A spatio-temporal reconstruction of Holocene temperature change in southern Scandinavia.

Holocene mean July (TJul) and mean January (TJan) temperatures were reconstructed at Lake Trehörningen in southwest Sweden using pollen–climate calibration functions and converted into anomalies relative to modern temperatures. The anomalies were applied to 28 meteorological stations in Denmark, with each station adjusted to account for spatial variability in both TJul and TJan. The resulting reconstructions were merged to create composite TJul and TJan records. The individual reconstructions were also used to establish the parameterization of the TJul and TJan values, resulting in Holocene temperature maps for all of Denmark. Low TJul values characterised southern Sweden and Denmark at the start of the Holocene, followed by an increase during the early Holocene. Likewise, TJan was initially low at the start of the Holocene, followed by an increase between 10 500 and 9900 cal. BP. Thereafter, TJan was relatively stable between 9900 and 8000 cal. BP. The general increase in temperature during the early Holocene was accompanied by a decrease in the amplitude of the mean monthly temperature record, indicating that a maritime climate was established at this time. Maximum TJul and TJan are recorded during the mid-Holocene interval from 8000 to 4500 cal. BP, with consistently high July temperatures (>18°C) between 6700 and 5400 cal. BP. During the late Holocene, both TJul and TJan gradually decreased. The Holocene temperature maps of Denmark reveal spatial patterns in both summer and winter temperature. In the summer, an east–west decreasing temperature gradient, related to a maritime effect, has persisted in Denmark throughout the Holocene. In contrast, the temperature in winter has varied spatially along subtle coastal–inland and topographical gradients. Various mechanisms have been invoked to explain the Holocene trends in temperature, including the melting of the Scandinavian Ice Sheet, changes in insolation, and changes in the dominant type of atmospheric circulation affecting northern Europe. [ABSTRACT FROM PUBLISHER]