Jörg F. W. Negendank

Influence of the intertropical convergence zone on the East Asian monsoon

The Asian–Australian monsoon is an important component of the Earth’s climate system that influences the societal and economic activity of roughly half the world’s population. The past strength of the rain-bearing East Asian summer monsoon can be reconstructed with archives such as cave deposits, but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct. Here we present high-resolution records of the magnetic properties and the titanium content of the sediments of Lake Huguang Maar in coastal southeast China over the past 16,000u2009years, which we use as proxies for the strength of the winter monsoon winds. We find evidence for stronger winter monsoon winds before the Bølling–Allerød warming, during the Younger Dryas episode and during the middle and late Holocene, when cave stalagmites suggest weaker summer monsoons. We conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone. Similar migrations of the intertropical convergence zone have been observed in Central America for the period ad 700 to 900 (refs 4–6), suggesting global climatic changes at that time. From the coincidence in timing, we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the Tang dynasty in China and the Classic Maya in Central America.

Rapid environmental changes in southern Europe during the last glacial period

Oxygen-isotope records from Greenland ice cores, indicate numerous rapid climate fluctuations during the last glacial period. North Atlantic marine sediment cores show comparable variability in sea surface temperature and the deposition of ice-rafted debris. In contrast, very few continental records of this time period provide the temporal resolution and environmental sensitivity necessary to reveal the extent and effects of these environmental fluctuations on the continents. Here we present high-resolution geochemical, physical and pollen data from lake sediments in Italy and from a Mediterranean sediment core, linked by a common tephrochronology. Our lacustrine sequence extends to the past 102,000 years. Many of its features correlate well with the Greenland ice-core records, demonstrating that the closely coupled ocean–atmosphere system of the Northern Hemisphere during the last glacial extended its influence at least as far as the central Mediterranean region. Numerous vegetation changes were rapid, frequently occurring in less than 200 years, showing that the terrestrial biosphere participated fully in last-glacial climate variability. Earlier than 65,000 years ago, our record shows more climate fluctuations than are apparent in the Greenland ice cores. Together, the multi-proxy data from the continental and marine records reveal differences in the seasonal character of climate during successive interstadials, and provide a step towards determining the underlying mechanisms of the centennial–millennial-scale variability.

Correlation and synchronisation of Lateglacial continental sequences in northern central Europe based on annually laminated lacustrine sediments

Abstract The present study focusses on correlation and synchronisation of Weichselian Lateglacial varved lake sediments from western Germany (Meerfelder Maar, Eifel region), northern Germany (Hamelsee, Lower Saxony), central Poland (Lake Gości a z) and eastern Poland (Lake Perespilno) by using varve chronology, tephrochronology, palynostratigraphy and stable isotopes. Comparison of the several independent time scales shows that biotic and abiotic parameters respond abruptly and quasi-synchronously, within the errors of the different chronologies, during the Younger Dryas/Preboreal transition. Moreover, there is a consensus about the length of the Younger Dryas cold stage of 1100–1150 varve years. In the Allerod the prominent Laacher See tephra (12,880 varve years BP) can be used to fix floating varve chronologies. The relative duration of this biozone has been determined in Meerfelder Maar and Hamelsee at between 625 and 670 varve years. In the Meerfelder Maar a combination of continuous varve counting and biostratigraphy has been possible for the almost entire Lateglacial. The comparison between continental limnic sequences and Greenland ice-core records should be made on the basis of independent chronologies in both archives. It is more practicable to develop regional stratotypes on the continental regions instead of simply using ice cores as stratotypes for the Lateglacial for terrestrial European records. In this respect, annually laminated lacustrine sequences have a great potential.

High resolution sediment and vegetation responses to Younger Dryas climate change in varved lake sediments from Meerfelder Maar, Germany

Abstract This work focuses on a 1900-year section of varved sediments from Lake Meerfelder Maar (MFM) extending from the Late Allerod to the Preboreal. Varve counting provides the chronological framework and determines the length of Younger Dryas to 1025–1090 years. A strong relation between climate change, environment response and depositional processes has been found. In consequence, varve microfacies variations are a sensitive proxy for environment changes. These are reflected, for example, in erosion processes within the lake’s catchment (minerogenic input) and lake productivity (diatom blooms). The observed varve changes have been quantified by multiproxy analyses of physical and chemical sediment parameters with a resolution of between 8 and 40 years depending on sedimentation rate. In addition, high resolution palynological investigations provide the biostratigraphical subdivision based on changes in the vegetation occurring during the same time interval. Varve observations reveal that environment changes at the beginning and the end of the Younger Dryas occurred within 20–50 years. Furthermore, sediment and vegetation changes were synchronous. Within the actual precision of the MFM and GRIP chronologies (divergence of only a few decades) terrestrial responses in Western Europe occurred quasi-synchronous to temperature changes in Greenland.

