Climatic changes during the last 35,000 years as indicated by land, sea, and air data

Detailed climatic records from land (glaciation curves, fossil records, etc.), sea (eustatic changes, deep-ses date), and air (Greenland 0¹⁸ curve) are almost identical for the last 35,000 years. This cannot be a mere coincidence: it indicates that even minor fluctuations are caused by global climatic changes. The various records seem to be easily correlated with each other. The Last Ice Age is characterized by drastic changes between colder and warmer periods. The Present (Flandrian) Interglacial (Holocene Epoch) is also characterized by climatic fluctuations, although of minor amplitude. Analysis of peaks and bottoms in six Atlantic deep-sea cores gives a climatic sequence identical to the eustatic transgression/regression sequence, indicating the recording of global short-term warm/cold fluctuations. From these fluctuations, the climatic cyclicity was calculated. Two drastically frequency-changing cycles were found, one varying from 230 to 1,000 years and one from 1,000 to 3,600 years. A third cycle of 21,000 years was also estabished. The transition from the Last Ice Age to the Present Interglacial is marked by three major steps towards interglacial conditions; viz. at 12,7000, 10,000 and 9,300 radiocarbon years B. P. The 10,000 boundary has earler been suggested as the Pleistocene/Holocene boundary.     

涠洲岛近1500年以来孢粉炭屑记录的环境变化

过去2000年来是人类高速发展的时期,环境变化已经从自然驱动主导转变为受人类和自然共同影响。涠洲岛位于南海西北部的北部湾海域中部,受南亚热带季风性气候和频繁的台风的影响,湿地沉积发育丰富,是研究亚热带海岛气候环境变化以及揭示人类活动的理想区域。本研究通过对涠洲岛湿地钻孔（WZD）长度160 cm的剖面开展高分辨率孢粉、炭屑和粒度分析等多指标综合分析,在AMS ¹⁴C测年的基础上,同时,结合当地历史文献资料,讨论了涠洲岛近1500年的植被演化与气候变化历史,并进一步揭示了人类活动影响下的涠洲岛环境变化过程。研究结果显示,涠洲岛环境变化过程分为4个阶段：1）1471~669 cal.a B.P.（479~1281 cal.A.D.）,剖面孢粉最低,优势植物基本以耐旱品种为主,表明此时期高温干旱。松花粉含量高,指示涠洲岛周围地区可能发育大量针叶林,形成以耐旱灌木、草本为主的稀树草原景观。在高温干旱的气候背景下,发生自然火灾的可能性大,此阶段的炭屑多为地方性火灾产生,涠洲岛基本保持着原始生态面貌。2）669~372 cal.a B.P.（1281~1578 cal.A.D.）,孢粉浓度增加,表明木本植物类型变丰富,气候温暖湿润。该时期涠洲岛上植被茂盛,变为从稀树草原到北亚热带季节性雨林的过渡型。温暖湿润的气候以及可供用于烧火的木材增多、有利于人类迁入并定居。3）372~93 cal.a B.P.（1578~1857 cal.A.D.）,喜凉的杜鹃花粉继续增加,耐寒冷的漆树科常有出现,表征此时气温进一步下降。十字花科、莴苣属等常见伴人植物花粉的出现以及剖面炭屑浓度和禾本科花粉迅速上升,说明人类在涠洲岛开始修建人工池塘,并开展水稻种植及其他农业活动。人类活动对岛上原始环境产生影响,但原始植被的防御力使得涠洲岛仍然部分保留了原始特征。4）93 cal.a B.P.~现在（1857 cal.A.D.）,木本植物花粉先减少后急剧增加,热带性植物木麻黄属增多指示此期间气候转暖。此时期大致对应现代暖期。仙人掌已经成为该岛优势植物,仙人掌、樟、楝、木麻黄、金合欢组合植被成为涠洲岛特有的植被景观。此外,D＜100 μm、D≥100 μm这两种粒径的炭屑和禾本科花粉含量急剧升至整个剖面的最高峰,中值粒径迅速细化,记录了强烈的人类活动。涠洲岛近1500年以来的孢粉炭屑记录表明,在中世纪暖期期间（900~700 cal.a B.P.）,涠洲岛高温干旱,海平面有所上升。在小冰期期间（500~350 cal.a B.P.）,气候温暖湿润并随着海平面下降。涠洲岛气候环境变化主要受太阳辐射调控,同时受ENSO活动等因子影响。

