A calibrated climate record from Gibraltar speleothem: the instrumental era, the Holocene and the last interglacial

直布罗陀洞穴的校准气候记录：器乐时代、全新世和最后一次间冰期

• 批准号: NE/G004315/1
• 负责人: Timothy Atkinson
• 金额: $ 8.57万
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2009
• 资助国家: 英国
• 起止时间: 2009 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FG004315%2F1
• 关键词: calibrated; climate; record; Gibraltar; speleothem

Speleothems (stalagmites and flowstones) are carbonate minerals deposited from dripping water in caves. They represent rich archives of past rainfall and climate change. Speleothem growth layers can be dated at very high precision and the ratio of oxygen isotopes (d18O) in particular can be related to climatic conditions such as sources of moisture, temperature and amount of rainfall above each cave. These oxygen isotope records give much insight into climate change but interpretation still tends to rest on simple assumptions without detailed understanding of which features of local climate the speleothem responds to, and whether the recording is biased or altered during the process of speleothem growth. Unlocking the real climatic information needs understanding of the full system of climate - vegetation - groundwater - cave - speleothem. Thus climate reconstruction from speleothem records depends on two critical steps. The first is close monitoring of the cave environment to identify speleothem sites which record rainwater d18O with good fidelity, and the second is formulating a 'calibration' relating d18O to other aspects of climate. We aim to accomplish both steps and develop a 'fully-calibrated' climate record from Gibraltar covering parts of the last 200,000 years. Our recent work in New St Michaels Cave, located high up in the Rock of Gibraltar, focused on the first step - understanding the climate recording process by monitoring the part of the system between the soil and the speleothem, using comprehensive measurements and novel instruments. Working closely with the Gibraltar Caving Group we tracked monthly and seasonal variations in chemistry and oxygen isotopes in cave drips and soil water, plus the movement and composition of cave air, temperatures, soil and vegetation changes, and related these to amounts of rainfall and its daily isotopic composition. From all this we can deduce the causes of the seasonal isotopic and chemical cycles we have found in a recently deposited stalagmite, and relate relevant parts of the seasonal signal to the isotopic composition of rainfall during the winter months. A key result is that there are specific conditions when speleothems record climate most accurately, and if these are met the isotopic composition of rainfall can be reconstructed. In our new work we shall examine the second step - how the modern part of Gibraltar's historic climate record can be used to derive a calibrated 'transfer function' relating d18O to climate. We intend to test this calibration using stalagmite formed before 1962, when isotope records for rainfall began, by comparing the d18O in speleothem with the value calculated from statistical analysis of the historic climate back to 1792. Furthermore, because Gibraltar has been slowly uplifted by geological forces, caves have been elevated as speleothem grew. We shall investigate how this has affected the d18O-climate 'transfer function' and how the calibration from modern records may have to be adapted for application in more ancient times. To achieve this last objective we must compare the microclimate, air and water chemistry of low and high level caves to understand the controls on speleothem isotopes at different altitude. We shall then date and analyse stalagmites formed since the last interglacial for their isotope ratios, trace elements and water trapped within the mineral, which directly fingerprints ancient cave water. This should allow us to reconstruct the average tracks of rain-bearing systems in the Atlantic. Our overall objective is to produce a well-dated, calibrated record that will be a yardstick for past climates in the western Mediterranean, and can be compared directly with computer climate models. Gibraltar's caves have very high potential for providing a record from a 'natural laboratory' environment running back from modern times to possibly one million years ago.

洞穴石（石笋和流石）是由洞穴中滴水沉积的碳酸盐矿物。它们代表了过去降雨和气候变化的丰富档案。洞穴生长层的年代测定精度非常高，氧同位素的比值（d18O）尤其可以与气候条件有关，如每个洞穴上方的水分来源、温度和降雨量。这些氧同位素记录对气候变化提供了许多见解，但解释仍然倾向于建立在简单的假设上，而没有详细了解洞穴对当地气候的哪些特征作出反应，以及在洞穴生长过程中记录是否有偏差或改变。解开真正的气候信息需要了解气候-植被-地下水-洞穴-洞穴的完整系统。因此，从洞穴记录中重建气候取决于两个关键步骤。第一个是密切监测洞穴环境，以确定具有良好保真度记录雨水d18O的洞穴点；第二个是制定d18O与气候其他方面的“校准”。我们的目标是完成这两个步骤，并从直布罗陀开发一个“完全校准”的气候记录，涵盖过去20万年的部分时间。我们最近在位于直布罗陀岩石高处的新圣迈克尔斯洞穴进行的工作集中在第一步——通过使用综合测量和新型仪器，监测土壤和洞穴之间的系统部分，了解气候记录过程。我们与直布罗陀洞穴探险小组密切合作，追踪洞穴水滴和土壤水中化学和氧同位素的月度和季节性变化，以及洞穴空气的运动和组成、温度、土壤和植被的变化，并将这些与降雨量及其每日同位素组成联系起来。由此，我们可以推断出我们在最近沉积的石笋中发现的季节性同位素和化学循环的原因，并将季节性信号的相关部分与冬季月份降雨的同位素组成联系起来。一个关键的结果是，在特定的条件下，洞穴化石可以最准确地记录气候，如果满足这些条件，就可以重建降雨的同位素组成。在我们的新工作中，我们将研究第二步-如何使用直布罗陀历史气候记录的现代部分来推导关于d18O与气候的校准“传递函数”。我们打算用1962年以前形成的石笋（开始有降水同位素记录）来验证这一校准，将石笋中的d18O与1792年以来历史气候统计分析计算的值进行比较。此外，由于直布罗陀在地质力量的作用下缓慢上升，洞穴随着洞穴的增长而升高。我们将研究这是如何影响d180 - o气候“传递函数”的，以及现代记录的校准如何适应更古老时代的应用。为了实现最后一个目标，我们必须比较低海拔和高海拔洞穴的小气候、空气和水化学，以了解不同海拔对洞穴同位素的控制。然后，我们将测定和分析自最后一次间冰期以来形成的石笋的同位素比率、微量元素和矿物中捕获的水，这直接反映了古代洞穴水的特征。这将使我们能够重建大西洋降雨系统的平均轨迹。我们的总体目标是产生一个年代准确、经过校准的记录，它将成为西地中海过去气候的标尺，并可以直接与计算机气候模型进行比较。直布罗陀的洞穴非常有可能提供从现代到可能一百万年前的“自然实验室”环境的记录。

项目成果

Methane in underground air in Gibraltar karst

• DOI: 10.1016/j.epsl.2013.05.011
• 发表时间: 2013-07-15
• 期刊: EARTH AND PLANETARY SCIENCE LETTERS
• 影响因子: 5.3
• 作者: Mattey, D. P.;Fisher, R.;Fairchild, I. J.
• 通讯作者: Fairchild, I. J.

d(18) O analysis of organic compounds: problems with pyrolysis in molybdenum-lined reactors.

d(18) 有机化合物的 O 分析：钼衬里反应器中的热解问题。

• DOI: 10.1002/rcm.6356
• 发表时间: 2012
• 期刊: RCM
• 作者: Lombino A

Seasonal microclimate control of calcite fabrics, stable isotopes and trace elements in modern speleothem from St Michaels Cave, Gibraltar

• DOI: 10.1144/sp336.17
• 发表时间: 2010-01-01
• 期刊: TUFAS AND SPELEOTHEMS: UNRAVELLING THE MICROBIAL AND PHYSICAL CONTROLS
• 作者: Mattey, David P.;Fairchild, Ian J.;Durell, Richard
• 通讯作者: Durell, Richard