Lateglacial and Holocene variation in aeolian sediment flux over the northeastern Tibetan Plateau recorded by laminated sediments of a saline meromictic lake

Predominantly laminated lake sediments from a saline closed‐basin lake on the northeastern Tibetan Plateau were investigated using a multi‐proxy approach (¹⁴C‐accelerator mass spectrometry dating, smear‐slide analysis, loss on ignition, grain size, X‐ray diffraction, elemental concentration, ostracod assemblages, stable isotopes of ostracod shells) to trace the regional environmental and climatic history in the Lateglacial and Holocene. Before about 15 cal. ka BP, small saline water bodies probably filled the basin under unstable cold and harsh environmental conditions. Soon after about 14.9 cal. ka BP, a relatively deep saline lake was established, probably as a result of runoff from melting snow, ice and frozen ground in the lake's catchment. Large changes in flux of aeolian material to the lake were recorded during this initial period of formation of Lake Kuhai. Highest lake levels, a low sediment accumulation rate and less saline conditions were maintained between about 12.8 and 7.1 cal. ka BP when the aeolian influx diminished significantly. After about 7.1 cal. ka BP, the aeolian influx remained at a moderate level apart from a strongly increased dust delivery to the lake between about 6.1 and 5.4 cal. ka BP and a minor short‐lived period of slightly enhanced aeolian influx at about 2.7 cal. ka BP. The strongly enhanced dust input to the lake between 6.1 and 5.4 cal. ka BP represented the largest influx of aeolian material to Lake Kuhai during the entire Holocene. However, evidence for climatic deterioration during this period is not seen at most other palaeoclimate sites on the Tibetan Plateau, but instead a significant increase in aridity has been recorded at numerous sites in the northern foreland of the Tibetan Plateau and on the Chinese Loess Plateau. The large dust input to Lake Kuhai between 6.1 and 5.4 cal. ka BP probably did not result from a severe climate deterioration on the Tibetan Plateau itself, but from the pronounced aridity in its northern and eastern foreland. In contrast, the increase in dust influx about 2.7 cal. ka BP seems to correspond to a brief warming spell recorded at other sites on the Tibetan Plateau too. A slight increase in lake level and decrease in salinity after about 0.6 cal. ka BP suggests a slightly higher effective moisture during the final lake stage, accompanied by a somewhat larger dust influx. This apparent contradiction possibly results from enhanced human activities on the northeastern Tibetan Plateau during the last 600 years. Copyright © 2009 John Wiley & Sons, Ltd.     

First lake record of Holocene climate and vegetation change of the Northern Kuril Islands

Investigation of Pernatoe Lake sediments in the south of Paramushir Island has enabled us to obtain the first continuous pollen record of climate and vegetation changes in the north of the Kurile archipelago during the Holocene. Series of radiocarbon datings of between 10 000 ± 40 and 2180 ± 40 years ago are evidence that the beginning of sediments accumulation, found after borehole development, is related to the Early Holocene. Diatom analysis has shown several stages in the lake development: raised bog on the border of the Pleistocene and Holocene, lagoon formation resulting from the sea level rise over 9–6 ky, and freshwater lake formation 6 ky and up to the present. Climate warming during the period attributed to the boreal and Atlantic periods of the Holocene is reflected by the dominance of Pinus pumila and Alnus serrulata assemblages in vegetation cover. Wide dune fields were formed in the Sea of Okhotsk and the Pacific shores of Paramushir Island 5–4 ky. Strengthening of atmogenic processes is related to cooling of the climate and drying of some areas of the underwater slope.     

Holocene climate variability in the Southern Ocean recorded in a deep-sea sediment core off South Australia

To understand Holocene climatic development and to determine drivers of climatic changes and climate variability, high-resolution marine proxy records are required from key oceanic locations. However, information on the Holocene climate development from the Southern Hemisphere is still rare and mainly based on terrestrial archives. Here, we present data with a high-resolution of circa 35 years from sediment cores taken east of the Great Australian Bight, where it is possible to determine Southern Ocean Holocene climate and the longer-term trends of the El Niño–Southern Oscillation (ENSO) conditions. For this purpose, we used the oxygen-isotope records of two planktonic foraminifer species Globigerinoides ruber and Globigerina bulloides which inhabit different water masses as well as faunal counts of planktonic foraminifers. After the ocean frontal systems off southern Australia were pushed northward by orbitally-forced insolation changes during the early Holocene, the data indicate increasing ENSO variability during the mid to late Holocene when the fronts shifted polewards again. A strong circa 1550 year cycle is found in the Globigerina bulloides record which reflects the wider Southern Ocean signal with prominent cold phases centred at circa 9.2, 7.3, 5.8, 4.3, 2.7, 1.4 ka BP and, possibly the Little Ice Age, which have global counterparts.     

