Delta15N measurements as a calibration tool for the paleothermometer and gas-ice age differences : A case study for the 8200 B.P. event on GRIP ice
Delta15N measurements as a calibration tool for the paleothermometer and gas-ice age differences : A case study for the 8200 B.P. event on GRIP ice
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Delta15N 测量作为古温度计和气冰年龄差异的校准工具：8200 B.P. 的案例研究
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发表时间：
1999
期刊：
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通讯作者：
J. Schwander
中科院分区：
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作者：
M. Leuenberger;C. Lang;J. Schwander
建立了冰芯中大气氮（δ 15 N）的同位素组成测量方法，作为重力富集的指示剂。最近，发现热扩散在大的温度波动期间对该参数具有显著影响[Severinghaus等人，1998年]。在这里，我们提出的结果8200 B. P.事件，最大的温度漂移在全新世，这巩固了这一观点，并将其扩展到中期的温度变化。热扩散分量约占该事件重力富集的三分之一。这一冷却事件的短暂性并不显著影响重力富集，这一点由相当恒定的封闭深度所证明。因此，δ 15 N残差可直接用于估算温度变化，从而标定古温度计。由于我们的δ 15 N记录可以解决几十年的温度变化，它补充了钻孔温度测量的校准技术，其分辨率随着年龄的增加而迅速下降。我们得到δ 18 Oice与温度的关系为0.30±0.11‰/K，与寒冷期的时间相关性（约0.30‰/K）很好地吻合，明显低于现今格陵兰的空间关系（0.67‰/K）。这对应于格陵兰中部8200 B. P.事件的地表温度变化范围在5.4和11.7 K之间，最佳估计为7.4 K。通过将δ 15 N变化与δ 18 Oice变化相匹配，我们估计平均气-冰年龄差为−209±15年，这与模型估计的结果非常一致。
Isotopic composition measurement on atmospheric nitrogen (δ15N) trapped in ice cores is established as a gravitational enrichment indicator. Recently, it was discovered that thermal diffusion has a significant influence on this parameter during periods of large temperature fluctuations [Severinghaus et al., 1998]. Here we present results for the 8200 B.P. event, the largest temperature excursion during the Holocene, which underpin this view and extend it to medium-range temperature changes. The thermal diffusion component is about one third of the gravitational enrichment for this event. The shortness of this cooling event does not significantly affect the gravitational enrichment as documented by rather constant close-off depths. Therefore the δ15N residuals can be directly used to estimate temperature changes, hence calibrating the paleothermometer. Since our δ15N record can resolve temperature variations as short as a few decades, it complements the calibration technique of borehole temperature measurements, for which the resolution decreases rapidly with increasing age. We obtained a relation δ18Oice- temperature of 0.30±0.11‰/K, which agrees nicely with the temporal dependence for cold periods (about 0.30‰/K) and is significantly lower than today's Greenland spatial relation (0.67‰/K). This corresponds to a range of the surface temperature shift for the 8200 B.P. event in Central Greenland between 5.4 and 11.7 K, with a best estimate of 7.4 K. By matching the δ15N variations with δ18Oice variations we estimate the mean gas-ice age difference to be −209±15 years, which is in good agreement with model estimates.