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Existing paleoclimate data are exceedingly sparse from southern Spitsbergen, a High Arctic region predicted to experience significant environmental changes because of amplified warming. We analyzed biotic and isotopic paleolimnological proxies to reconstruct past climate from a lacustrine sediment core, with a basal age of ∼5500 a BP, in southern Spitsbergen (77°N). We used fossil Chironomidae assemblages to quantitatively reconstruct past mean July air temperatures and stable oxygen isotope values (δ18O) of these fossils to estimate changes in mean annual air temperature. These proxy records are strikingly similar and show that the coldest anomaly since the mid-Holocene occurred between 350 and 50 cal a BP, during the ‘Little Ice Age’, whereas the warmest period in the summer temperature record occurred between 5500–5000 and ∼2000 cal a BP. Our findings indicate that the natural long-term air temperature dynamics in our study area are most likely connected to solar minima and positive feedback mechanisms from sea-surface temperature maxima. The results also highlight that the recent temperature increase is unprecedented in its rate with a ∼2 °C increase in the summer temperatures during the past ∼50 years.

To fully utilize palaeolimnological archives for tracking past environmental changes, methodological advances are necessary. We present a novel method to quantitatively reconstruct past summer air temperatures based on fossil chydorid (Cladocera: Chydoridae) ephippia assemblages. We examined a 76-lake training set from Finland for chydorid ephippia distribution to develop a transfer function for summer air temperatures. Subsequently, we tested its usability in downcore reconstructions by inferring Holocene temperatures from Lake Arapisto in southern Finland. Significant climate-related variation was found in the distribution and abundance of chydorid ephippia in the training set. A transfer function for palaeotemperature reconstructions was developed using the partial least squares technique, which showed favourable performance statistics, enabling the test use of the model in a downcore reconstruction. The ephippia assemblages were responding to the Holocene climate development in the Lake Arapisto core. The ephippium-inferred temperatures correlated closely with the previously available independent palaeoclimate data from Lake Arapisto and from an adjacent lake, although the early Holocene samples had poor modern analogues in the training set. The use of fossil chydorid ephippia in palaeoclimatological reconstructions is a promising tool and it can contribute as a valuable addition for multiproxy assessments of past climate changes.

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 chironomid-based 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 (r2) of 0.78, root mean squared error of prediction of 0.721°C and maximum bias of 0.794°C. Based on these values, the transfer function is a valid means of performing quantitative palaeotemperature estimates in downcore studies. Copyright © 2008 John Wiley & Sons, Ltd.