Home About us Contact
|
Home About us Contact | ||
|
|
||
Sediment Records (sediment + record)
Selected AbstractsA large carbon pool and small sink in boreal Holocene lake sedimentsGLOBAL CHANGE BIOLOGY, Issue 10 2004Pirkko Kortelainen Abstract Model-based estimates suggest that lake sediments may be a significant, long-term sink for organic carbon (C) at regional to global scales. These models have used various approaches to predict sediment storage at broad scales from very limited data sets. Here, we report a large-scale direct assessment of the standing stock and sedimentation rate of C for a representative set of lakes in Finland. The 122 lakes were selected from the statistically selected Nordic Lake Survey database, they cover the entire country and the water quality represents the average lake water quality in Finland. Unlike all prior estimates, these data use sediment cores that comprise the entire sediment record. The data show that within Finland, aquatic ecosystems contain the second largest areal C stocks (19 kg C m,2) after peatlands (72 kg C m,2), and exceed by significant amounts stocks in the forest soil (uppermost 75cm; 7.2 kg C m,2) and woody biomass (3.4 kg C m,2). Kauppi et al. (1997). The Finnish estimate extrapolated over the boreal region gives a total C pool in lakes 19,27 Pg C, significantly lower than the previous model-based estimates. [source] Evidence for a lacustrine faunal refuge in the Larsemann Hills, East Antarctica, during the Last Glacial MaximumJOURNAL OF BIOGEOGRAPHY, Issue 7 2006Louise Cromer Abstract Aim, There is no previous direct evidence for the occurrence of lacustrine refuges for invertebrate fauna in Antarctica spanning the Last Glacial Maximum (LGM). In the absence of verified LGM lacustrine refuges many species are believed to result from Holocene dispersal from sub-Antarctic islands and continents further north. If freshwater lake environments were present throughout the LGM, extant freshwater species may have been associated with Antarctica prior to this glacial period. This study looked at faunal microfossils in a sediment core from an Antarctic freshwater lake. This lake is unusual in that, unlike most Antarctic lakes, the sediment record extends to c. 130,000 yr bp, i.e. prior to the LGM. Location, Lake Reid, Larsemann Hills, East Antarctica (76°23, E; 69°23, S). Methods, Palaeofaunal communities in Lake Reid were identified through examination of faunal microfossils in a sediment core that extended to c. 130,000 yr bp. Results, Ephippia and mandibles from the cladoceran Daphniopsis studeri and loricae of the rotifer Notholca sp. were found at all depths in the sediment, indicating that these two species have been present in the lake for up to 130,000 years. Copepod mandibles were also present in the older section of the core, yet were absent from the most recent sediments, indicating extinction of this species from Lake Reid during the LGM. Main conclusion, The presence of D. studeri and Notholca sp. microfossils throughout the entire Lake Reid core is the first direct evidence of a glacial lacustrine refugium for invertebrate animals in Antarctica, and indicates the presence of a relict fauna on the Antarctic continent. [source] Climatic change during the last 4000 years in the southern Tarim Basin, Xinjiang, northwest China,JOURNAL OF QUATERNARY SCIENCE, Issue 7 2007Wei Zhong Abstract In this study, a ca. 4000,cal. yr ancient lacustrine (or wetland) sediment record at the southern margin of Tarim Basin is used to reconstruct the history of climate change. Six radiocarbon dates on organic matter were obtained. ,18O and ,13C of carbonate, pollen and sediment particle size were analysed for climate proxies. The proxies indicate that a drier climate prevailed in the area before ca. 1010 BC and during period 1010 BC,AD 500 climate then changed rapidly and continuously from dry to moist, but after about AD 500 climate generally shows dry condition. Several centennial-scale climatic events were revealed, with the wettest spell during AD 450,550, and a relatively wetter interval between AD 930,1030. Pollen results show that regional climate may influence human agricultural activities. Spectral analysis of mean grain size (MGS) proxy reveals statistically pronounced cyclic signals, such as ca. 200,yr, ca. 120,yr, ca. 90,yr, ca. 45,yr and ca. 33 or 30,yr, which may be associated with solar activities, implying that solar variability plays an important role in the decadal- and centennial-scale climate variations in the study area. Copyright © 2007 John Wiley & Sons, Ltd. [source] Multiproxy evidence of an early Holocene (8.2 kyr) climate oscillation in central Nova Scotia, CanadaJOURNAL OF QUATERNARY SCIENCE, Issue 7 2002Professor Ian Spooner Abstract An early Holocene lake sediment record from central Nova Scotia contains a minerogenic oscillation that is closely correlative with the 8.2 kyr event (ca. 8200 cal. yr BP), an event that has not been reported elsewhere in Atlantic Canada. A variety of biological and sedimentological indicators have been examined to characterise autochthonous and allochthonous changes that occurred during this time. The minerogenic upper oscillation (UO, ca. 8400 cal. yr BP) is marked by an increase in the chrysophyte:diatom ratio. Following the oscillation, the