     

Storminess variation during the last 6500 years as reconstructed from an ombrotrophic peat bog in Halland,southwest Sweden

Cores taken from an ombrotrophic peat bog in the coastal zone of Halland, southwest Sweden, were examined for wind transported mineral grains, pollen and humidity indicators. The core covers the period from 6500 cal. yr BP to present. Ombrotrophic conditions existed from ca. 4200 cal. yr BP onwards. Bog surface wetness fluctuated strongly until ca. 3700 cal. yr BP, with an apparent dominance of dry summer conditions from 4800–4500 cal. yr BP. Local wet shifts occurred around 4300, 2800, 2400 and 1500 cal. yr BP, whereas the most recent 600 years of the record show increasingly dry conditions. Mineral grain content, interpreted as aeolian sand influx (ASI), was used as a proxy for (winter) storm frequency and intensity until ca. 1500 cal. yr BP, after which increasing human impact, as reconstructed by pollen analysis, became a second important potential cause for increased sand drift. Strongly increased storminess occurred at 4800, 4200, 2800–2200, 1500, 1100 and 400–50 cal. yr BP, indicating a dominance of cold and stormy winters during these periods. Many of these storm periods apparently coincide with storm events in other sites in southwestern Scandinavia, suggesting that our ASI record reflects a regional scale climatic signal. Furthermore these stormy periods correlate to well‐known cold phases in the North Atlantic region, suggesting a link to large‐scale fluctuations in atmospheric circulation patterns. Copyright © 2006 John Wiley & Sons, Ltd.     

加拿大阿萨巴斯卡地区泥炭脂类分子记录的古气候信息

为了进一步了解泥炭中脂类分子化合物的分布与植被演化和气候变化的响应关系,对采自加拿大阿尔伯塔省东北部阿萨巴斯卡地区的JPH4、Mildred和McMurray泥炭柱样品中的脂类分子进行测定。根据正构烷烃、正烷酮、甾类和萜类等分子化合物的地球化学分析,结合年代学资料,重建了研究区近千年来的古气候演化过程。现代暖期以来(1990年以来),区内大范围的锈色泥炭藓发育,指示温暖干旱的气候条件;现代暖期早期(1900年以来),陆源高等植物和狭叶泥炭藓共存于干-湿交替的气候环境下;JPH4泥炭柱记录了小冰期期间寒冷干旱的气候环境,该时期莎草科等陆生维管植物发育;上述结论与前人记录的区域植被和气候变化具有较好的可比性。研究区发育的锈色泥炭藓种类特殊,多形成于干旱环境且具有C₃₁正构烷烃优势分布,ACL、P_aq、C₂₃/(C₂₇+C₃₁)正构烷烃指标能够有效表征植被输入特征和气候变化。正烷酮主要来源于相应正构烷烃的微生物氧化作用,正烷酮指标CPI-ket、ACL-ket和(K₂₃     

Rates of peat formation in relation to degree of humification and local environment, as shown by studies of a raised bog in Deninark

In the raised bog Draved Mose, rates of peat formation and degrees of humification were determined in two peat sections. Based on 59 calibrated C-14 dates, accumulation rates during the last 6500 years of 0.16 to 0.80 mm/year were found. The peat layers were analyscd for Sphagnum species, rhizopods, and pollen and spores. A clear relation between humification degrees and humidity at the time of formation was found, while the relation between measured growth rates and degrees of humification varied throughout the 2.5 m thick peat section. These variations are thought to be mostly a result of autocompaction.     

