Late Glacial and Holocene temperature changes at Egelsee, Switzerland, reconstructed using subfossil chironomids

A temperature reconstruction using chironomids was attempted at Egelsee, Switzerland, a site where pollen and macrofossil records showed a correspondence between vegetation and climatic changes inferred by other proxies in Europe. The general pattern of temperature changes inferred from chironomids during the Late Glacial [i.e. cold temperatures between ca. 16,500 and 14,800cal BP, close to present-day temperature between 15,000 and 13,000cal BP and colder temperatures during the Younger Dryas (YD)], and the major temperature changes of the Holocene (i.e. the Younger Dryas-Holocene transition and the Late Holocene cooling trend) at Egelsee, were mirrored in other European climate reconstructions using various proxies. However, the amplitude of temperature changes during the YD was smaller than reconstructed by other proxies at various sites, and the 8,200years BP event was not apparent. These differences between records were probably due to the dominance of Corynocera ambigua, with percentages reaching 60% in parts of the Egelsee sequence. This taxon was not present in any of the 103 lakes used for the transfer function and its absence may have yielded less accurate inferences. Its presence in samples only associated with cold inferences at Egelsee suggests that this taxon is a cold indicator. However, it was also found in warm Danish lakes and the factors that determine the presence of C. ambigua remain unexplained. Most samples had a poor fit to temperature and instead, dissolved organic carbon seemed to be a factor influencing the chironomid assemblages during the Holocene. These results illustrate the need to better understand the ecology of chironomids and to disentangle the various factors that affect chironomid communities through time. Ultimately, such information will lead to more accurate temperature reconstruction

Chironomid-inferred summer temperature development during the late Rissian glacial, Eemian interglacial and earliest Würmian glacial at Füramoos, southern Germany

Eemian pollen records from central Europe describe a transition from thermophilous tree taxa in the early Eemian to boreal tree taxa in the late Eemian with forest opening in the subsequent stadial. Available summer-temperature reconstructions for the mid- to late Eemian transition show decreasing values during that time. We present a new chironomid record from southern Germany that covers the mid-Eemian to the end of the first Würmian stadial ( c . 125-105 ka) and also parts of the late Rissian glaciation and early Brörup interstadial of the early Würmian glaciation. Based on this record we describe lake development in the former Füramoos palaeolake and quantitatively reconstruct July air temperature during the examined interval. Late Rissian sediments are dominated by two chironomid taxa, Sergentia coracina -type and Micropsectra radialis -type, indicating very cold conditions. Following an uncertain interval, probably including a hiatus at the late Rissian/Eemian transition, mid-Eemian sediments contain Tanytarsus glabrescens -type and Tanytarsus mendax -type suggesting relatively high July air temperatures. During the late Eemian, typically thermophilic taxa such as Tanytarsus glabrescens -type disappear, suggesting decreasing temperatures. Stadial A is associated with increases in Microtendipes pedellus -type suggesting more oligotrophic conditions. Early Brörup sediments contain Tanytarsus glabrescens -type, suggesting a slight increase in July air temperature. Reconstructed July air temperatures show temperatures of 7-8 °C during the late Rissian and a decline from ~15.5-12 °C during the mid- to late Eemian associated with decreasing Northern Hemisphere July insolation. July air temperature values vary between 12 and 14 °C in the late Eemian, while reconstructed temperatures remain within 12-13.5 °C during Stadial A. Our new chironomid-based temperature reconstruction provides valuable corroboration and new quantification of temperature development from the mid-Eemian to the early Brörup interstadial as well as for sections of the late Rissian from the alpine foreland of southern Germany

Distribution of diatoms, chironomids and cladocera in surface sediments of thirty mountain lakes in south-eastern Switzerland

Abstract.: Surface sediments from 30 mountain lakes in south-eastern Switzerland (Engadine, Grisons) were analysed for subfossil diatom, chironomid, and cladoceran assemblages. Ordination techniques were used to identify relevant physical and chemical environmental parameters that best explain the distribution of these biota in the studied lakes. Diatom assemblage composition showed a strong relationship with physical (e.g., lake depth, temperature, organic content of surface sediments) and chemical variables (e.g., lake-water pH, alkalinity, silica concentration). The greatest variance in chironomid and cladoceran assemblages is explained by dissolved organic carbon (DOC) content of lake water, temperature, and the organic content of surface sediments, all parameters which are highly correlated with lake elevation. Increasing lake depth is reflected in diatom and cladoceran assemblages by higher percentages of planktonic species, whereas chironomid assemblages in the deep Engadine lakes are characterised by a high proportion of lotic taxa. In contrast to similar studies in the Northern and Southern Alps, subfossil assemblages in the Engadine mountain lakes showed a strong relationship with DOC, which in these weakly buffered lakes is negatively correlated with altitude. According to our findings, chironomid and cladocera remains have a considerable potential as quantitative palaeotemperature indicators in the Engadine area. This potential is somewhat weaker for diatoms which seem to be more strongly influenced by water chemistry and lake bathymetr

