Journal of Conference Abstracts

Symposium B01

Session B01:1B

B01 : 1B/25 : F7

Climatic Changes as a Function of Ocean Circulation Changes

Nils-Axel Mörner (morner@pog.su.se)

Paleogeophysics & Geodynamics, Stockholm University, Stockholm, Stockholm

The ocean circulation is not only driven by thermal-haline forces. The interchange of angular momentum between the hydrosphere and the solid Earth is another fundamental factor. This can be demonstrated for the ENSO-events, for the last centuries' instrumental data, for decadal-to-century changes during the Holocene, for the high-amplitude climatic-eustatic changes some 13-10 ka ago, and for the main glacial/inter-glacial cycles. The oceans have a remarkable heat-storing capacity. Therefore, any change in the ditribution of the water masses will also have strong effects on the global temperature distribution. When the glacial eustatic sea level rise finished in Mid-Holocene time, the Earth came into a new dynamic mode where the feed-back interchange of angular momentum between the solid Earth and the hydrosphere got a dominant role for the distribution of heat (recorded in the regional paleoclimatic changes) and mass (recorded in the regional sea level changes) due to its effects on the ocean circulation (especially pulses in the Gulf Stream transport) generating climatic changes on a decadal-to-century basis (some sort of Super-ENSO events).

Mörner, 1984, Climatic Changes on Yearly to Millennial Basis, Reidel Publ. Co, 483-507, 637-651, (1984).

Mörner, 1988, Secular Solar and geomagnetic Variations in the last 10,000 years, Kluwer Acad. Publ, 455-478, (1988).

Mörner, 1993, Global and Planetary Change, 7, 211-217, 243-250, (1993).

Mörner, 1995, Geo. Journal, 37.4, 419-430, (1995).

Mörner, 1996a, Zeitschrift für geomorphologie, N. F. , Suppl-Bd, 102, 223-232, (1996).

Mörner, 1996b, An. Acad. bras. Ci, 68, supl.1, 77-94, (1996).

B01 : 1B/26 : F7

Millenial-Scale Climate Instability of Tropical Asia During the Last 60 kyr

Xiangjun Luo (xjluo@gfz-potsdam.de),

G. Schettler,

N. Nowaczyk,

J. Mingram,

J. Negendank &

Liu Jiaqi

GeoForschungsZentrum, Telegrafenberg A17, Germany

Millenial-scale climate changes not paced by orbital variations seem widely recorded in high latitutes and there is an asynchronous response between the Northern and southern hemispheres. However, the globalization of these cycles are not yet evidenced. The records of tropics in general and the Pacific in particular badly need to be enhanced. Here we describe a multiproxy network composing geophisical, geochemical and biomass datasets recovered from Lake Huguang Maar, south China, which clearly shows millenial-scale instability exsisting in Tropical Asia in time when they occurred in the high latitutes. It seems that warm events are sychronous in Asian tropic and Antarctica, whereas could variations are sychronous in Tropical and North Atlantic regions.

B01 : 1B/27 : F7

Palaeoenvironmental Informations Recorded in Speleothems from North-Western Romania

Tudor Tamas (tudort@hera.ubbcluj.ro)¹ &

Christiane Causse (causse@lsce.cnrs-gif.fr)²

¹ Fac. of Geology, Dpt of Mineralogy, Babes-Bolyai University, 3400 Cluj-Napoca, ROMANIA

² LSCE UMR CNRS-CEA, Domaine du CNRS Bat 12, 91198 Gif/Yvette Cedex, FRANCE

Caves commonly provide suitable sites for the accumulation of chemical, detrital and organic deposits, as in these environments the effects of sub-aerial weathering are much reduced. Such conditions favour long term preservation of the carbonated deposits. Thus, speleothems contain interesting palaeoenvironmental informations, which are closely related to their growth periods. The geographical position of Romania, south of the extension of the Pleistocene ice sheet, makes speleothem dating and stable isotope analyses valuable for palaeoenvironmental reconstitutions. Present climatic conditions of the studied region (Bihor Mountains, NW Romania) are typical of a continental area, with six months of snow, more than 1400 mm/year of rain, at an altitude around 1250 m asl.

Our present work was focused on the geochemical study of a 34 cm stalagmite, located in a remote fossil passage of V11 Cave. Several distinct superimposed growth levels have been sampled, each sample being 4 to 5 mm thick and weighing less than 1 gram. Each of them consists of pure, white or yellowish white calcite, apparently suitable for U-Th dating by means of thermal ionisation mass spectrometry. Uranium contents as well as ²³⁴U/²³⁸U activity ratios (AR) are relatively similar along the growth axis. Mean values are respectively equal to 0.384 ppm and 0.963. ²³⁰Th /²³²Th activity ratios are generally greater than 200.

All calculated ages showed no inversion along the growth axis. A calcite level from the lowest part of the stalagmite has given an age of 124 ka (±2 as 2<sigma>). The top level has given an age around 5634 years (±125). Several hiatuses were identified, some of which are marked by clay layers. The longest growing interruption, almost non visible on a vertical polished section, took place between 46.56 ka (±0.41) and 14.35 ka (±0.09).

The results of thermal ionisation mass spectrometric U-Th dating, stable isotope analyses and on-going measurements are presented, as well as palaeoenvironmental considerations.

B01 : 1B/28 : F7

Holocene Climate Instability on the Eastern Margin of the N. Atlantic; Evidence from Irish Speleothems

Frank McDermott (fmcder@macollamh.ucd.ie)¹,

YiMing Huang (y.huang@keele.ac.uk)²,

Antonio Longinelli (labgeois@univ.trieste.it)³,

Chris Hawkesworth (c.j.hawkesworth@open.ac.uk)⁴ &

Ian Fairchild (i.j.fairchild@keele.ac.uk)²

¹ Department of Geology, University College Dublin, Belfield, Dublin 4, Ireland

² Department of Earth Sciences, Keele University, Staffordshire ST5 5BG, U.K.

³ Dipartimento Scienze della Terra, via E. Weiss 6, University of Trieste, Trieste 34100, Italy

⁴ Department of Earth Sciences, The Open University, Milton Keynes, KK7 6AA, U.K.

A continuous time-series O isotope profile for the Holocene has been obtained from a TIMS U-Th dated stalagmite from a cave on the Atlantic margin (Crag Cave, S.W. Ireland). The stalagmite was deposited in isotopic equilibrium with its drip-water and it exhibits low ¹⁸O at 10,000 cal. yr. B.P. (-2 ") reflecting cool conditions. By the early to mid-Holocene (9000-6000 cal. yr. B.P.) ¹⁸O had increased to +3", reflecting warmer conditions on the Atlantic seaboard. Significantly, this shift to higher ¹⁸O was accompanied by a marked increase in the stalagmite growth-rate. The stalagmite growth-rate exhibits a gradual decline, accompanied by decreasing ¹⁸O through the Holocene until 3,500 years ago. This is interpreted as a cooling trend. There is evidence for a gradual increase in both ¹⁸O and growth-rate in the period from 3,500 cal. yr. B.P. to the present-day, suggesting a return to warmer conditions on the Atlantic seaboard. Superimposed on these first-order trends are several strong century-scale cooling events (excursions to low ¹⁸O) which coincide exactly with five of the six Holocene ice-rafting events recognised in two north Atlantic cores (Bond et al., 1997). These sub-Milankovitch cooling events also correlate with recently recognised Central European pre-Roman cooling events (Haas et al., 1998) indicating that the effects of these cooling events were not confined to the N. Atlantic margin. Carbon isotope ratios in the stalagmite vary independently of oxygen isotope ratios, but are highly correlated with the trace element ratios Mg/Ca and Sr/Ca. Studies of seasonal changes in modern cave drip-water chemistry indicate that the latter trace element ratios are sensitive to paleohydrology (water-rock contact times) and so are interpreted as reflecting paleo-precipitation changes.

Bond, G, Showers, W, Cheseby, M, Lotti, R, Almasi, P, deMenocal, P, Priore, P, Cullen, H, Hajdas, I & Bonani, G, Science, 278, 1257-1266, (1997).

Haas, JN, Richoz, I, Tinner, W & Wick, L, The Holocene, 8, 301-309, (1998).

