Paper in Press
GEOPHYSICAL RESEARCH LETTERS, doi:10.1029/2012GL051241
Greenland ice core evidence for spatial and temporal variability of the Atlantic Multidecadal Oscillation
- The past history of the AMO is preserved in ice core data
- The dominant quasi-periodicities are those of 20 years and 45-65 years
- The origin of 20-year periodicity is Atlantic and of 45-65 year the Arctic
An analysis of annual 18O data from six Arctic ice cores (five from Greenland and one from Canada's Ellesmere Island) suggests a significant AMO spatial and temporal variability within a recent period of 660 years. A dominant AMO periodicity near 20 years is clearly observed in the southern (Dye3 site) and the central (GISP2, Crete and Milcent) regions of Greenland. This 20-year variability is, however, significantly reduced in the northern (Camp Century and Agassiz Ice Cap) region, likely due to a larger distance from the Atlantic Ocean, and a much lower snow accumulation. A longer time scale AMO component of 45-65 years, which has been seen clearly in the 20th century SST data, is detected only in central Greenland ice cores. We find a significant difference between the AMO cycles during the Little Ice Age (LIA) and the Medieval Warm Period (MWP). The LIA was dominated by a ~20 year AMO cycle with no other multidecadal scale variability above the noise level. However, during the preceding MWP the 20 year cycle was replaced by a longer scale cycle centered near a period of 43 years with a further 11.5 year periodicity. An analysis of two coupled atmosphere-ocean general circulation models control runs (UK Met Office HadCM3 and NOAA GFDL CM2.1) agree with the shorter and longer time-scales of Atlantic Meridional Overturning Circulation (AMOC) and temperature fluctuations with periodicities close to those observed. However, the geographic variability of these periodicities indicated by ice core data is not captured in model simulations.
Received 5 February 2012; accepted 20 March 2012.
Citation: (2012), Greenland ice core evidence for spatial and temporal variability of the Atlantic Multidecadal Oscillation, Geophys. Res. Lett., doi:10.1029/2012GL051241, in press.