Ice core methodology - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 117

Figure 3.8. Example of a 1.2m segment of GRIP data from about 8,800 ybp . Visually
determined annual layer markings are shown as gray vertical bars. Annual layers were also
identified as matching pairs of spring and summer indicators: spring was characterized by high
dust content leading to peaks in [Ca 2 þ ] and dips in the [H 2 O 2 ] curve, while summer was
characterized by high [NH 4 ] and corresponding minima in the ECM curve. The annual layer
identification procedure was supported by high-resolution d 18 O data (Rasmussen et al. 2006).
Figure 3.9. Example of data and annual layer markings (gray vertical bars) from visual
stratigraphy during the early Holocene. A 0.95m long section of NGRIP data is shown.
Annual layers are marked at the summer peaks, which are defined by high [NH 4 ] and
[NO 3 ]. The spring is characterized by high dust mass leading to peaking [Ca 2 ] and dips in
the [H 2 O 2 ] profile, while the [Na þ ] peaks in late winter. The visual stratigraphy profile does not
contain clear annual layers, but does contain peaks corresponding to almost every dust peak.
The ECM anti-correlates strongly with the largest peaks in [NH 4 ], but does not itself allow safe
identification of annual layers.