A history of fire and vegetation in northeastern Minnesota as recorded in lake sediments

The record of charcoal in lake sediments indicates that fire has always been an important ecological factor in the forest history of northeastern Minnesota. The annually laminated sediments of Lake of the Clouds permit precise dating of the charcoal peaks and record the changes in the influx of various pollen types. A detailed record of the past 1000 yr shows that the average frequency of fire is approximately 60–70 yr, with a range of about 20–100 yr. The amount of charcoal in sediments dating between 1000-500 y.a. is consistently higher than that for the last 500 yr, although the fire frequency for the two periods was not appreciably different. Pollen analysis shows no change or only short-term changes in the percentages of major pollen types following charcoal peaks.     

Lateglacial and early Holocene climatic fluctuations recorded in the diatom flora of Xiaolongwan maar lake,NE China

A palaeolimnological study of the annually laminated sediment sequence of Lake Xiaolongwan, a small maar lake in northeastern China, revealed distinct diatom responses to Lateglacial and early Holocene climate change between c. 19 700 and c. 10 700 a BP. In addition to analyses of diatom assemblage composition and of the biovolume accumulation rate of planktonic diatoms, geochemical (total nitrogen, total organic carbon) and physical (varve type and thickness) indicators were used to assess past environmental change. The diatom assemblages reveal a complex interplay between direct climate effects on the seasonal lake conditions (timing of ice cover break‐up, water column mixing and thermal stratification), catchment‐mediated effects on the concentrations of nutrients and dissolved organic carbon and, possibly, biotic interactions between the different algal groups present in the phytoplankton of Lake Xiaolongwan (diatoms, Chrysophyceae and Dinophyceae). The most remarkable changes in the aquatic system were: (i) a sharp increase in Asterionella formosa and the collapse of Handmannia balatonis at c. 14 780 a BP, corresponding with the onset of the Bølling – Allerød interstadial; (ii) a sharp rise in Stephanodiscus minutulus at c. 12 840 a BP, marking the start of the Younger Dryas event and (iii) when the lake phytoplankton became dominated by Dinophyceae instead of diatoms at c. 11 170 a BP, after the Pre‐Boreal oscillation. Two diatom assemblage zones characterize the Younger Dryas at Lake Xiaolongwan, suggesting a bipartite division of this stadial event as in several records from eastern Asia and Europe. The quasi‐synchronicity of these events with the oscillations described in the North Atlantic realm demonstrates that during the Lateglacial, North Atlantic dynamics at centennial and millennial time scales had a strong control upon the climate in northeastern China.     

A bi-polar signal recorded in the western tropical Pacific: Northern and Southern Hemisphere climate records from the Pacific warm pool during the last Ice Age

Western tropical Pacific sea surface temperatures and Pacific Deep Water temperatures during Marine Isotope Stage 3 have been reconstructed from the δ¹⁸O and Mg/Ca of planktonic and benthic foraminifera from Marion Dufresne core MD98-2181. This 36 m marine core was collected at 6.3°N from a water depth of 2114 m. With sediment accumulation rates of up to 80 cm/ky, it provides a decadally resolved history of ocean variability during the Last Glacial period. Surface temperatures and salinities at this site varied in close association with millennial-scale atmospheric temperature swings at high northern latitudes as reflected in the GISP2 ice core. At times of colder atmospheric temperatures over Greenland, the western Pacific was more saline and summer season SSTs were ～2 °C colder. These millennial-scale changes within the tropics are attributed to a southward displacement of the summer season ITCZ in response to steeper meridional temperature gradients within the Pacific. The benthic δ¹⁸O record from MD98-2181 documents upper Pacific Deep Water temperature and salinity variability. Benthic δ¹⁸O variations of 0.3–0.5‰ during MIS 3 indicate deep waters within the Pacific were varying by ～1–1.5 °C, with the possibility that some of the variability was due to changing salinity and minor glacial–eustatic changes. The observed deep-water variability correlates to changes in Antarctic surface temperatures and thus reflects changes in Southern Ocean temperatures at the site of Pacific Deep Water formation. The combined planktonic and benthic records from MD98-2181 thus provide a northern and southern hemispheric climate record of anti-phased variability during MIS 3 as has been inferred previously from ice core records. Furthermore, the deep sea temperature excursions appear to have led millennial variations in atmospheric CO₂ as recorded in the EDML ice core by ～1 kyr.     

