青藏高原冰芯定年方法回顾及新技术展望

冰芯高分辨率高保真地记录了过去不同时间尺度气候环境变化历史,而冰芯精确定年是重建过去气候环境演化的先决条件。通过回顾青藏高原冰芯定年的常用方法,提出了目前冰芯定年仍存在的挑战和机遇。通常的冰芯定年方法包括基于冰芯季节变化信号的数年层方法、放射性标志层定年、冰川流动模型、基于其他已知时间序列的对比定年,以及放射性同位素定年。最可靠的方法是数年层的方法,但受到冰川中下部年层逐渐减薄的制约,冰川流动模型主要应用于冰芯中下部定年,但存在不确定性较大而且难以验证的难题。未来冰芯学科发展对冰芯定年提出了更高要求,随着测量技术与手段的突破,新的方法与技术开始在极地冰芯与高山冰芯定年研究中展示了广泛的应用前景。冰芯连续测量技术（如冰芯同位素连续测量技术、激光剥蚀等离子体质谱技术）大幅度提高了冰芯测量结果的时间精度,有可能把数年层的定年方法延推到冰芯底部;基于“原子阱痕量分析”（Atom Trap Trace Analysis,ATTA）的惰性气体（⁸⁵Kr、⁸¹Kr、³⁹Ar）放射性测年技术是一项革命性的技术,由于惰性气体在大气中的稳定性与均匀性使其在不同时间尺度冰川冰的绝对定年中发挥出优势。低浓度的可溶性有机碳的¹⁴C定年也从实验室探索阶段开始转入试用阶段,而且用冰量低,有望解决冰芯中碳含量低,定年困难的窘迫状况。此外,人类活动影响之前处于自然背景下的冰芯³H低本底测量技术结合数据处理方法,有望恢复过去100~200年与太阳活动周期相关的信号,将补充放射性标志层只有近代结果的不足。这些新的技术与方法在冰芯定年中的应用有望进一步推动中低纬度高山冰芯研究。     

青藏高原冰芯定年方法回顾及新技术展望北大核心CSCD

冰芯高分辨率高保真地记录了过去不同时间尺度气候环境变化历史,而冰芯精确定年是重建过去气候环境演化的先决条件。通过回顾青藏高原冰芯定年的常用方法,提出了目前冰芯定年仍存在的挑战和机遇。通常的冰芯定年方法包括基于冰芯季节变化信号的数年层方法、放射性标志层定年、冰川流动模型、基于其他已知时间序列的对比定年,以及放射性同位素定年。最可靠的方法是数年层的方法,但受到冰川中下部年层逐渐减薄的制约,冰川流动模型主要应用于冰芯中下部定年,但存在不确定性较大而且难以验证的难题。未来冰芯学科发展对冰芯定年提出了更高要求,随着测量技术与手段的突破,新的方法与技术开始在极地冰芯与高山冰芯定年研究中展示了广泛的应用前景。冰芯连续测量技术(如冰芯同位素连续测量技术、激光剥蚀等离子体质谱技术)大幅度提高了冰芯测量结果的时间精度,有可能把数年层的定年方法延推到冰芯底部;基于“原子阱痕量分析”(Atom Trap Trace Analysis,ATTA)的惰性气体(Kr、Kr、Ar)放射性测年技术是一项革命性的技术,由于惰性气体在大气中的稳定性与均匀性使其在不同时间尺度冰川冰的绝对定年中发挥出优势。低浓度的可溶性有机碳的14C定年也从实验室探索阶段开始转入试用阶段,而且用冰量低,有望解决冰芯中碳含量低,定年困难的窘迫状况。此外,人类活动影响之前处于自然背景下的冰芯3H低本底测量技术结合数据处理方法,有望恢复过去100~200年与太阳活动周期相关的信号,将补充放射性标志层只有近代结果的不足。这些新的技术与方法在冰芯定年中的应用有望进一步推动中低纬度高山冰芯研究。     