B01 : 1B/29 : F7

A Strontium, Carbon and Oxygen Isotopic Record of Climatic Changes from a Holocene Speleothem in Belgium

Sophie Verheyden (sverheyd@vub.ac.be)¹,

Dominique Weis (dweis@pop.ulb.ac.be)²,

Ian Fairchild (gga30@keele.ac.uk)³,

Frank McDermott (FMCDER@macollamh.ucd.ie)⁴,

Yves Quinif (yves.quinif@fpms.ac.be)⁵ &

Eddy Keppens (ekeppens@vub.ac.be)¹

¹ Department of Geology (GISO-WE), Vrije Universiteit Brussel, Pleinlaan 2, B 1050 Brussel, Belgium

² Departement des Sciences de la Terre et de l'Environnement, , Université Libre de Bruxelles, 50, Av. F.D. Roosevelt, B 1050 Bruxelles, Belgium

³ Department of Earth Sciences, Keele Unviersity, Straffordshire, ST5 5BG, UK

⁴ Department of Geology, University College Dublin, Belfield 4, Ireland

⁵ Faculté Polytechnique de Mons, 9 rue de Houdain, B 7000 Mons, Belgium

A speleothem (U/Th-dated : 12, 700 a BP-2000 a BP) from the Père Noël cave (Han, Belgium) was analysed for C, O (PDB, <sigma><0.1‰), Sr, Mg, Ca, and ⁸⁷Sr/⁸⁶Sr (<sigma><0.00002).

The C- and O-values are not in agreement with expected values for a C3 vegetation cover and display important shifts (see Figure.)

This observation (1), the outspoken covariation of C and O along the timeseries (2), in recent precipitates (sodastraws and collected on glass slabs) (3), along growth layers (4), and with Sr/Ca - and Mg/Ca - ratios along timeseries (5), support the concept that non-equilibrium conditions, due to evaporation, were often present during deposition of this stalagmite.

Consequently, we propose that this stable isotopic record reflects changes in the palaeohumidity, rather than those of the palaeotemperature. However, the long term O increase of about 0.7‰ between 12,000 a BP and 4,000 a BP may be related to a temperature rise of about 5.5°C, accepting a -1.2‰ shift in seawater (and meteoric waters) O over this same period.

The Sr isotopic curve along the time-axis (see Figure) somewhat follows (the ups and downs of) the d-curves and rather has an overall decreasing trend towards the more recent parts (excepted the top). Speleothem values (all over 0.7088) cannot be explained by mixing of dissolved bedrock carbonate (Givetian limestone: 0.70808 for calcite, 0.70818 for dolomite) with (airborne) modern marine Sr (0.7091) alone. Carbonaceous bedrock would then contribute for only O to 20% to the speleothem Sr. Obviously, high ⁸⁷Sr leachates (well above 0.709) from detrital radiogenic ⁸⁷Sr rich minerals (clays dispersed within the bedrock or in overlying soil) intervene. In this respect, the generally decreasing trend of the Sr isotopic signature may be explained by rapid weathering of a recent detrital sediment cover (last glacial loess ?).

The shorter term variations in the Sr isotopic signature however, may be induced, just like the other signals, by changes in palaeohumidity, affecting the balance of different Sr sources, also by differential leaching of various carbonate phases and detrital, ⁸⁷Sr enriched phases.

(This study was partially financed by the E.C.: EV5V-CT94-0509).

B01 : 1B/30 : F7

Travertine Record of Climate and Groundwater Change in Central Europe During the Late Quaternary

Norbert Frank

(fn@uphys1.uphys.uni-heidelberg.de)¹,

Augusto Mangini

(mg@uphys1.uphys.uni.heidelberg.de)¹,

Steve Goldstein (stve@ldeo.columbia.edu)² &

Sidney Hemming (sidney@ldeo.columbia.edu)²

¹ Heidelberger Akademie der Wiss., Im Neuenheimer Feld 366, Heidelberg, Germany

² LDEO of Columbia University, Palisades, NY-10964, USA

Travertine growth in Central Europe links to Interglacial periods, because calcite precipitation is dependent on the geochemical composition of the groundwater and climatic boundary conditions like temperature, precipitation and atmospheric CO₂. In this paper we present precise mass spectrometric Th/U and Pa/U ages as well as geochemical and Sr-isotope data of three pleistocene travertine deposits in Bad Cannstatt/Germany. Major episodes of travertine growth occured in Central Europe at site Deckerstrasse (DE) and quarry Biedermann (BI) at 99.8±1.3 ka and 105.9±1.3 ka, corresponding to marine isotope stage (MIS) 5/3. The absence of travertine accumulation between these two episodes reflects a growth interruption that may be linked to the transition between pollen derived climate episodes St. Germain I and II in Central Europe. A silt layer recorded in BI, may be linked to another cold episode, St. Germain I-B. Both deposits yield a distinct geochemical record and rather different ⁸⁷Sr/⁸⁶Sr values (0.7110-0.7112 DE and 0.7095 - 0.7098 BI) as well as distinct initial ²³⁴U/²³⁸U values (2.37 DE and 2.24 BI), reflecting either regional variability of groundwater composition or a time-dependent change of groundwater mixing from different sources. The deposit Haas/Lauster was suggested to reflect the "Holstein Interglacial" period. Th/U dating yield ages of 280-410 ka, thus corresponding to MIS 9 or 11.The geochemical record is less distinct compared to MIS 5 deposits but shows highest Sr-isotope values of 0.7119. Travertine formation further occured during the early Holocene and MIS 5/5, but so far we found no evidence of travertine formation during MIS 2,3,4, 5/1 and 7 confirming that calcite precipitation in the Bad Cannstatt area most likely occurs during times of specific climate boundary conditions, previously described as mediterranean type climate [Reiff, 1986; Koban und Schweigert, 1993]. Further, the geochemical- and isotope-record clearly indicate changes of the groundwater composition with time. The results indicate that dating of travertines, even when accumulation is discontinous, can provide important constrains on continental climate records. Further understanding of hydrology can be obtained by applying geochemical tracers.

Reiff W, Fundberichte aus Baden-Württemberg, 11, 2-24, (1986).

Koban CG & Schweigert G, Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, 189, 171-197, (1993).

B01 : 1B/33 : F7

Paleoclimatic Implications of the Oxygen Isotope Record from Mammoth Teeth and Bones: Late Pleistocene and Early Holocene on Wrangel Island, Eastern Siberia

Juha A. Karhu (Juha.Karhu@gsf.fi)¹,

Sergey L. Vartanyan (sv@SV1226.spb.edu)² &

Göran Possnert³

¹ Geological Survey of Finland, P:O: BOX 96, FIN-02151 Espoo, Finland

² Wrangel Island State Reserve, 687870 Ushakovskoye, Magadan Region, Russia

³ Uppsala University, P.O. BOX 534, 75121 Uppsala, Sweden

Wrangel Island in eastern Siberia is the last and only known Holocene refugee of mammoths (Vartanyan et al., 1993). Mammoth remains have been uncovered from permafrost and are generally very well preserved. In order to investigate climatic changes at the Pleistocene-Holocene transition and during the early Holocene, we determined the ¹⁸O values of carbonate (¹⁸O_c) and phosphate (¹⁸O_p) in skeletal apatite from mammoth teeth and bones recovered from the island. In addition to existing C-14 dated material, 23 new molar teeth, most of them collected during the 1997 expedition to the island, have been dated by AMS.

A great majority of the dated teeth and bones are Holocene with calibrated ages ranging from 4 to 9.5 ka BP. The ages of the Pleistocene samples vary from 14 to 26 ka BP (calib.). The ¹⁸O_c and ¹⁸O_p values are generally well correlated with an average fractionation of about 9 per mil between phosphate and carbonate oxygen, confirming good preservation of the samples. At the Pleistocene-Holocene boundary both isotope systems record a dramatic shift in isotope ratios: The ¹⁸O_c values change from about 14 to 19 per mil and ¹⁸O_p from about 5 to 10 per mil. The ca +5 per mil change in the isotope values of the skeletal components reflects an approximately equivalent shift in the isotopic composition of the local precipitation. The magnitude of the shift is in the same range as that in the published ¹⁸O records from Greenland ice cores and suggests that terminal Pleistocene warming was roughly equal everywhere in the Arctic. The Holocene ¹⁸O_p record shows relatively high values at about 10 per mil from 9.5 to 7.5 ka BP, a distinct minimum between 7 and 6 ka BP and high values again from 5.5 to 4 ka BP (calibr.). During the minimum the ¹⁸O_p values of mammoth skeletal remains are 1 to 2 per mil lower compared to the adjacent intervals indicating significantly lower surface temperatures during that period. The oxygen isotope trend has similarities with other reported paleoclimatic records from Eurasia and other continents suggesting that the observed pattern has wider than just local significance.