Complexity of the 8 ka climate event in Sweden recorded by varved lake sediments

Mineral magnetic and carbon analyses of a continuous varved lake sediment sequence in west-central Sweden (Lake Mötterudstjärnet) complement similar palaeoclimate proxies obtained from two varved lake sediment sequences in northern Sweden and one in central Finland. The varve chronology is supported by tephrochronology, palaeomagnetic secular variations and ¹⁴C AMS dating of terrestrial macrofossils. We apply a simple model in which the transport and deposition of catchment mineral matter reflect the amount of winter snow accumulation, spring snow-melt and stream discharge. Our data show that winter snow accumulation was generally enhanced in Sweden between 8100 and 7750 cal. yr BP. If dating errors are taken into account, the 350-year period of increased erosion is the geomorphic response to a multi-centennial scale climatic cooling that occurred some time between 8500 and 7500 cal. yr BP. The most significant erosion event in central Sweden was centred at 8050 cal. yr BP. It lasted 150 years (between 8100 and 7950 cal. yr BP) and is equivalent to the most extreme Holocene climate anomaly in the northern hemisphere, known as the 8 ka or 8200 cal. yr BP climate event. Our high-resolution paramagnetic susceptibility and ferrimagnetic grain-size parameters suggest that snowpack accumulation increased most significantly in northern Sweden between 7900 and 7750 cal. yr BP. We suggest that this north–south difference was a response to the re-establishment of moisture-laden westerly air masses, as meridional Atlantic overturning circulation was re-established at the beginning of the Holocene thermal maximum.     

Holocene climate changes in the central Mediterranean as recorded by lake-level fluctuations at Lake Accesa (Tuscany,Italy)

This paper presents a high-resolution lake-level record for the Holocene at Lake Accesa (Tuscany, north-central Italy) based on a range of sedimentological techniques validated in previous studies, with a chronology derived from 43 radiocarbon dates and four tephra layers. It gives evidence of centennial-scale fluctuations with major highstands at ca 11 500, 11 100, 10 200, 9400, 8200, 7300, 6200, 5700–5200, 4850, 4200, 3400, 2600, 1200 and 400 cal BP. Except for the Early Holocene until ca 10 500 cal BP, this pattern of hydrological changes appears to be in agreement with the regional pattern established for west-central Europe. Correlations with the Preboreal oscillation and the 8.2 ka event as well as with the atmospheric ¹⁴C residual series suggest that lake-level fluctuations developed at Accesa in response to (1) final steps of the deglaciation in the North Atlantic area and (2) variations in solar activity. For the period after 4500 cal BP, correlations with other palaeohydrological records from central Italy indicate that lake-level changes reconstructed at Accesa were mainly driven by climatic variations while anthropic activities and local geomorphological factors only played a secondary role. The Accesa lake-level record also highlights millennial-scale variations with a maximal lowstand at ca 9200–7700 cal BP contemporaneous with Sapropel event 1 in the Mediterranean. It was followed by generally higher lake-level conditions. This appears to be the opposite of that observed in Sicily (southern Italy) where a lake-level maximum developed at ca 9000–8200 cal BP and was followed by a general trend towards aridification. These opposite patterns were interpreted as contrasting hydrological responses to orbitally induced changes in summer insolation. This interpretation has to be tested by further lake-level studies in the central Mediterranean region. Finally, correlations between major lowstands and periods of maximal representation of Quercus ilex point to convergences between climate oscillations and Holocene vegetation history in the Accesa region. However, the maximal representation of Abies during the first half of the Holocene, including a time window where lake level reached a minimal level, suggests a more subtle impact of seasonality processes.     