青藏高原东缘盐源盆地古近纪风成沙丘及其古地理意义*

盐源盆地始新世丽江组沉积时期发育了一套具大型高角度交错层理的红色砂岩,其确切成因对于厘定青藏高原东缘古近纪古地理格局、恢复东亚新生代干旱带与古气候演化过程具有重要意义。文中通过对盐源盆地始新统丽江组红色砂岩的沉积特征进行系统分析,证明该套砂岩的岩性、粒度分布、石英颗粒表面特征与沉积构造等明显不同于水成沉积,而与典型风成沙丘相应特征完全一致,表明其为风成沙丘沉积。结合古近纪研究区的古气候条件、大气环流样式与大地构造背景,笔者进一步推断盐源盆地始新世风成沙丘可能沉积于中国古近纪干旱带内的沙漠环境。根据目前相关研究资料,确认青藏高原东缘存在一个厚度稳定的古近纪风成沙丘富集带。     

青藏高原古里雅冰帽冰碛和冰水沉积物粒度特征及其意义

冰冻圈演化不仅与青藏高原水塔变化、地表侵蚀风化及荒漠化密切相关,还深刻影响着亚洲季风系统和全球气候,冰碛物的粒度组成可以为冰冻圈演化提供重要信息,但高原冰碛物的特征粒度组成及其形成机理仍不清楚,高原冰碛物与高原冷黄土及河湖沉积物的关系也不明确。为此,选择青藏高原最大的冰帽——古里雅冰帽的冰碛物及系列冰水沉积物,开展系统粒度组成研究。研究发现:自终碛到冰川前端冰水扇及下游河流冰水沉积均表现出特征的双峰模态,即1～3φ(500～125μm)的中细砂峰和6～8φ(16～4μm)的细粉砂峰,前者可能由冰川压碎、寒冻风化崩裂作用造成,后者由冰川研磨作用形成,并受到源区基岩岩性软弱和组成颗粒大小的影响。冰川磨蚀的细粉砂组分含量,从冰碛物经冰水扇、河流到湖滩沉积物整体呈现减小趋势,粗粉砂在湖滩沉积中几乎完全被风吹走,粗粉砂直接成为下游黄土的物源并富集其中成为黄土特征组分,水流分选在开口湖泊中产生粗、细粉砂的明显富集,这些证据揭示出,无论是与冰川发育相关的尾闾湖沉积还是近源、远源的青藏高原及周边黄土沉积,其粉砂组成和来源,均可为高原冰冻圈的形成演化提供重要信息。     

Luminescence-dated aeolian deposits of late Quaternary age in the southern Tibetan Plateau and their implications for landscape history

Aeolian deposits are widely distributed in the interior of the Tibetan Plateau, and their chronology is poorly known. It is not yet clear whether they accumulated only after the last deglaciation, or over a longer time. We applied quartz OSL dating to aeolian samples from the Lhasa area with OSL ages ranging from 2.9 ± 0.2 to at least 118 ± 11 ka. The probability density frequency (PDF) distribution of 24 ages reveals age clusters at about 3, 8, 16–21, 33, and 79–83 ka, indicating enhanced sediment accumulation then. The results show that aeolian deposition occurred throughout most of the last 100 ka. This implies that: 1) an ice sheet covering the whole Tibetan Plateau during the last glacial maximum (LGM) could not have existed; and 2) erosion during the last deglaciation was not as strong as previously proposed, such that not all pre-Holocene loess was removed. The age distribution shown in the PDF indicates that aeolian accumulation is episodic. Sand-formation events revealed by age clusters at 3, 8, and 16–21 ka imply roughly synchronous environmental responses to corresponding global-scale arid events.     

