Late glacial to Holocene planktic foraminifera bioevents and climatic record in the South Adriatic Sea

Quantitative analyses of planktic foraminifera, sea‐surface temperatures (SSTs), oxygen isotope and radiocarbon dating from a deep‐sea core recovered in the South Adriatic Sea have been used to reconstruct a subcentennial climatic and biochronological record since the late glacial (the last 24 cal. ka BP). The identification and relative abundance of 25 species of planktic foraminifera along the core have provided a continuous record of the faunal changes over this time interval. These results have permitted the establishment of 10 biozones in the South Adriatic Sea based on the appearance and/or disappearance of the main specific taxa, from peaks of abundance and/or by modification in marine conditions. The robust chronology of the South Adriatic core allowed correlation of SST estimates to the GISP2 ice core record, indicating that the main climate changes recorded in Greenland ice cores over the last 24 ka are recorded and globally synchronous with those observed in the South Adriatic Sea. This finding further allows comparison of the planktic foraminifera record with the event stratigraphic scheme proposed by the INTIMATE group in order to better identify the relationship between past climatic changes and the response of microfaunal assemblages in the South Adriatic. Copyright © 2010 John Wiley & Sons, Ltd.     

Late-glacial climatic oscillations as recorded in Swiss lake sediments

Regional pollen assemblage zones for the late-glacial period of the Swiss Plateau are introduced and defined. They include four major zones (Artemisia, Juniperus—Hippophaë, Betula, Pinus PAZ) with several subzones. Pollen and oxygen-isotope analyses on lacustrine sediments from several lakes in the area reveal four distinct phases of climatic oscillation in the time period of 13 000-9500 yr BP. The first oscillation, termed the Aegelsee fluctuation, occurs shortly before 12 000 yr BP and varve counts suggest its duration was ca. 100 yr. It is characterised by a short decrease in the oxygen isotopes as well as a short increase in NAP associated with a depression in birch pollen values. The second oscillation, which occurs in the δ¹⁸O record shortly before the deposition of the Laacher See Tephra (ca. 11 000 yr BP), is termed the Gerzensee fluctuation. It occurs during a pine-dominated phase and its vegetational effects cannot be determined palynologically. The most prominent regressive phase is the Younger Dryas biozone (ca. 10 700-10 000 yr BP) characterised by an increase in heliophilous NAP and low δ¹⁸O values. The Younger Dryas biozone can often be subdivided palynologically into two parts: a first part rich in grasses and juniper and a second part with higher Filipendula and birch values. During the Preboreal biozone another distinct oscillation is evidenced only in the oxygen isotope ratios. Comparison of the Swiss oxygen isotope profiles with the Greenland Dye 3 record suggests that not only the three major shifts in the δ¹⁸O curves but also the minor ones are closely comparable, suggesting some common climatic control.     

Multiple oscillations during the Preboreal as recorded in a calcareous gyttja,Kingbeekdal, The Netherlands

Environmental changes, occurring during the Weichselian Lateglacial to Early Holocene transition, are supposed to be caused by rapid climate changes. Vegetation changes that occurred during the Early Holocene show a pattern of increased boreal forest development with dominance of birch (Friesland phase) to a more open vegetation with an increase of predominantly grasses (Rammelbeek phase), subsequently followed by renewed birch and, later on, pine forest development. Based on palynological evidence and botanical macrofossils, the Rammelbeek phase is supposed to have been caused by a change to dry, rather than cold climate. Detailed ¹⁴C-dating, using a wiggle-matched AMS-¹⁴C chronology, is used to place the vegetation changes in a time-stratigraphic framework. The Rammelbeek phase can be placed to around 11.3 ka cal BP. A direct correlation to the 11.2 ka event, as recorded in the Greenland ice-cores, is tempting. In this paper we propose an alternative approach by using a common proxy registered in both ice-core and terrestrial records. Based on oxygen isotopes, a Preboreal oscillation (PBO) appears to be present in many Early Holocene lacustrine carbonate-rich records. We used the δ¹⁸O signal of calcareous lake deposits (Kingbeekdal, Southern Netherlands), in which biostratigraphically a Rammelbeek phase is present. The signal in the stable isotopes seems to correlate to the Greenland ice-core records. This exercise shows that the PBO as recorded in the oxygen isotopes occurs not during the palynologically defined Rammelbeek phase but early in the Friesland phase. Moreover, the palynological record of the Kingbeekdal sequence shows, at the level of the δ¹⁸O reversal, a distinct opening of the birch forest and a temporary disappearance of thermophilous taxa, while the light requiring juniper increases. This implies a more complex pattern of climate response registered by the different proxies as previously thought.     

