5:15 PM - 6:45 PM
[ACC27-P05] Dating and mineral dust analysis of a shallow ice core drilled at EGRIP, Greenland
Keywords:Greenland, ice core, mineral dust, size distribution
Temporal variations in concentration and size distribution of mineral dust on the Greenland ice sheet are associated with temporal variations in ground surface conditions on their source regions. For example, the decrease of snow-covered area in the Greenland coasts due to global warming can increase soil area, thus increase mineral dust supplied from the coasts. The mineral dust from distant regions (e.g., Asian arid regions) is dominated by fine mineral particles, while that from the coasts contains coarse mineral particles. Therefore, the analysis of coarse mineral dust concentration can allow us to evaluate the mineral dust supply from the coasts and the snow-covered and soil areas in the coasts. To reconstruct the past ground surface conditions in the source regions of mineral dust, we analyzed a shallow ice core drilled at the East Greenland Ice Core Project (EGRIP) site. In this study, we will report the results of dating and size distribution analysis of mineral dust.
The ice core was analyzed using a continuous-flow analysis (CFA) system at NIPR. Stable water isotope ratios (δ18O and δD) and elemental concentrations (Na, Mg, Al, Si, S, K, Ca, and Fe) were measured by a water isotope analyzer (Piccaro, L2130-i) and an ICP-MS (Agilent technologies, 7700), respectively. Assuming that S was derived completely from SO4, SO4 concentrations were calculated from the S concentrations. For mineral dust analyses, a portion of meltwater was collected using a fraction collector at a depth interval of 0.12 m. Concentrations and size distributions (0.7–18 μm) of mineral dust in the collected samples were measured by a Coulter counter (Beckman Coulter, Multisizer 4e). Additionally, for tritium measurements, ice core samples at depths of 13–15 m were cut and melted. Tritium measurements of the samples were conducted using a scintillation counter (ParkinElmer, Quantulus 1220).
For the dating of ice core, we conducted annual layer counting primarily based on the seasonal variation in Na. As fixed date layers, we used a tritium peak, volcanic layers, and ice layers. The tritium peak was found at a depth of 14.1 m, thus we treated this depth as 1963. The SO4 concentration showed sharp peaks at depths of 23.3 m, 39.8 m, 44.7 m, 83.7 m, and 105.5 m. We assumed those peaks to correspond to the eruptions of Katmai (1912), Tambora (1815), Laki (1783), Kuwae (1458), and Samalas (1257), respectively. The ice layers found at depths of 2.1 m and 27.3 m were assumed to correspond to the widespread surface melting of the Greenland ice sheet in 2012 and 1889, respectively. Based on these results, the ice core was estimated to cover the past approximately 1000 years.
The average size distribution of mineral dust mass concentrations showed an unimodal shape with a mode diameter of around 2 μm. Thus, it is suggested that the mineral dust deposited on EGRIP came mainly from distant source regions. The concentration of coarse mineral dust (> 5 μm) increased after 1600, suggesting that the mineral dust supply from the Greenland coasts increased after that year. In the presentation, we will also report the result of time-series analysis of fine mineral dust concentration (< 5 μm) and back-trajectory analysis.
The ice core was analyzed using a continuous-flow analysis (CFA) system at NIPR. Stable water isotope ratios (δ18O and δD) and elemental concentrations (Na, Mg, Al, Si, S, K, Ca, and Fe) were measured by a water isotope analyzer (Piccaro, L2130-i) and an ICP-MS (Agilent technologies, 7700), respectively. Assuming that S was derived completely from SO4, SO4 concentrations were calculated from the S concentrations. For mineral dust analyses, a portion of meltwater was collected using a fraction collector at a depth interval of 0.12 m. Concentrations and size distributions (0.7–18 μm) of mineral dust in the collected samples were measured by a Coulter counter (Beckman Coulter, Multisizer 4e). Additionally, for tritium measurements, ice core samples at depths of 13–15 m were cut and melted. Tritium measurements of the samples were conducted using a scintillation counter (ParkinElmer, Quantulus 1220).
For the dating of ice core, we conducted annual layer counting primarily based on the seasonal variation in Na. As fixed date layers, we used a tritium peak, volcanic layers, and ice layers. The tritium peak was found at a depth of 14.1 m, thus we treated this depth as 1963. The SO4 concentration showed sharp peaks at depths of 23.3 m, 39.8 m, 44.7 m, 83.7 m, and 105.5 m. We assumed those peaks to correspond to the eruptions of Katmai (1912), Tambora (1815), Laki (1783), Kuwae (1458), and Samalas (1257), respectively. The ice layers found at depths of 2.1 m and 27.3 m were assumed to correspond to the widespread surface melting of the Greenland ice sheet in 2012 and 1889, respectively. Based on these results, the ice core was estimated to cover the past approximately 1000 years.
The average size distribution of mineral dust mass concentrations showed an unimodal shape with a mode diameter of around 2 μm. Thus, it is suggested that the mineral dust deposited on EGRIP came mainly from distant source regions. The concentration of coarse mineral dust (> 5 μm) increased after 1600, suggesting that the mineral dust supply from the Greenland coasts increased after that year. In the presentation, we will also report the result of time-series analysis of fine mineral dust concentration (< 5 μm) and back-trajectory analysis.