Model calculations of the age of firn air across the Antarctic continent
Model calculations of the age of firn air across the Antarctic continent
复制标题
南极大陆冷空气年龄的模型计算
DOI：
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
C. Brenninkmeijer
中科院分区：
文献类型：
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作者：
K. Kaspers;R. V. D. Wal;M. V. D. Broeke;J. Schwander;N.;P. M. V. Lipzig;C. Brenninkmeijer
南极洲在气孔关闭深度的降雪空气的年龄只在少数几个特定的地点已知，这些地点已经采集了降雪空气进行分析。我们提出了一个计算整个南极大陆气孔闭合深度的降雪空气年龄的模型。该模式基本采用4个气象参数(地面温度、气压、积累率和风速)作为输入。利用地面积雪密度、孔洞闭合密度和曲折度等参数，结合密度-深度模式和区域大气气候模式资料，确定了整个南极大陆的孔洞闭合深度分布。在东南极高原72°E，82°S附近，孔洞闭合深度最深，为15 0±15m(2σ)。气孔闭合深度处的CO2年龄用空气扩散模型计算。结果表明，最古老的降雪气体(CO2年龄)位于东经43°的富士穹顶、阿尔戈斯穹顶和沃斯托克之间，78°S年龄为148±23岁(1σ，2σ为38岁)。在这个位置，应该获得大气痕量气体记录。在这项研究中，我们以这个地点的痕量气体记录为例，表明可以以125年的预测长度记录到甲基氯。目前来自冰雪空气的最长记录来自南极，长达80年。敏感性试验表明，对于孔洞闭合深度为30%的模拟CO2年龄，具有古老降雪空气的地点(东南极高原)的估计不确定度(2σ)，对于具有较年轻降雪空气的地点(通常为40年)，估计不确定度约为40%。将模拟的孔洞闭合深度的CO2年龄与在7个地点直接测定的年龄进行比较，得到的相关系数为0.90，斜率接近1，表明尽管仍存在相当大的不确定性，但模拟结果的可信度很高。
The age of firn air in Antarctica at pore close-off depth is only known for a few specific sites where firn air has been sampled for analyses. We present a model that calculates the age of firn air at pore close-off depth for the entire Antarctic continent. The model basically uses four meteorological parameters as input (surface temperature, pressure, accumulation rate and wind speed). Using parameterisations for surface snow density, pore close-off density and tortuosity, in combination with a density-depth model and data of a regional atmospheric climate model, distribution of pore close-off depth for the entire Antarctic continent is determined. The deepest pore close-off depth was found for the East Antarctic Plateau near 72° E, 82° S, at 150±15 m (2σ). A firn air diffusion model was applied to calculate the age of CO 2 at pore close-off depth. The results predict that the oldest firn gas (CO 2 age) is located between Dome Fuji, Dome Argos and Vostok at 43° E, 78° S being 148±23 (1σ or 38 for 2σ) years old. At this location an atmospheric trace gas record should be obtained. In this study we show that methyl chloride could be recorded with a predicted length of 125 years as an example for trace gas records at this location. The longest record currently available from firn air is derived at South Pole, being 80 years. Sensitivity tests reveal that the locations with old firn air (East Antarctic Plateau) have an estimated uncertainty (2σ) for the modelled CO 2 age at pore close-off depth of 30% and of about 40% for locations with younger firn air (CO 2 age typically 40 years). Comparing the modelled age of CO 2 at pore close-off depth with directly determined ages at seven sites yielded a correlation coefficient of 0.90 and a slope close to 1, suggesting a high level of confidence for the modelled results in spite of considerable remaining uncertainties.