High resolution studies of cosmogenic beryllium isotopes (10Be and 7Be) at Law Dome

Metadata record for data from AAS (ASAC) Project 3064.Public 10Be and 7Be are naturally-occurring radioactive isotopes produced in the Earth's atmosphere and surface by cosmic rays, at a rate controlled by the activity of the Sun (and other factors). 10Be is long-lived while 7Be 'decays' much more quickly. Using the Air-link we now have an opportunity to return ice core samples containing the short-lived 7Be isotope to Australia for measurement. This project proposes to use 10Be and 7Be measurements in Antarctic ice to improve our interpretation of past solar activity and better understand its linkage to global climate change.Project objectives:Cosmogenic 10Be (t1/2 = 1.5 x 10^6 years) from polar ice cores is the most reliable proxy for investigating past solar variability on decadal to millennial time scales [Muschler et al., 2007; Beer 2000]. However, interpretation of 10Be records is currently hindered by a poor understanding of the processes which deliver 10Be to the polar ice core archives [Muscheler et al., 2007; Bard and Frank, 2006]. The processes responsible for the transport and deposition of 10Be to the polar ice sheets must be understood in order to reconstruct an accurate history of solar activity.This project uses a new technique, based on the rapid sample transport capability of the Air-link, to examine transport and deposition of 10Be. The Air-link opens the opportunity to retrieve and return to Australia in a reasonable time frame, samples of the shorter-lived cosmogenic Be isotope, 7Be (t1/2 = 53 days), alongside the longer-lived 10Be. The 10Be/7Be ratio can then be interpreted as a 'lock' for air mass age providing valuable information on atmospheric pathways and residence times [Dibb et al., 1994].The project will collect six shallow (5 m) PICO cores from Dome Summit South (DSS) Law Dome. The samples will be delivered by plane at first opportunity to Hobart and then transferred directly to Australian Nuclear Technology Organisation (ANSTO) in Sydney for measurement of 7Be by gamma ray spectroscopy and 10Be by accelerator mass spectroscopy. There will be sufficient material for a high resolution record of 7Be spanning eight months and 10Be spanning four years.Scientific objectives of the project are as follows:1. Use the 10Be/7Be ratio to inform on atmospheric pathways, atmospheric residence times and stratosphere / troposphere exchange patterns responsible for 10Be transport and deposition to Law Dome.2. Constrain the seasonal cycle in 10Be and the timing, pervasiveness and origin of the summer maximum in 10Be concentrations.3. Work toward quantifying climate modulation of 10Be concentrations at Law Dome.4. Provide guidelines for improving the interpretation of solar activity from ice core records of 10Be.Taken from the 2008-2009 Progress Report:Progress against objectives:7 samples from a snow pit (S0-S6) along with 2 'blank' samples have been measured by gamma spectroscopy for 7Be and then by accelerator mass spectrometry (AMS) for 10Be. Additionally, between these two measurements aliquots were taken from each sample and measured by Inductively Coupled Plasma (ICP) Atomic Emission Spectroscopy (AES) at two separate laboratories for 9Be (carrier) concentration. As at 16th April 2009 this data is still under interpretation. The data appears to be of good quality and we hope that it will advance the scientific objectives. Taken from the 2009-2010 Progress Report:Progress against objectives:1. 6 samples from a 0.6m snow pit plus 3 associated 'blanks' were prepared and measured for 7Be by gamma spectroscopy. Aliquots were taken and measured for 9Be concentration by ICP-AES. These samples were then further processed and have been measured for 10Be/9Be by AMS on the ANTARES accelerator. A preliminary plot of the 7Be and 10Be concentrations and 7Be/10Be ratio is available on request. Interpretation of this record, and the record from the 08/09 season, is underway and will be advanced by modeling output from EACHAM5-HAM; Joel Pedro is arranging this with Ulla Heikkila (further discussions in Europe in June 2010). Furthermore, the AMS cathodes have been re-measured twice for 7Be/9Be by AMS on the ANTARES accelerator, following successful development of this new technique in April 2010.2. 19 samples from 3x 2.66m PICO plus 2 associated 'blanks' were processed and have been measured for 10Be/9Be by AMS on the ANTARES accelerator. AMS data analysis is essentially complete however full interpretation of this record requires age/depth chronology from del18O analysis. I believe that this will be finalised by the end of April. The 10Be/9Be data is of high quality and apparently confirms the expected seasonal signal.3. The two data sets mentioned above will further advance this objective.4. Comparison of the measured 10Be concentration in Law Dome ice and the neutron monitor record from McMurdo, along with recognition of seasonal signals at Law Dome, are providing guidelines for interpreting the recent solar activity record at this site. Further comparison with modelled data should permit extension to the palaeo-record.5. This objective has not yet been achieved.We have developed a unique, high resolution (~ monthly) long-term (since 2000) record of 10Be concentration in Antarctic ice. In recent years we have been able to add 7Be concentration data to this record.Continuation of this unique record is scientifically important, as is evident from the scientific objectives stated above. It was particularly important that our record included in 7Be and 10Be measurements from this unprecedented (at least during the instrumental period) epoch of low solar activity. This offers special (perhaps once in a lifetime) opportunity to better understand production, transport and deposition of cosmogenic beryllium into the Antarctic ice sheet.Taken from the 2010-2011 Progress Report:Progress against the stated Scientific objectives of the project:1. To study the production and deposition of 7Be and 10Be during the deepest solar minimum in nearly a century (and possibly as the Sun enters a new cycle), at high temporal resolution.Samples collected, 7Be and 10Be measurements completed, chronology and interpretation pending.2. Use the 10Be/7Be ratio to inform on atmospheric pathways, atmospheric residence times and stratosphere / troposphere exchange patterns responsible for 10Be transport and deposition to Law Dome.This is ongoing work, building particularly on the good data collected last season (09/10). Progress against this objective will intensify when Post Doctoral student Dr Ulla Heikkila commences work at ANSTO on 04/08/11. Dr Heikkila will be modelling the production, transport and deposition of 7Be and 10Be to Law Dome using the EACHAM5-HAM General Circulation Model. Work has already commenced on installing and running this model at ANSTO.3. Identify short-term spikes in 10Be and 7Be caused by solar proton events (SPE).The new data has not yet been scrutinised for such events.4. Further constrain the observed seasonal cycle in 10Be and the timing, pervasiveness and origin of the summer maximum in 10Be concentrations.Once the chronology becomes available this objective will be achieved.5. Work toward quantifying climate modulation of 10Be concentrations at Law Dome.Ongoing.6. Provide guidelines for improving the interpretation of palaeo-solar activity from ice core records of 10Be.Ongoing See the child record(s) for the data.

