A three thousand year record of North Atlantic climate

Annual band counting on three radiometrically dated stalagmites from NW Scotland, provides a record of growth rate variations for the last 3000 years. Over the period of instrumental meteorological records we have a good historical calibration with local climate (mean annual temperature/mean annual precipitation), regional climate (North Atlantic Oscillation) and sea surface temperature (SST; strongest at 65-70 degree N, 15-20 degree W), although the correlation with the latter breaks down prior to the instrumental record. This suggests that the climatic factors that force NW Scottish climate and therefore our stalagmite growth varied through time, and include winter NAO strength, the strength of the thermohaline circulation and possibly solar output. Spectral analysis was performed on the stalagmite growth rate time series. A spectral frequency of 50-70 years is predominant in two stalagmites that were deposited from 1000 to 3000 BP; a slightly longer frequency of 72-94 years is dominant from 1000 BP to present. These are the same as that observed in ocean GCM output for the North Atlantic region SSTs. Our stalagmites provide high resolution, precisely dated evidence of a similar periodicity predominating over the last 3000 years in a climate proxy record known to be sensitive to changes in forcing functions relevant to the North Atlantic sector.