et al. # a comprehensive database of paleoclimate records is needed to place recent warming into the longer-term context of natural climate variability. We present a global compilation of quality-controlled, published, temperature-sensitive proxy records extending back 12,000 years through the Holocene. Data were compiled from 679 sites where time series cover at least 4000 years, are resolved at sub-millennial scale (median spacing of 400 years or finer) and have at least one age control point every 3000 years, with cutoff values slackened in datasparse regions. The data derive from lake sediment (51%), marine sediment (31%), peat (11%), glacier ice (3%), and other natural archives. The database contains 1319 records, including 157 from the Southern Hemisphere. the multi-proxy database comprises paleotemperature time series based on ecological assemblages, as well as biophysical and geochemical indicators that reflect mean annual or seasonal temperatures, as encoded in the database. This database can be used to reconstruct the spatiotemporal evolution of Holocene temperature at global to regional scales, and is publicly available in Linked Paleo Data (LiPD) format.

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Midge (Insecta: Diptera: Nematocera) assemblages were examined in surface sediment samples from Lake Pieni‐Kauro and the Saavanjoki River, eastern Finland, using their sedimentary remains. The aim was first to identify the forcing factors behind midge distribution within an aquatic ecosystem and second to develop new midge‐based calibration models for the reconstruction of past environmental conditions, with a special focus on paleohydrology. The third objective was to apply the models to a midge stratigraphy. The effect of sampling‐point selection in paleolimnological studies and its possible influence on chironomid‐inferred temperature reconstructions was also assessed. The species assemblages in Lake Pieni‐Kauro showed high levels of heterogeneity within the surface sediment samples, signifying that the assemblages predominantly incorporate locally dwelling fauna, instead of integrating remains from a larger area. Stream flow and water depth were the most important factors explaining the midge distributions in the lake. In addition, sampling distance from littoral vegetation (DLV), proximity of wetland, distance from shore, and organic content of the sediment were significantly correlated statistically with the midge assemblages. In the lacustrine samples, absolute midge abundance and taxon richness were highest at intermediate water depths. Because hydrological variables were the most important factors controlling the species' distributions, paleohydrological calibration models for water depth and stream flow were developed. Additionally, a transfer function for the sampling DLV was developed that can be used to track changes in the past location of littoral vegetation stands, which is often closely related to hydrological factors. The models' test use on the subfossil midge assemblages of the previously available downcore sediment sequence showed coherent and expected results, compared with previous studies and the modern observed environmental conditions of the lake. Based on the results of this study, these models can provide reliable estimates of past hydrological variability that is closely related to climatic changes and thus may provide a valuable tool for environmental management and global change assessments. This study also indicates that care should be taken in choosing the sampling point in chironomid‐based calibration studies because the influence of depth may distort the temperature estimations.

Luoto, T. P. 2009. Subfossil Chironomidae (Insecta: Diptera) along a latitudinal gradient in Finland: development of a new temperature inference model.ABSTRACT: Numerical techniques were used to study chironomid distribution and abundance in lakes from a 1000 km transect in Finland, with special interest on the effect of local summer air temperatures on chironomid assemblages. The final aim of the study was to develop a chironomidbased palaeotemperature inference model. The dataset consisted of 82 lakes (of which 77 were used in the model after deletion of outliers), with catchments spanning from boreal coniferous forests to mountain birch woodland and tundra vegetation. Numerical analysis showed that the mean July air temperature was the most significant variable explaining the distribution and abundance of chironomids in Finnish lakes. Weighted-averaging partial least squares techniques were used to develop a palaeotemperature inference model for mean July air temperature reconstructions. The model performance statistics were favourable, with cross-validated coefficient of determination (r 2 ) of 0.78, root mean squared error of prediction of 0.7218C and maximum bias of 0.7948C. Based on these values, the transfer function is a valid means of performing quantitative palaeotemperature estimates in downcore studies.

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Multiproxy palaeolimnological analyses of a sediment core record from Lake Einstaken, Nordaustlandet, give insight into long-term ecological and environmental dynamics in the High Arctic Svalbard during the last c. 13 000 cal yr BP. Fossil remains of foraminifera, chironomidae, cladocera and diatoms (Bacillariophyta) revealed several distinct ecological turnovers during the late Quaternary. The foraminiferal assemblages in a marine interval in the lower part of the core indicated one distinct faunal turnover and two subsequent minor changes. The foraminiferal assemblages reflected high-arctic, shallow-water conditions in an area of changing salinity conditions. A development of gradually more restricted marine conditions, presumably related to a decrease in water depth during the isostatic uplift, was evident from the foraminiferal assemblages. The Holocene was characterized by a freshwater environment in the isolated Lake Einstaken. The cladoceran assemblages experienced two complete faunal turnovers in the early part of the lacustrine sediment sequence, most likely related to inlake processes. The chironomid assemblages went through five distinct Holocene faunal changes that were probably mostly related to climate development and changes in nutrient conditions. The freshwater diatoms revealed four distinct episodes of change in their assemblages that could be related to their sensitivity to pH and nutrient status. The most distinct common feature in the Holocene faunal and floral assemblages was the pioneer phase during the early Holocene. The recent environmental changes, which were most visibly reflected in the chironomid records, are possibly related to a coupled effect of elevated nutrient conditions and increased temperatures.

Paleoclimate reconstructions based on biological proxies present methodological challenges, especially during non-analog conditions, such as the early Holocene. Here, two chironomid-based training sets from Finland were amalgamated to create a more accurate transfer function of summer air temperature. The aim was to reconstruct Holocene paleoclimate in northernmost Lapland, in an area that has been either too warm or too cold for reliable reconstructions using the original calibration models. The results showed that the combined calibration model had improved performance statistics. The temperature trends inferred from the downcore chironomid record using the original and combined models were very similar. However, there were major changes in their absolute values with the combined model showing greatly improved accuracy. The chironomid-based temperature reconstruction showed significant correlation with the previous pollen-based reconstructions from northwestern Finnish Lapland. However, differences were observed in the temperature trends of the early Holocene, when the chironomid-inferred temperatures rapidly increased, but the pollen-based reconstructions lagged behind suggesting that a cool climate continued for much longer. However, similar to the chironomid record, new plant macrofossil evidence from northwestern Finland also showed warmer-than-present early Holocene temperatures. Therefore, we conclude that the early Holocene was probably warm in northern Lapland.