Comparison between chironomid-inferred July temperatures and meteorological data AD 1850-2001 from varved Lake Silvaplana, Switzerland

Inferred temperatures from chironomids preserved in the varved sediment of Lake Silvaplana in the Eastern Swiss Alps were compared with instrumental data obtained from a meteorological station in Sils-Maria, on the shore of Lake Silvaplana, for the time interval 1850-2001. At near-annual resolution, the general patterns of chironomid-inferred temperature changes followed the meteorological record over the last ∼150years (r Pearson=0.65, P=0.01) and 87% of the inferences had deviations from the instrumental data below the root-mean-square error of prediction (RMSEP). When the inferences were compared with a 2-year running mean in the meteorological data, 94% of the inferences had differences with the instrumental data below the RMSEP, indicating that more than half of the inaccurate inferences may have been due to errors in varve counting. Larger deviations from the instrumental data were also obtained from samples with low percentages of fossil taxa represented in the training set used for temperature reconstruction and/or assemblages with poor fit to temperature. Changes in total phosphorus (TP, as inferred by diatoms) and/or greater precipitation were possible factors affecting the accuracy of the temperature reconstruction. Although these factors might affect the quantitative estimates, obtaining >80% accurate temperature inferences suggests that chironomid analysis is a reliable tool for reconstructing mean July air temperature quantitatively over the last ∼150years in Lake Silvaplan

Chironomid dataset from Mutterbergersee: A late-Holocene paleotemperature proxy record for the Central Eastern Alps, Austria

We present a dataset of subfossil chironomid assemblages in the MUT-10 sediment core obtained from the high alpine lake Mutterbergersee in the Austrian Alps in 2010. The data were presented in the research article by Ilyashuk et al. (2019) "The Little Ice Age signature in a 700-year high-resolution chironomid record of summer temperatures in the Central Eastern Alps". In addition to the results of the chironomid analysis of 100 sediment samples presented in this article, we also include chironomid assemblage data from an additional 48 sediment samples that complement this dataset. The data includes raw chironomid counts, percent abundance of chironomid taxa, as well as mean July air temperature estimates derived from the chironomid record based on a chironomid-temperature transfer function. We also provide information on age-dating of the sedimentary sequence. Given the high temporal resolution and the robust age-depth model of the record, the chironomid-based reconstruction of temperature since AD 1300 provides a detailed documentation of climate change in the Eastern Alps from the Little Ice Age onwards and can be used for comparison with other independent proxy-based climate reconstructions. In addition to the data, we detail the sample processing for subfossil chironomid analysis and provide a detailed description of the reconstruction technique used for producing chironomid-based quantitative temperature inferences

Summer temperatures and lake development during MIS 5a interstadial: New data from the Unterangerberg palaeolake in the Eastern Alps, Austria

Investigations of interstadials during early stages of glacial periods are of special interest, because they featured large-scale transformations of the climate system and the build-up of land-based ice sheets. Lacustrine sediment sequences are considered to be important natural archives that register past climate and environmental signals. Here, we present new multi-proxy data obtained from a palaeolake succession preserved in the inner-alpine terrace of Unterangerberg, Eastern Alps. These sediments formed during the second Early Würmian Interstadial, equivalent to Marine Isotope Stage (MIS) 5a, and were used to reconstruct changes in lake conditions and to infer past air temperatures. The sediment geochemical data and subfossil aquatic biota provide evidence of a cyclic lake-fen-lake development during this interstadial. The proxy records reveal stable lacustrine conditions with dense charophyte meadows and abundant aquatic fauna during the early part of the interstadial, a progressive shallowing of the lake resulting in the spreading out of fen vegetation in the middle part, and a transition from wetland to a renewed shallow lake stage towards the end of the interstadial. Chironomids were used to reconstruct mean July air temperatures, employing a combined Norwegian-Swiss chironomid temperature inference model. The reconstruction indicates a temperature close to present-day values of ca. 18 °C in the middle part of the record, while temperatures of ca. 13-14 °C are recorded for the lower and upper parts. The proxy data from this palaeolake provide evidence of heat and drought in the middle part of MIS 5a, supported by the chironomid-based temperature reconstruction. Our reconstruction shows a climate pattern broadly similar to that found in pollen-based estimates of mean July air temperatures from sites in the northern Alpine foreland and compares well to other European palaeoclimatic reconstructions of MIS 5a climate