Vartanyan SL, Garutt VE & Sher AV, Nature, 362, 337-340, (1993).

B01 : 1B/34 : F7

Climate and Boreholes: Basic Results of the First Year of the IGCP 428 Project

Vladimir Cermak (cermak@ig.cas.cz) &

Jan Safanda (jsa@ig.cas.cz)

Geophysical Institute, Czech Acad.Sci., 141-31 Praha 4, Czech Republic

A new International Geological Correlation Programme (IGCP) Project No.428 started under the activities of the UNESCO in 1998. Project focusses on the inversion of the borehole temperature-depth profiles into the ground surface temperature history (GSTH) in an attempt to reconstruct the climate changes of the past 300-400 years with special attention on the recent climate warming. The five year project (1998-2002) has grouped specialists from more than 30 countries all over the world and its major target includes to document the general feasibility of the method and to widely present a new independent technique to complete the instrumental and proxy data for climate reconstruction. The obtained GSTHs from various regions proved the general warming by about 1-2 K since the beginning of this century with relatively less pronounced local variations, both in warming magnitude and exact timing of its culmination, which may characterize the specific zones of climate development. By detailed quantitative evaluation one can demonstrate a certain role of the natural and anthropogenic climate forcing, such as deforestation, land use and urbanization. Even when the GST generally follows the surface air temperature (SAT), both temperatures are not identical, GST being slightly higher, and their differences reflect environmental factors, such as precipitation and evaporation character, snowfall and vegetation cover.

B01 : 1B/35 : F7

Cosmogenic He and Ne Dating of Glacial Striae, Polished Surfaces and Moraine Boulders in the Chilean High Cordillera (22°-28° S)

Konrad Hammerschmidt

(chemie@zedat.fu-berlin.de)¹,

Martin Grosjean (grosjean@giub.unibe.ch)²,

Anselmo Pedroni¹ &

Hans Friedrichsen¹

¹ Freie Universität Berlin, Malteserstrasse 74 - 100, D - 12249 Berlin, Germany

² Geographisches Institut,Universität Bern, Hallerstr 12, CH-3012 Bern, Switzerland

In the Chilean High Cordillera, between 18° and 30° S at 4200-5100 m a.s.l., glacial deposits and structures are found with a gap between 25° and 27° S devoid of signs of glaciation, the so-called Andean Dry Diagonal (ADD). The timing of glaciations N and S of the ADD is a challenging problem. To date, there are two contrasting scenarios: (a) the glaciations N and S of the ADD have been contemporaneous to the Late Glacial Maximum in Bolivia and Peru or (b) at least the last glaciation S of the ADD is older.

In order to establish time constraints to this problem, in-situ accumulated cosmogenic He and Ne have been investigated in mineral separates (Px, Hbl, Bt, Qtz and Plg) of andesite samples with glacial striae and polished surfaces from El Laco (23°47'-23°52'S) and Deslinde (22°17'S), and moraine boulders from Tres Croces (27°03'S) and Jotabeche (27°37'S). Cosmogenic ages calculated from ³He_cosm concentration in Hbl for Jotabeche and Tres Croces range from 271 to 297 ka and show an excellent agreement to ²¹Ne_cosm ages of between 280 and 304 ka. By contrast, Hbl and Px from Deslinde and El Laco reveal ³He_cosm ages in the range of 16.8 to 24.2 ka, but ²¹Ne_cosm age values near or below detection limit (approx. 20 ka). Px from an individual sample with a polished surface from El Laco (23°50'46") was found with ³He_cosm and ²¹Ne_cosm ages of 226 ka and 287 ka, respectively.

Loss of He_cosm of more than 90% was observed in Bt, Plg, and Qtz, but only a minor loss of Ne_cosm in Qtz and Plg indicating these minerals are not suitable for cosmogenic dating work.

The age values of about 270 ka suggest that an older Late Pleistocene glaciation has obviously occurred N and S of the ADD, whereas evidence for the Late Glacial Maximum, with ages of about 24 -15 ka, is found only N of the ADD.

B01 : 1B/36 : F7

"Lenin Isotope D-Effect" in Carbon Isotope Ratios in Tree-ring Cellulose: A Potential Toll to Reconstruct Variation in Fossil Fuel Burning

Mariusz Orion Jedrysek (morion@ing.uni.wroc.pl)¹,

Grzegorz Skrzypek,

Adam Kaluzny &

Marek Krapiec²

¹ Lab. Isot. Geol. & Biogeochem., Univ. Wroclaw, Cybulskiego 30, 50-205 Wroclaw, Poland

² Fac.Geology, Academy of Mining and Metallurgy, Mickiewicza 30, 30-059 Krakow, Poland

Carbon and hydrogen stable isotopes analyses have been carried out in vertical peat profiles and tree rings cellulose (Southern Poland). Anthropogenic impact caused by, neighboring to the sampling area, "Lenin" steelworks in Nowa Huta (constructed in 1950's near Kraków) has been observed. It has been found that the anthropogenic impact shift about 3 per mill the ¹³C into more positive values. This is in contrast to a negative shift expected (decrease in the atmospheric ¹³C (carbon dioxide) value resulted from fossil fuel burning). This could be called - "Lenin isotope d-effect" and is probably resulted from increased concentration of atmospheric carbon dioxide and elevated precipitation caused by increased concentration of industrial dust. In average, in the last millennium (X-XIX century), the peat is 0.93 per mill isotopically heavier as compared to the corresponding tree ring cellulose. The last century is excluded from this simple calculation as the fossil fuel burning significantly influenced carbon dioxide concentration and ¹³C (carbon dioxide) value in the atmosphere. It has been evidenced that the carbon and hydrogen isotope ratios in peat profiles and tree-ring cellulose is controlled by precipitation and temperature when air is clean, and by dust and CO₂ emission when the air is polluted. This could be a basis to calibrate a new toll to reconstruct (in the past) variations in local fossil fuel burning and CO₂ concentration in the atmosphere.

The Late Paleolake Sequence from the Santa Rosa Canyon, Northeastern Mexico

Miguel Angel Ruiz-Martinez

(miruiz@awi-potsdam.de)¹,

Hans-Wolf Hubbertem (hubber@a-potsdam.de)¹,

Jaime Urrutia-fucugauchi (juf@tonatiuh.igeofcu.unam.mx)²,

Thierry Adatte, (Thierry.Adatte@geol.unine.ch)³,

Leif Brandenburg

(LBrandenb.ABO-D@t-online.de)⁴,

Bernd Eccarius⁴,

Joerg Werner (fax: 52-821-2-43-26)⁵,

Alberto De Leon-Gutierrez ⁵ &

Luis Martinez-Llamas (FAX. 52-821-2-42-51)⁶

¹ Telegrafeberg str. 43 A, 47473 Potsdam, Germany

² Inst.Geofisica, UNAM, 04510 Mexico, D.F., Mexico

³ Inst. de Geologie, Neuchatel, 2007, Switzerland

⁴ inst. Geolgie, University Kiel, Germany

⁵ Fac. C.de la tierra, UANL, 67 700 Linares, N.L., Mexico

⁶ Fac. Ciencias Forestales, UANL, 67 700 Linares, NL., Mexico

A multidisciplinary research project was started to investigate the Quaternary paleoclimatic and paleoenvironmental evolution of northeastern Mexico. Geochemical, pollen, mineralogical, sedimentological, paleomagnetic and stratigraphic studies in sedimentary deposits of the Sierra Madre Orienta were carried out.

In this contribution we examined the records of the lacustrine sequence "Los Pinos3" which is situated in the upper Iturbide-El punte sector of the Santa Rosa canyon in the Iturbide-Linares at an altitude of 1100 m asl.

