Intraregional variability in chironomid-inferred temperature estimates and the influence of river inundations on lacustrine chironomid assemblages.

Floodplain lakes are rarely analysed for fossil chironomids and usually not incorporated in modern chironomid-climate calibration datasets because of the potential complex hydrological processes that could result from flooding of the lakes. In order to investigate this potential influence of river inundations on fossil chironomid assemblages, 13 regularly inundated lakes and 20 lakes isolated from riverine influence were sampled and their surface sediments analysed for subfossil chironomid assemblages. The physical and chemical settings of all lakes were similar, although the variation in the environmental variables was higher in the lakes isolated from riverine influence. Chironomid concentration and taxon richness show significant differences between the two classes of lakes, and the variation in these variables is best explained by loss-on-ignition of the sediments (LOI). Relative chironomid abundances show some differences between the two groups of lakes, with several chironomid taxa occurring preferentially in one of the two lake-types. The variability in chironomid assemblages is also best explained by LOI. Application of a chironomid-temperature inference model shows that both types of lakes reconstruct July air temperatures that are equal to, or slightly underestimating, the measured temperature of the region. We conclude that, although there are some differences between the chironomid assemblages of floodplain lakes and of isolated lakes, these differences do not have a major effect on chironomid-based temperature reconstruction. © 2007 Springer Science+Business Media B.V

Chironomid-based palaeotemperature estimates for northeast Finland during Oxygen Isotope Stage 3.

Quantitative palaeotemperature estimates for the earlier part of Oxygen Isotope Stage (OIS-) 3 are inferred from subfossil chironomid remains. The high-latitudinal study site of Sokli, northeast Finland, provides for a unique lacustrine deposit covering the earlier part of OIS-3, and the chironomid remains found in the sediments show that a shallow lake with a diverse fauna was present at the study site throughout the record. Using a Norwegian calibration data set as a modern analogue, mean July air temperatures are reconstructed. The chironomid-inferred July air temperatures are surprisingly high, reaching values similar to the current temperature at the study site. Other proxies that were applied to the sediments included the analysis of botanical and zoological macro-remains, and our results concur with temperature estimates derived from climate indicator taxa. Summer temperatures for interstadial conditions, reconstructed with climate models, are as high as our proxy-based palaeotemperatures

Late Holocene ecological shifts and chironomid-inferred summer temperature changes reconstructed from lake Uddelermeer, the Netherlands

This paper presents a Late-Holocene chironomid-inferred July-air temperature record from a core obtained from Lake Uddelermeer in the Netherlands. A core interval, which dates from 2500 to 400 cal. yr. BP, was analysed at multidecadal resolution for organic content, pollen, spores and NPPs (Non Pollen Palynomorphs), and chironomid head capsules. These proxies indicate that, from 2500 to 1140 cal. yr. BP, the lake was mesotrophic and sustained a Littorellion, while the chironomid assemblage was dominated by littoral species associated with macrophytes. At 1140 cal. yr. BP a shift in the lake ecology occurred from low-nutrient to high-nutrient conditions dominated by algae. This shift might be linked to a concurrent increase in human impact and is reflected in the chironomid assemblage by increases in eurytopic taxa, which are resistant to disturbances. Shifts in the chironomid record between 2500 and 1140 cal. yr. BP do not coincide with changes in lake ecology and are presumably driven by climate change. Using a Norwegian-Swiss calibration dataset as a modern analogue, we produced a chironomid-inferred temperature (C-IT) reconstruction. This reconstruction compares well to other regional temperature reconstructions in timing and duration with a Roman Warm period between 2240-1760 cal. yr. BP, a Dark Age Cold Period starting at 1760 cal. yr. BP and the Medieval Climate Anomaly beginning at 1280 cal. yr. BP. The C-IT record indicates a temperature drop of 1.5°C from the Roman Warm Period to the Dark Age Cold Period. Findings improve knowledge of the first millennium AD in NW Europe, which was characterised by changes in landscape, vegetation, society and climate

Environmental inferences and chironomid-based temperature reconstructions from fragmentary records of the Weichselian Early Glacial and Pleniglacial periods in the Niederlausitz area (eastern Germany)

We inferred past climate conditions from lacustrine sediments intercalated in Weichselian Early Glacial and Early Pleniglacial fluvial and aeolian sediments, exposed in two opencast lignite mines from the Niederlausitz area (eastern Germany). A chronology was established using radiocarbon and luminescence dating methods. Both lithology and chironomid fauna indicate that the former shallow lakes were situated on a floodplain. Palaeotemperature estimates calculated from the fossil chironomid-assemblages of the Early Glacial lacustrine deposit indicate mean July air temperatures of ca. 15 °C, which is in line with results derived in earlier studies from the Niederlausitz area and from northwestern Europe. The Early Pleniglacial lacustrine deposits consist of an organic-rich gyttja, intercalated with sand and silt lenses. The chironomid-assemblages show that a shallow meso- to eutrophic lake was present at the study site, and chironomid-inferred palaeotemperature estimates indicate an abrupt decline in July air temperatures from 15-16 °C to ca. 13 °C. In combination with other proxies from the same record, this suggests a Dansgaard/Oeschger like climate event. © 2008 Elsevier B.V. All rights reserved

Detection of Lateglacial distal tephra layers in the Netherlands

Three distal tephra layers or cryptotephras have been detected within a sedimentary sequence from the Netherlands that spans the last glacial-interglacial transition. Geochemical analyses identify one as the Vedde Ash, which represents the southernmost discovery of this mid-Younger Dryas tephra so far. This tephra was found as a distinct horizon in three different cores sampled within the basin. The remaining two tephras have not been geochemically 'fingerprinted', partly due to low concentrations and uneven distributions of shards within the sequences sampled. Nevertheless, there is the potential for tracing these tephra layers throughout the Netherlands and into other parts of continental Europe. Accordingly, the possibilities for precise correlation of Dutch palaeoenvironmental records with other continental, marine and ice-core records from the North Atlantic region are highlighted. © 2005 Taylor & Francis