青藏高原纳木错西缘新元古代中期岩浆事件:对北拉萨地块起源的约束

本文报道了青藏高原北拉萨地块纳木错西缘变质辉长岩和花岗片麻岩的锆石U-Pb定年、岩石地球化学和锆石Hf同位素分析结果。锆石LA-ICP-MS定年结果表明,变质辉长岩和花岗片麻岩的原岩形成时代分别为720±6Ma和732±7Ma,相当于新元古代中期。变质辉长岩为钙碱性系列,具有Nb、Ta和Ti负异常,与岛弧玄武岩类似。变质辉长岩中锆石具有较高的εHf(t)值(+5. 2～+9. 7),应当是源自俯冲环境下相对亏损的地幔楔。花岗片麻岩原岩为I型花岗质岩石,并且具有较为均一的锆石εHf(t)值(-3. 3～+0. 3),可能形成于地壳内古元古代变质火成岩的部分熔融作用。结合区域地质资料,变质辉长岩和花岗片麻岩的原岩应当形成于新元古代中期的洋壳俯冲消减过程。北拉萨地块上的前寒武纪岩浆和变质记录与东非造山带的活动时限较为一致,因而北拉萨地块可能与东非造山带具有亲缘性。     

青藏高原安多高压麻粒岩同位素年代学研究

本文报道了聂荣微陆块中新发现的高压麻粒岩锆石U-Pb定年结果及其围岩花岗片麻岩中黑云母Ar-Ar同位素年代学结果.高压麻粒岩中的锆石可分为两类,第一类具有核-边显微结构,核部残留锆石具典型岩浆结晶锆石特征,锆石U-Pb年龄541±8Ma～ 834±11Ma;第二类锆石具典型的变质锆石成因的结构特征,锆石U-Pb谐和年龄为179.0±1.7Ma.花岗片麻岩中黑云母Ar-Ar坪年龄为166.7±1.1Ma.年代学资料显示麻粒岩与其围岩均具有泛非期的年龄信息,麻粒岩的原岩经历了晚元古代-早古生代造山作用,并于早-中侏罗世发生了峰期高压变质作用改造,该变质事件可能代表着聂荣微陆块与羌南板块的碰撞拼合.伴随着早-中侏罗世的岩浆作用,麻粒岩及其围岩迅速抬升,抬升的时间跨度在13Myr左右,于166.7Ma左右抬升至地壳浅层部位或近地表.     

青藏高原腹地典型岩体热历史与构造—地貌演化过程的热年代学分析

通过对青藏高原腹地不同构造部位的班戈、雄梅、羊八井、拉萨花岗岩和甲岗、曲水花岗闪长岩的热年代学分析，剖析了青藏高原腹地构造－热事件与构造－地貌演化过程。结果表明，青藏高原腹地自中生代中、晚期以来发生4期重大区域性构造－热事件，包括121－116Ma沿班公－怒江缝合带发生的强烈中酸性岩浆侵位事件、93－45Ma沿雅鲁藏布江缝合带北缘发生的强烈中酸性岩浆侵位事件和随后发生于78－40Ma的快速隆升事件、25－15Ma沿冈底斯构造－岩浆带发生的强烈构造隆升事件及8－6．5Ma以来在拉萨地块中部发生的区域性伸展裂陷－差异隆升事件。区域性剥蚀夷平事件主要发生于40－25Ma与15－8Ma，区域性整体隆升主要发生在中新世早、中期即25－8Ma，区域性伸展裂陷与差异升降事件的开发时代约为8－6．5Ma。     

