全新世东地中海的陆源碎屑输入及其水文气候变化:海盆尺度地球化学分析

地中海位于非洲季风气候和欧洲温带气候的交界处,同时接受周边地区岩石性质和风化状况差异极大的碎屑物质,所以是研究地球表层水文循环的理想区域。前人的认识集中于撒哈拉风尘和尼罗河输入,往往忽视了其他的陆源碎屑沉积,尤其对不同水文气候条件下的潜在变化缺乏考虑。针对形成于全新世非洲湿润期的腐泥层S1页岩沉积,并结合采自岩心顶部的晚全新世/现代沉积物,文章从18个站位选取了30个样品开展碎屑组分的地球化学分析,通过在具有不同干湿环境背景的时间片段上开展盆地尺度的对比(约9.5~8.9 ka vs. 约1.7~0 ka),探讨全新世东地中海的陆源碎屑输入模式。Ti/Al、Zr/Al、Ca/Al、Y/Al都清晰显示了经向和纬向上的梯度变化,可用作撒哈拉风尘的可靠指标;这些碎屑元素之间的差异反映了北非风尘来源和传送路径的变化。这些风尘指标在南-北向上的一致变化指示了副热带高压与西风带的交互界限为36°N,该界限在全新世应稳定存在。与风尘相反,河流输入的指标值在早全新世时显著高于现代,并呈现不同的地理分布。K/Al具有西高东低、北高南低的分布特征,指示了地中海北部沿岸地区的河流输入。根据与Ti/Al、K/Al的差异,利用(Cr+Ni)/Al可较好地识别被增强的季风降雨所激活的北非古河流沉积。河流输入在早全新世时显著上升,但不同河流系统的影响范围差异很大,受制于源区水文气候、表层洋流搬运等因素。     

Relative sea level changes during the Holocene in the Sisimiut area,south‐western Greenland

Holocene relative sea level (RSL) changes have been investigated by analysing and dating isolation sequences from five lakes near Sisimiut in south‐western Greenland. The transitions between marine and lacustrine sediments were determined from elemental analyses and analyses of macroscopic plant and animal remains. Radiocarbon dating was used to provide minimum ages for the transitions and to construct a RSL curve. Dating of a shell of the marine bivalve Macoma balthica indicates that deglaciation of the lowlands occurred in the early Holocene, at around 10 900 cal a BP. The RSL curve shows initial rapid regression from the marine limit at around 140 m, implying strong glacio‐isostatic rebound. We suggest that the margin of the Greenland Ice Sheet was located at the shelf break during the Last Glacial Maximum. Frequent remains of the ostracode Sarcypridopsis aculeata, which is a thermophilous brackish water species that is unknown from the extant fauna of Greenland, in one of the basins around 8500 cal a BP may mark the beginning of the Holocene thermal maximum in the region. Copyright © 2011 John Wiley & Sons, Ltd.     