The study is based on a 75 m thick profile of an intermittent lacustrine deposit, which was divided into four work sections. The remains of the lacustrine sediments consisting of laminated fine grained layers, which are alternating between clayey silt and silt sand with remains of snail and organic carbon. AMS data of 26,25±500 yr B.P. and 33,515±yr B.P. were obtained for the altitude of 1008.0 m and 0.999 m respectively.

The initial pollen analysis on the basis layers shows presence of tree species as well as Picea, Abies, Pseudotsuga and liquidambar, which at present, have not distribution at these area. The geochemical record of Los Pinos profile show relatively average values of organic carbon. The ¹³C of Los pinos porfile indicate the coexistence of C4/C3 vegetation in more layers at the 1008 altitude. One aim of the rock-magnetic study was the identification of tephra layers which help in reconstructing stratigraphic relationship

B01 : 1B/38 : F7

Holocene Lacustrine Deposits of Caracarana Lake, Northeast Amazonia

Bruno Turcq (turcq@bondy.orstom.fr)¹,

Francisco Fernando Simoes Filho (flamego@ird.gov.br)²,

Abdelfettah Sifeddine (geosife@vm.uff.br)³,

Jacques Bertaux (bertaux@bondy.orstom.fr)¹,

Fernanda Oliveira² &

Arnaldo Carneiro Filho (carneiro@inext.com.br)⁴

¹ ORSTOM, 32 av. Henry Varagnat, 93143 Bondy cedex, France

² Departamento de Geoquimica UFF, Morro do Valonguinho s/n, 24020-007 Niteroi RJ, Brazil

³ ORSTOM Departamento de Geoquimica UFF, Morro do Valonguinho s/n, 24020-007 Niteroi RJ, Brazil

⁴ INPA, CP 478, 69011-970 Manaus AM, Brazil

Late quaternary paleo-environmental data are very scarce in Amazon. We present here the results of a sedimentological study of Caracarana Lake, in the north of the state of Roraima. This region is a contact area between Rainforest and Savanna. Small lakes are inumerous in this low relief sedimentary basin. Most of these lakes are filled by young (<2000 yrs BP) organic-rich deposits. The Caracarana Lake, the largest of the area, represents an exception because its deposits allow a record of environment changes since at least 10,000 yrs B.P. Three cores have been collected at different depth in the lake. Radiocarbon ages have been obtained on organic matter fraction through classical or AMS methods. Analysis include Total Organic Carbon (TOC) and Nitrogen (NOT), ¹³C and ¹⁽N isotopic ratios, and quantitative mineral composition (kaolinite, quartz, calcite and amorphous silica) determined by FTIR spectroscopy. Before 9000 ¹⁴C yrs B.P., the sediments are caracterised by a low organic carbon content (<1.2%) and the presence of calcite (1%). Quartz (20-35%) and kaolinite (40-60%) contents are maximum. This facies is interpreted as a low or ephemeral lake with strong supply of mineral material from the watershed. Between 9000 and 8300 ¹⁴C yrs B.P., an increase of COT (up to 5%) and Amorphous Silica (4 to 30%) from sponge spicules and diatoms indicate a better development of the lake. Between 8300 and 7400 the COT content lowered again (1-3%), amorphous silica (30-50%) and calcite (up to 3%) content are high. The presence of hardened nodules of kaolinite inticates the occurrence of dessication episodes during this low lake-level phase. Between 7400 and 4200 yrs B.P. the Organic Carbon content increases progressively (up to 7%) in relation with the development of the lake: amorphous silica, low at the beginning of that phase (3-5%) is also increasing (7-10%); C/N ratio is lowering from 17 to 12, indicating a growing proportion of the phytoplanctonic contribution, ¹³C remains stable around -23‰, ¹⁵N is lowering from 2‰ to 0. Since 4000 yrs B.P. the lake presents its present-day caracteristics. A last calcite peak is observed at 2200 yrs B.P. This lacustrine evolution brings new questions about Amazonia paleoclimate during the Holocene. The Holocene dryness, between 8300 and 7400 yrs B.P., has a different timing than the data obtained in Eastern Amazonia and seems to indicate that climate changes are not only controled by the migration of ITCZ forced by the insolation parameter. The lake development in the Middle Holocene and the short dry event at 2200 yrs B.P. are in good agreement with the Titicaca lake-level reconstruction.

Session B01:1P

B01 : 1P/01 : PO

The Konya Palaeolake (Turkey): Upper Pleistocene Environmental Changes and Climatic Significance

Catherine Kuzucuoglu

(kuzucuog@cnrs-bellevue.fr)¹,

Jacques Bertaux (bertaux@bondy.orstom.fr)²,

Stuart Black (s.black@reading.ac.uk)³,

Michel Fontugne (fmr@lsce.cnrs-gif.fr)⁴,

Mustafa Karabiyikoglu (karabyk@mtabim.mta.gov.tr)⁵ &

Jean-François Pastre (pastre@cnrs-bellevue.fr)¹

¹ URA 141-CNRS/Univ. Paris I, 1 Place A. Briand, 92195 Meudon cédex, France

² ORSTOM, 70-74 Route d'Aulnay, 93140 Bondy, France

³ Univ. of Reading, PO Box 227, Whiteknights, Reading, RG6 6AB, U.K.

⁴ LSCE, CEA-CNRS, Av. de la Terrasse,, 91198 Gif-sur-Yvette cédex, France

⁵ MTA General Directorate, Eskisehir Yolu, 06520 Ankara, Turkey

This study of climatic changes in inner Anatolia during the Upper Pleistocene (Marine ¹⁸O isotopic stages MIS 5e to 1) uses geomorphologic features and sediments in the Konya plain, a now dry, closed and semi-arid lacustrine basin at 1000 m altitude.

1. Last Interglacial-Last Glacial. Indicators studied in three 20 m deep sequences cored in the palaeolake fill are: magnetic susceptibility, grain-size distribution, petrographic and mineralogic composition of sand. Mineralogical content is detailed by infrared spectroscopy (IRS), RX diffractometry, and microprobe analyses. Environmental responses are traced by trends in authigenic carbonate, evaporite, and detrital mineral contents and by diatom-inferred salinity levels. Chronology is framed by U/Th dates on gypsum and carbonates. Other stratigraphic correlations use tephra layers (Kuzucuoglu et al., 1998a) or extreme drought levels (Kuzucuoglu et al., submitted). During the Last Interglacial (MIS 5e) peat and freshwater marshes expanded. During the Last Glacial (MIS 5d to 2), shallow saline lakes occupy the plain: three sub-phases are distinguished, with the strongest evaporation occurring during MIS 3 (ca 65-23 ky). Variations in precipitated carbonates and evaporites in closed basins can illustrate regional environmental changes, provided that, in shallow karstic lake systems, the spatial variations induced by the position of the sequences in the basin are taken into account.

2. Pleniglacial-Late Glacial-Holocene. The study of sections and cores (Fontugne et al. 1999) and of fossile dunes (Kuzucuoglu et al., 1998b) allows to propose a chronological scheme of the Late Pleistocene environmental changes studied using analyses of lacustrine, marshy, soil and aeolian deposits within a chronological frame supported by a large series of ¹⁴C dates. During the first part of MIS 2 (ca. 23-17 ky : Pleniglacial), the plain is occupied by a 12-20 m deep lake. Three episodes of high lake levels are identified before the abrupt and complete drying at 17 ky B.P., i.e. before the Late Glacial (Karabiyikoglu et al., 1999). During the Late Glacial a heavy drought is followed by a shallow freshwater lacustrine phase (ca 13.5-11 ky B.P.). The Late Glacial to Holocene transition (ca 11-9 ky B.P.) corresponds to a lack of deposits, suggesting a dry period. During Early Holocene, palaeosols dated 9-8 ky B.P. testify for an increase in humidity while Neolithic settlements occupy the southern alluvial fans (Çatal Höyük, Can Hasan III). A second humid phase occurs at the start of the 6th millenium B.P., followed by a severe drought (ca 5.5 ky B.P.). During Late Holocene, the causes of the environmental changes evidenced are difficult to assess: they represent either impacts of human activities on water availability and soil stability, or variations in rainfall amounts and erosion efficiency.

Note: All ¹⁴C dates presented are conv. yrs B.P.

