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| 2. |
- Engels, S., et al.
(author)
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Chironomid-based palaeotemperature estimates for northeast Finland during Oxygen Isotope Stage 3
- 2008
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In: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 40:1, s. 49-61
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Journal article (peer-reviewed)abstract
- 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.
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| 3. |
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| 4. |
- Larocque, I, et al.
(author)
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Comparison between chironomid-inferred July temperatures and meteorological data AD 1850-2001 from varved Lake Silvaplana, Switzerland
- 2009
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In: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 41:2, s. 329-342
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Journal article (peer-reviewed)abstract
- 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 150 years (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 150 years in Lake Silvaplana.
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| 5. |
- Schilder, J., et al.
(author)
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Spatiotemporal patterns in methane flux and gas transfer velocity at low wind speeds: Implications for upscaling studies on small lakes
- 2016
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In: Journal of Geophysical Research - Biogeosciences. - : AMER GEOPHYSICAL UNION. - 2169-8953 .- 2169-8961. ; 121:6, s. 1456-1467
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Journal article (peer-reviewed)abstract
- Lakes contribute significantly to the global natural emissions of methane (CH4) and carbon dioxide. However, to accurately incorporate them into the continental carbon balance more detailed surveys of lacustrine greenhouse gas emissions are needed, especially in respect to spatiotemporal variability and to how this affects the upscaling of results. We investigated CH4 flux from a small, wind-shielded lake during 10 field trips over a 14month period. We show that floating chambers may be used to calibrate the relationship between gas transfer velocity (k) and wind speed at 10m height (U-10) to the local system, in order to obtain more accurate estimates of diffusive CH4 flux than by applying general models predicting k based on U-10. We confirm earlier studies indicating strong within-lake spatial variation in this relationship and in ebullitive CH4 flux within the lake basin. However, in contrast to the pattern reported in other studies, ebullitive CH4 flux was highest in the central parts of the lake. Our results indicate positive relationships between k and U-10 at very low U-10 (0-3ms(-1)), which disagrees with earlier suggestions that this relationship may be negligible at low U-10 values. We estimate annually averaged open water CH4 emission from Lake Gerzensee to be 3.6-5.8mmolm(-2)d(-1). Our data suggest that estimates of greenhouse gas emissions from aquatic systems to the atmosphere based on the upscaling of short-term and small-scale measurements can be improved if both spatial and temporal variabilities of emissions are taken into account.
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| 6. |
- van Hardenbroek, M., et al.
(author)
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Evidence for past variations in methane availability in a Siberian thermokarst lake based on delta C-13 of chitinous invertebrate remains
- 2013
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 66, s. 74-84
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Journal article (peer-reviewed)abstract
- Understanding past methane dynamics in arctic wetlands and lakes is crucial for estimating future methane release. Methane fluxes from lake ecosystems have increasingly been studied, yet only few reconstructions of past methane emissions from lakes are available. In this study, we develop an approach to assess changes in methane availability in lakes based on delta C-13 of chitinous invertebrate remains and apply this to a sediment record from a Siberian thermokarst lake. Diffusive methane fluxes from the surface of ten newly sampled Siberian lakes and seven previously studied Swedish lakes were compared to taxon-specific delta C-13 values of invertebrate remains from lake surface sediments to investigate whether these invertebrates assimilated C-13-depleted carbon typical for methane. Remains of chironomid larvae of the tribe Orthocladiinae that, in the study lakes, mainly assimilate plant-derived carbon had higher delta C-13 than other invertebrate groups. delta C-13 of other invertebrates such as several chironomid groups (Chironomus, Chironomini, Tanytarsini, and Tanypodinae), cladocerans (Daphnia), and ostracods were generally lower. delta C-13 of Chironomini and Daphnia, and to a lesser extent Tanytarsini was variable in the lakes and lower at sites with higher diffusive methane fluxes. delta C-13 of Chironomini, Tanytarsini, and Daphnia were correlated significantly with diffusive methane flux in the combined Siberian and Swedish dataset (r = -0.72, p = 0.001, r = -0.53, p = 0.03, and r = -0.81, p < 0.001, respectively), suggesting that delta C-13 in these invertebrates was affected by methane availability. In a second step, we measured delta C-13 of invertebrate remains from a sediment record of Lake S1, a shallow thermokarst lake in northeast Siberia. In this record, covering the past ca 1000 years, delta C-13 of taxa most sensitive to methane availability (Chironomini, Tanytarsini, and Daphnia) was lowest in sediments deposited from ca AD 1250 to ca AD 1500, and after AD 1970, coinciding with warmer climate as indicated by an independent local temperature record. As a consequence the offset in delta C-13 between methane-sensitive taxa and bulk organic matter was higher in these sections than in other parts of the core. In contrast, delta C-13 of other invertebrate taxa did not show this trend. Our results suggest higher methane availability in the study lake during warmer periods and that thermokarst lakes can respond dynamically in their methane output to changing environmental conditions. (C) 2012 Elsevier Ltd. All rights reserved.
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| 7. |
- van Hardenbroek, M, et al.
