Calibration of laser-light scattering measurements of dust concentration for Wisconsinan GISP2 ice using instrumental neutron activation analysis of aluminum: Results and discussion

In past work we used laser-light scattering (LLS) from bubble-free ice to measure how the dust concentration varied along the Wisconsinan (glacial) section of the Greenland Ice Sheet Project 2 (GISP2) ice core from central Greenland. In this paper we show how we calibrated this dust profile using instrumental neutron activation analysis (INAA) of aluminum. In the course of the calibration, we found that excluding NO₃^-, all the major impurities (soluble and insoluble) present in the ice covaried linearly. With respect to the dust concentration, we find that the LLS signal from ice below a depth of 2600 m follows a different linear trend than the LLS signal from shallow ice. We attribute this to the presence of numerous microbubbles (diameter < 0.3 mm) that emerged in the deeper ice following core extraction.