Analysis Of Lacustrine Sediments Research Articles

A 1640-Year Vegetation and Fire History of the Lake Haixihai Catchment in Northwestern Yunnan, Southwest China

Vegetation and fire archives of the late Holocene are essential for understanding the importance of natural and anthropogenic forcings on past and future vegetation successions as well as climate changes. Here we present a 1640-year record of vegetation and fire history of the Lake Haixihai catchment in northwestern Yunnan, southwest China. Pollen and charcoal analyses as well as XRF (X-ray fluorescence) analysis of lacustrine sediments from Lake Haixihai were employed to reveal its regional vegetation, forest fire, and soil erosion intensity changes over the last 1640 years. The results show their significant changes attributed to both climatic conditions and human activities: The lake catchment witnessed the densest forests (including pine and hemlock forests, and evergreen broadleaved forests) and the weakest soil erosion of the last 1640 years as well as relatively frequent forest fires at 380–880 AD, when vegetation succession, forest fire, and soil erosion were mainly driven by natural forcings, i.e., climatic conditions. A significant and abrupt drop in forest density, minor changes in abundance of forest components, and gradually strengthening soil erosion occurred at the transition from 880 to 1040 AD, when anthropogenic forcings such as the development of agriculture and systematic deforestation gradually became dominant ones driving vegetation succession and soil erosion. After this transition, forest density and soil erosion intensity never returned to the level before 880 AD, implying that the modern landscape in the lake catchment was already established approximately at as early as ca. 1040 AD. No significant changes in forest component and density as well as forest fire and soil erosion occurred until 1940 AD. The most frequent forest fires, the strongest soil erosion, and low forest density after 1940 AD might be attributed partially to climatic conditions and partially to extensive deforestation around 1960 AD.

The early Holocene paleogeography of Yurumkuveem river basin (Central Chukotka)

Abstract. Results of radiocarbon dating and spore-pollen analysis of lacustrine sedi ments in the Nyrki sectionfrom the Yurumkuveem river basin (Central Chukotka) show the wider distribution of floodplain forests and the warmer climate in this time in the region in the early Holocene than in the present time. The occurrence of larch (Larix) in the vicinity of Nyrki lake in the early Holocene is also discussed. Our data suggest that the larch range was expanded to the Yurumkuveem river valley and its inflows during the early Holocene, but this tree disappeared from there in the late Holocene.

The dynamic land-cover of the Altai Mountains: Perspectives based on past and current environmental and biodiversity changes.

We present climate-dependent changes in the high-mountain forest ecotone, old-growth forests, alpine phytocenoses, and deglaciated forelands in the Aktru glacial basin (Altai Republic, Russia). A number of independent sources (variations in upper treeline altitude, dendrochronological data, analysis of lacustrine sediments and botanical and geographical studies linked with the dynamics of glacial-dammed lakes in the Chuya and Kurai intermountain depressions) suggest Holocene temperatures reached about 4°C higher than today. Unlike the European Alps, glaciers in the continental Altai Mountains disappeared before forming again. Also, the upper altitudinal limit of mountain forests during the Holocene was greater than in the European Alps. The high variability of mountain ecosystems in southern Siberia suggests their potential instability in a currently changing climate. However, periglacial successions associated with the strong continental climate and glacier retreat represent an area of increasing biodiversity and plant cover. The historical and current sensitivity of the continental mountains to climate variations which exceeds that of the European Alps requires greater understanding, environmental protection, and increased social responsibility for the consequences of anthropogenic contributions to climate change: the isolated Altai areas contribute little to climate changes, but are greatly affected by them.

A high-resolution 1200-year lacustrine record of glacier and climate fluctuations in Lofoten, northern Norway

Here we present the first high-resolution late-Holocene glacier record from the Lofoten archipelago in northern Norway. The study is based on analyses of lacustrine sediments from the distal glacier-fed lake Kveitvikvatnet (30.1 m a.s.l.), as well as glacial-geomorphological mapping of the ~4.2-km2 surrounding catchment. The lake sediment cores have been examined for input of glacial-derived sediments by using physical, geochemical and magnetic sediment properties, including x-ray fluorescence (XRF), magnetic susceptibility (MS), grain size analyses, dry bulk density (DBD) and loss-on-ignition (LOI). Former glacier extent has been reconstructed using aerial photography and glacial-geomorphological mapping. Lichenometric dating has been used to construct a moraine chronology covering the recent fluctuations of the largest glacier (back to AD ~1740). AMS radiocarbon dating reveals that the lake sediment record covers the last 1200 years, thereby including both the ‘Little Ice Age’ (LIA) and the ‘Medieval Climate Anomaly’ (MCA). By linking continuously deposited lake sediment proxies of glacier fluctuation to known glacier frontal positions and an independent temperature reconstruction, former fluctuations in the equilibrium-line altitude (ELA) and winter precipitation have been reconstructed. Reconstructed winter precipitation estimates have also been correlated to instrumental data from the region back to AD 1895 and show a remarkable correlation, which further strengthens our approach. We found that both MCA and LIA were periods of substantial glacier variations with respect to the present, with a maximum lowering of the ELA of ~75 and ~85 m, respectively. Increased precipitation during these intervals, associated with more frequent and/or intense winter storms, is suggested to be the major driving force of glacier fluctuations in Lofoten.