Kuzucuoglu C, Pastre JF, Black S, Ercan T, Fontugn M, Guillou H, Hatté C, Karabiyikoglu M, Orth P, Turkecan A, Journal of Volcanology and Geothermal Research, 86, (1998a).

Kuzucuoglu C, Bertaux J, Black S, Fontugne M, Karabiyikoglu M, Kashima K, Mouralis D, Orth P, Pastre J-F, Geological Journal, (submitted).

Fontugne M, Kuzucuoglu C, Karabiyikoglu M, Hatté C, Pastre J-F, Quaternary Science Reviews, 18/2, (1999).

Kuzucuoglu C, Parish R, Karabiyikoglu M, Geomorphology, 23, 257-271, (1998b).

Karabiyikoglu M, Kuzucuoglu C, Fontugne M, Kaiser B, Mouralis D, Quaternary Science Reviews, 18/2, (1999).

B01 : 1P/02 : PO

Permafrost in Sedimentary Rocks During Glaciations ­ Implications to Geothermal Field

Argo Jõeleht (ajoeleht@ut.ee)¹ &

Jan Safanda (JSA@ig.cas.cz)²

¹ Institute of Geology, University of Tartu, Vanemuise 46, 51014 Tartu, Estonia

² Geophysical Institute of Academy of Sciences, Sporilov, Bocni II/1a, 141-31 Praha 4, Czech Republic

During glaciations the ground surface temperature fell below zero over large areas and rocks started to freeze. This freezing depends on rock porosity i.e. water content in the rocks. Under similar climatic conditions, the creation of permafrost is quicker in non-porous medium (such as crystalline rocks) in comparison to porous medium (such as sedimentary rocks) where additional heat loss must occur when the phase of water changes from liquid to solid. Similarly, the thawing of permafrost is also more time-consuming compared to non-porous medium and is mainly controlled by geothermal heat flow.

On the other hand, water, which transfers heat when flows and produces disturbances to geothermal field, cannot flow through the frozen rocks. When an area becomes covered by glacier, the temperature at a base of glacier, i.e. at the ground surface starts to increase due to frictional and geothermal heat, and often reaches the pressure melting temperature. The driving force - hydraulic head of subglacier meltwater is close to ice floatation point (Piotrowski & Kraus, 1997) and is far above the normal conditions. Such inflow of cold meltwater to the tilted aquifers may produce significant heat flow density disturbances. However, flow can take place only after the permafrost has disappeared. Calculations indicate that the period when glaciers covered Estonia was longer than is needed for permafrost to thaw under glacier conditions and aquifers were opened for groundwater flow. This is supported by very low ¹⁸O values and ¹⁴C datings of groundwater of the Cambrian-Vendian aquifer system (Mokrik, 1997). The proper estimation of thermal disturbances related to glaciers requires coupled simulations of permafrost and groundwater flow.

Mokrik R, The Palaeohydrogeology of the Baltic Basin - Vendian & Cambrian, 138, (1997).

Piotrowski J & Kraus A, Journal of Glaciology, 43, 495-502, (1997).

B01 : 1P/03 : PO

Mineral Fluxes, Pollen and Diatom Data from Three Lacustrine Sites Around the Gulf of Guinea: Evidences of Long-Term and Abrupt Climatic Changes During the Last 6kyr

Jacques Bertaux (bertaux@bondy.orstom.fr)¹,

Denis Wirrmann (wirrmann@bondy.orstom.fr)¹,

Dominique Schwartz

(schwartz@equinoxe.u-strasbg.fr)² &

Annie Vincens (vincens@cerege.fr)³

¹ Orstom, 32 Avenue H. Varagnat, 93143 Bondy cedex, France

² Université L. Pasteur - U.R.A. 95 CNRS, Strasbourg, France

³ CEREGE, Aix en Provence, France

Western Equatorial Africa corresponds to the permanent atlantic monsoon area which is also the guinean rain forest realm. The decisive climatic factor susceptible to vary today as during the Holocene is the precipitation availability. Inter-annual to millenial rainfall intensity variations in the Gulf of Guinea region are related to several mechanisms, mainly the monsoon intensity linked to the 23 Kyr precessional cycle of insolation and to Sea Surface Temperatures fluctuations in the East Tropical Atlantic.

A peculiar sedimentary dynamics has been observed in three catchment basins covered at 6 Kyr by rain forest (two in Congo, one in Cameroon): the mineral inputs from the adjacent soils into the lakes, mainly dependent on tributaries inflows, are a direct consequence of the rainfall intensity. This sedimentary dynamics is interpreted in the context of a general upper holocene dry phase documented by several sites from Western Equatorial Africa according to the vegetation changes recorded by pollen. The mineral fluxes variations with time are remarkably similar in the three sites showing: a decrease between 6 and ca 2,5 Kyr, very low inputs until 1,2 Kyr in Congo and until 700 yr in Cameroon, and after that respectively a restart of mineral supplies into the lakes. Nevertheless the timing of the mineral fluxes changes and of the vegetation ones is not the same. The onset of mineral fluxes decrease since 6 Kyr, preceeded the vegetation changes which are characterized in all the sites by a transformation/degradation of the forest cover. This transformation/degradation culminated around 2,500 yr BP in all the sites. The farther the study area is located from the ocean (source of the moisture transported onto the continent by the monsoon), the strongest and the earliest the vegetation has changed. Two sites recorded a slight forest degradation, while in the third one savanna replaced the forest. Then wetter conditions (enhanced rainfall inducing higher mineral fluxes) appeared from 1,200 yr BP in Congo and around 700 yr BP in Cameroon.

Two kinds of climatic changes are deduced from the rainfall pattern described above. The gradual lowering of mineral fluxes is consistent with the palaeomonsoon decreasing trend over west Africa as inferred from boreal summer solar radiation at 20°N. The abrupt changes recorded by vegetation, mineral fluxes and diatom content around 2,500 yr BP in Cameroon and Congo, are superimposed to this palaeomonsoon trend. Such sudden change might be related to SSTs variations in Eastern Tropical Atlantic.

B01 : 1P/04 : PO

Holocene Climatic Changes Recorded by Palustro-Lacustrine Sediments in the Eastern Bolivian Andes

Radia Djennadi (djennadi@bondy.orstom.fr)¹,

Saphia Yahiaoui (yahiaoui@bondy.orstom.fr)¹,

Jacques Bertaux (bertaux@bondy.orstom.fr)¹,

Elisabeth Lallier-Verges

(E.Lallier-Verges@ univ-orleans.fr)²,

Fatima Laggoun-Defarge

(Fatima.Laggoun-Defarge@ univ-orleans.fr)²,

Philippe Mourguiart

(mourguia@pop.reaumur.u-bordeaux.fr)³ &

Abdelfettah Sifeddine (geosife@vm.uff.br)⁴

¹ ORSTOM Prog. PVC, 32, Av. H. Varagnat, 93143 Bondy cedex, France

² UMR 6531, FR 09 CNRS-Université d'Orléans, France

³ ORSTOM-Univ. de Pau, France

⁴ Univ. Fluminense, Rio de Janeiro, Brasil

Peats and sediments deposited in a high altitude site on the andean amazonian side (Siberia, 17°50' S, 64°43'W, 2920 m) have recorded the Holocene climate changes over the eastern bolivian Andes. The rainfall variations on this part of tropical south America are controlled by i) the penetration of Atlantic humidity during austral summer, ii) the northward move of cold air masses mainly during austral winter, and iii) the occurrence of El Nino events. The two first mechanisms are limited in extension by the position of the Inter-Tropical Convergence Zone (ITCZ), the summer southward shift of ITCZ was weaker during the lower Holocene than today. The Siberia site is today located at the southern limit of penetration of summer Atlantic humidity. Holocene environmental changes over the Siberia site have been inferred from the characteristics of a 360 cm-long core, as revealed by the nature and content of mineral and organic particles, as well as the palynological record. These informations serve to describe the vegetation changes over the catchment basin and the depression, the intensity of the supply of allochthonous particles (minerals or plant debris from surrounding soils) toward the depression, the conditions of peat formation or lacustrine sedimentation, and the degree of organic matter preservation. The chronology was based on eight conventional ¹⁴C dates performed on total organic matter. In the lower Holocene, between ca 10000 and 8000 yrs B.P., the catchment area was covered by a dense altitude forest. A peatland rich in ligno-cellulosic tissues from higher plants developped. The abundance of reddish amorphous organic matter reveals an in situ degradation. These characteristics point to a high rainfall availibility. The low mineral and allochthonous organic particles content reveals a low supply of particles from soils protected by the dense vegetal cover. A trend toward dryer conditions is outlined by changes in the forest type around 9000 yrs B.P..A hiatus between ca 8000 and 5000 yrs B.P. is revealed by a change in the peat/sediment deposit and the available dates. It is interpreted as the result of strong dry climatic conditions. After ca 5000 yrs B.P. a short period of lacustrine sedimentation with abundant minerals and allochthonous organic matter deposition is followed by the re-establishment of a peatland. At that time, pollen content indicates the development of a cloud forest over the catchment area. This kind of forest, still present today, is the result of a permanent humidity due to the ascending of the atlantic warm and humid air along the East Andean slope.