diatom community reflects a shift to more productive, less acidic conditions. The pollen record shows no major response to this short-lived event. Lithostratigraphic analyses indicates that the UO is characterised by an increase in clastic content, magnetic susceptibility and mean sediment grain size, all indicators of changing environmental conditions, most likely the result of regional cooling. The Taylor Lake record adds to a growing body of evidence for a widespread, hemispheric climate oscillation at 8.2 kyr. Copyright © 2002 John Wiley & Sons, Ltd. [source] A 3000-year palaeoenvironmental record from annually laminated sediment of Lake Korttajarvi, central FinlandBOREAS, Issue 4 2003MIA TILJANDER High-resolution physical analyses (varve thickness and relative X-ray density) were conducted on a 3000-year varved sediment sequence in Lake Korttajarvi, central Finland. Climate and the local environment strongly influence the properties of the lake sediments, and, through a combination of physical proxies, severe and favourable climate periods and anthropogenic effects on sedimentation with an annual to decadal resolution could be detected. We observed previously identified historical climate periods in the Lake Korttajarvi varve record. The Medieval Climate Anomaly (often termed the Medieval Warm Period) of AD 980,1250, which is characterized by highly organic sediment and a minor minerogenic flux during mild winters, started and terminated abruptly, but also included a short (30-year) colder period lasting between AD 1115 and AD 1145. The Little Ice Age, however, was not clear in our record, although there were two minor cooling periods in AD 1580,1630 and AD 1650,1710. Natural variability in the sediment record was disrupted by increased human impact in the catchment area at AD 1720. There is a distinct positive anomaly in mineral matter accumulation between 907 and 875 BC, which indicates more severe climate conditions. This period exists contemporary with a cold event, recorded worldwide, c. 2800 years ago. [source] Climatic influence on the inter-annual variability of late-Holocene minerogenic sediment supply in a boreal forest catchmentEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2010Gunilla Petterson Abstract Processes controlling sediment yield vary over a range of timescales, although most process-based observations are extremely short. Lake sediments, however, can be used to extend the observational timescale and are particularly useful when annually laminated (varved) sediment is present. The sediment record at Kassjön (N. Sweden) consists of ,6400 varves, each 0·5,1 mm thick. Image analysis was used to determine grey-scale variation and varve thickness from which annual minerogenic accumulation rate (MinAR) (mg cm,2 year,1) was inferred for the period 4486 BC , AD 1900. MinAR varies on annual to centennial scales and mainly reflects channel bank erosion by the inflow streams. The mineral input reflects the intensity of the spring run-off, which is dependent on the amount of snow accumulated during the winter, and hence MinAR is a long-term record of variability in past winter climate; other factors will be a variable response to catchment uplift, vegetation succession and pedogenesis. A major shift from low to high MinAR occurred ,250 BC, and peaks occurred around AD 250, 600, 1000, 1350 and 1650. Wavelet power spectrum analysis (confirmed by Fourier analyses) indicated significantly different periodicities throughout the period 4000 BC , AD 1700, including 275 years for the period 4000 BC , 2900 BC, 567 years for the period 2901 BC , 1201 BC, and 350 and 725 years for the period 1200 BC , AD 1700. The long-term, centennial scale variability (,350 years) may reflect solar forcing (cf the 385-year peak in tree-ring calibrated 14C activity) but interestingly, there is no obvious link to high frequency forcing, such as the North Atlantic Oscillation. The high resolution component of the record highlights the relevance of varved lake sediment records for understanding erosion dynamics in undisturbed forested catchments and their link to long-term climate dynamics and future climate change. Copyright © 2010 John Wiley & Sons, Ltd. [source] The sedimentary records in Mediterranean rockshelters and caves: Archives of environmental changeGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 4 2001Jamie C. Woodward It is important to develop rigorous methods and robust conceptual models for the interpretation of rockshelter and cave sediment records so that the cultural sequences they contain can be considered in their proper environmental context. Much of what we know about the prehistory of the Mediterranean region and adjacent areas has largely been pieced together from materials excavated from sedimentary sequences in these environments. The rockshelters and caves of the region form important environmental and sedimentary archives. Recent work has begun to consider if the remarkable climatic variability evident in the high resolution lacustrine and ice core records is manifest in the rockshelter and cave sediment records of the area. In this context, the two main characteristics of a rockshelter or cave site which control its usefulness as an archive of environmental change are the temporal resolution of the