本数据集为AAS（ASAC）3064号项目的元数据记录。
10Be与7Be均为天然放射性同位素，由宇宙射线在地球大气及地表产生，其产生速率受太阳活动（及其他因素）调控。10Be为长寿命同位素，而7Be的衰变速度显著更快。依托Air-link项目，我们如今有机会将含有短寿命7Be同位素的冰芯样本运回澳大利亚开展检测。本项目提议通过分析南极冰芯中的10Be与7Be含量，优化对过去太阳活动的解读，并深入理解其与全球气候变化的关联。

### 项目目标
极地冰芯中的宇宙成因10Be（半衰期t1/2 = 1.5×10^6年）是研究十年至千年尺度太阳活动变化的最可靠代用指标[Muschler等，2007；Beer，2000]。然而，当前对10Be输送至极地冰芯档案的过程认知不足，制约了10Be记录的解读[Muscheler等，2007；Bard与Frank，2006]。若要准确重建太阳活动历史，必须明晰10Be输送并沉积至极地冰盖的相关过程。

本项目依托Air-link快速样本运输能力，采用新技术开展10Be输送与沉积过程研究。Air-link使我们能够在合理时限内获取并运回短寿命宇宙成因铍同位素7Be（半衰期t1/2 = 53天）的样本，与长寿命的10Be样本一同检测。随后可将10Be/7Be比值作为气团年龄的“锁定指标”，为大气路径与停留时间提供宝贵信息[Dibb等，1994]。

本项目将从劳穹顶（Law Dome）的南穹顶（Dome Summit South, DSS）采集6根5米浅表层PICO冰芯。样本将通过航班第一时间运往霍巴特，随后直接转送至悉尼的澳大利亚核科学技术组织（Australian Nuclear Science and Technology Organisation, ANSTO），分别通过γ射线能谱法检测7Be含量，通过加速器质谱法（accelerator mass spectroscopy, AMS）检测10Be含量。样本量足以构建覆盖8个月的高分辨率7Be记录，以及覆盖4年的10Be记录。

