Giesecke T.,University of Gottingen |
Wolters S.,Lower Saxony Institute for Historical Coastal Research |
Brande A.,TU Berlin
PLoS ONE | Year: 2012
In mid to high latitudes glacial and interglacial cycles have repeatedly changed the area available for plant growth. The speed at which plants are able to colonize areas at the onset of an interglacial is hypothesized to limit their distribution ranges even today (migrational lag). If the spread of plants would have been generally slow then plant diversity in previously glaciated areas would be expected to increase over time. We explore this hypothesis using results from six palynological investigations from two previously glaciated regions: central Sweden and north-eastern Germany. Rarefaction, slope of rank order abundance, and taxa accumulation plots were used to evaluate richness and evenness in pollen data in an attempt to separate richness from evenness. These analyses show little change in palynological richness for the northern sites throughout the Holocene. In contrast, the southern sites show an increase in richness and evenness during the early Holocene; this may be explained by the different initial conditions at the onset of the Holocene. A strong rise in palynological richness around 6000 and 1000 years ago at the southern sites can be attributed to the regional initiation of agriculture and major opening of the forest, respectively. For the northern sites there is no evidence for increased taxonomic diversity through time that could be due to delayed immigration of species. © 2012 Giesecke et al.
Wischnewski J.,University of Potsdam |
Kramer A.,Lower Saxony Institute for Historical Coastal Research |
Kong Z.,CAS Institute of Botany |
Mackay A.W.,University College London |
And 3 more authors.
Global Change Biology | Year: 2011
Rapid population growth and economic development have led to increased anthropogenic pressures on the Tibetan Plateau, causing significant land cover changes with potentially severe ecological consequences. To assess whether or not these pressures are also affecting the remote montane-boreal lakes on the SE Tibetan Plateau, fossil pollen and diatom data from two lakes were synthesized. The interplay of aquatic and terrestrial ecosystem response was explored in respect to climate variability and human activity over the past 200 years. Nonmetric multidimensional scaling and Procrustes rotation analysis were undertaken to determine whether pollen and diatom responses in each lake were similar and synchronous. Detrended canonical correspondence analysis was used to develop quantitative estimates of compositional species turnover. Despite instrumental evidence of significant climatic warming on the southeastern Plateau, the pollen and diatom records indicate very stable species composition throughout their profiles and show only very subtle responses to environmental changes over the past 200 years. The compositional species turnover (0.36-0.94 SD) is relatively low in comparison to the species reorganizations known from the periods during the mid- and early-Holocene (0.64-1.61 SD) on the SE Plateau, and also in comparison to turnover rates of sediment records from climate-sensitive regions in the circum arctic. Our results indicate that climatically induced ecological thresholds are not yet crossed, but that human activity has an increasing influence, particularly on the terrestrial ecosystem in our study area. Synergistic processes of post-Little Ice Age warming, 20th century climate warming and extensive reforestations since the 19th century have initiated a change from natural oak-pine forests to seminatural, likely less resilient pine-oak forests. Further warming and anthropogenic disturbances would possibly exceed the ecological threshold of these ecosystems and lead to severe ecological consequences. © 2011 Blackwell Publishing Ltd.
Zech M.,University of Bayreuth |
Zech M.,Martin Luther University of Halle Wittenberg |
Tuthorn M.,University of Bayreuth |
Zech R.,ETH Zurich |
And 4 more authors.
Journal of Paleolimnology | Year: 2014
We investigated a late glacial-Holocene lacustrine sediment archive located at 4,050 m a.s.l. in the small carbonate-free catchment of Lake Panch Pokhari, Helambu Himal, Nepal. A δ18O sugar biomarker record was established by applying novel compound-specific δ18O analysis of plant sugar biomarkers (Zech and Glaser in Rapid Commun Mass Spectrom 23:3522-3532, 2009). This method overcomes analytical challenges such as extraction and purification faced by previous methods aimed at using δ18O of aquatic cellulose as a paleoclimate proxy. The δ18O results for sugar biomarkers arabinose, xylose and fucose agree well and reveal a pronounced trend towards lower δ18O values during the deglaciation and the onset of the Bølling/Allerød interstadial. By contrast, the period of the Younger Dryas is characterized by higher δ18O values. The early Holocene again reveals lower δ18O values. We suggest that our lacustrine δ18O record reflects coupled hydrological and thermal control. It is strongly related to changes in the oxygen isotopic composition of paleo-precipitation and resembles the δ18O records of Asian speleothems. With respect to the 'amount effect,' the record is interpreted as reflecting the Indian Summer Monsoon intensity. The precipitation signal is, however, amplified in our record by evaporative 18O enrichment that is controlled by the ratio of precipitation to evaporation. We suggest that our δ18O record reflects the variability of the Indian Summer Monsoon, which was strong during the Bølling/Allerød interstadial and early Holocene, but weak during the Younger Dryas stadial. This interpretation is corroborated by a pollen-based index for Lake Panch Pokhari that estimated the strength of the Indian Summer Monsoon versus the strength of the Westerlies. Millennial-scale synchronicity with the Greenland δ18O temperature records highlights the previously suggested strong teleconnections between the Asian Monsoon system and North Atlantic climate variability. © 2013 Springer Science+Business Media Dordrecht.