Climate and human impact during the past 2000 years as recorded in the Lagunas de Yala,Jujuy, northwestern Argentina

²¹⁰Pb, ¹³⁷Cs and ¹⁴C dated sediments of two late Holocene landslide lakes in the Provincial Park Lagunas de Yala (Laguna Rodeo, Laguna Comedero, 24°06′S, 65°30′W, 2100 m asl, northwestern Argentina) reveal a high-resolution multi-proxy data set of climate change and human impact for the past ca. 2000 years. Comparison of the lake sediment data set for the 20th century (sediment mass accumulation rates MARs, pollen spectra, nutrient and charcoal fluxes) with independent dendroecological data from the catchment (fire scars, tree growth) and long regional precipitation series (from 1934 onwards) show that (1) the lake sediment data set is internally highly consistent and compares well with independent data sets, (2) the chronology of the sediment is reliable, (3) large fires (1940s, 1983/1984–1989) as documented in the local fire scar frequency are recorded in the charcoal flux to the lake sediments and coincide with low wet-season precipitation rates (e.g., 1940s, 1983/1984) and/or high interannual precipitation variability (late 1940s), and (4) the regional increase in precipitation after 1970 is recorded in an increase in the MARs (L. Rodeo from 100 to 390 mg cm⁻² yr⁻¹) and in an increase in fern spores reflecting wet vegetation. The most significant change in MARs and nutrient fluxes (C_org and P) of the past 2000 years is observed with the transition from the Inca Empire to the Spanish Conquest around 1600 AD. Compared with the pre-17th century conditions, MARs increased by a factor of ca. 5 to >8 (to 800 _{+130, −280} mg cm⁻² yr⁻¹), PO₄ fluxes increased by a factor of 7, and C_org fluxes by a factor of 10.5 for the time between 1640 and 1930 AD. 17th to 19th century MARs and nutrient fluxes also exceed 20th century values. Excess Pb deposition as indicated by a significant increase in Pb/Zr and Pb/Rb ratios in the sediments after the 1950s coincides with a rapid expansion of the regional mining industry. Excess Pb is interpreted as atmospheric deposition and direct human impact due to Pb smelting.     

Dinoflagellate cysts reflecting surface-water conditions in Voldafjorden, western Norway during the last 11 300 years

Abundant dinocysts in a high-resolution core from Voldafjorden, western Norway, reflect changes in sea surface-water conditions during the last c. 11 300 BP. The period from c. 11 300 to 10 800 BP (Late Allerφd) was characterized by cool temperate surface-waters, high annual temperature variation and relatively strong stratification of the water column, which is characteristic of fjord environments. Due to the stratification of the surface waters, the uppermost layer may have warmed considerably. This generated a principal difference in temperature conditions between land and sea, with slightly higher temperatures in the marine environments. The period from c. 10 800 to 10 000 BP is characterized by very harsh conditions, with sea surface-water temperatures close to freezing and long lasting seasonal sea-ice cover. Similar temperature changes at the beginning and end of the Younger Dryas are characteristic for NW Europe, but those in Voldafjorden differ from those in the open sea and in the Norwegian Channel by being significantly larger. The stratification of the water column during the Late Allerφd was probably broken down because of incipient inflow of temperate normal saline waters, which caused a marked sea surface-water warming, at c. 10 000 BP. Surface-water conditions close to those of today were gradually established between c. 10000 and 9500 BP. However, these interglacial conditions were abruptly interrupted by a significant drop in winter sea surface-water temperature and salinity occurring around 9700 BP. From c. 9500 to 7000 BP the influence of temperate normal saline water masses increased stepwise until full interglacial conditions were established around c. 7000 BP. The change in the dinocyst assemblage around 7000 BP in Voldafjorden was probably related to the onset of the modern Norwegian Coastal Current, previously documented in cores from the Skagerrak and the Mid-Norwegian Continental Shelf. The last c. 7000 BP is characterized by relatively stable surface-water conditions, possibly interrupted by periods of cooling or decreased inflow of temperate normal saline water. Like several other dinoflagellate cyst records from the Norwegian-Greenland Sea, O. centrocarpum peak values are between 4000 and 5000 BP, suggesting a regional-scale oceanographic change.     