Interactions between vegetation and climate variability: what are the lessons of models and paleovegetation data

The climate reconstruction by using pollen data is classically done by statistical methods. The use of a conceptual model of niches show a few weaknesses of this approach which is not enough supported by causal relationships. A solution is to take into account ecophysiological processes through a mechanistic model. On the one hand, these models help to test the biases that can bring some changes in the distribution of the extremes, and, on the other hand, they help to understand the effect of some external constraints such as the concentration of the atmospheric CO₂. At a shorter time scale, dendrochronological series are useful to test the response of the Aleppo pine to a warming combined to a stronger water stress. This approach is facilitated by the use of vegetation models used in inverse mode or with climatic scenarios. This paper illustrates that purpose through several examples.     

The Lateglacial and early Holocene vegetation and environment in the Dovre mountains,central Norway,as signalled in two Lateglacial nunatak lakes

By using heavy coring equipment in two high-altitudinal lakes (1253 and 1316 m a.s.l.) at Dovre, Central Norway, 1–1.5 m of unsorted coarsely minerogenic sediments were retrieved below the Holocene organic sediments. The minerogenic sequence contained well-preserved pollen and chironomid remains, revealing new and detailed palaeoenvironmental knowledge of the mountains in Central Norway during the last 5–6000 years of the Lateglacial (LG) period. However, the LG chronology is based on biostratigraphical correlations and not on ¹⁴C-dates, due to low organic content in the minerogenic sediments. The emerging LG nunataks, probably indicating a thin and multi-domed Scandinavian ice-sheet, was rapidly inhabited by immigrating species which could explain the present centric distributions of certain arctic-alpine plants. The LG vegetation development included a pre-interstadial dominated by mineral-soil pioneers, an interstadial dominated by shrubs and dwarf-shrubs, and the Younger Dryas cold period with recurring dominance of pioneers. Pollen and stomata of Pinus and Picea indicate their local LG presence at Dovre. LG climate oscillations are indicated by pollen stratigraphy and for the later part of LG also by chironomids. These oscillations could correspond to Heinrich event 1, GI-1d, GI-1b, and the Younger Dryas cold events. The LG interstadial reached July mean temperatures of more than 7–8 °C, similar to the present. Chironomids colonized the lake already during the onset of the interstadial, albeit at very low richness and abundances. Starting from YD, there are sufficient chironomid head capsules to perform a temperature reconstruction. The Holocene warming of about 2 °C initiated a vegetation closure from snow beds and dwarf-shrub tundra to shrubs and forests. Birch-forests established about 10 ka cal BP, slightly earlier than pine forests. Alnus expanded ca 9.2 ka cal BP and a thinning of the local forests occurred from ca 7 ka cal BP. Two short-lasting climate deteriorations found in the pollen record and the chironomid record may represent the Preboreal Oscillation and the 8.2 event. The Holocene Thermal Maximum is indicated around ca 7.8–7.3 ka cal BP showing a chironomid-inferred July mean of at least 11 °C. This is ca 3 °C warmer than today.     

苏北平原沉积孢粉组合记录的全新世气候突变

通过中国东部苏北平原厚3.4 m的PM4剖面孢粉分析结果,重建了该地区全新世以来古植被更替过程,查明了5.20~3.00 cal.ka B.P.中国东部沿海平原百年尺度的海平面变化历史,并探讨了沿海平原植被对海平面变化的响应。孢粉结果表明,全新世以来该地区的植被与气候经历了以下5个阶段:1)11.90~8.80 cal.ka B.P.,亚热带常绿、落叶阔叶混交林繁盛,气候温暖湿润;2)8.80~7.40 cal.ka B.P.,发育了常绿、落叶阔叶混交林-草地,气候相对冷干;3)7.40~5.20 cal.ka B.P.,植被为常绿、落叶阔叶混交林,温度降低,降水增加;4)5.20~1.08 cal.ka B.P.,植被退化为盐生草甸;5)1.08 cal.ka B.P.以来植被中湿生草本群落繁盛。根据藜科、蒿属、禾本科和莎草科花粉的含量变化及粒度、有孔虫特征重建了相对海平面的变化历史,5.20~4.55 cal.ka B.P.、4.25~4.05 cal.ka B.P.与4.55~4.25 cal.ka B.P.、4.05~3.00 cal.ka B.P.分别为海平面上升和下降的阶段。研究区4.25~4.05 cal.ka B.P.海平面上升可与大范围尺度的"4.2 ka B.P.气候事件"相对应,可能受到了当时东亚季风减弱、苏北平原强降水与大规模洪水事件的共同驱动。     