Early-Holocene climatic oscillations recorded by lake-level fluctuations in west-central Europe and in central Italy

On the basis of lake-level data, the period of the Preboreal oscillation (PBO) at 11 300–11 150 cal yr BP as defined by the GRIP oxygen-isotope record appears to correspond to wetter climatic conditions in west-central Europe and to a marked drying in north-central Italy. Additional short-lived phases of higher lake level have been identified before the PBO at ca 11 450–11 400 and 11 350 cal yr BP in west-central Europe, and at ca 11 500 cal yr BP in Italy. Such multiple climatic oscillations around the PBO have been observed in various records in northwestern Europe. On the basis of various proxies, a map of changes in moisture over western Europe during the PBO indicates a mid-latitude zone between 58 and 43°N characterised by wetter conditions, while a drier climate developed in southern and northern Europe. This wet middle zone shows a larger extension and suggests a more meandering, weaker Atlantic Westerly Jet during the PBO than during the 8.2 kyr event. A comparison of lake-level records in west-central Europe with (1) outbursts from North American and north-European proglacial lakes, and (2) variations in solar activity as reflected by ¹⁴C and the ¹⁰Be records supports the hypothesis that the PBO was a response to successive meltwater pulses at 11 300, 11 250, 11 200 and 11 170 cal yr BP and to a sudden decrease in solar activity at 11 250 cal yr BP. This study points to the necessity of developing integrated multi-proxy approaches to construct more robust regional event stratigraphies, and of better documenting palaeohydrological changes in the Mediterranean area.     

Sedimentary responses to the Pleistocene climatic variations recorded in the South China Sea

Grain-size analyses, coupled with end-member modelling, have been performed on the terrigenous fraction of two Leg 184 Ocean Drilling Program sites (1144 and 1146) from the South China Sea. The grain-size distributions over the last 1.8 Ma enable a new interpretation of their connections to sea-level variations and East Asian monsoon strength. Previous investigations in this area have associated grain-size variability with enhanced eolian input during glacial stages. End-member modelling downgrades the importance of this eolian contribution and indicates that the sediments can be described as a mixture of three end-members: fluvial mud inputs, shelf reworking and river mouth migration. Grain-size variations in the Pleistocene section of the cores indicate a multiple-stage evolution: (i) from 1.8 to 1.25 Ma, the downcore grain-size variations are low but show a correspondence between monsoon rainfall intensity and the fine grain-sized fluvial inputs; no link with sea-level variations is noticeable; (ii) from 1.25 to 0.9 Ma, there is an increase (decrease) in the intermediate (fine) end-member (∼ 100 kyr cycle) that is associated with the onset of a stronger summer monsoon and modest shelf reworking; (iii) from 0.9 to 0 Ma the grain-size record is dominated by global sea-level variations; each glacial stage is associated with extensive shelf reworking and conveyance of coarse particles to the basin.     

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.     

Historical tsunamis in the Adriatic Sea

Tsunami activity in the Adriatic Sea from the sixteenth century until the present has been analysed with the ultimate goal to improve the European tsunami catalogue and provide data for a new geo-database of tsunami events in the European-Mediterranean region. The study encompasses twenty-seven events, nine on the western and eighteen on the eastern coast of the Adriatic, with special attention being devoted to contemporary sources and to local journals and newspapers. For all the analysed events, the path of information from coeval sources, through the nineteenth century and up to modern tsunami catalogues, has been constructed. Tsunamis on the western coast have already been studied, but to obtain a coherent picture of tsunamigenic activity in the Adriatic Sea, they have been included in this work. Furthermore, the study was extended to see whether they had propagated to the opposite coast. Most of the events on the eastern coast have now been systematically analysed for the first time. The search of bibliographical sources revealed three new reports on tsunamis on the eastern coast that had not been previously recorded in international publications. The study established that, out of the eighteen eastern Adriatic events, twelve can be considered false, while six were true tsunamis. In the last 600 years, fifteen true tsunami events occurred in the Adriatic. One was very strong, six were strong or rather strong, and eight were light tsunamis. As a final result of this analysis, carried out according to standardised criteria, fifteen Adriatic tsunami events will be inserted in the TRANSFER (Tsunami Risk ANd Strategies For the European Region) database for the European-Mediterranean region.     

