A sedimentary record from lake Stora Viðarvatn in northeast Iceland records environmental changes over the past 2000 years. Downcore data include chironomid (Diptera: hironomidae) assemblage data and total organic carbon, nitrogen, and biogenic silica content. Sample scores from detrended correspondence analysis (DCA) of chironomid assemblage data are well correlated with measured temperatures at Stykkishólmur over the 170 year instrumental record, indicating that chironomid assemblages at Stora Viðarvatn have responded sensitively to past temperature changes. DCA scores appear to be useful for quantitatively inferring past temperatures at this site. In contrast, a quantitative chironomid-temperature transfer function developed for northwestern Iceland does a relatively poor job reconstructing temperature shifts, possibly due to the lake’s large size and depth relative to the calibration sites or to the limited resolution of the subfossil taxonomy.
The pre-instrumental climate history inferred from chironomids and other paleolimnological proxies is supported by prior inferences from historical documents, glacier reconstructions, d paleoceanographic studies. Much of the first millennium AD was relatively warm, with temperatures comparable to warm decades of the 20th century. Temperatures during parts of the 10th and 11th centuries AD may have been comparably warm. Biogenic silica concentrations declined, carbon:nitrogen ratios increased, and some chironomid taxa disappeared from the lake between the 13th and 19th centuries, recording the decline of temperatures into the Little Ice Age, increasing soil erosion, and declining lake productivity. All the proxy reconstructions indicate that the most severe Little Ice Age conditions occurred during the 18th and 19th centuries, a period historically associated with maximum sea-ice and glacier extent around Iceland.