B01 : 1P/05 : PO

Dating of Paleolake in the Central Altiplano of Bolivia

Michel Fornari (fornari@unice.fr)¹,

François Risacher (risacher@illite.u-strasbg.fr)² &

Gilbert Féraud (feraud@unice.fr)¹

¹ UMR 6526 Géosciences Azur, Faculté des Sciences, 06108 Nice Cedex 02 France,

² Centre de Géochimie de la Surface, 1 rue Blessing, 67084 Strasbourg Cedex, France

Extensive paleolakes in the Bolivian Altiplano are known for more than a century from lacustrine outcrops. Alternating episodes of lake expansion and dry periods with salt crusts deposition are related to climatic changes although the precise mechanisms are not yet well identified. Change in atmospheric circulation and deglaciation are the two main suggested explanations for the paleolakes highstands. The precise dating of these deposits give important constraints in the reconstruction of the paleolakes evolution and therefore of the climatic conditions in this region of the Andes.

Five paleolakes occupied successively the Titicaca basin in the northern Altiplano: Tauca, Minchin, Ballivian, Cabana and Mataro (the oldest known). In the central Altiplano (Poopo, Coipasa and Uyuni basins), three lacustine phases have been reported: Tauca, Minchin and Escara. Up to now, only the two more recent paleolakes have been dated: Tauca (10 000 - 15 000 yr BP) and Minchin (27 000 - 72 000 yr BP).

A 121 meters deep well cored in the giant salar of Uyuni disclosed 11 lacustrine layers (L1 to L11) separated by 12 salt crusts. ¹⁴C and U/Th. dating showed that the upper layers L1 and L2 are related to the Tauca phase and layers L3 and L4 to the Minchin phase. Layer L5, located at - 46 m under the surface, and related to the Escara lake, contains a volcanic ash bed with well-preserved biotites. Their age was determined by ⁴⁰Ar/³⁹Ar; analyses were performed by laser probe on single or small clusters of 3 grains and by step heating on bulk sample.

The measured age of about 190 000 yr is, to our knowledge, the first dating of a pre-Minchin paleolake in the Bolivian Altiplano. This age constraints the rate of deposition which was controlled by both the local endoreic environment and climatic variations in the northern Altiplano. Stratigraphically, Escara paleolake seems correlated with the northern Ballivian paleolake. However, Escara was a shallow lake whereas Ballivian lake was large and deep. Escara could have been originated by the overflow of lake Ballivian from the Titicaca basin into the Uyuni basin. Therefore, it appears that the variations of lacustrine deposits of the Escara paleolake may be partly du to variable interconnections between lakes.

B01 : 1P/06 : PO

Stable Isotopes and Hydrochemistry of Ground Ice as Paleoclimate Indicator for Northern Siberia

Hanno Meyer (hmeyer@awi-potsdam.de)¹,

Alexander Dereviagin (dereviagin@glasnet.ru)²,

Christine Siegert (csiegert@awi-potsdam.de)¹ &

Hans Hubberten (hubbert@awi-potsdam.de)¹

¹ Alfred-Wegener-Institute for Polar- and Marine Research - Research Unit Potsdam, Telegrafenberg A43, D-14473 Potsdam, Germany

² Moscow State University, Department of Permafrost Studies - Faculty of Geology, Moscow, Russia

About 25% of the Earth's land surface is characterized by permafrost. Permafrost is a common feature in Siberia, which may reach up to 1500 m of thickness. Vast areas in Northern Siberia were non-glaciated because winter precipitation was not enough for the formation of a glacier. In these areas, the winter precipitations are bound in ice-rich permafrost instead of glacier ice. Ice-rich permafrost with ground ice bodies (which is limited to the upper part of permafrost) generally consists of loess-like sediment with volumetric ice contents up to 80% Vol. Formation of ground ice is mostly due to syngenetic freezing during accumulation of sediments in flood plains, deltas, shallow lakes or slope deposits, especially in the Late Pleistocene. During the Holocene the formation of these deposits continued, however was restricted to few areas. Ground ice can be used as a climate archive. Most promising archives for paleoclimate reconstruction are huge ground ice bodies, called ice wedges. Syngenetic ice wedges may reach widths of 8 m and heights up to 40 m. They form principally by freezing of melt water of last years winter precipitation. To reconstruct the paleoclimatic changes in Northern Siberia, we measured stable isotopes and hydrochemistry of ice wedges and texture ice. In this poster, we present first results of a 1998 expedition to Bykowsky Peninsula, Lena Delta area, Siberia. We performed a high sampling resolution horizontally and vertically (10 cm intervals) corresponding to time intervals smaller than 100 years. According to Kunitsky (1989) the sampled ice wedges were formed during the Weichselian and Holocene times.

Kunitksy, VV, (1989): Cryolithology of the Lower Lena River - Permafrost, Permafrost Institute Press, 1-164, (1989).

B01 : 1P/07 : PO

Sub-Millennial Scale Variations in the East Asian Monsoon System Recorded by Dust Deposits from the North-Western Chinese Loess Plateau

Eleanor Parker (des2ejp@liv.ac.uk)¹,

Jan Bloemendal (jan@liv.ac.uk)¹,

David Heslop (daveh@liv.ac.uk)²,

John Shaw (shaw@liv.ac.uk,)² &

Chen Fahu (fhchen@spin.lzu.edu.cn)³

¹ Department of Geography, University of Liverpool, Liverpool L69 3BX, United Kingdom

² Department of Earth Sciences, University of Liverpool, Liverpool L69 3BX, United Kingdom

³ Department of Geography, University of Lanzhou, Lanzhou, Gansu, China

Following the discovery of rapid climate variation and climate instability on millennial time scales in Greenland ice cores, evidence of similar millennial scale climate instability has been found in sediment from the Chinese Loess Plateau, suggesting that climate instability is global (Ding et al 1992). Recent publications have correlated magnetic and grain size records from the NW loess plateau with increased ¹⁸O interstadial events in ice cores and Dansgaard-Oeschger events in marine cores (An et al 1994). Loess layer L1L1 and Paleosol L1S1 have been investigated in detail for a new site in the NW loess plateau, at Caoxian. Climate proxy indices, grain size and magnetic susceptibility, have been measured at 2 cm intervals from 26 m of loess covering the 60 ky following the beginning of MIS 3 (Sm). The high sedimentation rate at Caoxian may mean 2 cm intervals in L1Sm cover ~ 60yrs and in L1L1 25-30yrs. Our ongoing research investigates regions in the section where discrepancies exist between loess climate proxies and the ice core record (Chen et al. 97). For example, Heinrich events correspond to periods of increased grain size, but not all periods of increased grain size have a corresponding Hienrich event (Porter and An 1995). Interstadials generally coincide with a paleosol layer. We look at differences in the grain size and magnetic signatures of paleosols that do and the few that do not. We hope that by investigating these differences we may be able to quantify apparent inertia of the East Asian Monsoon suggested in the grain size and magnetic climate proxies.

An Z, Kukla GJ, Porter SC & Xiao J, Quat Res, 36, 29-36, (1994).

Chen FH, Bloemendal J & Wang JM, Li JJ, Oldfield F, Palaeogeogr. Palaeoclimatol. Palaeoecol, 130, 323-335, (1997).

Ding Z, Rutter N, Han J & Lui TS, Quat Res, 45, 1-16, (1992).

Porter SC & An Z, Nature, 375, 305-308, (1995).

