Glacial-interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-δ15N measurements
Glacial-interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-δ15N measurements
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DOI：
10.5194/cp-9-983-2013
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发表时间：
2013-01-01
影响因子：
4.3
通讯作者：
Prie, F.
中科院分区：
文献类型：
--
作者：
Capron, E.;Landais, A.;Prie, F.
正确估计雪锁深度是正确连接的气体和冰的冰芯研究年表的关键。在这里，两种方法来限制在南极洲的积雪深度演变的最后一次冰消期：积雪致密化模型的输出，和测量的N-15的N-2在空气中被困在冰芯，假设三角洲N-15只受重力分馏在积雪柱。由于积雪致密化过程在很大程度上取决于表面温度和积累速率，我们已经调查了四个冰芯钻在沿海（伯克纳岛，BI和詹姆斯罗斯岛，JRI）和半沿海（TALDICE和EPICA Dronning Maud Land，EDML）南极地区。结合EPICA Dome C（EDC）冰芯N-15的实测数据，研究区域的地表积雪速率和温度条件变化范围很大，N-15剖面揭示了积雪结构对冰期-间冰期气候变化的异质响应。虽然积雪致密化模拟正确地预测了TALDICE Δ N-15的变化，他们系统地未能捕捉到BI测量的大千年尺度三角洲N-15变化以及JRI和EDML测量的三角洲N-15冰川水平--这是以前报告的中东部南极冰芯的不匹配。（类似于41 ka）和最后一次冰消期不赞成的假设，一个大的对流区内的积雪作为解释的冰川积雪模型三角洲N-15数据不匹配的这个网站。虽然我们无法从现有的数据集进行深入的研究雪中的杂质的影响，我们的详细比较之间的三角洲N-15配置文件和积雪模型模拟不同的温度和积累率的情况下表明，积累率的作用可能被低估了在目前的描述的积雪模型。
Correct estimation of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice core studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: outputs of a firn densification model, and measurements of delta N-15 of N-2 in air trapped in ice core, assuming that delta N-15 is only affected by gravitational fractionation in the firn column. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI) and semi-coastal (TALDICE and EPICA Dronning Maud Land, EDML) Antarctic regions. Combined with available ice core air-delta N-15 measurements from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rates and temperature conditions.Our delta N-15 profiles reveal a heterogeneous response of the firn structure to glacial-interglacial climatic changes. While firn densification simulations correctly predict TALDICE delta N-15 variations, they systematically fail to capture the large millennial-scale delta N-15 variations measured at BI and the delta N-15 glacial levels measured at JRI and EDML - a mismatch previously reported for central East Antarctic ice cores.New constraints of the EDML gas-ice depth offset during the Laschamp event (similar to 41 ka) and the last deglaciation do not favour the hypothesis of a large convective zone within the firn as the explanation of the glacial firn model-delta N-15 data mismatch for this site. While we could not conduct an in-depth study of the influence of impurities in snow for firnification from the existing datasets, our detailed comparison between the delta N-15 profiles and firn model simulations under different temperature and accumulation rate scenarios suggests that the role of accumulation rate may have been underestimated in the current description of firnification models.