Ryo Inoue, Shuji Fujita, K. Kawamura, Ikumi Oyabu, F. Nakazawa, Hideaki Motoyama, T. Aoki
{"title":"南极洲富士圆顶附近近地表杉林垂直密度和微观结构剖面的空间分布","authors":"Ryo Inoue, Shuji Fujita, K. Kawamura, Ikumi Oyabu, F. Nakazawa, Hideaki Motoyama, T. Aoki","doi":"10.5194/tc-18-425-2024","DOIUrl":null,"url":null,"abstract":"Abstract. To better understand the near-surface evolution of polar firn in low-accumulation areas (<30 mm w.e. yr−1), we investigated the physical properties – density, microstructural anisotropy of ice matrix and pore space, and specific surface area (SSA) – of six firn cores collected within 60 km of Dome Fuji, East Antarctica. The physical properties were measured at intervals of ≤0.02 m over the top 10 m of the cores. The main findings are (i) a lack of significant density increase in the top ∼4 m, (ii) lower mean density near the dome summit (∼330 kg m−3) than in the surrounding slope area (∼355 kg m−3) in the top 1 m, (iii) developments of a vertically elongated microstructure and its contrast between layers within the top ∼3 m, (iv) more pronounced vertical elongation at sites and periods with lower accumulation rates than those with higher accumulation rates, (v) a rapid decrease in SSA in the top ∼3 m, and (vi) lower SSA at lower-accumulation sites, but this latter trend is less pronounced than that of microstructural anisotropy. These observations can be explained by a combination of the initial physical properties on the surface set by wind conditions and the metamorphism driven by water vapor transport through the firn column under a strong vertical temperature gradient (temperature gradient metamorphism, TGM). The magnitude of TGM depends on the duration of firn layers under the temperature gradient, determined by the accumulation rate; longer exposure causes a more vertically elongated microstructure and lower SSA. Overall, we highlight the significant spatial variability in the near-surface physical properties over the scale of ∼100 km around Dome Fuji. These findings will help us better understand the densification over the whole firn column and the gas-trapping process in deep firn and possible difference in them between existing deep ice cores and the upcoming “Oldest-Ice” cores collected tens of kilometers apart.\n","PeriodicalId":509217,"journal":{"name":"The Cryosphere","volume":"93 2","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2024-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Spatial distribution of vertical density and microstructure profiles in near-surface firn around Dome Fuji, Antarctica\",\"authors\":\"Ryo Inoue, Shuji Fujita, K. Kawamura, Ikumi Oyabu, F. Nakazawa, Hideaki Motoyama, T. Aoki\",\"doi\":\"10.5194/tc-18-425-2024\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"Abstract. To better understand the near-surface evolution of polar firn in low-accumulation areas (<30 mm w.e. yr−1), we investigated the physical properties – density, microstructural anisotropy of ice matrix and pore space, and specific surface area (SSA) – of six firn cores collected within 60 km of Dome Fuji, East Antarctica. The physical properties were measured at intervals of ≤0.02 m over the top 10 m of the cores. The main findings are (i) a lack of significant density increase in the top ∼4 m, (ii) lower mean density near the dome summit (∼330 kg m−3) than in the surrounding slope area (∼355 kg m−3) in the top 1 m, (iii) developments of a vertically elongated microstructure and its contrast between layers within the top ∼3 m, (iv) more pronounced vertical elongation at sites and periods with lower accumulation rates than those with higher accumulation rates, (v) a rapid decrease in SSA in the top ∼3 m, and (vi) lower SSA at lower-accumulation sites, but this latter trend is less pronounced than that of microstructural anisotropy. These observations can be explained by a combination of the initial physical properties on the surface set by wind conditions and the metamorphism driven by water vapor transport through the firn column under a strong vertical temperature gradient (temperature gradient metamorphism, TGM). The magnitude of TGM depends on the duration of firn layers under the temperature gradient, determined by the accumulation rate; longer exposure causes a more vertically elongated microstructure and lower SSA. Overall, we highlight the significant spatial variability in the near-surface physical properties over the scale of ∼100 km around Dome Fuji. 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引用次数: 0
摘要
摘要为了更好地了解低积累区(<30 mm w.e. yr-1)极地杉岩的近地表演化,我们研究了在南极洲东部富士圆顶60千米范围内采集的6个杉岩岩心的物理性质--密度、冰基质和孔隙空间的微结构各向异性以及比表面积(SSA)。物理特性是在岩芯顶部 10 米处以 ≤0.02 米的间隔测量的。主要发现有:(i) 顶部∼4 米的密度没有明显增加;(ii) 穹顶顶附近顶部 1 米的平均密度(∼330 kg m-3)低于周围斜坡区域(∼355 kg m-3);(iii) 垂直拉长的微观结构及其顶部∼3 米内各层之间的对比发展、(iv)在堆积率较低的地点和时期,垂直伸长比在堆积率较高的地点和时期更为明显;(v)在顶部 ∼3 m,SSA 快速下降;(vi)在堆积率较低的地点,SSA 较低,但后一种趋势不如微结构各向异性的趋势明显。这些观测结果可以解释为:由风力条件设定的地表初始物理性质,以及在强烈的垂直温度梯度(温度梯度变质作用,TGM)作用下,通过枞树柱的水汽输送驱动的变质作用。温度梯度变质的程度取决于枞树层在温度梯度下的持续时间,由累积率决定;暴露时间越长,微观结构的垂直伸长越大,SSA越低。总之,我们强调了富士圆顶周围∼100 km范围内近地表物理特性的显著空间变化。这些发现将有助于我们更好地理解整个枞树柱的致密化和深层枞树的气体捕集过程,以及现有深冰芯和即将采集的相距数十公里的 "最老冰 "芯之间可能存在的差异。
Spatial distribution of vertical density and microstructure profiles in near-surface firn around Dome Fuji, Antarctica
Abstract. To better understand the near-surface evolution of polar firn in low-accumulation areas (<30 mm w.e. yr−1), we investigated the physical properties – density, microstructural anisotropy of ice matrix and pore space, and specific surface area (SSA) – of six firn cores collected within 60 km of Dome Fuji, East Antarctica. The physical properties were measured at intervals of ≤0.02 m over the top 10 m of the cores. The main findings are (i) a lack of significant density increase in the top ∼4 m, (ii) lower mean density near the dome summit (∼330 kg m−3) than in the surrounding slope area (∼355 kg m−3) in the top 1 m, (iii) developments of a vertically elongated microstructure and its contrast between layers within the top ∼3 m, (iv) more pronounced vertical elongation at sites and periods with lower accumulation rates than those with higher accumulation rates, (v) a rapid decrease in SSA in the top ∼3 m, and (vi) lower SSA at lower-accumulation sites, but this latter trend is less pronounced than that of microstructural anisotropy. These observations can be explained by a combination of the initial physical properties on the surface set by wind conditions and the metamorphism driven by water vapor transport through the firn column under a strong vertical temperature gradient (temperature gradient metamorphism, TGM). The magnitude of TGM depends on the duration of firn layers under the temperature gradient, determined by the accumulation rate; longer exposure causes a more vertically elongated microstructure and lower SSA. Overall, we highlight the significant spatial variability in the near-surface physical properties over the scale of ∼100 km around Dome Fuji. These findings will help us better understand the densification over the whole firn column and the gas-trapping process in deep firn and possible difference in them between existing deep ice cores and the upcoming “Oldest-Ice” cores collected tens of kilometers apart.