Twenty years of spatially coherent deepwater warming in lakes across Europe related to the North Atlantic Oscillation

• Main Authors: Martin T. Dokulil, Albert Jagsch, Glen D. George, Orlane Anneville, Thomas Jankowski, Bernd Wahl, Brigitte Lenhart, Thorsten Blenckner, Katrin Teubner
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: North Atlantic; North Atlantic oscillation
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.420.8844; http://www.aslo.org/lo/toc/vol_51/issue_6/2787.pdf

Twenty to fifty years of annual mean deepwater (hypolimnetic) temperature data from twelve deep lakes spaced across Europe (2u959W to14u09E, 46u279 to 59u009N) show a high degree of coherence among lakes, particularly within geographic regions. Hypolimnetic temperatures vary between years but increased consistently in all lakes by about 0.1–0.2uC per decade. The observed increase was related to the weather generated by largescale climatic processes over the Atlantic. To be effective, the climatic signal from the North Atlantic Oscillation (NAO) must affect deep lakes in spring before the onset of thermal stratification. The most consistent predictor of hypolimnetic temperature is the mean NAO index for January–May (NAOJ–M), which explains 22–63 % of the interannual variation in deepwater temperature in 10 of the 12 lakes. The two exceptions are remote, less windexposed alpine valley lakes. In four of the deepest lakes, the climate signal fades with depth. The projected hypolimnetic temperature increase of approximately 1uC in 100 yr, obtained using a conservative approach, seems