Numerical simulation of Holocene depositional wedge in the southern Po Plain-northern Adriatic Sea (Italy)

In the last 10 kyr BP, a coastal depositional wedge formed along the southern Po Plain margin. Shoreline regression accelerated abruptly in the Iron Age, and especially in the last 2 kyr, due to the increased woodland removal on the Apennines. The deposition of the Holocene sedimentary wedge is simulated here, along four coast-tranversal transects, using a finite-element two-dimension mathematical model. The model was constrained using the present topographic surface, the maximum flooding line of the Holocene transgression, architecture and texture of depositional wedge, the location of coastlines, aeolian dunes and ancient offshore delta-sand. The sediment volume required to calibrate the simulations along the sections ranges from about 165,000–870,000 m³ m⁻¹; the maximum tectonic subsidence varies from 0.1 to 0.7 mm yr⁻¹. The minimum sand amount required by the model to stop the accelerated erosion of the Cervia beach is about five times the one employed in recent (April 2002) recovery works.     

Holocene and late-Pleistocene sedimentation in the Adriatic Sea

The following paper is a summary of sedimentological data on the Adriatic Sea (with the exception of the areas along the Jugoslavian and Albanian coasts). Because it is difficult to summarize a summary, only a few of the main conclusions will be mentioned here.Geophysical investigations indicate that the top of the limestone series, underlying the clayey and sandy deposits of the Pliocene and the Quaternary in the Adriatic area has a very uneven topography. Its greatest depths (4–6 km) are found a) between Ravenna and Rimini, b) between San Benedetto and Pescara, and c) below the Albanian shelf.Recent sands are mainly limited to the littoral zone; pleistocene sand, originally supplied by rivers, covers the greater part of the deeper shelf. Between these zones a terrace-shaped pro-littoral mud belt is present, where the bulk of the recent terrigenous mud is deposited. The maximum rate of accumulation in this belt is probably about 4 1/2 mm per year.The remaining part of the recent mud is transported in the sea water as floccules of such small size that they remain suspended over the deeper zones of the shelf. Most of it is deposited in the basins of the Central Adriatic (maximum accumulation rate for the Holocene on the average circa 1/2 mm per year) and in the bathyal basin in the southeast. The deepest area of the latter basin is formed by an almost horizontal plain (circa 1218 m deep). The longest core from this plain (240 cm of Holocene and 400 cm of late Pleistocene) is composed for roughly 61% of turbidite material, 5% of volcanic ash (coarser than fine silt), 0,2% of organic carbonate remains (coarser than silt) and 34% of normal terrigenous mud. The ash falls were limited to the central and southeastern parts of the Adriatic.

