Volcanic ash in bare ice south of Sør Rondane Mountains, Antarctica: geochemistry, rock magnetism and nondestructive magnetic detection with SQUID gradiometer

Abstract

Nondestructive magnetic detection of tephra layers in ice cores will be an important method to identify and correlate stratigraphic horizons of ice bearing volcanic ash particles. Volcanic ash particles were extracted from tephra-bearing ice samples collected from Nansen Ice Field south of the Sør Rondane Mountains, Antarctica. Particles are fresh glassy volcanic ash with diameters of ~50 μm, and chemical composition of the matrix glass belongs to a low-K basaltic andesite group, ranging from SiO 2 60-62 wt% and K 2 O 0.40-0.50 wt%. Considering the grain size of ash particles and chemical composition of volcanic glass, the ash in tephra-bearing ice samples might be originated from the South Sandwich Islands located 2800 km northwest of the sampling sites. Correlations on major element concentrations with tephra layers associated with South Sandwich Islands in EPICA-Dome C, Vostok, and Dome Fuji ice cores show high similarity. Rock magnetic experiments show that the magnetic mineral is pseudo-single-domain titanomagnetite with ulvospinel content of 0.2-0.35 mixed with single-domain to superparamagnetic (titano)magnetite. Small blocks of the tephra-bering ice were measured with a SQUID gradiometer at 1-mm intervals with a spatial resolution of ~3 mm. With DC magnetic field of 25 mT, magnetic signal could be enhanced and detected for all the samples including the one with invisible amount of tephra particles. In order to simulate a thin ash layer in ice core, volcanic ash particles extracted from the tephra-bearing ice were used to fabricate a thin ash layer, which were subsequently magnetized, measured with the gradiometer. The noise level for Z axis gradiometer was about 0.6 pT. Detection limit for a half-cylinder with 29 mm radius and a thickness of 1 mm uniformly magnetized in X axis direction is ~9 × 10

Unravelling the high-altitude Nansen blue ice field meteorite trap (East Antarctica) and implications for regional palaeo-conditions

“…5a for location). By comparing the chemical composition of this volcanic ash with that of other ashes retrieved from major Antarctic ice cores, Oda et al (2016) proposed that the volcanic ashes in the northern part of Nansen C originate from the South Sandwich Islands (for details on geochemical composition ash layers, refer to Table 3 in Oda et al (2016)). The chemical composition of the ashes correlates particularly well with that of ashes from two post-LGM eruptions (see Table 4 in Oda et al (2016)):…”

Special issue on “Recent advances in environmental magnetism and paleomagnetism”

“…ARM increased slightly at water depths greater than 16 m. Although it is not clear whether the ARM carriers were the result of authigenic iron sulfide formation or the deposition of material suspended in the hypolimnion water layer, they suggest that the magnetic properties of the surficial sediments on the lake floor are controlled Open Access *Correspondence: hirokuni-oda@aist.go.jp 1 Geological Survey of Japan, Research Institute of Geology and Geoinformation, AIST, Tsukuba, Japan Full list of author information is available at the end of the article by both their location within the basin and the limnological stratification of the brackish lake water. Oda et al (2016) presented volcanic ash particles extracted from tephra-bearing ice samples collected from the Nansen Ice Field south of the Sør Rondane Mountains, Antarctica. Major element concentrations of the volcanic particles show high similarity with those of tephra layers associated with the South Sandwich Islands in the EPICA-Dome C, Vostok, and Dome Fuji ice cores.…”

Multimethod Approach to the Study of Recent Volcanic Ashes from Tengger Volcanic Complex, Eastern Java, Indonesia

“…Cicchino et al [10] measured the geochemistry, as well as the magnetic remanence and AMS (anisotropy of magnetic susceptibility), of two islands in the Aeolian Islands to improve the stratigraphic correlation between the deposits cropping out on these two islands. Oda et al [11] carried out rock magnetic and geochemical analyses on volcanic ash particles extracted from tephra-bearing ice samples collected from the Nansen Ice Field south of the Sør Rondane Mountains (Antarctica) and found that the magnetic mineral in the volcanic particles was titanomagnetite with an ulvöspinel content of 0.2-0.35 (in 0 to 1 scale). Oda et al [11] also compared the geochemistry of the volcanic ash with that of three tephra layers from three different locations in Antarctica and found that these samples had a high geochemical similarity.…”

“…Oda et al [11] carried out rock magnetic and geochemical analyses on volcanic ash particles extracted from tephra-bearing ice samples collected from the Nansen Ice Field south of the Sør Rondane Mountains (Antarctica) and found that the magnetic mineral in the volcanic particles was titanomagnetite with an ulvöspinel content of 0.2-0.35 (in 0 to 1 scale). Oda et al [11] also compared the geochemistry of the volcanic ash with that of three tephra layers from three different locations in Antarctica and found that these samples had a high geochemical similarity. The source of the tephra layers was suspected to be South Sandwich Island, located 2800 km from the Sør Rondane Mountains.…”