青藏高原唐古拉哈日钦冰芯表层和深层可培养细菌特征

对唐古拉哈日钦冰芯表层0.04~3.04 m及深层127.44~130.36 m中可培养细菌进行了对比研究。发现表层和深层可培养细菌数没有表现出显著差异性,表层冰芯中可培养细菌数为0~9.8×10³ CFU·mL^-1,略高于深层冰芯的0~8.4×10³ CFU·mL^-1。表层冰芯中微生物总数为10³~10⁶ cells·mL^-1,深层冰芯中微生物总数为10²~10³ cells·mL^-1。冰芯中可培养细菌属于Firmicutes（厚壁菌门）、Proteobacteria（变形菌门）、Actinobacteria（放线菌门）、Bacteroidetes（拟杆菌门）和Deinococcus-Thermus（异常球菌门） 5大类。但表层和深层可培养细菌属于不同的优势门,表层为Proteobacteria（38%）,深层为Firmicutes（42%）。表层和深层优势属均为Bacillus（芽孢杆菌属）,占比分别为18%和29%。已有研究表明哈日钦冰芯98.8 m达到了公元1000年的历史记录,因此对比千年尺度上可培养细菌数量及多样性的差异,能够为进一步发掘新基因,丰富微生物多样性,为了解可培养细菌的进化历史奠定基础。     

青藏高原西北缘第四纪火山岩的年龄、地球化学特征及意义

对青藏高原西北缘普鲁北钾质火山岩进行40Ar-39Ar定年得到的最新年龄为0.81Ma±0.21Ma。火山岩的SiO2含量为53.08%~55.12%,全碱含量为7.36%~8.04%,K2O/Na2O比值为1.17~1.2,属橄榄安粗岩系列。岩石以高度富集LREE、LILE(K、Rb、Sr、Ba、Th等)和高度亏损HREE、HFSE(Nb、Ta、Ti等)元素为特征。岩石具高的(87Sr/86Sr)i比值(0.7088~0.7089)和低的εNd值(-6.05~-5.54),表明火山岩源区为EMⅡ型的经古俯冲作用改造的大陆岩石圈富集地幔。同时,其Ti/Y、Zr/Y、La/Rb、Zr/Rb、K/La、Pb/La比值类似于板内洋岛玄武岩(OIB),可能暗示岩浆源区经历过软流圈流体或者深部流体对古俯冲地幔楔的叠加交代作用。普鲁北钾质火山岩为青藏高原西北缘晚新生代陆-陆碰撞造山深部岩石圈拆沉作用在地表响应的岩浆产物。     

青藏高原西北缘第四纪火山岩的年龄、地球化学特征及意义

对青藏高原西北缘普鲁北钾质火山岩进行40Ar-39Ar定年得到的最新年龄为0.81Ma±0.21Ma.火山岩的SiO2含量为53.08%～55.12%,全碱含量为7.36～8.04%,K2O/Na2O比值为1.17～1.2,属橄榄安粗岩系列.岩石以高度富集LREE、LILE(K、Rb、Sr、Ba、Th等)和高度亏损HR...     

NOAA IMS雪冰产品在青藏高原积雪监测中的适用性分析

在系统评估青藏高原积雪观测典型气象站历史定位坐标精度基础上,利用站点雪深资料对NOAA IMS 4 km和1 km分辨率雪冰产品在青藏高原的精度和适用性进行了验证和评估,定量分析了IMS 4 km到1 km空间分辨率提高和气象站历史定位与GPS定位坐标之间的差异对青藏高原IMS积雪监测精度的影响。结果表明：青藏高原个别气象站历史坐标与当前GPS接收机定位之间存在较大的差异,如安多气象站经度偏小0.6°,纬度偏大0.08°。IMS 4 km雪冰产品在青藏高原的总精度介于76.4%~83.2%,平均为80.1%,积雪分类精度介于35.8%~60.7%,平均为47.2%,平均误判率为17.1%,平均漏判率为45.5%,总体上呈现地面观测的积雪日数越多、平均雪深越大,其总体监测精度越低,而积雪分类精度越高的特点。IMS分辨率从4 km到1 km总体精度平均提高了2.9%,积雪分类精度平均提高了0.9%,主要是由于个别站点的精度提升较大引起的,对高原多数台站积雪监测精度的改进和提升很小。除个别台站外,目前气象站历史坐标和GPS定位坐标之间的差异,对IMS 4 km积雪监测精度验证结果没有影响。然而,今后随着卫星遥感技术的发展,更高时空分辨率的遥感积雪产品将用于积雪监测和研究,精确的地面观测站坐标信息是对这些遥感数据开展精度验证与实际应用的前提。     