The Holocene shallowing‐upward parasequence of north‐west Andros Island,Bahamas

Many pre‐Mesozoic records of Earth history are derived from shallow water carbonates deposited on continental shelves. While these carbonates contain geochemical proxy records of climate change, it is the stratal architecture of layered carbonate units that often is used to build age models based on the idea that periodic astronomical forcing of sea‐level controls the layering. Reliable age models are crucial to any interpretation of rates and durations of environmental change, but the physical processes that actually control this stratal architecture in shallow water carbonates are controversial. In particular, are upward‐shallowing stacks of carbonate beds bounded by flooding surfaces (‘parasequences’) truly a record of relative sea‐level change? The purpose of this study is to examine a tidal flat that is actively accumulating carbonate stratigraphy, and to determine the relative importance of tidal channel migration (poorly known, but investigated here) and Holocene sea‐level rise (well‐known) in controlling post‐glacial parasequence architecture. This work represents a field study of peritidal carbonate accumulation at Triple Goose Creek, north‐west Andros Island. By integrating surface facies maps with differential global positioning system topographic surveys, a quantitative relationship between facies and elevation is derived. Sedimentary facies are sensitive to elevation changes as small as 5 cm, and are responding to both internal (distance to nearest tidal channel) and external (sea‐level rise) controls. The surface maps also are integrated with 187 sediment cores that each span the entire Holocene succession. While flooding of the Triple Goose Creek area should have occurred by ca 4500 years ago, preservation of Holocene sediment did not begin until 1200 years ago. The tidal channels are shown to be stationary, or to migrate sluggishly at up to 6 cm per year. Therefore, while the location of tidal channels is responsible for the modern mosaic of surface facies, these facies and the channels that control them have not migrated substantially during the ca 1200 years of sediment accumulation at Triple Goose Creek. Once the region was channellized, vertical and lateral shifts in facies, such as the landward retreating shoreline, expanding mangrove ponds and seaward advancing inland algal marsh, are driven by changes in relative sea‐level and sediment supply, not migrating channels. While stratigraphic columns look different depending on the distance to the nearest tidal channel, the overall parasequence architecture everywhere at Triple Goose Creek records an upward‐shallowing trend controlled by the infilling of accommodation space generated by post‐glacial sea‐level rise.     

Early to mid‐Holocene climate change at Lago dell'Accesa (central Italy): climate signal or anthropogenic bias?

Despite the high potential of pollen records for climate reconstruction, pollen–climate relationships may be biased due to past and present human activities on the landscape. We use (i) transfer functions based on modern pollen–climate relationships to infer seasonal temperature and summer precipitation for the period 11 500–4500 cal. a BP and (ii) lake‐level change records based on different sedimentary proxies in multiple cores that are mainly indicative for summer hydrology at Lago dell'Accesa (central Italy). Quantitative reconstructions indicate lowest summer precipitation during two phases (8500–7700 cal. a BP and after 6000 cal. a BP) and a gradual winter temperature increase from 11 500 to ca. 8000 cal. a BP. Lowest summer precipitation was reconstructed during these phases characterised by vegetation shifts from open forests dominated by summergreen oaks (Quercus) to forests dominated by evergreen oaks (Quercus ilex), which are at present most abundant where summer drought is stronger. Similarly, the lake‐level record indicates two long‐lasting low summer precipitation phases (8800–7700 and 6400–4400 cal. a BP) that were interrupted by short‐term high summer precipitation events. Based on the broad agreement between the pollen‐inferred summer precipitation and the low‐frequency lake‐level changes, we suggest that the duration of the high summer precipitation events may have been too short to maintain drought‐sensitive trees, which may have been affected by high mortality rates when summer dry conditions returned. Although past and modern pollen–climate relationships may very likely have been affected by human activities since the Neolithic (i.e. when exploitation of the landscape started), we reject the hypothesis of a significant anthropogenic bias in the pollen‐based climate reconstruction. In addition, we suggest that pollen‐based and lake‐level reconstructions may have different inherent abilities of capturing high‐ and low‐frequency precipitation signals. Copyright © 2010 John Wiley & Sons, Ltd.     

Middle and late Holocene sea-levels along the Israel Mediterranean coast — evidence from ancient water wells

During the course of a study of historical water wells along the Israeli shore, which has been in progress since 1984, an innovative method for investigating sea-level fluctuations was developed. Eighteen ancient water wells were re-dug, 14 by the author, and four by archaeologists. Most of the re-dug wells are found at archaeological sites located a very short distance inland from the present shoreline. Evidence of ancient ground-water levels found in the wells directly reflects on historic eustatic sea-level changes, and the rate at which the end of the post-glacial transgression advanced. A critical question concerns the durability and life span of these wells, as the true age is very important for the accurate reconstruction of a sea-level curve. The Pre-Pottery Neolithic well of Atlit-Yam, which is the oldest known well in the world (ca. 8000 yr old), enabled the most accurate sea-level reconstruction for early Holocene times. Sea-level rise during that period of the Atlit-Yam site was of the order of 20 mm yr⁻¹ at the beginning, slowing to 6–8 mm yr⁻¹ at the abandonment of this site at ca. 7.5 ka BP, when it was flooded by the advancing and rising sea. After reaching its present level, sea-level fluctuations for the past 2.5 millennia were not greater than 1.5 to 2 m. © 1997 John Wiley & Sons, Ltd.     