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Zusammenfassung Eine kurze Übersicht wird gegeben über die sedimentologische Kenntnis der Adria (mit Ausnahme der jugoslawischen und albanischen Küstengewässer).Geophysikalische Untersuchungen zeigen, daß die Kalkstein-Oberfläche unter den tonig-sandigen Ablagerungen des Pliozäns und des Quartärs, ein starkes Relief besitzt. Sie hat ihre größten Tiefen (4–6 km) a) zwischen Ravenna und Rimini; b) zwischen San Benedetto und Pescara und c) im Untergrund des Albanischen Schelfes.Rezente Sande sind in der Hauptsache auf eine schmale Küstenzone beschränkt. Dagegen haben pleistozäne Residual-Sande, ursprünglich von Flüssen herbeigebracht, eine große Ausdehnung auf dem Schelf. Zwischen diesen beiden sandigen Zonen findet man einen pro-littoralen Schlicksaum, wo die Hauptmasse des rezent ins Meer gebrachten terrigenen Schlickes abgelagert wird. Die maximale Akkumulationsgeschwindigkeit in dieser Zone beträgt wahrscheinlich ungefähr 4 1/2 mm pro Jahr.Der Anteil des terrigenen Schlickes, der nicht in diesem prolittoralen Schlicksaum zur Ablagerung kommt, besteht aus Flocken von so kleinen Abmessungen, daß sie während ihres Transportes über den äußeren Schelf-Regionen suspendiert bleiben. Sie sedimentieren größtenteils in den Becken der Zentral-Adria (mittlere Ablagerungsrate während des Holozäns maximal etwa 1/2 mm pro Jahr) und im bathyalen Becken der Südost-Adria.Der tiefste Teil dieses südöstlichen Beckens wird von einer fast horizontalen Ebene (auf etwa 1218 m Tiefe) eingenommen. Der längste Kern, der in dieser Ebene entnommen wurde (640 cm, wovon 240 cm Holozän), hat ungefähr die folgende Zusammensetzung: 61% Turbidit-Material, 5% vulkanische Asche (Sand- und grobe Schluff-Fraktionen), 0,2% organische Kalkreste (gröber als Schluff) und 34% normaler terrigener Schlick. Die Aschenfälle waren auf die mittleren und südöstlichen Teile der Adria beschränkt.

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Résumé L'auteur donne un bref résumé de la connaissance sédimentologique de la Mer Adriatique (à l'exception des parties le long des côtes Jugoslaves et Albanaises).Des recherches géophysiques indiquent que la surface du calcaire couvert par les dépôts argileux-sableux du Pliocène et du Quaternaire a un relief prononcé. Cette surface atteint des profondeurs maximales (4–6 km) a) entre Ravenna et Rimini, b) entre San Benedetto et Pescara et c) au-dessous du plateau continental Albanais.Les dépôts sableux d'âge Holocène sont limités pratiquement à l'étroite zone du littoral. Par contre, des sables pléistocènes résiduels, d'origine fluviale, couvrent de vastes étendues du plateau continental sous-marin. Entre ces deux zones sableuses, on trouve la bande vaseuse «pro-littorale», où se dépose la plus grande partie de la matière vaseuse terrigène, apportée à la mer sous les conditions actuelles. L'accumulation maximale dans cette zone est probablement de l'ordre de 4 1/2 mm par an.La partie de la vase terrigène qui dépasse cette bande pro-littorale est transportée dans la mer à l'état de flocons d'une taille si petite qu'ils restent en suspension au-dessus des parties extérieures du plateau continental. Ils sont déposés surtout dans les bassins de l'Adriatique Centrale (vitesse moyenne d'accumulation pendant l'Holocène au maximum environ 1/2 mm par an), et dans le bassin bathyal du Sud-Est.La partie la plus profonde dans ce dernier bassin est formée par une plaine presqu' horizontale (à environ 1218 m). La carotte la plus longue, tirée de cette plaine (640 cm, dont 240 cm d'Holocène) est constituée approximativement de 61% de matériel turbiditique, de 5% de matière volcanique (fractions de sable et de silt grossier), 0,2% de restes calcaires organiques (plus grossier que du silt) et 34% de vase terrigène normale. Les chutes de matière volcanique étaient limitées aux parties centrales et sud-orientales de l'Adriatique.

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— . , . (4–6 ) : a) Ravenna Rimini; ) San Benedetto Pescara ) . , , - , , pro-litto-ralen , . 4,5 . , ( 1/2 ) - . 1218 . , 640 , 240 . : 61% , 5% , 0,2% 34% . - .