青藏高原那曲中部土壤温湿分布特征

青藏高原土壤水热状况对气候变化和植被退化方面的研究具有重要意义,土壤湿度的准确刻画还会影响到数值预报模式对当地及其下游地区降水的模拟能力。为此,采用中国科学院那曲高寒气候环境观测研究站安多观测点2014年1—12月的土壤温度、土壤湿度观测资料以及同期安多气象站观测数据,分析了青藏高原那曲中部不同深度土壤温湿度的分布特征及其与气温、降水量等气象要素的关系。结果表明：土壤温度在浅层为正弦曲线,随着土壤深度的增加,曲线逐渐接近直线。土壤升温迅速而降温过程缓慢。封冻和解冻日期随土壤深度的增加而推迟,封冻期逐渐缩短。不同层次土壤湿度日内变化较小。月变化呈单峰型结构,峰值和谷值基本出现在8月和12月。土壤湿度上升速率较下降速率缓慢。区域尺度上GLDAS-NOAH资料显示出类似的变化特征。土壤温湿度在一年中的变化不一致,但土壤温湿度呈显著正相关。浅层土壤的温度梯度明显大于深层;浅层土壤湿度最大,中间层较大,深层土壤湿度最小。随着干季向湿季的转换,由于太阳辐射的增加,非绝热加热呈增加的趋势。土壤湿度与气象要素在不同时段的相关性存在一些差异,但总体上土壤湿度与气温、降水量和相对湿度呈正相关,与风速、日照时数相关性不显著。     

青藏高原初春积雪的多尺度变化与北大西洋海温的关系

青藏高原冬、春季积雪变化影响东亚甚至全球春、夏季的环流及气候异常。利用中国西部环境与生态科学数据中心提供的中国雪深长时间序列数据集,美国大气海洋局提供的全球逐月扩展重建海表温度,以及欧洲中期天气预报中心提供的逐月再分析数据,对青藏高原初春（3、4月）积雪的多尺度变化与北大西洋海表温度的关系进行了研究。结果表明,初春青藏高原雪深异常与初春北大西洋关键区海温异常有显著的负相关关系。当初春关键区海温正（负）异常时,初春高原中部偏北腹地地区、东南部地区积雪深度减少（增加）;初春北大西洋关键区海温异常通过激发下游青藏高原上空大气波列以及波作用通量异常来影响高原局地区域的温度和垂直运动,从而影响降雪的产生和积雪的累积。该结果为青藏高原初春积雪的多尺度变化及其影响提供了依据。     

西藏东南部察隅地区德玛拉岩群的同位素年代学研究及其意义

青藏高原冈底斯地块东南部的德玛拉岩群为一套角闪岩相变质岩系,一直被认为是前寒武纪变质基底,但并没有可靠的年代学证据。论文对采自其中的黑云角闪片岩和黑云母石英片岩进行了锆石LA-ICP-MS U-Pb定年和黑云母³⁹Ar-⁴⁰Ar定年,测试表明,黑云角闪片岩原岩锆石U-Pb年龄为217.1Ma,由黑云母³⁹Ar-⁴⁰Ar获得的变质年龄为22.3Ma,黑云母石英片岩中碎屑锆石主要为岩浆成因,年龄范围主要集中在520~600Ma和900~1100Ma,黑云母³⁹Ar-⁴⁰Ar变质年龄为16.3Ma和22.3Ma。上述结果虽不能完全否定西藏东南部察隅地区前寒武纪基底变质岩系的存在,但至少说明现今的德玛拉岩群中还包含有遭受中生代岩浆侵入的古生代沉积岩,它们在新生代经历了变质和岩浆作用的再造,是一套变质杂岩。     