Lateglacial environmental and climatic changes at the Maloja Pass,Central Swiss Alps,as recorded by chironomids and pollen

Chironomids and pollen were studied in a radiocarbon-dated sediment sequence obtained from a former lake near the Maloja Pass in the Central Swiss Alps (1865 m a.s.l.) to reconstruct the Lateglacial environment. Pollen assemblages imply a vegetation development around the Maloja Pass from shrub tundra at the beginning of the Allerød to coniferous forest during the early Holocene with a lowering of the timberline during the Younger Dryas. Chironomid assemblages are characterized by several abrupt shifts in dominant taxa through the Lateglacial. The occurrence of taxa able to survive hypoxia in the second part of the Allerød and during the Preboreal, and their disappearance at the onset of the Younger Dryas cold phase suggest summer thermal stratification and unfavourable hypolimnetic oxygen conditions in the palaeo-lake during the warmer periods of the Lateglacial interstadial and early Holocene. Mean July air temperatures were reconstructed using a chironomid-temperature transfer function from the Alpine region. The pattern of reconstructed temperature changes agrees well with the Greenland δ¹⁸O record and other Lateglacial temperature inferences from Central Europe. The inferred July temperatures of ca 10.0 °C during most of the Allerød were slightly lower than modern values (10.8 °C) and increased up to ca 11.7 °C (i.e., above present-day values) at the end of the Allerød. The first part of the Younger Dryas was colder (ca 8.8 °C) than the second part (ca 9.8 °C). During most of the Preboreal, the temperatures persisted within the limits of 13.5–14.5 °C (i.e., ca 3 °C above present-day values). The amplitudes of temperature changes at the Allerød–Younger Dryas–Preboreal transitions were ca 3.5–4.0 °C. The temperature reconstruction also shows three short-lived cooling events of ca 1.5–2.0 °C, which may be attributed to the centennial-scale Greenland Interstadial events GI-1d and GI-1b, and the Preboreal Oscillation.     

Sebkhas as ecological archives and the vegetation and landscape history of southeastern Tunisia during the last two millennia

Sebkhas are temporary lacustrine systems depending on the number and extension of floodings. They may create laminated sediments which can be exploited as ecological archives. Contrary to those of meromictic lakes they are seasonal but not annual. After each flooding a detritus layer and a plasmo-condensed layer of bacteria and algae are formed in the water body or film and during the subsequent dessication a third subaeric layer of evaporites is build up. These laminae show a quasi-textile fabric and they can trap and conserve any dust and fine grained material. A high resolution pollendiagram covering the last two millennia as well as geochemical analysis from a southeastern Tunisian sebkha demonstrate the potentials of these ecological archives.     

Holocene hydrological changes in south-western Mediterranean as recorded by lake-level fluctuations at Lago Preola,a coastal lake in southern Sicily,Italy

