Solid electrical conductivity (ECM) from four Agassiz ice cores, Ellesmere Island NWT, Canada: high-resolution signal and noise over the last millennium and low resolution over the Holocene

The solid DC electrical conductivity (ECM - Electrical Conductivity Method) of polar ice cores has become an important tool in identifying and quantifying volcanic acid layers, and this paper addresses the question of how much signal and noise there is in single ECM series. A number of high-resolution (10 samples/year) ice-core ECM records from the Agassiz Ice Cap are correlated over the last 900 years. Correlations decrease with distance apart due to local drift and melt layer noise, but correlations are probably reduced also by differences in methodology and core storage. It is found that only peak sizes in the uppermost two percentiles retain their ranking and recognizability from core to core. With continuous sampling, however, the smaller peaks can be cross-identified between cores, even though they lose their size rank. Averaging or stacking several ECM records reduces the noise. Five-year averages of ECM for the Holocene are presented for the Agassiz cores and their correlations interpreted as functions of distance apart and differences in method. The large-scale melting in the early Holocene (8 ka to 10 ka) almost completely de-acidifies the ice in all the Agassiz cores.