The past valley glacier network in the Himalayas and the Tibetan ice sheet during the last glacial period and its glacial-isostatic, eustatic and climatic consequences

Since 1973 new data were obtained on the maximum extent of glaciation in High Asia. Evidence for an ice sheet covering Tibet during the Last Glacial Period means a radical rethinking about glaciation in the Northern Hemisphere. The ice sheet's subtropical latitude, vast size (2.4 million km²) and high elevation (6000 m asl) are supposed to have resulted in a substantial, albedo-induced cooling of the Earth's atmosphere and the disruption of summer monsoon circulation. Moraines were found to reach down to 460 m asl on the southern flank of the Himalayas and to 2300 m asl on the northern slope of the Tibetan Plateau, in the Qilian Shan region. On the northern slopes of the Karakoram, Aghil and Kuen-Lun mountains, moraines occur as far down as 1900 m asl. In southern Tibet radiographic analyses of erratics suggest a former ice thickness of at least 1200 m. Glacial polish and roches moutonnées in the Himalayas and Karakoram suggest former glaciers as thick as 1200–2700 m. On the basis of this evidence, a 1100–1600 m lower equilibrium line (ELA) has been reconstructed, resulting in an ice sheet of 2.4 million km², covering almost all of Tibet. Radiometric ages, obtained by different methods, classify this glaciation as isotope stage 3–2 in age (Würmian = last glacial period). With the help of 13 climate measuring stations, radiation- and radiation balance measurements have been carried out between 3800 and 6650 m asl in Tibet. They indicate that the subtropical global radiation reaches its highest energies on the High Plateau, thus making Tibet today's most important heating surface of the atmosphere. At glacial times 70% of those energies were reflected into space by the snow and firn of the 2.4 million km² extended glacier area covering the upland. As a result, 32% of the entire global cooling during the ice ages, determined by the albedo, were brought about by this area — now the most significant cooling surface. The uplift of Tibet to a high altitude about 2.75 Ma ago, coincides with the commencement of the Quaternary Ice Ages. When the Plateau was lifted above the snowline (= ELA) and glaciated, this cooling effect gave rise to the global depression of the snowline and to the first Ice Age. The interglacial periods are explained by the glacial-isostatic lowering of Tibet by 650 m, having the effect that the initial Tibet ice – which had evoked the build-up of the much more extended lowland ices – could completely melt away in a period of positive radiation anomalies. The next ice age begins, when – because of the glacial-isostatic reverse uplift – the surface of the Plateau has again reached the snowline. This explains, why the orbital variations (Milankovic-theory) could only have a modifying effect on the Quaternary climate dynamic, but were not primarily time-giving: as long as Tibet does not glaciate automatically by rising above the snowline, the depression in temperature is not sufficient for initiating a worldwide ice age; if Tibet is glaciated, but not yet lowered isostatically, a warming-up by 4 °C might be able to cause an important loss in surface but no deglaciation, so that its cooling effect remains in a maximum intensity. Only a glaciation of the Plateau lowered by isostasy, can be removed through a sufficiently strong warming phase, so that interglacial climate conditions are prevailing until a renewed uplift of Tibet sets in up to the altitude of glaciation.An average ice thickness for all of Tibet of approximately 1000 m would imply that 2.2 million km³ of water were stored in the Tibetan ice sheet. This would correspond to a lowering in sea level of about 5.4 m.     

班戈错晚第四纪湖泊发育、湖面变化与藏北高原东南部末次大湖期湖泊演化

班戈错是因湖面阶段性下降而于晚更新世末期从母湖色林错东部分离出来的小离湖.2003年5-7月,我们对班戈湖沿岸进行了详细的地貌与第四纪地质调查,湖面高程及6条剖面湖岸阶地的水准测量,并采集了沿岸及邻区的湖相沉积物样品进行U系年龄测定.研究结果表明,班戈错湖岸阶地共6级,其中T1为与色林错分离后所形成,T2至T6的拔湖高...     

