Neotropical vegetation response to rapid climate changes during the last glacial period: Palynological evidence from the Cariaco Basin

We present new palynological information from the anoxic Cariaco Basin, off Venezuela, that provides insight into the response of northernmost South American vegetation to rapid climate changes between 68 and 28 ka, specifically during North Atlantic Heinrich events (HEs) and Dansgaard/Oeschger cycles. We defined three different vegetation modes: (1) an interstadial mode characterized by the highest pollen concentration and the maximum extension of semi-deciduous and evergreen forests; (2) a stadial mode characterized by increases of salt marshes, herbs, and montane forests; and (3) a Heinrich event mode characterized by the lowest pollen concentrations, abrupt increases of salt marshes, and decreased forest abundance. Similarly, indices of C4/C3 plants show increases during stadials with clear peaks during the onset of HEs, though grasslands did not become dominant during these periods. We alternatively propose that these expansions of C4 plants are associated with the expansion of coastal salt marshes. Our vegetation record suggests the prevalence of humid conditions during interstadials, dry and cold conditions during stadials, and dry and cold conditions together with changes in sea level during HEs. This new palynological evidence supports previous interpretations that main environmental changes in northernmost South America were driven by latitudinal displacements of the Intertropical Convergence Zone and sea-level changes.     

Land snails from the last glacial maximum on Andikithira,southern Greece and their palaeoclimatic implications

An assemblage of land snails from an aeolianite deposit on the coast of the southern Greek island of Andikithira is shown to date to 16 000 yr BP and thus represents the period of the last glacial maximum (LGM; Oxygen Isotope Stage 2). The assemblage has no modern analogue. Five of the ten species are extinct on the island and some of these now live only at high elevations (> 950 m). Significantly cooler temperatures, some 5-8°C below present, and slightly drier moisture conditions (lower rainfall, partially offset by reduced evapotranspiration at the lower temperature) are inferred. The large temperature depression at the LGM, well documented in northern and central Europe, extended also to the Mediterranean climate of southern Europe. Late Quaternary climatic changes had a considerable impact on the fauna of this isolated island.     

High-resolution climate records from two stalagmites in Qixin Cave, southern Guizhou, and Heinrich events during the last glacial period

The time sequence of high-resolution paleoclimatic changes since the last glacial period--60,500 yr B.P.--has been reconstructed with high-precision TIMS-U series dates and analyses of the oxygen isotopes from Q4 and Q6 stalagmites of the Qixin Cave in southern Guizhou. Comparative analyses of δ^18O curves from the GISP2‘ ice core and the two stalagmites shows that the depositional records of the Dansgaard-Oeschger cycle events 1-18 and Heinrich‘s events H1-H5 from the records of the two stalagmites reflect rapid climate changes over a short time scale since the last glacial stage, and indicates the precise boundary lines at which the cold events occurred. The study results have shown that the records of the cold and warm events from the two stalagmites since 60,500 yr B.P. are the reflection of the paleo-monsoon circulation. Changes are clearly affected by the climate oscillation of the North Atlantic Ocean, and indicate that they have a strong teleconnection with the paleoclimate changes that occurred in the North Polar region. The records of δ^18O from the Q4 and Q6 stalagmites indicate that the δ^18O values from 60,590 yr B.P. to 11,290 yr B.P. changed from a more negative (or lighter)drift to a heavier or positive drift trend in the last glacial period. The data reflect the weakening of the Asian summer monsoon and the climate which generally became drier and cooler.     

Interhemispheric anti-phasing of rainfall during the last glacial period

We have obtained a high-resolution oxygen isotopic record of cave calcite from Caverna Botuverá (27°13′S, 49°09′W), southern Brazil, which covers most of the last 36 thousand years (ka), with an average resolution of a few to several decades. The chronology was determined with 46 U/Th ages from two stalagmites. Tests for equilibrium conditions show that oxygen isotopic variations are primarily caused by climate change. We interpret our record in terms of meteoric precipitation changes, hence the variability of South American Monsoon (SAM) intensity. The oxygen isotopic profile broadly follows local insolation changes and shows clear millennial-scale variations during the last glacial period with amplitudes as large as 3‰ but with smaller centennial-scale shifts (<1‰) during the Holocene. The overall record is strikingly similar to, but strongly anti-correlated with, a number of records from the Northern Hemisphere.We compared our record to other precisely dated contemporaneous records from Hulu Cave eastern China. Minima in δ¹⁸O (wet periods, intense SAM) at our site are synchronous with maxima in δ¹⁸O (dry periods, weak East Asian Monsoon, EAM) in eastern China (within precise dating errors) and vice versa. This anti-phased precipitation relationship between two low-latitude locations may be interhemispheric in extent, based on comparison with records from other sites. Precipitation anti-phasing may be related to north–south shifts in the mean position of the intertropical convergence zone (ITCZ) and asymmetry in Hadley circulation in two hemispheres, associated not with seasonal changes as observed today, but with millennial-scale climate shifts. The millennial-scale atmospheric see-saw patterns that we observe could have important controls and feedbacks on climate within hemispheres because of water vapor's greenhouse properties.     

