Concentration and Size Distribution of Microparticles in the NGRIP Ice Core (Central Greenland) during the Last Glacial Period
The concentration and size distribution of mineral microparticles were investigated in the deep North Greenland Ice Core Project (NGRIP) ice core. The measurements were accomplished using a novel, optical detector which is based on laser light attenuation by individual particles. The device works on a flow-through basis, and together with sample preparation via continuous melting allows for very efficient analyses at high depth resolution. The presented work also covers the partial development and application of a continuous ice core melting setup as well as analytical systems of electrolytical conductivity and acidity. In the NGRIP ice core, the concentration of microparticles was found to be around 70 ¹g kg¡ 1 during Preboreal Holocene and 8000 ¹g kg¡ 1 during the last glacial maxi-mum (LGM). Strong variations of the insoluble particle mass were encountered corresponding to the Dansgaard/Oeschger (D/O) events within the last glacial period, with concentration changes by typically a factor of 8 across the rapid D/O transitions. The (Ca 2+ )/(insoluble microparticle) mass ratio was investigated in various selected core sections. Relatively low Ca contents were found concurring with high crustal concentrations. Such systematic variations were observed on long time scales (> 1000 years) and also on seasonal to multi-annual time scales. Strong enhancements of the (Ca 2+ )/(insoluble microparticle) ratio by up to a factor of 3 were found during volcanic events due to increased dissolution of CaCO3 by volcanic acids. These findings question the use of Ca 2+ as an unequivocal quantitative reference species for mineral dust. Systematic variations of the size distribution were observed with the tendency to-wards larger particles during colder climates. The lognormal mode of the volume distribution was found at about 1.3 ¹m during Preboreal Holocene and 1.7 ¹m during peak LGM. Size changes occurred largely synchronous with concentration changes.
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