青藏高原北麓河地区降水量观测与对比分析

根据2011年11月至2012年9月通过Thies激光雨滴谱仪、 T-200B雨雪量计和TE525翻斗式雨量筒获取的青藏高原北麓河地区降水量数据, 按3个时间段分别对3种仪器记录的降水量行了对比分析. 结果表明: 激光雨滴谱仪获取的固态降水量与经Jimmy校正公式修正后的T-200B降水量极为接近. 但在测量雨夹雪时, 激光雨滴谱仪对降水类型、 颗粒直径的误判造成了获取的降水量远高于T-200B雨量筒. 而3种仪器获取的液态降水量有很好的一致性. 但是, 当小时降雨量在2 mm以上时, 激光雨滴谱仪获取的降雨量比T-200B和TE525雨量筒小20%左右. 同时, 在风吹雪对激光雨滴谱仪的影响方面做了相关的分析研究, 初步认为风吹雪的颗粒直径主要集中在0.5 mm以下.     

Overbank flooding and human occupation of the Shalongka site in the Upper Yellow River Valley,northeast Tibet Plateau in relation to climate change since the last deglaciation

Increased flooding caused by global warming threatens the safety of coastal and river basin dwellers, but the relationship of flooding frequency, human settlement and climate change at long time scales remains unclear. Paleolithic, Neolithic and Bronze Age cultural deposits interbedded with flood sediments were found at the Shalongka site near the north bank of the upper Yellow River, northeastern Tibetan Plateau. We reconstruct the history of overbank flooding and human occupation at the Shalongka site by application of optically stimulated luminescence and radiocarbon dating, grain size, magnetic susceptibility and color reflectance analysis of overbank sediment and paleosols. The reliability of OSL dating has been confirmed by internal checks and comparing with independent ¹⁴C ages; alluvial OSL ages have shown a systematic overestimation due to poor bleaching. Our results indicate that the Yellow River episodically overflowed and reached the Shalongka site from at least ~ 16 ka and lasting until ~ 3 ka. Soil development and reduced flooding occurred at ~ 15, ~ 8.3–5.4, and after ~ 3 ka, and prehistoric populations spread to the Shalongka site area at ~ 8.3, ~ 5.4, and ~ 3 ka. We suggest that climate change influenced the overbank flooding frequency and then affected prehistoric human occupation of the Shalongka site.     

Evidence for Holocene environmental changes in the northern Fertile Crescent provided by pedogenic carbonate coatings

Holocene environmental changes in the northern Fertile Crescent remain poorly understood because of the scarcity of local proxy records in the region. In this study we investigated pedogenic (soil-formed) carbonate coatings on stones at the Pre-Pottery Neolithic site Göbekli Tepe as an indicator of local early-mid Holocene environmental changes. The ¹⁴C ages and stable isotopic composition of carbon and oxygen in thin (0.2–0.3 mm thick) pedogenic carbonate lamina indicate two main periods of coating formation: the early-Holocene (ca. 10000–6000 cal yr BP) and the mid-Holocene (ca. 6000–4000 cal yr BP). During the first period, there was an inverse relationship between δ¹³C and δ¹⁸O curves: a decrease in δ¹³C values coincide with an increase in δ¹⁸O values. For this period a trend towards higher temperatures is suggested. In the mid-Holocene, the mean rate of coating growth was 2–3 times higher than in the early Holocene. Both δ¹³C and δ¹⁸O reached their maximum values during this time and the direction of changes of the δ¹³C and δ¹⁸O curves became similar. The combination of data suggests that this period was the most humid in the Holocene and on average warmer than the early Holocene. At ca. 4000 cal yr BP secondary accumulation of carbonate ceased, presumably reflecting a shift to a more arid climate.