Holocene seasonal sea‐surface temperature variations in the southern Adriatic Sea inferred from a multiproxy approach

Holocene cooling events have been reconstructed for the southern Adriatic Sea (central Mediterranean) by means of analyses of organic walled dinoflagellate cysts, planktonic foraminifera, oxygen isotopes, calcareous nanoplankton, alkenones and pollen from a sediment core. Two cooling events have been detected, during which sea‐surface temperatures (SSTs) were ca. 2°C lower. Unravelling the SST signal into dominant seasonal components suggests maximum winter cooling of 2°C at around 6.0 ka, whereas the cooling at ca. 3.0 ka might be the result of a spring temperature cooling of 2–3°C. The events, lasting several hundred years, are apparently synchronous with those in the Aegean Sea, where they have been related to known cooling events from the Greenland ice‐core record. A distinct interruption in Adriatic Sea sapropel S1 is not clearly accompanied by a local drop in winter temperatures, but seems to be forced by ventilation, which probably occurred earlier in the Aegean Sea and was subsequently transmitted to the Adriatic Sea. Copyright © 2003 John Wiley & Sons, Ltd.     

1956—2010年中国水热季节性特征分析

流域水文平衡不仅决定于降水和潜在蒸散发总量,而且还受到其年内季节性变化特征的影响。收集1956—2010年中国743个国家级气象站逐日气候资料,采用FAO-Penman公式计算潜在蒸散发量,插值计算10 km网格日降水和潜在蒸发,进行水热季节性特征的变化分析。结果表明,82.8%的区域潜在蒸散发量均值有下降趋势,但减少量不大,同时其年内季节性特征没有显著变化。表征降水年内波动振幅的季节性指数在全国范围均有显著下降趋势,且北方流域更为明显,变化率最大的西北诸河达到6.4%/10 a;峰值时间和雨季长度则变化不显著。这种水热季节性的变化被认为会导致流域径流的减少,在今后中国径流变化的归因研究中,应该考虑降水季节性变化的贡献。     

Holocene palaeoenvironmental reconstruction based on fossil beetle faunas from the Southern Altai region,north‐west China

We present here the results of the first‐ever Quaternary entomological research in China. The Halashazi Wetland, located in the southern Altai Mountain region in the northernmost part of Xinjiang Province, yielded Holocene insect fossils (mostly beetles) from two peat profiles. In total, 55 Coleoptera taxa were found, including 37 identified species. A new species, Helophorus sinoglacialis, was identified. The fauna is strongly northern Holarctic in character. The interval from 10 424 to 9705 cal a BP was probably a cold and wet period, and the study site was above the treeline. From 9665 to 9500 cal a BP it was probably warmer and drier, and treeline moved to higher elevations. Following a depositional hiatus, mid‐Holocene (5400–4400 cal a BP ) insect assemblages represent cold conditions with the site above the treeline. The exception was a brief warming around 5450 cal a BP , when bark beetle evidence suggests that the treeline moved to a higher elevation. Of the 37 identified beetle species from the Halashazi site, 34 (92%) have modern records in Siberia. The Altai Mountains probably served as a dispersal corridor between the Siberian arctic and alpine regions of northern China. Copyright © 2019 John Wiley & Sons, Ltd.     