Direct evidence of central European forest refugia during the last glacial period based on mollusc fossils

Although there is evidence from molecular studies for the existence of central European last glacial refugia for temperate species, there is still a great lack of direct fossil records to confirm this theory. Here we bring such evidence in the form of fossil shells from twenty strictly forest land snail species, which were recorded in radiocarbon-dated late glacial or older mollusc assemblages of nine non-interrupted mollusc successions situated in the Western Carpathians, and one in the Bohemian Massif. We proposed that molluscs survived the last glacial period in central Europe in isolated small patches of broadleaf forest, which we unequivocally demonstrate for two sites of last glacial maximum age.     

Late‐glacial to Holocene environmental changes and climate variability: evidence from Voldafjorden,western Norway

Sedimentological, micropalaeontological (benthic foraminifers and dinoflagellate cysts), stable isotope data and AMS ¹⁴C datings on cores and surface samples, in addition to acoustic data, have been obtained from Voldafjorden, western Norway. Based on these data the late glacial and Holocene sedimentological processes and variability in circulation and fjord environments are outlined. Glacial marine sedimentation prevailed in the Voldafjorden between 11.0 kyr and 9.2 kyr BP (radiocarbon years). In the later part of the Allerød period, and for the rest of the Holocene, there was deposition of fine‐grained normal marine sediments in the fjord basin. Turbidite layers, recorded in core material and on acoustic profiles, dated to ca. 2.1, 6.9–7.6, ca. 9.6 and ca. 11.0 kyr BP, interrupted the marine sedimentation. The event dated to between 6.9 and 7.6 kyr BP probably corresponds to a tsunami resulting from large‐scale sliding on the continental margin off Norway (the Storegga Tsunami). During the later part of the Allerød period, Voldafjorden had a strongly stratified water column with cold bottom water and warm surface water, reaching interglacial temperatures during the summer seasons. During the Younger Dryas cold event there was a return to arctic sea‐surface summer temperatures, possibly with year‐round sea‐ice cover, the entire benthic fauna being composed of arctic species. The first strong Holocene warming, observed simultaneously in bottom and sea‐surface temperature proxies, occurred at ca. 10.1 kyr BP. Bottom water proxies indicate two cold periods, possibly with 2°C lowering of temperatures, at ca. 10.0 (PBO 1) and at 9.8 kyr BP (PBO 2). These events may both result from catastrophic outbursts of Baltic glacial lake water. The remainder of the Holocene experienced variability in basin water temperature, indicated by oxygen isotope measurements with an amplitude of ca. 2°C, with cooler periods at ca. 8.4–9.0, 5.6, 5.2, 4.6, 4.2, 3.5, 2.2, 1.2 and 0.4–0.8 kyr BP. Changes in the fjord hydrology through the past 11.3 kyr show a close correspondence, both in amplitude and timing of events, recorded in cores from the Norwegian Sea region and the North Atlantic. These data suggest a close relationship between fjord environments and variability in large‐scale oceanic circulation. Copyright © 2001 John Wiley & Sons, Ltd.     

Millennial-scale oscillations of the westerly jet path during the last glacial period

It has been established that East Asian summer monsoon intensity varies with Dansgaard–Oeschger cycles, suggesting a connection between the climates of East Asia and the North Atlantic on a millennial timescale. However, the dynamics of such a connection are still unsolved. Here we demonstrate that temporal changes in the provenance of aeolian dust in Japan Sea sediments, which we interpret to reflect changes in the westerly jet path over East Asia, exhibit variations in harmony with Dansgaard–Oeschger cycles. The dominance of dust with a Mongolian Gobi provenance during stadials suggests a westerly jet axis located to the south of the Himalaya–Tibetan Plateau throughout most of the year, whereas the co-dominance of dust from both the Taklimakan Desert and the Mongolian Gobi during interstadials suggests that the westerly jet axis jumped to the north of the Tibetan Plateau at latest in summer. As the shift of the westerly jet axis to the north of the Tibetan Plateau is closely related to the onset of the East Asian summer monsoon, changes of the westerly jet path apparently critically affect the teleconnection between the climates of Asia and North Atlantic on a millennial timescale.     