(author)
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Relationship between d13C of chironomid remains and methane flux in Swedish lakes
- 2012
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In: Freshwater Biology. - : Blackwell Publishing. - 0046-5070 .- 1365-2427. ; 57:1, s. 166-177
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Journal article (peer-reviewed)abstract
- 1. Methanogenic carbon can be incorporated by methane-oxidising bacteria, leading to a 13C-depleted stable carbon isotopic composition (d13C) of chironomids that feed on these microorganisms. This has been shown for the chironomid tribe Chironomini, but very little information is available about the d13C of other abundant chironomid groups and the relationship between chironomid d13C and methane production in lakes.
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| 8. |
- van Hardenbroek, M., et al.
(author)
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Taxon-specific δ13C analysis of chitinous invertebrate remains in sediments from Strandsjön, Sweden
- 2014
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In: Journal of Paleolimnology. - : Springer Netherlands. - 0921-2728 .- 1573-0417. ; 52:1-2, s. 95-105
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Journal article (peer-reviewed)abstract
- Taxon-specific stable carbon isotope (delta C-13) analysis of chitinous remains of invertebrates can provide valuable information about the carbon sources used by invertebrates living in specific habitats of lake ecosystems (for example, sediments, water column, or aquatic vegetation). This is complementary to delta C-13 of sedimentary organic matter (SOM), which provides an integrated signal of organic matter produced in a lake and its catchment, and of diagenetic processes within sediments. In a sediment record from Strandsjon (Sweden) covering the past circa 140 years, we analyzed SOM geochemistry (delta C-13, C:N-atomic, organic carbon content) and delta C-13 of chitinous invertebrate remains in order to examine whether taxon-specific delta C-13 records could be developed for different invertebrate groups and whether these analyses provide insights into past changes of organic carbon sources for lacustrine invertebrates available in benthic and planktonic compartments of the lake. Invertebrate taxa included benthic chironomids (Chironomus, Chironomini excluding Chironomus, Tanytarsini, and Tanypodinae), filter-feeders on suspended particulate organic matter (Daphnia, Plumatella and Cristatella mucedo), and Rhabdocoela. delta C-13 of chironomid remains indicated periodic availability of C-13-depleted carbon sources in the benthic environment of the lake as delta C-13 values of the different chironomid taxa fluctuated simultaneously between -34.7 and -30.5 aEuro degrees (VPDB). Daphnia and Bryozoa showed parallel changes in their delta C-13 values which did not coincide with variations in delta C-13 of chironomids, though, and a 2-3 aEuro degrees decrease since circa AD 1960. The decrease in delta C-13 of Daphnia and Bryozoa could indicate a decrease in phytoplankton delta C-13 as a result of lower lake productivity, which is in accordance with historical information about the lake that suggests a shift to less eutrophic conditions after AD 1960. In contrast, Rhabdocoela cocoons were characterized by relatively high delta C-13 values (-30.4 to -28.2 aEuro degrees) that did not show a strong temporal trend, which could be related to the predatory feeding mode and wide prey spectrum of this organism group. The taxon-specific delta C-13 analyses of invertebrate remains indicated that different carbon sources were available for the benthic chironomid larvae than for the filter-feeding Daphnia and bryozoans. Our results therefore demonstrate that taxon-specific analysis of delta C-13 of organic invertebrate remains can provide complementary information to measurements on bulk SOM and that delta C-13 of invertebrate remains may allow the reconstruction of past changes in carbon sources and their delta C-13 in different habitats of lake ecosystems.
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| 9. |
- von Gunten, L., et al.
(author)
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Seasonal temperatures for the past ~400 years reconstructed from diatom and chironomid assemblages in a high-altitude lake (Lej da la Tscheppa, Switzerland)
- 2008
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In: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 39, s. 283–299-
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Journal article (peer-reviewed)abstract
- We analysed a 42 cm long sediment record from Lej da la Tscheppa, a high-altitude lake (2,616 m a.s.l.) in the Upper Engadine valley (Switzerland) for subfossil diatoms, chironomids and pollen. The chronology of the top 21 cm of the record was established using 210Pb analysis using a constant-rate-of-supply model, and validated with 137Cs measurements and the content of spheroidal carbonaceous particles. A tentative chronology for the lower part of the core was obtained through extrapolation of the sedimentation rates in the uppermost part of the record. Pollen assemblages in the record reflect regional changes in forestation and land-use patterns in the Upper Engadine valley and show no evidenceof significant local human activity in the lake’s catchment. Diatom assemblages record a distinct increase in planktonic taxa since the early 19th century, suggesting a decrease in the duration of ice-cover. In contrast, chironomid assemblages remained stable during a large part of the record. We applied an established chironomid-based July air temperature transfer function and a newly developed diatom-based spring air temperature transfer function to reconstruct past seasonal air temperature changes at Lej da la Tscheppa. The reconstructions indicate a diatom-inferred warming trend in spring temperatures during the past ca. 400 years, whereas chironomid-inferred summer temperatures suggest a slight cooling trend.
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