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1

Electronic Resource

Mid-Holocene stable isotope record of corals from the northern Red Sea (2000)

Moustafa, Y. A. ; Pätzold, J. ; Loya, Y. ; [et al.]

Springer

International journal of earth sciences 88 (2000), S. 742-751

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ISSN: 1437-3262

Keywords: Key words African monsoon ; Corals ; Holocene ; Northern Red Sea ; Stable isotopes

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract We present a study based on X-ray chronologies and the stable isotopic composition of fossil Porites spp. corals from the northern Gulf of Aqaba (Red Sea) covering the mid-Holocene period from 5750 to 4450 14C years BP (before present). The stable oxygen and carbon isotopic compositions of five specimens reveal regular annual periodicities. Compared with modern Porites spp. from the same environment, the average seasonal δ 18O amplitude of the fossil corals is higher (by ca. 0.35–0.60‰), whereas annual growth rates are lower (by ca. 3.5 to 2 mm/year). This suggests stronger seasonality of sea surface temperatures and increased variability of the oxygen isotopic composition of the sea water due to changes in the precipitation and evaporation regime during the mid-Holocene. Most likely, summer monsoon rains reached the northern end of the Red Sea at that time. Average annual coral growth rates are diminished probably due to an increased input and resuspension of terrestrial debris to the shallow marine environment during more humid conditions. Our results corroborate published reports of paleodata and model simulations suggesting a northward migration of the African monsoon giving rise to increased seasonalities during the mid-Holocene over northeastern Africa and Arabia.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s005310050302

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Changes in fossil midge (Chironomidae) assemblages in response to cultural activities in a shallow, polymictic lake (2000)

Little, J.L. ; Smol, J.P.

Springer

Journal of paleolimnology 23 (2000), S. 207-212

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ISSN: 1573-0417

Keywords: chironomids ; nutrient enrichment ; macrophytes ; paleolimnology ; shallow lakes ; Rideau Canal ; alternative lake equilibria ; Ontario

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences

Notes: Abstract Chironomid (Diptera: Chironomidae) head capsules were studied from a core of recent sediments from shallow, macrophyte-dominated Lake Opinicon, Ontario, Canada, to determine if assemblages have changed in response to lake-level changes and other watershed disturbances, including deforestation and agriculture. Our results indicate that the construction of the Rideau Canal in the early 1830s and subsequent flooding of Lake Opinicon has had the greatest impact on this system, but that even this disturbance did not greatly affect chironomid assemblages. Despite other significant cultural disturbances in the watershed, the lake sediments have recorded only minor changes in its recent history, providing support for the hypothesis of alternative lake equilibria. These results correspond well with diatom inferences of only minor changes in past lake trophic status.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1008005604602

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3

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A 6000 year water level history of Europe Lake, Wisconsin, USA (2000)

Miller, Barry B. ; Schneider, Allan F. ; Smith, Alison J. ; [et al.]

Springer

Journal of paleolimnology 23 (2000), S. 175-183

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ISSN: 1573-0417

Keywords: Late Holocene ; paleolimnology ; oxygen isotopes ; molluscs ; ostracodes

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences

Notes: Abstract Europe Lake occupies a small, closed, basin that would have been an embayment in Lake Michigan during the high water level events in the larger lake. Cores recovered from the lake reveal late Holocene water level fluctuations in the basin that are inferred from changes in taxa and abundance of molluscs, ostracodes, magnetic susceptibility, organic carbon, and oxygen isotopes. Non-glacial, Holocene lacustrine/paludal sedimentation in this portion of the Europe Lake basin started after 6600 RCYBP and was probably initiated by a rise in the water table of the deep bedrock aquifer, during the Nipissing transgression in Lake Michigan. Isotopically light ground water from this source was probably a major contributor during this phase to the negative δ18O spikes in Valvata tricarinata and Amnicola limosa. The start of stable lacustrine conditions is marked by maximum diversity of ostracode and mollusc taxa and a shift toward much more positive δ18O values. The Europe Lake basin at this time became an embayment of Lake Michigan. This event was probably coeval with the peak of the Nipissing transgression, when the water plane reached an altitude of about 183 m. The isolation of Europe Lake from Lake Michigan started at about 2390 RCYBP and is probably due to a drop in water level in Lake Michigan and/or to isostatic uplift of the Door Peninsula. Since isolation from Lake Michigan, water levels in Europe lake have been controlled primarily by fluctuations in local precipitation, evaporation and ground water discharge.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1008009805511

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4

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Holocene environmental history of thermokarst lakes on Richards Island, Northwest Territories, Canada: Theocamoebians as paleolimnological indicators (2000)

Dallimore, Audrey ; Schröder-Adams, Claudia J. ; Dallimore, Scott R.