Lateglacial calendar year chronology based on annually laminated sediments from Lake Meerfelder Maar, Germany

Abstract Annually laminated sediments from Lake Meerfelder Maar (MFM) in the Eifel, Germany, provide an independent calendar year timescale for the last glacial/interglacial transition. Changes in varve thickness and varve facies reflect significant environment variations during this period. The general micro facies pattern confirms that diatomaceous organic varves are favoured during warm climatic phases while cold periods generate higher allochthonous sediment fluxes. An exception is the significant increase in diatom blooms at the beginning of the Younger Dryas. Six Lateglacial biozones have been defined by Litt and Stebich (Quaternary International, 1999). The sediment record comprises two tephra layers as chronomarkers. The Laacher See Tephra (12,880 varve years BP) is a continent-wide correlation horizon while the Ulmener Maar Tephra provides regional chronological links. The beginning of the lateglacial warming is dated at 14,450 varve years (vyrs) BP which is regarded as the minimum age. Three abrupt cold spells interrupted the lateglacial interstadial at 13,800 vyrs BP (Oldest Dryas), 13,540 vyrs BP (Older Dryas) and 12,680 vyrs BP (Younger Dryas). The Oldest Dryas (130 years) and the Older Dryas (190 years) were rather short while the Younger Dryas lasted much longer (1090 years). The MFM chronology was compared with ice core timescales from GISP2 and GRIP. There is a good agreement between these timescales, with the GRIP model age (ss09) providing the best match to the MFM chronology.

High‐resolution geological record of historic earthquakes in the Dead Sea basin

A 2000 year paleoseismic record of the Dead Sea area was recovered from a lacustrine sedimentary section. The section is being exposed at the Zeelim Terrace on the shores of the Dead Sea due to the fast retreat of the lake. The section consists of laminated detrital and chemical (mainly aragonite) sediments that were deposited in the Holocene paleo-Dead Sea. Eight layers in the section show deformed sedimentary structures and are identified as seismites. Their chronology was determined by radiocarbon dating on organic remains. The seismite ages are well correlated with the historically documented earthquakes of 64 and 31 B.C. and 33, 363, 1212, 1293, 1834 and 1927 A.D. The few historically documented earthquakes that have no correlatives in the Zeelim seismite record occurred in times of sedimentary hiatuses at this site (e.g., 749 A.D.). Based on modern analogues and the association of similar disturbed layers with syndepositional faults, the Zeelim Terrace seismites indicate M>5.5 earthquakes. The average recurrence interval is estimated as ∼100–300 years and represents slip events on different faults in the Dead Sea area. The Zeelim section provides a unique opportunity to correlate two independent and extensive data sets, the historical and sedimentary records. This study opens the way for better understanding of spatial and temporal distribution of earthquakes along the Dead Sea Transform and elsewhere.

Climate Development and History of the North Atlantic Realm

Concepts and Ideas: Climate History and the Great Geophysical Experiment Towards a History of Ideas on Anthropogenic Climate Change.- Decadal to Millennial Variability: Climate Dynamics of the North Atlantic and NW-Europe Holocene Climate Variability on Centennial-to-Millennial Time Scales Solar Forcing of Climate Change in Recent Millennia Times of Quiet, Times of Agitation: Sverdrups Conjecture and the Bermuda Coral Record A Case for Climate Cycles: Orbit, Sun and Moon Tracing Climate Variability: The Search for Climate Dynamics on Decadal to Millennial Time Scales.- Holocene Variability: Holocene Climate and Past Volcanism in Greenland and Northern Europe Holocene Climate Evolution of the North Atlantic Ocean and the Nordic Seas Holocene Climate History of Northern Europe - the Evidence from Late Deposits Climate Changes Duringn the Holocene Recorded by Lakes from Europe The Post-Glacial Evolution of the Baltic Sea Holocene Climatic History of Northern Europe as Recorded by Vegetation Changes Late Glacial and Holocene Glacier Fluctuations and Climatic Variations in Southern Norway Holocene Paleoenvironmental Changes in North-West Europe.- Climate History and Human Activity: Landscape Development and Occupation History along the Southern North Sea Coast Climatic Change in Northern Europe over the Last 2000 Years and its Possible Influence on Human Activitiy Human Stature and Climate Malaria around the North Sea Patterns of Climate in Central Europe Since Viking Times On the Holocene Water Balance in Central Europe and Several Historical Consequences Narrowest-Ring Events in the Irish Oak Chronology.- Coastal Zone and Human Activity: The Pleistocene and Holocene Development of the Southeastern North Sea Basin Effects of Climate and Human Interventions on the Evolution of the Wadden Sea Depositional System Historic Storms in the North Sea Area, an Assessment of the Storm Data, the Present Position of Research and the Prospects for Future Research Climate Variability and Historical NW European Fisheries Changes in Coastal Zone Ecosystems The Impact of Harmful Algal Blooms in Natural and Human-Modified Systems of Northern Europe Climate and Human Induced Impacts on the Coastal Zone of the Southern North Sea.