全新世东亚夏季风降水穿时性的模拟研究

全新世期间东亚夏季风经历了较为复杂的演变过程,针对其降水的时空变化规律还存在争议。本研究利用TraCE-21 ka气候瞬变模拟的全强迫试验和敏感性试验数据,分析了全新世东亚不同区域降水极大值出现的时间,即东亚季风降水的"穿时性"问题,并就降水量的演变趋势和主要影响因子进行了分析。结果表明,全强迫试验中,全新世期间东亚夏季风总降水和净降水极大值最早在北方出现,然后逐渐南移,直到近代出现在南方及沿海地区,这与全新世期间东亚夏季风强度逐渐减弱相符;利用水汽收支方程对全新世东亚夏季风总降水变化进行分解,北方地区降水变化主要受动力因子的控制,热力因子的贡献占比较小,随着地区的南移,热力因子也起到了一定的贡献,不过动力因子仍是主导因素;敏感性试验进一步揭示,全强迫试验中东亚季风降水的这种"穿时性"主要受到地球轨道变化导致的海陆热力差异变化调控。     

全新世两次典型突变事件下北半球季风降水的变化对比

利用通用气候系统模式（Community Climate System Model version 3,简称CCSM3）模拟的TraCE-21ka全新世以来的试验数据,分析了全新世两次突变事件（8.2 ka B.P.和4.2 ka B.P.）前后（分别为9200~8800 a B.P.、8800~8000 a B.P.和4800~4500 a B.P.、4500~4000 a B.P.）北半球夏季（6~8月）气温和季风降水的时空变化特征,并通过对比4个单因子（地球轨道参数、温室气体浓度、大陆冰盖和淡水注入）敏感性试验结果来分析北半球季风降水变化的成因。结果表明：1）两次典型突变事件前后欧亚大陆中高纬大范围的地表气温均明显下降,但是8.2 ka B.P.事件的降温程度大于4.2 ka B.P.事件,此外,在8.2 ka B.P.事件下北美中部有明显的增温,而在4.2 ka B.P.事件下该地区为降温;2）两次典型突变事件前后的北半球季风降水变化的空间分布类似,主要表现为北美季风区、北非季风区西部和印度季风降水一致减少,而东亚季风降水呈现"南涝北旱"的分布型;3）两次典型突变事件前后环流场变化的空间型相似,但是4.2 ka B.P.事件的环流强度变化明显弱于8.2 ka B.P.事件;4）8.2 ka B.P.事件下北半球季风降水变化主要是淡水注入所导致,而4.2 ka B.P.事件主要由于地球轨道参数和气候系统内部变率的共同影响。     

Early Holocene climate change and human occupation along the semiarid coast of north‐central Chile

The brief, terminal Pleistocene archaeological site at Santa Julia (SJ, 31° 50′ S; 71° 45′ W) is the only one with fluted projectile preforms and megafauna consumption known from the Chilean semiarid coastline. Here, we present the climatic history at SJ during the early Holocene reconstructed from pollen and charcoal analyses spanning 13.2–8.6 ka (=10³ calibrated ¹⁴C yr BP). Elevated charcoal concentrations confirm human activity by 13.2 ka. Human occupation decreased in intensity and charcoal practically disappears from the record after 10.6 ka, followed by wetland expansion at SJ between 10.5 and 9.5 ka. Local dominance of coastal shrubland reveals that dry phases occurred between >11.2–10.5 and 9.5–9.0 ka. Overall, these findings imply that by modulating available resources at both local and landscape levels climate change may have played an important role in explaining the peopling of semiarid coastal Chile. Copyright © 2010 John Wiley & Sons, Ltd.     