sedimentary record and the environmental sensitivity of the site. Many rockshelters and caves can be described as either Active Karst Settings (AKS) or Passive Karst Settings (PKS) and site type is an important influence on climatic sensitivity with a direct influence upon the usefulness of the sedimentary sequence as a proxy record of climate change. It is now clear that some sites may preserve detailed paleoclimatic records and the climatic signal may be represented by distinctive suites of micromorphological features, by variations in the input of allogenic sediment, or by fluctuations in the mineral magnetic properties of the fine sediment fraction. It can be argued that data derived from the analysis of bulk coarse-grained samples often lacks the stratigraphic resolution and environmental sensitivity that can be obtained from other approaches. The most favorable sites for detailed paleoclimatic reconstruction appear to be in active karst settings such as Theopetra Cave (Greece) and Pigeon Cave (Morocco) where micromorphological analyses offer insights into the stratigraphic record that are not otherwise obtainable. The temporal resolution of a site can only be established through a rigorous stratigraphic analysis and a comprehensive dating program. These are fundamental considerations in the study of rockshelter sediment records, especially when attempting to correlate between sites and draw comparisons with other proxy records of environmental change derived from sedimentary environments with rather different characteristics. Rockshelters and caves are part of a wider sediment system, and their investigation must be accompanied by detailed geomorphological, sedimentological, paleoecological, and geochronological studies of the off-site Quaternary record. © 2001 John Wiley & Sons, Inc. [source] The geochemical characterization and correlation of Late Holocene tephra layers at Ambra Crater and Kuk Swamp, Papua New GuineaGEOLOGICAL JOURNAL, Issue 5 2009Sarah E. Coulter Abstract Major element geochemical analyses of volcanic glass shards from visible, macroscopic tephra layers in Papua New Guinea were used to test field-based correlations between local Late Holocene sequences. Previously, synchronization of sediment records at archaeological and palaeoecological sites across the Papua New Guinea highlands had been based largely on the physical properties and stratigraphic relationships of visible volcanic layers. The geochemical analysis of tephra-derived glass demonstrates miscorrelations and enables more robust tephrostratigraphic links to be made between a globally significant archaeological site, Kuk Swamp, and a nearby volcanic cone, Ambra Crater. The results indicate that field-based correlations of tephras can be problematic, especially given variable post-depositional changes in colour and texture of relatively thin tephra layers in different depositional environments. Additionally, the findings call into question some previous tephrochronological associations at archaeological and palaeoecological sites in the Papua New Guinea highlands, and demonstrate the necessity of grain-discrete geochemical analysis of glass shards as a basis for future tephrochronological studies in this region. Copyright © 2009 John Wiley & Sons, Ltd. [source] Palaeomagnetic records of the Brunhes/Matuyama polarity transition from ODP Leg 124 (Celebes and Sulu seas)GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2000Hirokuni Oda Palaeomagnetic records of the Brunhes/Matuyama geomagnetic polarity transition were obtained from deep-sea sediments of ODP Leg 124 in the Celebes and Sulu seas. Advanced piston core (APC) samples with high magnetization intensities (2,200 mA m,1,) and high sedimentation rates (8.4,10 cm kyr,1,) were recovered from this cruise. Rock-magnetic measurements revealed the carrier of the remanence to be nearly pure magnetite in the pseudo-single-domain range. Pass-through measurements at intervals of 5 mm on APC cores across the Brunhes/Matuyama polarity transition for Holes 767B, 769A and 769B were deconvolved with the magnetometer sensor response using the ABIC-minimizing method. Discrete samples were also taken from the polarity transition zones and subjected to either thermal or alternating field stepwise demagnetization. The results were generally consistent with the pass-through data after the deconvolution. Results from the three holes are in good agreement, particularly those from the two holes 100 m apart at Site 769. The transitional VGP paths from these two holes show two small loops near New Zealand before the equator is crossed. The VGPs continue to swing eastwards to the North Atlantic and then move to the northeastern margin of the Pacific Ocean. The positions of the VGP loops obtained from Site 769 are different from the VGP clusters obtained from both the known volcanic records and the sediment records at the Boso Peninsula and the North Atlantic sites with high sedimentation rates. Such a difference may imply the predominance of the non-dipole field during the transition. Relatively stable mid-high northern latitude VGPs are recognized on all three cores just after the reversal, lasting about 4000 years. The plot of relative intensity versus VGP latitude for the sediment records from the North Atlantic (DSDP Hole 