High-resolution microparticle profiles at NorthGRIP, Greenland: Case studies of the calcium-dust relationship

Abstract

A novel flow-through microparticle detector was deployed concurrently with continuous flow analyses of major ions during the North Greenland Icecore Project 2000 field season. The easy-handling detector performs continuous counting and sizing. In this deployment the lower size-detection limit was conservatively set to 1.0 μm equivalent spherical particle diameter, and a depth resolution of ≤1 cm was achieved for microparticle concentrations. The dust concentration usually followed the Ca2+ variability. Here results are presented from an inspection of the Ca/dust mass ratio in 23 selected intervals, 1.65 m long each, covering different climatic periods including Holocene and Last Glacial Maximum (LGM). A (Ca2+)/(insoluble dust) mass ratio of 0.29 was found for the Holocene and 0.11 for LGM. Changes to the Ca/dust ratio occur on an annual to multi-annual time-scale exhibiting the same pattern, i.e. a lower Ca/dust ratio for higher crustal concentrations. Moreover, the Ca2+/dust ratio may increase significantly during episodic events such as volcanic horizons due to enhanced dissolution of CaCO3. This calls into question the notion of deploying Ca2+ as a quantitative mineral dust reference species and shows the importance of variable source properties or fractionating processes during transport and deposition.