#### 项目科学目标
1. 利用10Be/7Be比值，解析驱动10Be输送并沉积至劳穹顶的大气路径、大气停留时间以及平流层/对流层交换模式。
2. 明确10Be的季节周期，以及10Be浓度夏季峰值的出现时间、普遍性与成因。
3. 尝试量化劳穹顶10Be浓度的气候调制效应。
4. 为优化基于10Be冰芯记录解读太阳活动的方法提供指导。

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摘自2008-2009年度进展报告：
#### 项目目标完成进展
已通过γ能谱法检测雪坑的7份样本（S0-S6）与2份“空白”对照样本的7Be含量，随后通过加速器质谱法检测其10Be含量。此外，在两次检测之间，从每份样本中提取等分试样，分别送至两家实验室通过电感耦合等离子体原子发射光谱法（Inductively Coupled Plasma Atomic Emission Spectroscopy, ICP-AES）检测9Be（载体）浓度。截至2009年4月16日，该数据仍处于解读阶段。现有数据质量良好，有望推进本项目的科学目标实现。

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摘自2009-2010年度进展报告：
#### 项目目标完成进展
1. 对0.6米雪坑采集的6份样本及3份配套空白对照样本进行前处理，通过γ能谱法检测7Be含量；提取等分试样通过ICP-AES检测9Be浓度。随后对样本进一步处理，通过ANTARES加速器的AMS检测10Be/9Be比值。7Be、10Be浓度及7Be/10Be比值的初步图谱可应要求提供。目前正在对本次记录与2008/2009季的记录进行解读，并将通过EACHAM5-HAM模式输出结果推进解读工作；Joel Pedro正与Ulla Heikkila协调此项工作（2010年6月在欧洲进行了进一步讨论）。此外，2010年4月该新技术成功开发后，已通过ANTARES加速器的AMS两次复测7Be/9Be比值。
2. 对3根2.66米PICO冰芯采集的19份样本及2份配套空白对照样本进行前处理，通过ANTARES加速器的AMS检测10Be/9Be比值。AMS数据分析已基本完成，但完整解读该记录需要基于δ18O分析得到的年龄-深度年代标尺。预计该标尺将于4月底最终确定。10Be/9Be数据质量优异，且明显验证了预期的季节信号。
3. 上述两套数据集将进一步推进本项目目标的实现。
4. 对劳穹顶冰芯中实测的10Be浓度与麦克默多站的中子监测器记录进行对比，结合劳穹顶观测到的季节信号，可为该站点的近期太阳活动记录解读提供指导。进一步与模式数据对比，有望将该方法拓展至古气候记录解读。
5. 本项目目标尚未达成。
我们已建立了一套独特的高分辨率（约每月一次）南极冰芯10Be浓度长期记录（自2000年起）。近年来，我们还为该记录补充了7Be浓度数据。
延续这套独特记录具有重要科学价值，正如前述科学目标所述。尤为关键的是，我们的记录需纳入本次前所未有的（至少在仪器观测时期）低太阳活动周期的7Be与10Be测量数据。这为我们提供了一次特殊的（或许一生仅一次）机会，以更深入理解宇宙成因铍在南极冰盖中的产生、输送与沉积过程。

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摘自2010-2011年度进展报告：
#### 针对本项目既定科学目标的完成进展
1. 以高时间分辨率研究近一个世纪以来最严重的太阳极小期（以及太阳可能进入新周期阶段）期间7Be与10Be的产生与沉积过程。
样本已采集完成，7Be与10Be的检测工作已结束，年代标尺构建与结果解读尚在进行中。
2. 利用10Be/7Be比值，解析驱动10Be输送并沉积至劳穹顶的大气路径、大气停留时间以及平流层/对流层交换模式。
本工作正在推进中，尤其基于上一季（2009/2010）采集的优质数据。博士后研究员Ulla Heikkila博士将于2011年8月4日入职ANSTO，届时本项目的相关工作将加快推进。Heikkila博士将使用EACHAM5-HAM大气环流模式，模拟7Be与10Be在劳穹顶的产生、输送与沉积过程。目前，该模式在ANSTO的安装与运行工作已启动。
3. 识别由太阳质子事件（solar proton events, SPE）引发的10Be与7Be短期峰值。
新数据集尚未针对此类事件进行详细排查。
4. 进一步明确观测到的10Be季节周期，以及10Be浓度夏季峰值的出现时间、普遍性与成因。
待年代标尺确定后，本项目目标即可达成。
5. 尝试量化劳穹顶10Be浓度的气候调制效应。
工作正在进行中。
6. 为优化基于10Be冰芯记录解读古太阳活动的方法提供指导。
工作正在进行中。
详情可查阅本数据集的子记录。