This paper presents a high-resolution lake-level record for the Holocene at Lago Preola (Sicily, southern Italy) based on a specific sedimentological approach, with a chronology derived from AMS radiocarbon dates. It gives evidence of three major successive palaeohydrological periods, with (1) a pronounced dryness during the early Holocene until ca 10300 cal BP, (2) a highstand from ca 10300 to 4500 cal BP, and (3) a marked lowstand from 4500 cal BP to present. Large amplitude lake-level fluctuations characterise two transition phases at ca 10300–9000 and 6400–4500 cal BP. Period 2 was interrupted between 8300 and 7000 cal BP by a dry phase that was punctuated to ca 7300 cal BP by the deposition of a tephra from neighbouring Pantelleria Island. Comparisons of the Preola record with other palaeohydrological records along north–south and west–east transects in the Mediterranean show contrasting patterns of hydrological changes: north (south) of around 40°N latitude, the records highlight a mid-Holocene period characterised by lake-level minima (maxima). Humid mid-Holocene conditions over the Mediterranean south of 40°N were probably linked to a strong weakening of the Hadley cell circulation and of monsoon winds. We suggest that the maximum of humidity in the Mediterranean during the mid-Holocene was characterised by humid winters to the north of 40°N and humid summers to the south. On a multi-centennial scale, the high-resolution palaeohydrological reconstructions in the central Mediterranean area reveal a strong climate reversal around 4500–4000 cal BP, with contrasting changes in the hydrological cycle. In addition to seasonal and inter-hemispherical changes related to orbital forcing, this major oscillation might be related to non-linear responses of the climatic system to the gradual decrease in summer insolation at northern latitudes. Another major climate oscillation around 7500–7000 cal BP may have resulted from the combined effects of (1) a strong rate of change in insolation, and (2) variations in solar activity. Finally, comparisons of the Preola lake-level record with Sicilian pollen records suggest a strong influence of moisture availability on vegetation development in Sicily. Very dry early Holocene conditions probably prevented the expansion of coastal evergreen forests, while decreasing moisture availability since the onset of the late Holocene may have exacerbated effects of intensive land-use.     

Lateglacial and early Holocene vegetation and climate gradients in the Nordfjord–Ålesund area,western Norway

Birks, H. H. & van Dinter, M. 2010: Lateglacial and early Holocene vegetation and climate gradients in the Nordfjord–Ålesund area, western Norway. Boreas, Vol. 39, pp. 783–798. 10.1111/j.1502‐3885.2010.00161.x. ISSN 0300‐9483. Modern climate in western Norway shows a strong west–east gradient in oceanicity–continentality (coast to inner fjord) and altitudinal temperature gradients that control the regional and altitudinal zonation of vegetation. To discover if similar gradients existed during the Lateglacial and early Holocene, plant‐macrofossil analyses were made from five lacustrine sediment sequences in the Nordfjord–Ålesund region selected to sample the present climatic gradients. The macrofossil assemblages could be interpreted as analogues of the present vegetation, thus allowing reconstruction of past vegetation and climates. When the five sites were compared, climatic gradients could be detected. During the Lateglacial interstadial, mid‐alpine assemblages with Salix herbacea and S. polaris occurred at the lowland coast and upland inland sites, whereas the inland lowland site had low‐alpine dwarf‐shrub heath dominated by Betula nana, demonstrating a strong west–east gradient in temperature and precipitation and an altitudinal gradient inland. During the Younger Dryas stadial, assemblages at the lowland coast and upland inland sites resembled high‐alpine vegetation, whereas the inland lowland site was warmer with mid‐alpine vegetation, demonstrating west–east and altitudinal temperature gradients. Gradients became less pronounced in the Holocene. The early abundance of Betula nana in the inner fjord sites but its rarity at the coast is striking and reflects the oceanicity gradient. All sites became forested with Betula pubescens a few centuries into the Holocene. This forest was probably close to tree line at 370 m a.s.l. at the coast. Inland, there was no detectable altitudinal gradient, with the tree line well above 400 m a.s.l. reflecting the present pattern of tree‐line elevation.     

Timing of Lateglacial vegetation dynamics and respective palaeoenvironmental conditions in southern Estonia: evidence from the sediment record of Lake Nakri

This paper investigates a detailed well‐dated Lateglacial floristic colonisation in the eastern Baltic area, ca. 14 000–9000 cal. a BP, using palynological, macrofossil, loss‐on‐ignition, and ¹⁴C data. During 14 000–13 400 cal. a BP, primarily treeless pioneer tundra vegetation existed. Tree birch (Betula sect. Albae) macro‐remains and a high tree pollen accumulation rate indicate the presence of forest‐tundra with birch and possibly pine (Pinus sylvestris L.) trees during 13 400–12 850 cal. a BP. Palaeobotanical data indicate that the colonisation and development of forested areas were very rapid, arising within a period of less than 50 years. Thus far, there are no indications of conifer macrofossils in Estonia to support the presence of coniferous forests in the Lateglacial period. Signs of Greenland Interstadial 1b cooling during 13 100 cal. a BP are distinguishable. Biostratigraphic evidence indicates that the vegetation was again mostly treeless tundra during the final colder episode of the Lateglacial period associated with Greenland Stadial 1, approximately 12 850–11 650 cal. a BP. This was followed by onset of the Holocene vegetation, with the expansion of boreal forests, in response to rapid climatic warming. Copyright © 2011 John Wiley & Sons, Ltd.     

