Overview of the chemical composition and characteristics of Na⁺ and Cl^– distributions in shallow samples from Antarctic ice core DF01 (Dome Fuji) drilled in 2001

抄録

Ice core samples record information about the geological history of the Earth, including past climate changes. Dome Fuji, situated at the highest point of Queen Maud Land, is considered one of the best drilling locations for procuring samples to reconstruct past climates and environments. We present here fundamental data on the concentrations of dissolved ions in shallow samples, between 7.7 m and 65.0 m depth, from the Dome Fuji ice core drilled in 2001. The measured anions were HCOO^–, CH₃COO^–, CH₃SO₃^–, F^–, Cl^–, NO₂^–, NO₃^–, SO₄^2–, C₂O₄^2–, and PO₄^3–, and the cations were Na⁺, K⁺, Mg²⁺, Ca²⁺, and NH₄⁺. The temporal resolution of the depth profiles of the ion concentrations was less than one year. No significant correlations were observed among the ions except between Na⁺ and Cl^–. The ion balance in the core, based on the averaged ion concentrations of the samples, was different to that of sea salt, a result consistent with the findings of previous studies. In several samples, however, synchronous concentration peaks of Na⁺ and Cl^– were identified, and the Cl^–/Na⁺ ratios of the corresponding samples were close to the sea salt ratio. This observation indicates the possibility that climate conditions were such that precipitation containing sea salt occurred in the Dome Fuji area. The Cl^–/Na⁺ ratio of samples that did not exhibit Na⁺ and Cl^– peaks in the depth profile differed from that previously reported for the covering snow. This result implies that Cl^–, but not Na⁺, was redistributed after deposition. High concentrations of SO₄^2– in some samples may account for this alteration of Cl^–/Na⁺ ratios. To interpret these observations and elucidate the climatic conditions, further studies, such as isotopic analyses of δ¹⁸O and δD, are required.