天目山泥炭类脂物记录的微生物特征和植被演替

为进一步了解泥炭中微生物特征和植被的变化,对采自浙江天目山的样品进行了类脂生物标志物与有机碳同位素(δ13Corg)的测定。有机碳δ13Corg值整体偏负,显示C3植物占优势的特点。正构烷烃的分布特征表明,大多数样品来源于陆生高等植物和低等菌藻类生物,其中高碳数正构烷烃主要以C29为主峰,显示植被类型以木本植物为主,但草本植物的相对比例也发生了多次变化,且这种变化与有机质的相对贡献量密切相关。在深度100~68cm,不同来源的有机质,特别是低等菌藻类的相对贡献量都相对较少;在深度68~30cm,低等菌藻类生物的贡献逐渐变大;而表层泥炭的有机质主要来源于高等植被,菌藻类的输入较少。泥炭有机碳同位素与类脂生物标志物的综合特征表明,该区植被经历了几次明显变化,并据此可将研究区中全新世以来环境演化分为早(4100~3200aB.P.)、中(3200~700aB.P.)、晚(700aB.P.以来)三个环境演化阶段,其结论与前人的环境演化与全球气候变化研究具有较好的可比性。     

青海可鲁克湖孢粉记录的14 cal. ka B.P.以来植被和气候演化历史

末次冰消期以来,我国东部季风区和西部干旱区分别呈现出"季风"和"西风"的两种降水模式。柴达木盆地位于二者的过渡区,由于缺乏可靠年代控制下的定量古气候记录,末次冰消期以来该盆地植被和降水变化的过程和模式,以及全新世适宜期季风降水是否影响到该区域至今仍存争议。本研究通过柴达木盆地东北部可鲁克湖西侧湿地深520 cm的沉积物钻孔14 cal.ka B.P.以来的孢粉记录,重建了植被和降水演化历史。结果显示青藏高原东北部干旱-半干旱区末次冰消期和早全新世（约14.1~8.0 cal.ka B.P.）以旱生灌丛-荒漠草原植被为主,降水量从约28 mm增至约249 mm;中全新世（约8.0~3.9 cal.ka B.P.）草原植被扩张到末次冰消期以来的最高水平,降水显著增加,最高值可达约292 mm;晚全新世（约3.9~0.3 cal.ka B.P.）荒漠草原再次扩张,降水量大幅度下降至约20 mm。可鲁克湖区降水过程呈现典型的东亚"季风模式",显示在全新世适宜期东亚季风的影响范围可以向西推进到柴达木盆地东北部。分析认为,柴达木盆地东北部的降水变化受北半球太阳辐射量变化、高纬冰盖及青藏高原热动力强迫的协同影响。     

Paleoclimatic changes during the last 2.5 myr recorded in the Kathmandu Basin,Central Nepal Himalayas

Palynological and sedimentological studies of a series of slimes collected from a 284 m-long drill-well from the Kathmandu Basin reveal paleoclimatic records and environmental changes within the Kathmandu Valley during the last 2.5 myr. The slimes are composed of fluvio-deltaic and lacustrine sediments comprising sand beds of 66.3 m and mud beds of 218 m in length. Pollen analyses show Quercus and Cyclobalanopsis are predominant, with frequencies exceeding 70%. Pinus, Alnus and Gramineae are the next dominant taxa. Three fossil pollen zones were discriminated; each zone reflects major climatic change: Zone I, the oldest stage, indicates a cool and rather wet climate during 400 kyr from ca. 2.5 to 2.1 Ma; Zone II, the middle stage, reflects a warm and relatively dry climate without remarkable fluctuation; Zone III is characterized by seven cycles of warm-and-wet and cold-and-dry climate, which reflect the alternation of glacial and interglacial periods. The last cold maximum, 11 m deep, corresponds to the last glacial age around 20 kyr bp, judging from the ¹⁴C dating of the uppermost part of the lacustrine sediments.The Paleo-Kathmandu Lake is likely to have been initiated at around 2.1 Ma and to have been filled with black organic mud, the Kalimati Clay. The top of the Kalimati Clay is eroded and was overlain by fluvial sand after the last glacial age. The abrupt appearance of a 4 m-thick fossiliferous sand bed at the top of the middle member suggests a lowering of water level at around 1 Ma.     