Quantitative reconstruction of Holocene precipitation changes in southern Patagonia

Holocene variations in annual precipitation (P_ann) were reconstructed from pollen data from southern Argentinian Patagonia using a transfer function developed based on a weighted-averaging partial least squares (WA-PLS) regression. The pollen–climate calibration model consisted of 112 surface soil samples and 59 pollen types from the main vegetation units, and modern precipitation values obtained from a global climate database. The performance (r² = 0.517; RMSEP = 126 mm) of the model was comparable or slightly lower than in other comparable pollen–climate models. Fossil pollen data were obtained from a sediment core from Cerro Frias site (50°24'S, 72°42'W) located at the forest-steppe ecotone. Reconstructed P_ann values of about 200 mm suggest dry conditions during the Pleistocene–Holocene transition (12,500–10,500 cal yr BP). P_ann values were about 300–350 mm from 10,500 to 8000 cal yr BP and increased to 400–500 mm between 8000 and 1000 cal yr BP. An abrupt decrease in P_ann at about 1000 cal yr BP was associated with a Nothofagus decline. The reconstructed P_ann suggests a weakening and southward shift of the westerlies during the early Holocene and intensification, with no major latitudinal shifts, during the mid-Holocene at high latitudes in southern Patagonia.     

Millennial‐scale precipitation changes over Central Africa during the late Quaternary and Holocene: evidence in sediments from the Gulf of Guinea

We combine environmental magnetism, geochemical measurements and colour reflectance to study two late Quaternary sediment cores: GeoB 4905‐4 at 2° 30′ N off Cameroon and GeoB 4906‐3 at 0° 44′ N off Gabon. This area is suitable for investigating precipitation changes over Central and West Africa because of its potential to record input of aeolian and fluvial sediments. Three magnetozones representing low and high degree of alteration of the primary rock magnetic signals were identified. The magnetic signature is dominated by fine‐grained magnetite, while residual haematite prevails in the reduced intervals, showing increase in concentration and fine grain size at wet intervals. Our records also show millennial‐scale changes in climate during the last glacial and interglacial cycles. At the northern location, the past 5.5 ka are marked by high‐frequency oscillations of Ti and colour reflectance, which suggests aeolian input and hence aridity. The southern location remains under the influence of the Intertropical Convergence Zone and thus did not register aeolian signals. The millennial‐scale climatic signals indicate that drier and/or colder conditions persisted during the late Holocene and are synchronous with the 900 a climatic cycles observed in Northern Hemisphere ice core records. Copyright © 2009 John Wiley & Sons, Ltd.     

青藏高原全新世1月和7月气温序列重建

青藏高原自然环境受人类干扰相对较小,为利用古孢粉记录重建气候因子提供了可能,高原过去气候因子的重建对于预测未来气候变化趋势有重要意义.通过选取的29条高原化石孢粉记录,利用现代类比法和化石孢粉点与高原气温的函数关系,把化石孢粉点古气温转化为青藏高原古气温,重建了高原全新世1月和7月古气温序列.结果表明：对于1月和7月气温而言,全新世早期（11.5～8.5 ka BP）为气温波动上升期;全新世中期（8.5～4.6 ka BP）为全新世大暖期,气温整体高于现代;全新世晚期（4.6 ka BP～至今）又可分为两个阶段,一个是4.6～2.4 ka BP,在此阶段1月和7月气温都有减小的趋势,另一个阶段则是2.4 ka BP至今,气温出现反常的趋势.     

Fluvial response to Holocene climate change in low‐order streams of central Mexico

Alluvial sequences constitute a recognised source of information on past environmental change, but one that has scarcely been tapped in central Mexico. This paper reviews what is currently known about the Holocene alluvial stratigraphy of the region, focusing on the interplay between climate and the pace and style of sedimentation in the incised headwater reaches of stream networks. The records obtained in five different drainage basins – four in the state of Tlaxcala and one in Guanajuato – are presented and compared to published reconstructions of climate change. A near‐synchronous incision of all stream networks occurred close to 10 200 ¹⁴C a BP in response to an increase in precipitation and stream discharge. A spell of very humid but markedly seasonal conditions ensued, resulting in the formation of wet meadows along streams and the accumulation of thick fine‐textured valley fills dominated by cumulic soil A horizons. After 9100 ¹⁴C a BP a transition to a warmer and more arid climate provoked the thinning of vegetation cover on slopes, accelerated runoff and increased sediment delivery to streams. The aggradation of coarser‐textured valley fills poor in organic matter set in. It ceased or slowed down significantly after a few millennia as the studied stream reaches achieved a near‐graded condition adjusted to the relatively stable climate. Arid mid Holocene conditions are also reflected in the abundant precipitation of secondary carbonates in Guanajuato. At 3100 ¹⁴C a BP higher precipitation caused more frequent flooding and a resumption of aggradation. Shortly after that date sedentary farmers colonised Tlaxcala. Agriculture altered runoff and sediment delivery to streams and accelerated cut‐and‐fill cycles on a scale that masked the impact of any climatic fluctuations. Guanajuato was colonised later and its alluvial record suggests the persistence of a humid climate at least until 1000 ¹⁴C a BP. Copyright © 2009 John Wiley & Sons, Ltd.     