     

Preboreal climate oscillations in Europe: Wiggle-match dating and synthesis of Dutch high-resolution multi-proxy records

In order to compare environmental and inferred climatic change during the Preboreal in The Netherlands, five terrestrial records were analysed. Detailed multi-proxy analyses including microfossils (e.g., pollen, spores, algae, and fungal spores), macroremains (e.g., seeds, fruits, wood, mosses, etc.), and loss on ignition measurements were carried out with high temporal resolution. To link the five Preboreal records, accurate chronologies were produced by AMS ¹⁴C wiggle-match dating. The Dutch records show that following the Lateglacial/Holocene climate warming, birch woodlands expanded between 11,530 and 11,500 cal BP during the Friesland Phase of the Preboreal. After the Friesland Phase, two distinct climatic shifts could be inferred: (1) around 11,430–11,350 cal BP the expansion of birch forests was interrupted by a dry continental phase with open grassland vegetation, the Rammelbeek Phase. This phase was coeval with the coldest part of the Preboreal oscillation (PBO) as observed in the δ¹⁸O record of the Greenland ice-core records and has been attributed to a large meltwater flux that resulted in a temporary decrease of the thermohaline circulation in the North Atlantic. (2) At the start of the Late Preboreal, between 11,270 and 11,210 cal BP, a sudden shift to a more humid climate occurred and birch forests expanded again. A simultaneous increase in the cosmogenic nuclides ¹⁴C and ¹⁰Be suggests that these changes in climate and vegetation were forced by a sudden decline in solar activity. Expansion of pine occurred during the later part of the Late Preboreal. At the onset of the Boreal, between 10,770 and 10,700 cal BP, dense woodlands with hazel, oak, elm and pine started to develop in The Netherlands.     

Seasonal and interannual variations in pigments in the Adriatic Sea

Spatial and temporal variability of pigments was studied from the CZCS satellite data and fromin situ chlorophyll and transparency for the period 1979-1985. The three Adriatic sites, Northern, Middle, and Southern Adriatic are differently influenced by meteorological, hydrological and oceanographic parameters. The differences between seasonalin situ chlorophyll and remotely sensed pigment concentrations (from CZCS satellite data) from the Adriatic are large in winter. Through the correlation analysis, pigments were compared to meteo-oceanographic and hydrological parameters from different Adriatic sites. The PCA (principal component analysis) was applied to the pigment data series and significant components were compared. Different correlations are obtained for warm and cold periods of the year pointing to seasonal differences in the underlying mechanism of pigment variability. The first PC is influenced mainly by temperature. In the warm period more parameters seem to influence the pigment field, than in the cold period. The pigments in the Adriatic are in good correlation to a number of hydrologic and meteo-oceanographic factors.     

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.     

Recent climatic tendencies in the Barents Sea

Based on the results of multiannual oceanographic research at the Murmansk Marine Biological Institute in the “Kola Meridian” secular section, the recent tendencies of cyclic climate changes in the Barents Sea are discussed on the basis of the data on ice coverage and coastal meteorological conditions. It has been shown that a return from the extremely warm and warm state to the normal one was observed in the period of winter 2005/06–winter 2010/11. Further, this may be changed both to cooling and warming, which verifies the hypothesis about predominance of cyclic natural variability in the thermal and ice characteristics of the Arctic Region.     

Calibrating pollen data in climatic terms: Improving the methods

When properly calibrated, Holocene pollen data provide an important source of quantitative information about Holocene climates. Multiple linear regression of modern climate and pollen data allows the development of statistical calibration functions that transform percentages of certain pollen types into quantitative estimates of climatic variables, and these functions, when applied to Holocene pollen data, yield estimates of climatic variables for past times. Confidence intervals for the climatic variables provide estimates of the statistical errors. These interval estimates are based upon the following statistical assumptions: (1) the regression model is appropriate; (2) the errors in measuring the climate variables are independent, normally distributed and have constant variance; and (3) no outliers are present. We outline the steps to be followed in calculating calibration functions, including (1) selecting the calibration region; (2) selecting a pollen sum; (3) analyzing scatter diagrams of a given climate variable against each pollen type; (4) deleting outliers and transforming pollen data; (5) performing the regression; and (6) testing the appropriateness of the statistical assumptions. We used available computer programs for most of this study. In addition, we developed new software to compute the Moran statistic to test for spatial autocorrelation among the regression residuals, using the dual of the Voronoi diagram to describe the spatial relationships among the sites. In order to illustrate the sequence of procedures, we used data from the lower peninsula of Michigan to develop a calibration function for July mean temperature and then used Holocene pollen data from central lower Michigan to estimate past temperatures.     

