment cores and diatom-based transfer functions, showed changes in lakewater pH and total phosphorus concentration between the preindustrial era and 1992. Since 1992, there has been further change, which we have documented for the same set of lakes, using similar methods. For example, dissolved organic carbon has increased and there have been significant increases in planktonic diatoms (e.g. Cyclotella stelligera) commonly associated with climate warming. More striking diatom changes have occurred in the past 15 years than between pre-industrial times and 1992. Significant changes observed in both chemical (e.g. pH, Ca, DOC) and biological data suggest that novel stressors, such as declines in lake calcium concentrations, acting in conjunction with climate and land-use change, have created ecosystems for which there are no historical analogs.     

Eutrophication assessment of the Baltic Sea Protected Areas by available data and GIS technologies

Concerning increased degradation of marine ecosystems, there is a great political and institutional demand for an array of different tools to restore a good environmental status. Thereby, eutrophication is acknowledged as one of the major human induced stressors which has to be monitored and reduced. The present study concentrates on an assessment of the eutrophication status of the Baltic Sea Protected Areas by use of available data and GIS technologies. Two geodata layers were used for analysis: (1) a map on the eutrophication status of the Baltic Sea generated by the Helsinki Commission applying the HELCOM Eutrophication Assessment Tool (HEAT), and (2) modelled data on atmospheric nitrogen deposition made available by the European Monitoring and Evaluation Programme (EMEP). The results yielded comprehensive and conclusive data indicating that most of the BSPAs may be classified as being 'affected by eutrophication' and underlining the need to decrease the overall emissions of nutrients.     

Simulating compound flooding events in a hurricane

Ocean Dynamics - Compound flooding is usually induced by the concurrence of coastal storm surge and heavy precipitation induced river flooding, with the former involving oceanic processes and the...     

Hydrothermal alteration as a control of regional geochemistry and ore formation in the central Baltic Shield

In a geochemical study of the Proterozoic volcano-sedimentary Bergslagen ore province in central Sweden, more than 1000 eruptive rocks were analyzed for main and trace elements. The volcanic rocks form a bimodal suite dominated by rhyolites but deficient in andesites. Igneous geochemical variation bears little relevance to the occurrence and distribution of ores which mostly appear related to secondary alteration patterns. Hydrothermal metasomatic alteration occurs on a regional scale and has affected markedly more than half of the 732 analyzed, macroscopically fresh, porphyritic volcanic rocks. Metasomatism produced extreme Na- and K-differentiation, and Fe-Mg-Si relationships incompatible with igneous variation patterns. Enrichment in Na and Mg, and leaching of ore-forming metals are prominent in the lower parts of the volcanic pile, whereas meta-volcanics enriched in K and volcanogenic sediments associated with ores and marbles dominate the upper levels. The metasomatic alteration of the volcanic rocks and the formation of most ores are two aspects of a comprehensive process of hydrothermal convection which circulated sea water, extracted the ore-forming elements from the lower levels of the volcanic pile and enriched them at or close to the top of the volcanic sequence.

---

Zusammenfassung Über 1000 proterozoische Eruptivgesteine der vulkanisch-sedimentären Erzprovinz in Mittelschweden wurden auf Haupt- bzw. Spurenelemente analysiert. Die Gesteine bilden eine Folge mit Schwerpunkt auf basaltischen und insbesondere rhyolitischen Zusammensetzungen, während Andesite nur schwach vertreten sind. Die primärmagmatische Zusammensetzung hat wenig Bezug zu den Erzen, die genetisch größtenteils an sekundäre Veränderungen gebunden sind. Hydrothermale Metasomatose hat eine regionale Verbreitung. Auch von den makroskopisch intakten, 732 analysierten, sauren porphyrischen Eruptivgesteinen sind mehr als die Hälfte durchgreifend verändert. Die metasomatischen Prozesse führten zu extremer Natriumund Kaliumdifferenzierung und zu Fe-Mg-Si-Beziehungen, die nicht auf magmatische Differentiation zurückzuführen sind. Anreicherung von Na und Mg und Auslaugen der erzbildenden Metalle treten in den tieferen Teilen der vulkanischen Schichtenfolge auf. Die höheren Lagen werden von kalireichen Metavulkaniten, Karbonatgesteinen und vulkanogenen, erzassoziierten Sedimenten beherrscht. Metasomatische Gesteinsumwandlung und Erzbildung sind zwei Teilprozesse einer großräumigen hydrothermalen Konvektion, durch die Meereswasser durch die Schichtenfolge getrieben wurde. Die erzbildenden chemischen Bestandteile wurden dabei den tieferen Teilen des Vulkanitpaketes entzogen und an oder nahe der Oberfläche angereichert.

---

Résumé Dans le cadre d'une étude géochimique de la province protérozoïque volcano-sédimentaire minéralisée de Bergslagen (Suède centrale), plus de 1000 échantillons de roches magmatiques ont été analysés (éléments majeurs et traces). Ces roches volcaniques forment une suite dominée par les rhyolites et les basaltes, tandis que les andésites sont peu représentées. Les variations géochimiques montrent peu de relation avec la distribution des minerais, ceux-ci étant surtout engendrés lors de processus d'altération secondaires. En effet, une métasomatose hydrothermale s'est manifestée à l'échelle régionale au point d'affecter plus de la moitié des 732 porphyres volcaniques acides analysés, en dépit de l'aspect de fraîcheur qu'ils présentent macroscopiquement. La métasomatose se traduit par un fractionnement extrême de Na et K, ainsi que par des relations entre Fe-Mg-Si incompatibles avec la différenciation magmatique. La partie inférieure de la série volcanique stratifiée montre un enrichissement en Na et Mg ainsi qu'un lessivage des métaux des minerais. Dans la partie supérieure de la série, les termes dominants sont des métavolcanites riches en K, des marbres et des sédiments volcanogènes associés aux minerais. La modification métasomatique et la genèse des minerais sont deux aspects d'un vaste processus de convection hydrothermale qui a fait circuler l'eau de mer à travers la pile stratifiée, en enlevant les métaux des minerais dans la partie inférieure pour les concentrer dans la partie pouche du sommet.

---

1000 - . , , ; . ; . . 732 , . , , , . . , , , , , . — , , . .