Summer temperatures and environmental dynamics during the Middle Würmian (MIS 3) in the Eastern Alps: Multi-proxy records from the Unterangerberg palaeolake, Austria

Several millennial-scale warm phases perturbed the glacial climate during Marine Isotope Stage 3 (MIS 3, ca. 57-29 ka BP). Little is known about the impact of these climatic changes on Alpine ecosystems due to the sparsity of undisturbed sediment records in the Alps and their foreland. In this study, multiple sediment-archived proxies (sediment geochemistry, stable oxygen and carbon isotopes of autochthonous carbonate, and subfossil remains of macrophytes and aquatic invertebrates) were examined in five drill cores from an ancient inner-Alpine lake at Unterangerberg (Eastern Alps) to reconstruct the palaeolake environment and to estimate summer temperature changes for the first half of MIS 3. The lacustrine sedimentation in the basin began ca. 54.6 ka, tentatively correlated with the start of Greenland Interstadial (GI) 14. We identified three distinct phases in the development of the lake. (1) A cold, oligotrophic water body influenced by snow/glacier meltwater ca. 54.6-52.2 cal ka BP. (2) A clear-water, macrophyte-dominated, productive lake ca. 52.2-44.9 cal ka BP. Submerged macrophytes were dominated by the charophyte alga Chara hispida and chironomid assemblages - by Corynocera ambigua , which is absent from the present-day fauna of the Alpine region. (3) A turbid-water, less productive lake ca. 44.9-41.5 cal ka BP. This shift towards a turbid-water state, as evidenced by the drastic reduction in the abundance of submerged macrophytes and associated invertebrates, likely occurred due to increased input of meltwater. The regime shift is tentatively correlated with the start of GI 11, for which the highest temperatures of the studied MIS 3 interval are inferred. Chironomid-based reconstructions of mean July air temperatures provide interstadial temperature estimates between ca. 11 and 12.5°C (i.e. ca. 5-6°C below present-day values), which concurs with reconstructions available from the northern Alpine foreland. Cooler July temperatures (ca. 9-10°C) are reconstructed for MIS 3 stadials. The Unterangerberg lacustrine records provide valuable new insights into MIS 3 climate dynamics inside the Eastern Alps and contribute to a better understanding of the effects of climate change on the Alpine environment

Limnological changes and chironomid-inferred summer air temperature from the Late Pleniglacial to the Early Holocene in the East Carpathians

Here we provide the first chironomid record and associated summer air-temperature (T VII ) reconstruction between ca. 16,800-9100 cal yr BP from Lake Saint Anne (SZA), situated in the Eastern Carpathians. SZA was formed by the youngest volcanic eruption of Ciomadul volcano at ca. 29,600 cal yr BP. Our main goals in this study are to test whether warming after Heinrich event 1 (H1; ca. 16,200 cal yr BP) had similar amplitude to the late glacial warming, while Younger Dryas (YD) summers remained relatively warm in this region of Europe. We found the most remarkable chironomid assemblage change with a T VII increase of ~3.5-3.8°C at ca. 16,350 cal yr BP at SZA, followed by another slight T VII increase of ~0.8-1.0°C at ca. 14,450 cal yr BP. Only very minor temperature variations were recorded between 14,450 cal yr BP and 11,700 cal yr BP, with an unexpected T VII decrease in the Early Holocene. Variations in water depth together with increasing analogue problems and paludification from ca. 14,200 cal yr BP onwards may have influenced the reliability of our paleotemperature record obtained from SZA. In addition, Sphagnum -indicated decreasing pH, and hence decreasing nutrient level, likely overrode the effect of summer air-temperature changes during the Early Holocene, and this may explain the bias in the chironomid-inferred summer air-temperature reconstruction in the Early Holocene section