Reconstructing lake evaporation history and the isotopic composition of precipitation by a coupled δ18O–δ2H biomarker approach

Summary Over the past decades, δ 18 O and δ 2 H analyses of lacustrine sediments became an invaluable tool in paleohydrology and paleolimnology for reconstructing the isotopic composition of past lake water and precipitation. However, based on δ 18 O or δ 2 H records alone, it can be challenging to distinguish between changes of the precipitation signal and changes caused by evaporation. Here we propose a coupled δ 18 O– δ 2 H biomarker approach that provides the possibility to disentangle between these two factors. The isotopic composition of long chain n -alkanes ( n -C 25 , n -C 27 , n -C 29 , n -C 31 ) were analyzed in order to establish a 16 ka Late Glacial and Holocene δ 2 H record for the sediment archive of Lake Panch Pokhari in High Himalaya, Nepal. The δ 2 H n -alkane record generally corroborates a previously established δ 18 O sugar record reporting on high values characterizing the deglaciation and the Older and the Younger Dryas, and low values characterizing the Bolling and the Allerod periods. Since the investigated n- alkane and sugar biomarkers are considered to be primarily of aquatic origin, they were used to reconstruct the isotopic composition of lake water. The reconstructed deuterium excess of lake water ranges from +57‰ to −85‰ and is shown to serve as proxy for the evaporation history of Lake Panch Pokhari. Lake desiccation during the deglaciation, the Older Dryas and the Younger Dryas is affirmed by a multi-proxy approach using the Hydrogen Index (HI) and the carbon to nitrogen ratio (C/N) as additional proxies for lake sediment organic matter mineralization. Furthermore, the coupled δ 18 O and δ 2 H approach allows disentangling the lake water isotopic enrichment from variations of the isotopic composition of precipitation. The reconstructed 16 ka δ 18 O precipitation record of Lake Panch Pokhari is well in agreement with the δ 18 O records of Chinese speleothems and presumably reflects the Indian Summer Monsoon variability.

Cambios en la vegetación durante el Holoceno en la región Norte del Iberá, Corrientes, Argentina

Vegetation changes during the Holocene in the North Iberá, Corrientes, Argentina. Wetlands are very important sites for palynological studies, since they represent one of the most suitable environments for fossil pollen preservation. The aim of this work was to determine, by palynological analysis of lacustrine sediments, the vegetal communities and the predominant environment during the Holocene in NW of Iberá. Two lagoons were studied: San Sebastián and San Juan Poriahú. Sediment samples were obtained with witness using a "Levingstone square-rod sampler", processed with Faegri e Iversen techniques and dated with C14. The palynological graphs were divided in zones using the Tilia program. The palynological analysis allowed visualizing diverse changes in the vegetation: from 6 140 +/- 50 to 5 170 +/- 100 a. C., the NW of Iberá was characterized by marsh-herbaceous vegetation and arboreal vegetation typical of dry vegetation. From 5 170 +/- 100 to 3 460 +/- 60 a. C., a decrease in the species frequency, typical of wet environments, is produced, and the clogging of the waterbody, from 3460 +/- 60 a. C. onwards, while continuing the dominance of herbaceous vegetation typical of these environments, the arboreal pollen, indicates the beginning of a hygrophilous forest development.

Biogeological Raman spectroscopic studies of Antarctic lacustrine sediments

Analysis of lacustrine sediments is an accepted method for deciphering the palaeoenvironment of a lake's catchment area, as each strata of the sediment gives information about the rock type it was eroded from and also the state of the lake, i.e. oxic or anoxic. Antarctica has long been accepted as a putative analogue for Mars, so the analysis of Antarctic material may give results that can be compared to sediments on Mars. Raman spectroscopy has been selected as the method of analysis as it does not destroy the sample, can be used in situ and requires very little sample preparation. It is a suitable method for analysing both inorganic and organic matter and a miniature spectrometer is currently being developed for use in the field. The results from the spectrometers can serve as a guide for analysing sediments on Mars. It has been shown that Raman spectroscopy can detect and differentiate between oxic and anoxic sediments. Both 1064 and 785 nm wavelengths are suitable for laser excitation of organic and inorganic matter.

Environmental change of Gucheng Lake of Jiangsu in the past 15 ka and its relation to palaeomonsoon

The high-resolution and multi-proxy analysis of lacustrine sediments from the Gucheng Lake has revealed the palaeodimatic and palaeoenvironmental evolutionary process since 15 ka B.P. The formation, expansion and shrinkage of the lake is closely related to monsoon rain caused by strength change of monsoon circulation which is controlled by orbit forcing. An abrupt descending of temperature occurring from 11.3 to 11.0ka B.P. may be correlative to Younger Dryas event, which trancated the monsoon climate cycle. Through the correlation with adjacent regions, it can be known that there were twice north shifts and twice south migrations for polar front of monsoon.

Chronology of a Wisconsin age proglacial lake in the Miers Valley, Antarctica

Abstract Mapping and oxygen isotopic, C-14, and U/Th analyses of lacustrine sediments have shown that a lake (Glacial Lake Trowbridge) proglacial to the Ross Sea I Ice Sheet occupied Miers Valley from at least 23 000 years B.P. until 10 000 years B.P. This lake was at least 80 m deep and extended to more than 156 m above present sea level at its maximum extent 18 000–19 000 years ago. The lake was filled with waters with a similar isotopic composition to the modern Koettlitz Glacier. By 13 000–14 000 years B.P. evaporation had considerably reduced the size of the lake and resulted in the precipitation of calcite and gypsum evaporites. The isotopic composition of abundant sulphates within the evaporite sequences shows that although they were precipitated from isotopically depleted glacial meltwaters, the sulphates originated from seawater. Lake occupation of the Miers Valley was synchronous with proglacial lakes occupying other valleys in southern Victoria Land during the period of late Wisconsin glacial m...