Monacci N.M.,University of Alaska Fairbanks |
Meier-Grunhagen U.,Lower Saxony Institute for Historical Coastal Research |
Meier-Grunhagen U.,University of Gottingen |
Finney B.P.,Idaho State University |
And 2 more authors.
Quaternary Research | Year: 2011
This study examines a sediment core (SR-63) from a mangrove ecosystem along the Sibun River in Belize, which is subject to both changes in sea-level and in the characteristics of the river's drainage basin. Radiocarbon dates from the core show a decreased sedimentation rate from ~6ka to 1calka BP and a marked change in lithology from primarily mangrove peat to fluvial-derived material at ~2.5calka BP. Changes in the sedimentation rates observed in mangrove ecosystems offshore have previously been attributed to changes in relative sea-level and the rate of sea-level rise. Pollen analyses show a decreased abundance of Rhizophora (red mangrove) pollen and an increased abundance of Avicennia (black mangrove) pollen and non-mangrove pollen coeval with the decreased sedimentation rates. Elemental ratios ([N:C] a) and stable isotope analyses (δ 15N and δ 13C) show that changes in the composition of the organic material are also coeval with the change in lithology. The decrease in sedimentation rate at the site of core SR-63 and at offshore sites supports the idea that regional changes in hydrology occurred during the Holocene in Belize, influencing both mainland and offshore mangrove ecosystems. © 2011 University of Washington.
Schlutz F.,Lower Saxony Institute for Historical Coastal Research |
Schlutz F.,University of Gottingen |
Shumilovskikh L.S.,University of Gottingen
Fungal Ecology | Year: 2013
This study links the spores of the recent ascomycete genus Potamomyces with the fossil form-taxa Mediaverrunites. Spores of the only known representative of Potamomyces, P.armatisporus, were found in recent material from Nepal together with a previously unknown spore type described here for the first time as Potamomyces nepalensis-type. Potamomyces is thus not a monotypic genus. The rarely isolated type species P. armatisporus is known as a lignicolous freshwater ascomycete from tropical rivers. Our findings indicate that the genus also lives in damp conditions in terrestrial habitats, and is recently distributed also in subtropical regions. Based on the fossil findings of Mediaverrunites, the genus Potamomyces evolved at least 25 million yrago at the onset of younger Tertiary. Potamomyces is an excellent example of the potential of interdisciplinary fungal research, combining insights from fungal evolution, taxonomy, ancient and recent distribution and ecology. © 2013 Elsevier Ltd and The British Mycological Society.
Kramer A.,Lower Saxony Institute for Historical Coastal Research |
Bittmann F.,Lower Saxony Institute for Historical Coastal Research
Journal of Quaternary Science | Year: 2015
The present study aims to improve our understanding of the chronology of vegetation changes in north-western Germany during the Neolithic. Therefore, four archived peat profiles from small mires that had been pollen analysed and partly conventionally radiocarbon dated during the 1990s were re-evaluated. Based on new accelerator mass spectrometry (AMS) dates, there are considerable differences between the existing and the newly developed age-depth models. These are also caused by the exclusion of pollen events that were previously assumed to be synchronous, and results from archaeological investigations as dating horizons, hence avoiding circular reasoning in the present study. In addition to the re-evaluation of archived material, a new profile was recovered, pollen analysed and AMS radiocarbon dated to gain insights into the regional vegetation development and to put local human impact on the landscape in a broader context. The results indicate three different phases of human-induced vegetation changes. The local vegetation changes do not follow this general pattern, but reflect a very patchy landscape which in turn probably refers to quite small pollen source areas. The study emphasizes that vegetation changes seen in local pollen profiles should neither be regarded as general trends nor be used as dating horizons for neighbouring sites. © 2015 John Wiley & Sons, Ltd.