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。

     

Assessing meteotsunami potential of high-frequency air pressure oscillations observed in the middle Adriatic

High-resolution air pressure series collected from a triangle of middle Adriatic microbarograph stations between April 2009 and March 2011 have been analysed to extract the rapid pressure changes normally found during meteotsunamis. Five-minute air pressure tendencies were used to detect an event. Wavelet and cross-wavelet analysis showed that the energies of high-frequency pressure changes that occurred during the warm part of the year were an order of magnitude higher than those that occurred during the cold part of the year. Coherence between stations was normally found at periods longer than 1 h, while air pressure disturbances were dispersive and not coherent at shorter periods. This implies that the disturbances had little to no potential to generate meteotsunamis in the middle Adriatic area, as the eigenoscillations in bays and harbours of the region are over timescales of minutes up to a few tens of minutes.     

Brine formation recorded by stable isotopes of Recent benthic foraminifera in Storfjorden,Svalbard: palaeoceanographical implications

We discuss water oxygen isotopes (δ¹⁸O_w) and carbon isotopes of dissolved inorganic carbon (δ¹³C_DIC) of brine‐enriched shelf water (BSW) from Storfjorden (southern Svalbard) in comparison to Recent benthic foraminiferal δ¹⁸O_c and δ¹³C_c calcified in the same water. We determined relatively high δ¹⁸O_w values of 0.15±0.03‰ VSMOW in BSW below sill depth at temperatures below ?1.8 °C, and high δ¹⁸O_c values of 3.90±0.18‰ VPDB. Such high BSW δ¹⁸O_w cannot significantly deplete ¹⁸O_w contents of Arctic Ocean deep water; furthermore, such high δ¹⁸O_c cannot be distinguished from δ¹⁸O_c values of 3.82±0.12‰, calcified in warmer Arctic and Nordic seas intermediate and deeper waters. Today, in Storfjorden low benthic δ¹³C_c and high δ¹⁸O_c reflect the low δ¹³C_DIC and relatively high δ¹⁸O_w of BSW. High benthic δ¹⁸O_c is in contrast to expected low δ¹⁸O_c as brine rejection is widely thought to predominantly take place in surface water diluted by meteoric water with very low δ¹⁸O_w. Low epibenthic δ¹³C_c values of 0.50±0.12‰ partly reflect low δ¹³C_DIC caused by enhanced uptake of atmospheric low δ¹³C_CO2 decreased by anthropogenic activities. An adjustment for preindustrial higher values would increase δ¹³C_c by about 0.6‰. Therefore, in Storfjorden brine formed before the industrial era would be characterized by both high δ¹³C_c as well as high δ¹⁸O_c values of benthic foraminiferal calcite. Our data may cast doubt on scenarios that explain negative excursions in benthic foraminiferal stable isotope records from the Atlantic Ocean during cold stadials in the last glacial period by enhanced brine formation in Nordic seas analogously to modern processes in Storfjorden.     

基于叶蜡正构烷烃重建的南海及周边地区植被类型

陆地植被类型的变迁是对地质历史时期古环境变化的响应, 而植物表层产生的叶蜡则记录了这些变化。叶蜡中长链正构烷烃的参数指标CPI、∑Odd(C25~33)、ACL和δ13Cn-alkane 为判识沉积物的来源、陆源物质供应量、植被类型变化等提供了重要参考。本文利用现代遥感技术提供的植被类型、植被覆盖度等信息, 初步调查了南海周边植被类型的覆盖情况, 结果表明C3植被覆盖率具有压倒性优势, 而C4植被大多分布在中国云南省附近以及柬埔寨境内; 南海北部表层沉积物的δ13C31记录与遥感数据得到的珠江流域平均δ13C31值较为一致, 据此我们认为南海北部沉积物的记录能够反映周边河流流域的植被变迁。本文还将南海北部MD12-3433站位作为实例, 通过分析长链正构烷烃的几个参数, 认为末次盛冰期早期南海海平面降低, 气候相对变干, C4植被相对增多; 而后C4植被丰度逐渐降低, 在新仙女木事件期间植被类型存在明显波动变化, 在较为暖湿的中晚全新世时期C3植被占据主导优势。