B01 : 1P/08 : PO

Climate Signals ( and 13C) in Tree Rings from NE China and the East Asia Monsoon

Anne-Marie Aucour (aucour@univ-lyon1.fr)¹,

Faxiang Tao² &

Simon Sheppard (ssheppar@ens-lyon.fr)³

¹ UMR 5565, Université Lyon 1, 69622 Villeurbanne France

² Institute of Geochemistry, Guiyang, Guizhou, China

³ CNRS UMR 5570, ENS de Lyon, 69364 Lyon, France

Tree ring archives provide seasonal to pluriannual records of climate and environmental changes over past ten thousand years. Compared with North America and Europe, few studies apply to Asia. In NE China (latitude 42°32'N) sensitivity of cellulose D and 13C to climatic variations was tested in annual tree rings from a red pine (Pinus korainensis, tree RP-1). In the studied area, precipitation falls mainly in summer (June to August) via the East Asia Monsoon. Tree ring samples cover the period from 1958 to 1988, and meteorological data are taken from a nearby (~ 30 km) station .

Coherence between RP-1 and another tree (RP-2) growing 20 m away was tested for the period 1982-1988. The D and ¹³C values of RP-1 are typically 16‰ and 0.8‰ lower respectively than those of RP-2. Isotopic variations between the two trees can be related to difference in soil moisture and/or to intraring variability. However, the overall trend in D in the two trees are similar. For the period 1958-1988, the D values of RP-1 range between -100 and -70‰ and the ¹³C between -20.3 and -22.3‰. Correlation analyses were performed on RP-1 isotopic data and precipitation amount, temperature, relative humidity. The best correlations resulted when relating ¹³C and D to May-June temperatures (positive correlations) and when relating D to March-May precipitation amounts (negative correlation). There is a significant positive correlation between the ¹³C and D. These results indicate sensitivity of the D and ¹³C to premonsoon spring (March-May) climatic conditions rather than to the summer monsoon. Spring wood should be enriched in ¹³C and D because of dry climatic conditions. A proposed interpretation is that spring temperature controls the fraction of spring (enriched) wood in the ring. These results also suggest that the main factor controlling D interannual variations in the feeding water is the spring precipitation.

Session B01:2A

B01 : 2A/01 : F7

Climatic Records in Paleosoils Under Archaeological Monuments of Eastern European Steppes

Vitaliy A. Demkin (demkin@issp.serpukhov.su) &

Tatyana S. Demkina (demkina@issp.serpukhov.su)

Institute of Basic Biological Problems, RAS, Pushchino, Moscow Region, Russia

Soils buried beneath archaeological monuments (the kurgans of the Russian steppe) are good indicators of the environment during different periods of the Holocene. Among the most informative soil properties for reconstruction of the steppe environments are the amounts and profile distributions of humus, easily soluble salts, carbonate and gypsum, and the degree of solonetz formation. Comparison of soils buried under kurgans of Bronze Age, Early Iron Age and Middle Age suggests the following chronology of climatic changes in the Eastern European steppes during the Middle and Late Holocene:

1. In the late 3rd to 2nd millennium BC the climate became continental and arid.

2. From the mid-2nd to the mid-1st millennium BC the climate became less continental, with a slight increase in humidity.

3. In the second half of the first millennium BC aridity returned.

4. From the late-1st millennium BC to the mid-1st millennium AD the climate returned to milder and the atmospheric humidity increased.

5. From the mid-1st to the late-2nd millennium AD the climate was relatively stable arid. Humidity "Middle Age climatic optimum" took place during XII-XIV centuries AD.

Taking into account the rate of migration of pedogeographic zones throughout the Middle and Late Holocene, we can estimate the annual rainfall to 230-300 mm. The average rainfall today is near 280 mm per year.

This work was carried out with support of the Russian Foundation for Basic Research and Soros Foundation.

B01 : 2A/02 : F7

Microbocenoses of Steppe Paleosoils of Archaeological Monuments as Indicators of Paleoenvironment

Tatyana S. Demkina (demkina@issp.serpukhov.su) &

Vitaliy A. Demkin (demkin@issp.serpukhov.su)

Institute of Basic Biological Problems, RAS, Pushchino, Moscow Region, Russia

Understanding the regularities of development and functioning of microbocenoses in soil evolution and secular dynamics of climate are important but practically not studied problems of paleosoil science. An attempt to study the status of microbial communities in paleosoils of archaeological monuments of the Bronze epoch (III-II mill. B.C.), Early Iron epoch (V cent. B.C.- IV cent. A.D.) of the steppes of Eastern Europe has been carried out for the first time. For the characterization a complex of parameters such as microbial biomass, number of various ecologic trophic groups of microorganisms, values of basal and substrate-induced respiration, intensity of humus mineralization was advanced. The data provided the calculation of original coefficients including microbial respiration (QR), oligotrophicity, saprotrophicity, pedotrophicity, the ratio C_mic/C_org. The values of these coefficients allowed us to estimate the level of the sustainability of microbial communities in various paleoecological conditions and to reveal the domination of a certain trophic group, as well as to describe the conditions of habitation during different historical epoches. From the comparative analysis the direction and the scale of the space-temporal variability of the microbial parameters were established in soils of evolutional range: chestnut residual meadow nonsolonetz -> light chestnut weak solonetz -> light chestnut strong solonetz -> solonetz. The regularities of the changes of microbocenoses along the soil profile during the Late Holocene development of the solonetz process were revealed. Complex of microbial parameters, which allows the characterization of the status of the environment and the dynamics of paleoclimatic conditions within various historical epoches is advanced. The work was performed with the support of Russian Foundation for Basic Research

B01 : 2A/03 : F7

2100-yr Rhythm of Holocene Glacier Variability in the Central Alps (Switzerland and Italy)

Anne C. Hormes (anne.hormes@geo.unibe.ch),

Benjamin U. Müller (bmueller@geo.unibe.ch) &

Christian Schlüchter (christian.schluechter@geo.unibe.ch)

Geological Institute, Baltzerstrasse 1, CH-3012 Bern, Switzerland

We present a new radiocarbon data set on wood and peat samples, which show that several glaciers were smaller in extent in the past compared to present conditions. Tree logs have been accumulated in the outwash plains of Unteraargletscher during jökulhlaup-type flooding. At Stein- and Steinlimigletscher in the Berner Oberland and at Riedgletscher, Glacier du Mont Miné and Glacier du Trient in the Valais tree logs have been sheared to the glacier surface from below the ice. Organic rich sediments, which clearly indicate reduced ice extent compared to the present situation at 2600 m above sea level, have been deformed by a glacier advance at Lago di Musella in the Bernina Massif. A question remains open concerning the storage of the samples beneath the glaciers and the course of the erosion event and the real place of tree growth. Was it right there where the glaciers are today or were broken trees brought up to the glacier from surrounding valley slopes? The tree line were not cogent much higher than today. The actual tree line is situated around 1900 m, but the potential natural one between 2000 and 2200 m. The tree logs and organic materials were found between 1750 and 2600 m. A statement on the past positions of the glacier tongues or equilibrium line altitudes (ELA) is not admissible on the tree logs. However, the samples indicate a different growth condition than today. The ¹⁴C ages of the samples give information about periods when glaciers have been at least as small as today or smaller. Therefore we can reconstruct a chronology of smaller ice extent at least peaking around 8000, 5900, 3800 and 1750 yr BP, indicating an approximately 2100-yr rhythm. Additional indications for smaller glacier extensions exist for 8700, 7200, 4850, 4500 and 3250 yr BP. A comparison with other climate variability records from Central and Northern Europe is given: The comparison of different proxy-records requires a careful look on dating and interpretation problems: What kind of material is dated? Which dating method is used? How is the studied material interpreted with regard to climate variability?

