Glaciochemical horizons

Glaciochemical horizons are intervals of core with substantially higher or lower than average concentrations of certain chemical constituents. If a historical event of known age can be correlated with the event horizon in the core, the assigned age of that interval can be used to confirm the depth-age relationship which has been determined from seasonal variations or other dating methods. In addition, in deep ice where annual layers are too thin to count seasons reliably and dating is only possible by model calculations [15,30], these horizons provide check points for calculated ages. 

The application of glaciochemical horizons to ice core dating is a recent and rapidly evolving development. A concerted search is under way to determine the impact of known events on the chemical composition of polar snow. So far, two types of universally applicable horizons have been detected in polar ice cores volcanic eruptions and Late Wisconsin dust. 

A second type of glaciochemical horizon, a long-term interval of anomalous concentrations rather than a sporadic peak, is demonstrated by Late Wisconsin dust. Greenland and Antarctic snow... 

Figure 6. Concentrations of SOt2 and Cl" (in ng/g) in Milcent, Greenland ice core samples deposited following the 1783 eruption of Laki in Iceland. The acid precipitation that followed this eruption left an unmistakable glaciochemical horizon...

Glaciochemical horizons not only provide checks on depth-age relationships but are of great intrinsic interest. Continuous chemical analysis of a well-dated core promises to greatly extend and refine the record of explosive volcanism [13]. Each well-dated eruption or other horizon then becomes of use as a time marker for cores where the dating is less precise. 

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