Kramer A.,Lower Saxony Institute for Historical Coastal Research |
Bittmann F.,Lower Saxony Institute for Historical Coastal Research |
Nosler D.,Landkreis Stade Archaologische Denkmalpflege
Vegetation History and Archaeobotany | Year: 2014
Palynological investigations on two well-dated peat profiles provide insights into Neolithic vegetation and settlement history from Hümmling in north-western Germany. The site selections allow comparisons between local and regional vegetation changes and are used to estimate the extent of Neolithic influence on the vegetation. The interpretation of the fossil spectra relied on radiocarbon dating, evaluation of pollen indicator taxa, non-pollen palynomorphs and multivariate techniques. During the late Mesolithic the vegetation was dominated by mixed oak forests while openings in forest cover were detected, with a decline in elm reflected in the regional pollen record around 4250 cal. b.c. The presence of humans is shown by settlement indicators that are first recorded at ca. 3800 cal. b.c. Vegetation changes were small between 4300 and 3600 cal. b.c. This suggests that regional vegetation was relatively resilient to small-scale disturbances. Possible indications of grazing were recorded in the spectra of the local pollen profile but there is no clear-cut evidence for Neolithic activity. Between 3520 and 2260 cal. b.c. decreases in forest cover were inferred from both profiles and increases in settlement indicators reflect farming activity. These changes coincide with the emergence in the area of the Funnel Beaker Culture and the subsequent Single Grave Culture. Both profiles suggest that settlement probably ceased between ca. 3230 and 3050 cal. b.c. This lull or cessation in activity was probably regional in character. After 2260 cal. b.c. human impact on the vegetation decreases and woodlands regenerate. The longevity of the regeneration phase-ca. 690 years-was probably connected with the low resilient capability of the vegetation on the poor soils. © 2013 Springer-Verlag Berlin Heidelberg.
Behre K.-E.,Lower Saxony Institute for Historical Coastal Research
International Journal of Earth Sciences | Year: 2012
The article highlights the difficulties connected with getting secure fixed-points for sea-level curve construction and emphasises the care that should be taken with data interpretation. As such, it is a welcome contribution to this important topic. On the other hand, the paper has, in my opinion, several weaknesses. It not only disregards a large body of reliable and highly relevant information on sea-level changes available from investigations carried out using a variety of methodologies, but also makes assumptions that seem to be based, to varying degrees, on misconceptions and misunderstandings. Many of these misunderstandings might have been avoided had the discussions, that are referred to in the Acknowledgements, actually taken place. I wish to take this opportunity to set the record straight by stating that no such discussions took place. © 2011 Springer-Verlag.
Irion G.,Senckenberg Institute |
de Morais J.O.,State University of Ceará |
Bungenstock F.,Lower Saxony Institute for Historical Coastal Research
Quaternary Research | Year: 2012
Beach-rock exposures provide a record of Holocene sea-level rise along the 560-km-long northeast-facing coast of Ceará, Brazil, that differs from the record available along the other 4300. km of Brazilian coastline further south. Whereas documentation is available from southern Brazil to show Holocene sea levels as much as 5. m above today's level, our observations along the northeastern coast indicate that sea level here was not above the present-day level during the Holocene. Near Jericoacoara, about 240. km northwest of Fortaleza, characterized by strong surf, Precambrian rocks crop out from under a temporary cover of sand in small protected locations with less surf. Here in this upper tidal zone beach rock is being formed, while it is being dismembered synchronously by erosion at lower tide levels. This shows a rising sea level. Along the entire coast of Ceará west of Ponta Grossa the absence of beach rock higher than spring tide level indicates that sea-level was not above its present-day level during the Holocene.Notches in bedrock situated between 2. m and 6. m above spring-tide high-water level that we formerly described as Holocene, are now believed to be Sangamonian. © 2011 University of Washington.
Mauz B.,University of Liverpool |
Baeteman C.,Geological Survey of Belgium |
Bungenstock F.,Lower Saxony Institute for historical coastal research |
Plater A.J.,University of Liverpool
Quaternary Geochronology | Year: 2010
The accuracy of optical ages derived from tidal sediments depends largely upon the transport processes. These processes constrain the degree of bleaching by the time of deposition and the choice of grain size for dating. This study looks at flow regime, sediment bedding, particle size and suspended sediment concentration (SSC) over tidal flats in order to identify the tidal sub-environment from which reliable multigrain optical ages are most likely to be achieved. The resulting conceptual model is then compared with empirical OSL data obtained from Holocene sediments of the southern North Sea tidal coastal plain of continental Europe. Optical dating of the tidal sediments included single-aliquot-regenerative dose protocol applied to multigrain aliquots of fine sand and fine silt, statistical analysis using weighted skewness, standardised kurtosis and over-dispersion. It is inferred from the model that smaller grains should be better bleached than larger grains. However, because transport and deposition processes are extremely variable in both space and time, unequivocal "bleaching rules" could not be assigned to a particular tidal sub-environment. In this context more than 85% of our samples return accurate ages and around 13% of our optical ages are overestimated when compared with ages from established well-constrained stratigraphic frameworks. The empirical study confirms the concept of "variable bleaching rules": both accurate and inaccurate ages are obtained from silty and sandy OSL samples regardless of the sub-environment and well-bleached samples may be obtained from all tidal sub-environments. Although our study is based on multiple-grain aliquots it also shows that an independent statistical treatment of equivalent dose data is an indispensable procedure to detect and correct for insufficient bleaching. © 2010 Elsevier B.V.