福建梅花山泥炭腐殖化度记录的过去千年气候变化

全球变暖背景下频发的极端气候事件, 严重影响了经济社会可持续发展。研究过去人类活动背景下的气候变化特征可为预测气候变化趋势、制定应对策略提供历史借鉴。本研究选取福建梅花山国家级自然保护区山间泥炭岩芯(长度238cm)119个沉积物进行腐殖化度分析, 结合粒度和烧失量记录, 重建近千年来福建地区高分辨率气候历史。研究结果显示, 在东亚季风区的低纬亚高山山间盆地, 泥炭沉积物腐殖化度越高, 指示气候越冷干; 腐殖化度越低, 指示气候越暖湿。梅花山泥炭腐殖化度在980~1529A.D.呈现低值(均值8.4%), 指示中世纪暖期较强的东亚季风和暖湿气候; 1529~1926A.D.呈显著高值(均值24.8%), 指示明清小冰期较弱的季风和冷干气候; 1926A.D.以来波动下降(均值22.8%), 对应了现代暖期。梅花山泥炭腐殖化度记录与区域沉积记录显示出对东亚季风的同步响应。研究结果记录了小冰期的第二次和第三次冷期, 分别为1589~1757A.D.和1842~1926A.D.。梅花山泥炭腐殖化度记录的近千年气候变化可能受太阳辐射、热带辐合带和厄尔尼诺/南方涛动等的共同驱动。

     

Continuous record of environmental changes in Chukotka during the last 350 thousand years

The comprehensive study of the upper 1283 cm of sediment from Lake El’gygytgyn, which formed nearly 4 Ma ago following a meteorite impact in northern Chukotka, yielded the first continuous record of the extreme changes in the Beringian climate and vegetation from the middle Middle Pleistocene to recent time (equivalent of marine isotope stages of 1–7 and the upper part of isotope stage 8). During this period, the climate was warmer than at present between 8600 and 10 7000 ¹⁴C years and during the Late Pleistocene (isotope substage 5e, 116–128 ka ago). In 2003, the German-Russian-USA expedition continued studying sediments of Lake El’gygytgyn to obtain new evidence of the change in the vegetation cover in the Middle Pleistocene and the first information on the Middle Pleistocene interglacial (isotope stage 9; 297–347 ka ago). Pollen spectra characterizing the Middle Pleistocene interglacial are similar to spectra of the early stage of the Early Pleistocene interglacial and the climatic optimum in the Pleistocene to Holocene transitional period. The climatic history of Lake El’gygytgyn is basic for stratigraphic interpretations and correlations in the eastern sector of the Arctic. These data also expand our understanding of climatic changes that are studied within the framework of the “Pole-Equator-Pole Paleoclimate,” “Past Global Changes,” and other international projects.     

The pattern of Neoglacial glacier variations in the Okstindan region of northern Norway during the last three millennia

BOREAS Griffey, N. J. & Worsley, P. 1978 03 01: The pattern of Neoglacial glacier variations in the Okstindan region of northern Norway during the last three millennia (Okstindan Research Project Report 26). Boreas, Vol. 7, pp. 1–17. Oslo. ISSN 0300–9483.
Historical, lichenometrical and stratigraphical evidence is combined to establish a provisional history of Neoglacial glacier variation in a mountainous environment approx. 66^oN. Attention is focussed on end moraine chronology. At five sites, derived organic materials have been located within end moraines and at two others in situ palaeosols occur buried beneath distal slopes. Organic rich samples from all the sites have been radiocarbon dated and the results permit the recognition of three major glacier expansion episodes, each of which contributes to the diachronous nature of the Okstindan outer Neoglacial limit. A widespread 'Little Ice Age' event with a maximum extent of probable eighteenth century age is confirmed. Limited areas of older moraine ridges peripheral to the 'Little Ice Age' maximal limit appear to date from about 3000-2500 ¹⁴C years B.P. and a younger period tentatively dated as about 1250-1000 ¹⁴C years B. P. which agrees with recent data from Engabreen in northwest Svartisen. No evidence for any extensive glacial activity after the inlandice wastage approx. 9000 ¹⁴C years B. P. and prior to 3000 ¹⁴C years B.P. was forthcoming.     