Polyphase thrusting and dyke emplacement in the central Southern Alps (Northern Italy)

The Triassic succession of the central Southern Alps (Italy) is stacked into several units bounded by south-verging low-angle thrust faults, which are related to two successive steps of crustal shortening. The thrust surfaces are cut by high-angle extensional and strike-slip faults, which controlled the emplacement of hypabissal magmatic intrusions that post-date thrusts motions. Intrusion ages based on SHRIMP U–Pb zircon dating span between 42 ± 1 and 39 ± 1 Ma, suggesting close time relationships with the earliest Adamello intrusion stages and, more in general, with the widespread calc-alkaline magmatism described in the Southern Alps. Fission-track ages of magmatic apatites are indistinguishable from U–Pb crystallization ages of zircons, suggesting that the intrusion occurred in country rocks already exhumed above the partial annealing zone of apatite (depth < 2–4 km). These data indicate that the central Southern Alps were already structured and largely exhumed in the Middle Eocene. Although we describe minor faults affecting magmatic bodies and local reactivations of older structures, no major internal deformations have occurred in the area after the Bartonian. Neogene deformations were instead concentrated farther south, along the frontal part of the belt.     

中更新世气候转型时期南海生态环境的南北差异

中更新世气候转型在南海浮游有孔虫、氧同位素和其它生物记录上主要反映在900 ka BP前后发生高频率变化,特别是指示表层水骤然降温。北部冬季表层水温从24~25℃降至17~28℃,而南部也从26~27℃降至23~24℃。总的降温趋势与开放西太平洋一致,直接反映了西太平洋暖池在900 ka BP之后MIS22期间有明显的减弱。表层水大幅度降温还发生在后继的MIS 20、18、16几大冰期,说明主要冰期旋回周期由41 ka转变为100 ka经历了长达400 ka的过渡时期,并且冬季风增强也在过渡时期的后半段最明显。南海南北生物组合和δ18O值的差异,突出了中更新世气候转型期边缘海区南北气候梯度反差和冬季风在冰期增强的讯号。结论是：生态环境系统反应总体表现与冰期旋回一致的同时,还包含了独特的地区性系统演变特征。但是,南海—西太平洋地区在0.9 Ma BP前后表层海水盐度因东亚冬季风和海平面下降的定量变化,以及这些变化对气候转型时期海—气耦合过程和生态环境系统的影响,尚缺乏足够的资料和证据。     

河北安固里淖孢粉记录的晚冰期以来的植被演替与气候变化

河北安固里淖地处东南季风的边缘地区,是研究古气候环境演化的理想地区之一。文章以安固里淖的沉积岩芯（长18.4 m）为研究对象,利用AMS ¹⁴C测年和孢粉数据,重建了安固里淖湖区14.3 cal.ka B.P.以来的植被与气候演化历史。结果表明：14.3~11.0 cal.ka B.P.期间,湖区以疏林草原植被为主,气候偏干;11.0~6.0 cal.ka B.P.以森林草原植被为主,气候湿润;6.0~3.2 cal.ka B.P.以疏林草原植被为主,气候偏湿;3.2~0 cal.ka B.P.以荒漠草原植被为主,气候干旱。总体而言,自晚冰期以来安固里淖的气候经历了由干变湿再逐渐变干的过程,全新世适宜期出现在早中全新世。通过区域对比发现,安固里淖揭示的晚冰期以来东南季风的气候演化特征与西南季风的演化具有很大的相似性,表明晚冰期以来东南季风与西南季风在轨道尺度上的演化并无太大差异,太阳辐射是二者演化的共同驱动力。