地中海东部地幔演化过程:来自希腊Lesvos岛中新世钾质岩浆作用的启示

希腊Lesvos岛广泛出露的中新世钾质岩浆岩为深入探讨地中海东部地区新生代构造演化和深部过程提供了宝贵机会.本文对Lesvos岛碰撞后钾质岩石开展了系统的矿物电子探针分析、锆石U-Pb定年和Hf同位素分析及全岩地球化学分析.研究结果表明:Lesvos岛出露的碰撞后火山岩主要由玄武粗安岩、玄武安山岩和粗面岩组成,锆石U-...     

Sub‐millennial climate shifts in the western Mediterranean during the last glacial period recorded in a speleothem from Mallorca,Spain

Very few high‐resolution and directly dated terrestrial archives of the last glacial period exist for the western Mediterranean region, yet this is a key locality for recording sub‐millennial North Atlantic and Mediterranean climate change. Here, we present evidence of effective precipitation changes based on growth history and δ¹³C of calcite in a Mallorcan stalagmite that grew between 112 and 48 ka. Effective precipitation in Mallorca appears to have been sensitive to proximal sea surface temperature variations and at certain times, ca. 76 ka for example, changed rapidly from moist to arid conditions in only a few centuries. A sea‐level highstand during Marine Isotope Stage (MIS) 5a interrupted growth. Regrowth started promptly after this, but effective precipitation decreased markedly for much of the later part of MIS 5a, and also for shorter periods correlative with Heinrich events H8 (ca. 90 ka) and H6 (ca. 65 ka), with growth ceasing during H5 (ca. 48 ka). Arid episodes in Mallorca appear to be expressions of extremely cold periods recorded further north in Europe and occur contemporaneously with rapid decreases in Greenland temperature. Copyright © 2008 John Wiley & Sons, Ltd.     

Mineralogy and Geochemistry of the Pliocene Iron—Rich Laterite in the Vatera Area,Lesvos Island,Greece and Its Genesis

A nickel laterite deposit occurs in the Vatera area of Lesvos Island,Greece ,and is transgressively developed on serpentinized basic rock (norite).The overlying sedimentary rocks include marls and marly limestones with sandstone intercalations and belong to the Pliocene sed-iments.The following alteritic zones are defined from the bottom to top layers:a)bedrock (norite);b)serpentinized zone;c)goethitic zone.The bedrock consists of the following pri-mary minerals:basic plagioclase,orthopyroxenes and clinopyroxenes.The serpentinized zone includes clinochrysotile,lizardite,antigorite clinoenstatite,calcite and dolomite while in the goethic zone there are goethite,quartz,pyrite,chromite,dolomite.Al2O3 ,Fe2O3,CaO,Na2O,K2O,Ba,Sr,Ni,C and S are enriched in the goethitic zone .Nickel enrichment is re-lated to the formation of nickeliferons minerals substituting for Mg or/and Fe in the goethite and pyrite.Enrichment of Ni in the matrix may be due to the presence of amorphous Ni-sili-cates(pimelite).There is a significant change(decrease)in the concentration of Ni from the top to bottom parts of the laterite formation,indicating that there was no tendency to migrate downwards(immature laterite).A second support of the immaturity of the Vatera laterite is the incomplete oxidation of ferrous iron to form ferric iron hydroxides.Under tropical/subtropical conditions,which dominated from the end of Miocene to the Pliocene the norite rocks of the Vatera area altered in response to reaction with acid solutions enriched in CO2.Due to hydrolysis and oxidation of pyroxenes,Mg^2 ,H4SiO4 and Ni^2 were removed in the continental acid solutions.     

Status of glacial Lake Columbia during the last floods from glacial Lake Missoula

The last floods from glacial Lake Missoula, Montana, probably ran into glacial Lake Columbia, in northeastern Washington. In or near Lake Columbia's Sanpoil arm, Lake Missoula floods dating from late in the Fraser glaciation produced normally graded silt beds that become thinner upsection and which alternate with intervals of progressively fewer varves. The highest three interflood intervals each contain only one or two varves, and about 200–400 successive varves conformably overlie the highest flood bed. This sequence suggests that jökulhlaup frequency progressively increased until Lake Missoula ended, and that Lake Columbia outlasted Lake Missoula. The upper Grand Coulee, Lake Columbia's late Fraser-age outlet, contains a section of 13 graded beds, most of them sandy and separated by varves, that may correlate with the highest Missoula-flood beds of the Sanpoil River valley. The upper Grand Coulee also contains probable correlatives of many of the approximately 200–400 succeeding varves, as do nearby parts of the Columbia River valley. This collective evidence casts doubt on a prevailing hypothesis according to which one or more late Fraser-age floods from Lake Missoula descended the Columbia River valley with little or no interference from Lake Columbia's Okanogan-lobe dam.     