River inflow and salinity changes in the Caspian Sea during the last 5500 years

Pollen, spores and dinoflagellate cysts have been analysed on three sediment cores (1.8–1.4 m-long) taken from the south and middle basins of the Caspian Sea. A chronology available for one of the cores is based on calibrated radiocarbon dates (ca 5.5–0.8 cal. ka BP). The pollen and spores assemblages indicate fluctuations between steppe and desert. In addition there are some outstanding zones with a bias introduced by strong river inflow. The dinocyst assemblages change between slightly brackish (abundance of Pyxidinopsis psilata and Spiniferites cruciformis) and more brackish (dominance of Impagidinium caspienense) conditions. During the second part of the Holocene, important flow modifications of the Uzboy River and the Volga River as well as salinity changes of the Caspian Sea, causing sea-level fluctuations, have been reconstructed. A major change is suggested at ca 4 cal. ka BP with the end of a high level phase in the south basin. Amongst other hypotheses, this could be caused by the end of a late and abundant flow of the Uzboy River (now defunct), carrying to the Caspian Sea either meltwater from higher latitudes or water from the Amu-Daria. A similar, later clear phase of water inflow has also been observed from 2.1 to 1.7 cal. ka BP in the south basin and probably also in the north of the middle basin.     

Lowland rainforest response to hydrological changes during the last 1500 years in Gabon, Western Equatorial Africa

Pollen and δ¹³C_TOM data obtained from two contrasting lake sequences (Lakes Kamalété and Nguène), located 200 km apart in the lowland rainforest of Gabon, provide complementary local and regional 1500-yr records of high resolution (15–30 yr) vegetation change. A combination of aquatic, semi-aquatic and terrestrial pollen showed in both records that the tropical rainforest increased during periods of high rainfall and decreased during drought intervals. The strong fluctuations of water balance at decadal scale during the “Medieval Warm Period” ( 1100–800 cal yr BP) coincided with a noticeable increase in shade-intolerant taxa, indicating recurring rainforest canopy disturbance. The δ¹³C_TOM signal showed high-amplitude variations in both records, which positively correlates with the rainforest dynamics and local vegetation changes. The similar trends in both the pollen and the δ¹³C_TOM signals between these sites demonstrate the regional broadly synchronous timing of shifting hydrological conditions. The largely positive co-variation between strong fluctuations of hydrological conditions and changes in rainforest structure and composition indicate that regional climatic change is probably the driving force for major rainforest dynamics in Gabon. Any significant anthropogenic impact on vegetation has not been clearly identified, and this issue still needs to be resolved independently by obtaining detailed archeological records across the interval 1400–800 BP, which currently seem to be extremely rare or not easily available.     

Temporal changes in the phytoplankton community of the southern basin of Lake Baikal over the last 24,000 years recorded by photosynthetic pigments in a sediment core

Photosynthetic pigments and other indicators of phytoplankton were analyzed in a dated undisturbed sediment core obtained from the southern basin of Lake Baikal to reveal temporal changes in the phytoplankton community in the lake through the last glacial/post-glacial transition. The sedimentation age of the core spans the last 24 ¹⁴C ka. Chlorophyll a, its derivatives, carotenoids and total organic carbon (TOC) started to increase after 15 ¹⁴C ka, and the onset of biogenic silica occurred at 10 ¹⁴C ka. This indicated that the post-glacial growth of diatoms was preceded by that of other phytoplankton groups. In the record of the pigments and TOC, a temporary decrease was observed in the period 11.5–10.5 ¹⁴C ka, corresponding to the Younger Dryas cold period. The similarity found between the depth profiles of pyropheophytin a and steryl chlorin esters formed through predation of phytoplankton by zooplankton and that of TOC suggested the important contribution of fecal pellets to sedimentary organic matter in the lake.