609B) shows a remarkable similarity with our records. Similar patterns were also obtained for the plot of the palaeointensity versus VGP latitude for the La Palma volcanic lava records. These results may suggest the existence of a metastable state of the geodynamo, producing a zonal component just after the Brunhes/Matuyama boundary, which may have played a role in the change of the field intensity. [source] THE TYCHOPELAGIC DIATOM, PARALIA SULCATA, AS PALEOINDICATOR SPECIES IN COASTAL MARINE ENVIRONMENTSJOURNAL OF PHYCOLOGY, Issue 2000M.R. McQuoid Paralia sulcata is a diatom commonly found in both the plankton and benthos of coastal environments. This species is heavily silicified and, thus preserves well in sedimentary records making it a potentially useful paleoindicator species. However, its tychopelagic nature and its association with a wide range of environmental conditions have made detailed paleoecological interpretations complicated. High-resolution sediment records from coastal fjords in both Canada and Sweden show variations in the abundance and morphology of P. sulcata that provide evidence of changes in benthic habitat distribution and surface water properties in the fjords on timescales of decades to centuries. These studies suggest that P. sulcata can be an important paleoindicator species when interpretations are made in the context of its complex ecology. [source] Holocene climate change in the eastern Mediterranean region: a comparison of stable isotope and pollen data from Lake Gölhisar, southwest Turkey,JOURNAL OF QUATERNARY SCIENCE, Issue 4 2007Warren J. Eastwood Abstract Stable isotope and pollen data from Gölhisar Gölü, a small intramontane lake located in southwest Turkey, provide complementary records of Holocene climate change. Modern oxygen and hydrogen isotope water data are used as a means of comparing present-day isotope composition of the lake water to the past oxygen isotope composition of the lake water as calculated from 18O/16O ratios in calcite precipitated in the summer months. Despite the lake system being chemically dilute, the modern isotope data clearly establish that the lake water is evaporated in relation to its spring input, suggesting that the palaeo data can be interpreted primarily in terms of changing precipitation/evaporation ratios. ,18O and ,13C values from authigenic calcite through the Holocene show predominantly negative values indicating climatic conditions wetter than today. Particularly notable are low (depleted) isotope values during the earliest Holocene (ca. 10,600,8800 cal. yr. BP), a period for which pollen data imply drier conditions than at present. This divergence between pollen-inferred and stable isotope palaeoclimate data is found in other east Mediterranean lake sediment records, and suggests that vegetation may have taken several millennia to reach climatic equilibrium at the start of the Holocene. Isotopic fluctuations during the early-to-mid Holocene (8800,5100 cal. yr. BP) suggest oscillations between aridity and humidity. Higher ,18O and ,13C values for the second half of the Holocene indicate generally drier conditions than during the period before ca.5100 cal. yr BP although there is some evidence for increased humidity coinciding with pollen evidence for increasing human impact and intensification of agriculture, notably during the so-called Bey,ehir Occupation Phase (Classical and early Byzantine periods). The modern trend towards aridity started about 1300 yr ago. Copyright © 2006 John Wiley & Sons, Ltd. [source] Pollen- and diatom based environmental history since the Last Glacial Maximum from the Andean core Fúquene-7, ColombiaJOURNAL OF QUATERNARY SCIENCE, Issue 1 2003Maria Isabel Vélez Abstract The late Pleistocene,Holocene ecological and limnological history of Lake Fúquene (2580 m a.s.l.), in the Colombian Andes, is reconstructed on the basis of diatom, pollen and sediment analyses of the upper 7 m of the core Fúquene-7. Time control is provided by 11 accelerator mass spectrometry (AMS) 14C dates ranging from 19 670 ± 240 to 6040 ± 60 yr BP. In this paper we present the evolution of the lake and its surroundings. Glacial times were cold and dry, lake-levels were low and the area was surrounded by paramo and subparamo vegetation. Late-glacial conditions were warm and humid. The El Abra Stadial, a Younger Dryas equivalent, is reflected by a gap in the sedimentary record, a consequence of the cessation of deposition owing to a drop in lake-level. The early Holocene was warm and humid; at this time the lake reached its maximum extension and was surrounded by Andean forest. The onset of the drier climate prevailing today took place in the middle Holocene, a process that is reflected earlier in the diatom and sediment records than in the pollen records. In the late Holocene human activity reduced the forest and transformed the landscape. Climate patterns from the Late-glacial and throughout the Holocene, as represented in our record, are similar to other records from Colombia and northern South America (the Caribbean, Venezuela and Panama) and suggest that the changes in lake-level were the result of precipitation variations driven by latitudinal shifts of the Intertropical Convergence Zone. Copyright © 2003 John Wiley & Sons, Ltd. [source] | ||||||||||||||||