Two decadally resolved records from north‐west European peat bogs show rapid climate changes associated with solar variability during the mid–late Holocene

Two ¹⁴C accelerator mass spectrometry (AMS) wiggle‐match dated peat sequences from Denmark and northern England record changes in mire surface wetness reconstructed using plant macrofossil and testate amoebae analyses. A number of significant mid–late Holocene climatic deteriorations (wet shifts) associated with declines in solar activity were recorded (at ca. 2150 cal. yr BC, 740 cal. yr BC, cal. yr AD 930, cal. yr AD 1020, cal. yr AD 1280–1300, cal. yr AD 1640 and cal. yr AD 1790–1830). The wet shifts identified from ca. cal. yr AD 930 are concurrent with or lag decreases in solar activity by 10–50 years. These changes are replicated by previous records from these and other sites in the region and the new records provide improved precision for the ages of these changes. The rapidly accumulating (up to 2–3 yr cm^?1, ～1310 yr old, 34 ¹⁴C dates) Danish profile offers an unprecedented high‐resolution record of climate change from a peat bog, and has effectively recorded a number of significant but short‐lived climate change events since ca. cal. yr AD 690. The longer time intervals between samples and the greater length of time resolved by each sample in the British site due to slower peat accumulation rates (up to 11 yr cm^?1, ～5250 yr old, 42 ¹⁴C dates) acted as a natural smoothing filter preventing the clear registration of some of the rapid climate change events. Not all the significant rises in water table registered in the peat bog archives of the British and Danish sites have been caused by solar forcing, and may be the result of other processes such as changes in other external forcing factors, the internal variability of the climate system or raised bog ecosystem. Copyright © 2008 John Wiley & Sons, Ltd.     

Holocene changes in precipitation seasonality in the western Mediterranean Basin: a multi‐species approach using δ13C of archaeobotanical remains

Precipitation has been of utmost importance in shaping the evolution of landscapes and human settlements in the Mediterranean. However, information on seasonal precipitation patterns through the Holocene is scarce. This study attempts to quantify the evolution of seasonal precipitation in the East Iberian Peninsula (5000 BC to AD 600) based on the carbon isotope composition (δ¹³C) of archaeobotanical remains. Data on Holm oak, Aleppo pine and small‐grain cereals were combined, and precipitation was inferred from models relating present‐day records to the δ¹³C of modern samples. Subsequently, charred grains were used as a proxy for ancient moisture during April–May, whereas oak and pine charcoals provided complementary rainfall estimates for September–December and January–August, respectively. The results reveal aridity changes throughout the Holocene in the western Mediterranean. Past spring–summer precipitation was consistently higher than at present. In contrast, autumn and early winter precipitation showed stronger fluctuations, particularly during the first millennium BC, and often exhibited values below those of the present. The high contribution of autumn precipitation to the annual water budget, typical of the present Mediterranean climate, was definitively established at the beginning of the current era. This study shows how a combination of species holding complementary environmental signals can contribute to a wider knowledge of local precipitation dynamics. Copyright © 2011 John Wiley & Sons, Ltd.