末次冰期以来松嫩盆地东部榆树黄土堆积及其环境意义

通过对松嫩盆地东部末次冰期以来榆树黄土剖面的粒度、磁化率等指标分析研究后认为:(1)该地区的黄土至少于4万年前的末次冰期开始沉积,沉积物类型为黄土与河流沙混合沉积,粒度可有4个组分,其中46kaB.P.以前主要是以第④组分为主导的水成河流沙,46kaB.P.以后主要以第③组分为主的黄土粉尘。(2)松嫩盆地东部的黄土粉尘主要来源于科尔沁、松嫩等西北广大沙地,末次冰期是科尔沁等沙地大规模发育的时期。(3)东北地区全新世气候演化可分成5个阶段:10000aB.P.左右,9000aB.P.左右,6000aB.P.前后,4500aB.P.左右,2500aB.P.以后。     

Factors controlling the mineralogy and geochemistry of the recent surface sediments of the Kalloni Gulf,Lesvos Island,Greece

Detailed chemical and mineralogical data are presented for 37 samples of surface sediments collected from the Kalloni gulf, (eastern half), Lesvos island, northern Greece. The sediments are largely carbonate-rich muds, though near the eastern and northern coast of the gulf higher proportions of biogenic and lithogenic sands and gravels occur. The main minerals are quartz, feldspar (andesine), clay minerals (montmorillonite, illite, Kaolinite) and the carbonate minerals (calcite, Mg-calcite, aragonite). The mathematical method of factor analysis was applied in order to explain the mineralogical and geochemical variations. These variations can be interpreted in terms of variations in provenance and depositional environment. Six factors were produced accounting for 83.6 % of the total data variance: (a) a Si-Al-Na-K-Ti-Rb-Ba-Y-Zr factor controlled by clays and detrital minerals such as feldspars and zircon opposed by a CaCO₂-Cu-Sc-Sr-La association (carbonate, minerals), (b) an organic carbon factor (C-Fe-Ce-Zn-Rb-Ni-Y-Nb), (c) a Fe-Mg-Cr-Ni factor representing control by peridotite, (d) a Ce-Nd-Fe-Ni-Zn-La factor controlled by silicate minerals, (e) a Al-Fe-Ti-P-V factor controlled by chlorite amphiboles or pyroxenes of volcanic or basaltic intrusions, (f) a Mn-Fe-Zn-factor controlled by iron-manganese oxides. Similarities in trace element composition among Kalloni gulf bottom sediments, and source lithologies indicate that the trace elements are derived from the adjacent landmasses. The AI/Ti ratio of the sediments is consistent with the terrigenous nature of sendimentation in the Kalloni gulf.     

Interstadial records of the last glacial period at Pantai Remis,Malaysia

Two eustatic high sea stands during the last glacial period are recognised at Pantai Remis. These highstands, lower than present-day sea-level, are tropical manifestations of the ameliorating interstadial climate during the Weichselian/Devensian/Wisconsin glaciation in the Northern Hemisphere. The earlier highstand corresponds to a sea-level of 14.6 m below mean sea-level (MSL). It is interpreted as synchronous with Oyxgen Isotope Stage 5a and is correlated with other known sea-level curves in other parts of the world. The younger high sea stand, dated 55810 ± 1140 to 53870 ± 1400 yr BP, indicates sea-level of 4.3 m below MSL. It represents an interstadial equivalent that lasted for at least 2000 yr, whereas the earlier interstadial period indicates a minimum duration of twice this amount or very likely even longer, as reflected from the thickness of the accumulated deposits. The palynological records indicate that during interstadial times, climatic stability in the tropics is attained and was sufficiently long for vegetation to thrive and develop. The palynofloral constituents of the earlier interstadial phase at Pantai Remis showed the establishment of vegetation in a coastal setting, initiated by Pandanus swamp forests. Simultaneously, mangrove swamp flourished in the lower lying parts of the area, hence the presence of direct tidal influence is evident. Both the Pandanus and mangrove swamps were succeeded by mixed freshwater swamp forests of a Campnosperma–Calophyllum assemblage. Subsequently a slightly open and somewhat drier mixed swamp forest prevailed, marked by the increase in fern spore representation. The later interstadial phase showed shorter vegetation successions, which commenced on the landward edge of a mangrove swamp forest. The mangrove was successively replaced by strand forest, as indicated by domination of Casuarina equisetifolia. The palynological assemblages in both the interstadial periods indicate similarity to the present-day coastal vegetation. This implies that during the interstadials the climate in the lowlands of Peninsular Malaysia and presumably throughout the equatorial region, was as that prevailing today. © 1997 John Wiley & Sons, Ltd.     