Ams Radiocarbon Dating of Annually Laminated Sediments From Lake Holzmaar, Germany

AMS radiocarbon ages have been determined on terrestrial macrofossils selected from the annually laminated sediments of lake Holzmaar (Germany). The radiocarbon chronology of this lake covers the last 12.6 ka. Comparison of the radiocarbon dated varve chronology with tree ring data shows that an additional 878 years have to be added to the varve chronology. The corrected C-14 varve chronology of Holzmaar reaches back to ca. 13.8 ka cal. BP and compares favourably with the results from Soppensee (Switzerland) (Hajdas et al., 1993). The corrected ages for the onset and the end of the Younger Dryas biozone are 11,940 cal. BP and 11,490 cal. BP, respectively. The ash layer of the Laacher See volcanic eruption is dated at 12,201 +/- 224 cal. BP and the Ulmener Tephra layer is dated at 10,904 cal. BP.

A Lateglacial and Holocene organic carbon isotope record of lacustrine palaeoproductivity and climatic change derived from varved lake sediments of Lake Holzmaar, Germany.

Abstract A composite varve-dated 11.4xa0m long sediment sequence from Lake Holzmaar, situated in the Eifel region of western Germany, was investigated for total organic matter content, total nitrogen content and stable organic carbon isotopes. Mean time resolution is 75 years for TN and 14 years for δ 13 C org . On millennial time scales primary production of lacustrine algae strongly depends on the delivery of nutrients from the catchment. The respective carbon isotope record is characterized by marked variations of δ 13 C org ranging from −36.0‰ to −27.0‰ and includes a number of pronounced shifts. Reactions of the lacustrine system and the catchment to changes of environmental parameters, e.g. runoff, solar radiation and temperature, induce changes of algal associations and of lacustrine primary production which are reflected in the sediments as carbon isotope variations. Clear evidence of ecosystem reorganizations is detected by the carbon isotope record around 14,200, 10,400, 9600, 5500, 2700, 1700 and 900 varve years BP. In particular, the Holocene events of 9600, around 5500 and 2700 are interpreted as the expression of massive changes of the climate system. The steady rise of δ 13 C org values during the mid-Holocene is interpreted as a continuous climatic amelioration reaching an optimum around 6500 varve years BP. Rapid and large changes of δ 13 C org values from 2700 varve years BP to the present indicate major disturbances in the catchment area. These are most probably related to deforestation or reforestation and runoff changes, presumably in conjunction with human impact. Carbon isotopes, thus, characterize the Holzmaar ecosystem in time revealing lacustrine palaeoproductivity as well as providing palaeoenvironmental and palaeoclimatic information.

Sediments from Lago di Mezzano, central Italy: a record of Lateglacial/Holocene climatic variations and anthropogenic impact

Microscopic, geochemical and pollen analysis of sediment samples of a Lateglacial/Holocene profile from Lago di Mezzano, a maar lake in central Italy, reveals evidence of significant climatic and human-induced environmental changes. Time control is provided by a combination of varve chronology and radiocarbon dating. The well-known Lateglacial climatic variations, a warmer interstadial and the Younger Dryas cold phase are clearly represented in all the parameters. During the interval between 9200 and 5600 cal. BP of the Holocene climatic optimum, annually laminated, organic-rich diatom gyttja was deposited. Two periods of diminished total organic carbon are identified within this interval. The first one (P1) ranges from 8200 to 7800 cal. BP while the second (P2) is centred around 6500 cal. BP. During P1, a predominance of diatoms (Stephanodiscus parvus and S. minutulus) over other algae (represented by the total organic carbon content) is observed. The timing of this period coincides with the early to mid-Holocene climatic transition, reported from ice cores and lake sediments (Stager and Mayewski, 1997). P2 is characterized by a decrease in all biogenic parameters including biogenic opal, organic carbon as well as arboreal pollen. From 5000 cal. BP to date, the sediment pattern changes coincide with the mid-Holocene climatic deterioration. In addition to these natural variations, human impact has been recorded and recognized from sedimentological features such as turbidites and charcoal, as well as from reduced arboreal pollen content. Two Middle Bronze Age (3700 cal. BP and 3300 cal. BP), Etruscan/early Roman (2500 cal. BP), Longobardic (ad 900) and‘modern settlements’ (since ad 1700) have been distinguished on the basis of these data.