B01 : 2A/04 : F7

Cold-Based Alpine Glaciers on Mount Kenya

Wibjörn Karlén (Wibjorn.Karlen@natgeo.su.se)

Dep. Physical Geography, Stockholm University, Stockholm, Sweden

A pro-glacial lacustrine sediment core from Mount Kenya reveals information about rock-flour influx, which is a measure of the glacier erosion of the substrate. The interpretation is made that glaciers were large prior to 5700 Cal. years BP. They then retreated rapidly up to around 5000 Cal. years BP. This event, which is interpreted as a warm event, was followed by a cold event lasting to about 2000 Cal. years BP. Glaciers retreated during several short periods of warmer climate. The most distinct warm event was about on 3700 Cal years BP. Short cold events during the last 2000 years have been dated to around 1300, 600 and 400 Cal. years BP. In general, the sediments from between 2800 and 2300 Cal years BP, in which the rock-flour content was relatively low and therefore first was interpreted as having accumulated during a period of small glaciers, differ from other sediments in the core by being relatively homogenous. ¹⁸O studies on biogenic silica from both just before and the end of this period indicate low temperature at this time. Paleoclimatic data from several East African localities indicate cool and dry climate during this same period. A possible explanation for the low rock-flour influx could be that the glaciers were cold-based and therefore not eroding. Paleoclimatic studies from around the world indicate that the period between 3000 and 2000 cal. years BP was a major cold Holocene event.

Major climatic events dated to approximately the same period are described for several localities e.g. tree limit in Sweden 3200-1900, tree ring width in western USA 3200-2200, and cave temperatures in South Africa 3300-2400. The period of the most distinct change in climate coincides with a period of low solar radiation. This low solar activity has been determined from the difference between dendrochronological age and ¹⁴C age of tree rings (2800-2200) BP.

Karlén, WFastook, JL, Holmgren, K, Malmström; M, Matthews, JA, Odada, E, Risberg, J, Rosqvist, G, Sandgren, P, Shemesh, A, and Westerberg, L-O, manuscript

Rietti-Shati, M, Karlén, Wand Shemesh, A, Science, 281, 980-982, (1998).

B01 : 2A/05 : F7

Holocene Climatic Change Reflected in Scandinavian Forest Dynamics

Richard Bradshaw (rhwb@geus.dk)¹,

Sharon Cowling (Sharon@planteco.lu.se)² &

Bjorn Holmqvist (Bjorn. Holmqvist@ess.slu.se)³

¹ Geological Survey of Denmark and Greenland, Thoravej 8, DK-2400 Copenhagen NV, Denmark

² Climate Impacts Group, Ecology House, S-223 62 Lund, Sweden

³ Quaternary Geology, Tornavagen 13, S-223 63 Lund, Sweden

Palaeoecological studies have revealed major changes in the distributions of forest trees in Scandinavia during the Holocene. In southern Scandinavia, during the late Holocene, Tilia cordata, Alnus glutinosa and Quercus robur have become less abundant while Fagus sylvatica, Picea abies and Pinus sylvestris have increased in importance. Simple descriptions of the dynamics of these changes yield few insights into the driving forces that brought them about. The major competing hypotheses proposed to explain forest development are 1) response to climate change, 2) soil maturation and 3) consequences of anthropogenic activities. Willis et al. (1997) showed that soil maturation processes are unlikely to have been a major influence on forest development, and anthropogenic activities were on a small scale until the late Holocene. Thus for much of the Holocene, climate change is probably reflected rather directly in forest composition, although some doubts remain about lags in response to rapid climate change. Inverse modelling can be used to reconstruct selected climatic parameters.

During the late Holocene the influence of climate and anthropogenic activities are closely linked. The forest gap model FORSKA simulates forest dynamics that result from climate change when driven by independent climatic data. Pollen data-model comparisons covering the last 1500 years indicate those forest dynamics that can be accounted for by climatic change. The pollen data were taken from small forest hollows in Denmark and Sweden at the same spatial scale as the FORSKA plots. The climate data were derived from independent estimates of temperature and precipitation during the Medieval Warm Period and the Little Ice Age using both historical records and climate-proxy data (tree rings, lake-level fluctuations, peat bog studies). We conclude that anthropogenic influence has often served to amplify the vegetational consequences of climatic change, and the Little Ice Age had a significant impact on Scandinavian forest vegetation.

Willis KJ, Braun, M, Sumegi P & Toth A, Ecology, 78, 740-750, (1997).

B01 : 2A/06 : F7

Distribution, Age and Geochemical Composition of the Vedde Ash in Scandinavia and the British Isles

Stefan Wastegård (stefan.wastegard@geo.su.se)¹,

Chris S. M. Turney (Chris.Turney@anu.edu.au)²,

Jonas Björck (jonas.bjorck@geo.su.se)¹,

Svante Björck (svante@geo.geol.ku.dk)³,

J. John Lowe (J.Lowe@rhbnc.ac.uk)⁴,

Göran Possnert (Goran.Possnert@Material.uu.se)⁵,

Stephen J. Roberts (sjr@geo.ed.ac.uk)⁶ &

Barbara Wohlfarth (Barbara.Wohlfarth@Geol.lu.se)⁷

¹ Department of Quaternary Research, Stockholm University, S-106 91 Stockholm, Sweden

² Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia

³ Geological Institute, University of Copenhagen, Øster Voldgade 10, DK-1350, Copenhagen K, Denmark

⁴ Centre for Quaternary Research, Department of Geography, Royal Holloway, University of London, Egham, Surrey TW20 0EX, England, UK

⁵ Tandem Laboratory, Uppsala University, Box 533, S-751 21, Uppsala, Sweden

⁶ Department of Geography, University of Edinburgh, Drummond Street, Edinburgh EH8 9XP, Scotland, UK

⁷ Department of Quaternary Geology, Lund University, Tornavägen 13, S-223 63, Lund, Sweden

Recent discoveries of tephra assigned to the Vedde Ash in sites in Sweden and Scotland have extended the known distribution of this important marker horizon (e.g. Turney et al., 1997; Wastegård et al., 1998). This research has been facilitated by the development of a new technique for extracting rhyolitic micro-tephra particles from minerogenic deposits (Turney, 1998). The highest concentration of tephra particles is to be found in lake sediments in western Norway (e.g. Birks et al., 1996), but concentrations are also high in south-western Sweden, suggesting that the main ash-cloud travelled eastwards from its volcanic source of Katla, in south-west Iceland (Wastegård et al., submitted). The discovery of the Vedde Ash at three sites in southern and south-eastern Sweden suggests that the tephra is likely to be detectable in suitable sites throughout the whole of southern Sweden.

Pollen stratigraphy and organic carbon curves indicate that the peak Vedde tephra concentrations occur in the middle of the Younger Dryas stadial, which accords with other records of Vedde Ash reported from sites in north-western Europe. A series of AMS radiocarbon measurements from Lake Madtjärn in south-western Sweden places the radiocarbon age of the tephra within a ¹⁴C plateau at 10,400-10,300 ¹⁴C years BP (Wastegård et al. 1998). Based on a linear Younger Dryas sedimentation rate and certain assumptions about the apparent synchroneity of changes in lake sediments, tree rings and ice-core records, the calendar year age of the tephra concentrations is estimated at 12,045-11,975 BP, which accords well with the age of the equivalent tephra in the GRIP core (11,980 ± 80 ice-core years BP; Grönvold et al., 1995). Geochemical analyses (major element ratios determined by electron microprobe) of the rhyolitic component of tephra shards extracted from sediments in Scotland and Sweden show no geochemical evolution within the data.

The extended area of distribution of the Vedde Ash reported here suggests that other areas in northern Europe, such as northern Germany, Denmark and Poland, may also have received significant fall-out from the Katla-Vedde eruption. An area around the southern Baltic may an ideal one for further research, since sites there may contain Lateglacial records not only of tephra of Icelandic origin, but possibly also of the Central European Laacher See Tephra (c. 11,200 ¹⁴C years BP).

Birks HH, Gulliksen, S, Haflidason, H, Mangerud J & Possnert, G, Quaternary Research, 45, 119-127, (1996).

Grönvold, K, Óskarsson, K, Johnsen, SJ, Clausen, HB, Hammer, CU, Bond, G & Bard, E, . Earth and Planetary Science Letters, 135, 149-155, (1995).

Turney, CSM, Journal of Palaeolimnology, 19, 199-206, (1998).

Turney, CSM, Harkness, DD & Lowe, JJ, Journal of Quaternary Science, 12, 525-531, (1997).

Wastegård, S, Björck, S, Possnert, G & Wohlfarth, B, Journal of Quaternary Science, 13, 271-274, (1998).

Wastegård, S, Turney, CSM, Lowe, JJ & Roberts, SJ, Submitted to Boreas