中亚黄土沉积与西风区末次冰期快速气候变化

气候快速变化过程与机制一直是古气候研究的热点科学问题,随着不同地区高分辨率地质记录的增多,年代学方法的改进,此类快速气候变化事件的区域差异性日益突出,对比和认识这些区域之间的变化细节,有助于认识快速气候变化的规律和驱动机制。文章以中亚黄土为主要研究对象,根据黄土沉积特征与现代气候特征,将中亚黄土分为西部、北部和东部3个亚区,在总结中亚西风区黄土古气候研究进展的基础上,回顾了近年来中亚地区末次冰期西风区气候突变事件研究现状与问题,初步探讨了在亚轨道尺度上末次冰期快速气候变化发生过程和机制。结果表明,粒度、矿物学、地球化学等指标均指示中亚这3个黄土亚区末次冰期确实存在千年尺度的快速气候波动信号,但在年代和变率上存在区域差异,这种差异除了缺乏精确的年代学控制外,还与区域水热组合和区域地形结构有关。这些冷暖的快速气候变化与北大西洋高纬地区冰盖收缩扩张、西伯利亚高压强度和范围的变化导致风动力变化和西风带南北迁移有关。今后需进一步加强高分辨率年代序列的建立,进一步遴选中亚黄土中有效的、能够独立反映风力强度、源区信息、古温度、古降水等代用指标,并结合古气候模拟试验研究其驱动机制。

     

Hydrothermal alteration of basic island-arc volcanic rocks north and south of Mytilini Town,Lesvos Island,Greece

The mobilities of major and trace elements have been investigated in hydrothermally altered volcanic rocks of Pliocene age on the island of Lesvos. One type of hydrothermal assemblage, montmorillonite-K-feldspar-goethite, was recognized in outcrops north of Mytilini town. The alteration occurs a few metres under the surface of unaltered volcanic rocks of high-K andesite and high-K basaltic andesite composition. The unaltered latite-andesite consists of plagioclase, clinopyroxene, sanidine and magnetite with quartz, calcite, pumpellyite and montmorillonite as subordinate secondary minerals. The main control over major oxide distribution appears to be the extent of conversion of plagioclase to K-feldspar. Three distinct groups of elements were revealed to be positively correlated:

• 1 Si, Mg, Ca, Na, Mn, Sr and Ba, which are leached during the alteration process. This group of elements reflects their association with plagioclase feldspar and clinopyroxene.
• 2 Fe, K, Ti, P, Nb, Zr, Y, Rb, Ni, Cr, V. This group includes elements which are enriched relative to the unaltered volcanic rock, reflecting their association with K-feldspar, iron hydroxides and Ti and P-bearing minerals.
• 3 Ti, P, Nd, La, Ce. From this group of elements it is indicated that Nd, La and Ce are associated with Ti- and P-bearing minerals.

There is no evidence of Cu or Zn addition to the system by hydrothermal fluids since there are no correlations between these base metals and elements enriched in the K-feldspar, montmorillonite-rich zone. This potassic rich zone may be connected with hidden epithermal sulphide mineralization with gold.     

Glacier fluctuations in the southern Peruvian Andes during the late‐glacial period,constrained with cosmogenic 3He

The occurrence of pronounced climate reversals during the last glacial termination has long been recognised in palaeoclimate records from both hemispheres and from high to low latitudes. Accurate constraint of both the timing and magnitude of events, such as the Younger Dryas and Antarctic Cold Reversal, is vital in order to test different hypotheses for the causes and propagation of abrupt climate change. However, in contrast to higher‐latitude regions, well‐dated records from the Tropics are rare and the structure of late‐glacial tropical climate remains uncertain. As a step toward addressing this problem, we present an in situ cosmogenic ³He surface exposure chronology from Nevado Coropuna, southern Peru, documenting a significant fluctuation of the ice margin during the late‐glacial period. Ten tightly clustered ages from a pair of moraines located halfway between the modern glacier and the Last Glacial Maximum terminus range from 11.9 to 13.9 ka and give an arithmetic mean age of 12.8 ± 0.7 ka (1σ). These data constitute direct evidence for a readvance, or prolonged stillstand, of glaciers in the arid Andes of southwestern Peru. Copyright © 2011 John Wiley & Sons, Ltd.