Visual stratigraphy of the North Greenland Ice Core Project (NorthGRIP) ice core during the last glacial period

Abstract

[1] A continuous high-resolution record of digital images has been obtained from the North Greenland Ice Core Project (NorthGRIP) ice core (75.1°N, 42.3°W) in the depth interval from 1330 m to the bedrock at 3085 m. The ice core stratigraphy is clearly visible throughout the glacial period with the most frequent and brightest visible layers appearing during the coldest events. Down to a depth of 2600 m the horizontal layering is very regular; below this depth, small irregularities in the layering start to appear, and below 2800 m the visual stratigraphy becomes more uncertain, perhaps because of penetration into climatically warmer ice. Comparison of the visual stratigraphy with high-resolution continuous records of chemical impurities and dust reveals a high degree of correlation, which indicates that the visible layers are caused by these impurities. A new approach is used to automatically determine annual layer thicknesses from the visual stratigraphy record by carrying out a frequency analysis of the most prominent visible layers in the profile. The result gives strong support for the NorthGRIP timescale model.

The Greenland Ice Core Chronology 2005, 15–42ka. Part 1: constructing the time scale

“…For the glacial part these measurements include Continuous Flow Analysis (CFA) of chemical impurities, insoluble dust and electrolytical conductivity on continuously melted ice samples (Ro¨thlisberger et al, 2000;Ruth et al, 2003;Bigler, 2004), Electrical Conductivity Measurement (ECM) on the solid ice (Hammer, 1980;Dahl-Jensen et al, 2002) and the VS grey-scale profile (Svensson et al, 2005). All Fig.…”

“…The ECM record was also sampled at 1 mm resolution and has an effective resolution of about 4 mm . The VS is based on digital imaging of the ice core (Svensson et al, 2005). Due to the very high resolution especially the VS record shows a high degree of sub-annual variations which can make the identification of the annual layers more complicated.…”

“…It has also been shown that visible stratigraphy and variations in physical properties of the ice can reveal the annual layering Meese et al, 1997;Svensson et al, 2005).…”

Layer disturbances and the radio-echo free zone in ice sheets

“…The line-scan camera images 1-m segments of the ice core at a resolution of 0.1 mm with light (Svensson et al, 2005). While being moved along the core, the camera records light which is scattered by grain boundaries, air-bubbles and microparticles.…”

“…3) display the stratigraphy of high-scattering zones for light, called cloudy bands (CBs). They correlate with the impurity content of ice (Svensson et al, 2005) and we take them as a proxy for the layering of RES horizons.…”