Springer

Journal of paleolimnology 23 (2000), S. 261-283

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ISSN: 1573-0417

Keywords: thecamoebians ; paleolimnology ; Holocene ; thermokarst lakes ; Arctic

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences

Notes: Abstract Richards Island, Northwest Territories, Canada, is characterized by thermokarst lakes which record Holocene limnological change. This study is the first report of thecamoebian assemblages and continuous annual lake water temperatures from these Arctic lakes. Ecological environments on Richards Island are influenced by a climatic gradient resulting from the contrasting influences of the cold Beaufort Sea to the north and the warm waters of the Mackenzie Delta to the east and west. This climatic gradient in turn influences modern thecamoebian assemblages, and is an indication of the complexity involved in interpreting past conditions from core material in this area. Population abundance and species diversity of thecamoebian assemblages on Richards Island are not significantly different from those reported from temperate and semi-tropical latitudes. However, certain assemblage characteristics, such as large and coarse agglutinated tests, dominance of assemblages by one or two species and low morphological variation are interpreted to be diagnostic of Arctic conditions. Thecamoebian assemblages in core material from the area indicate that the local paleolimnological conditions may have changed within the last 3 ka, and this is unrecorded in previously reported pollen data. Paleoenvironmental interpretations in a permafrost landscape have to take into account morphological instability of thermokarst lakes, which can be the cause of paleolimnological and consequently faunal change. In this area ecosystem development is clearly related to geomorphology and local climatic effects and is not exclusively controlled by regional climate change.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1008184522637

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5

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Paleolimnological investigation of recent acidity changes in Sawanoike Pond, Kyoto, Japan (2000)

Yoshikawa, Shunnichi ; Yamaguchi, Shigeo ; Hata, Akio

Springer

Journal of paleolimnology 23 (2000), S. 285-304

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ISSN: 1573-0417

Keywords: paleolimnology ; acidification ; sediment chemistry ; diatoms ; metals ; spheroidal carbonaceous particles ; pollen ; radionuclides ; Japan

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences

Notes: Abstract Sawanoike Pond, an artificial reservoir constructed ca. 150 yrs. ago, lies in an area geologically sensitive to acidification and contains water that is presently weakly acidic (pH 5.5; alkalinity 15 μeq 1-1). Sediments from a core obtained from the northern part and a core from the central part of the pond were analyzed for organic matter, total organic carbon, total nitrogen, natural and artificial radionuclides, pollen, diatoms, metals and spheroidal carbonaceous particles. A peaty silt layer at the bottom of the central core was replaced by a silt layer initially rich in humic substances, but became more mineral-rich near the surface. Although most of the dominant diatoms throughout the cores were acidophilous taxa, some acidobiontic species increased moderately in abundance after the middle 1960's. Diatom-inferred pH values for the northern core are relatively low before about 1930, then increase, reaching a maximum level between the 1930's and the late 1940's. They then decrease to the surface and reach minimum level during the middle 1980's. Diatom-inferred pH declined by 0.4-0.5 units in the northern core and 0.2-0.3 units in the central core since ca. 1910, when vegetation around the shore changed to a community similar to that of recent years. An increase in labile Pb, Zn, Cd and spheroidal carbonaceous particles, indicative of atmospheric deposition of fossil fuel combustion by-products, preceded the decline in inferred pH. The inferred pH decline of the pond could be an acidification due to acidic precipitation caused by fossil fuel combustion.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1008199830698

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6

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Holocene regional and local vegetation history and lake-level changes in the Torneträsk area, northern Sweden (2000)

Barnekow, Lena

Springer

Journal of paleolimnology 23 (2000), S. 399-420

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ISSN: 1573-0417

Keywords: Holocene ; lake-level changes ; climate changes ; vegetation history ; tree-line ; northern Sweden

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences

Notes: Abstract A combination of pollen and macrofossil analyses from six lakes at altitudes between 370 and 999 m above sea level (a.s.l.) in the Torneträsk area reflect the Holocene vegetation history. The main field study area has been the Abisko valley at altitudes around 400 m a.s.l. The largest lake, Vuolep Njakajaure has annually laminated (varved) sediments. The chronology and sedimentation rates in the pollen-influx calculations are based on varve yrs in this lake and on radiocarbon dated terrestrial plant macrofossils in the other lakes. A strong increase of mountain birch (Betula pubescens ssp. tortuosa) during the early Holocene with a tree-line c. 300 m above the present, indicates that the summer temperature was c. 1.5 °C higher than today, assuming that the land uplift has been 100 m since then. Scattered stands of pine (Pinus sylvestris) may have been growing in the area immediately after the deglaciation but a forest consisting of pine and mountain birch expanded first at low elevations and reached the eastern parts of the Torneträsk area at c. 8300 cal BP and the western parts at c. 7600 cal BP. The highest pine-birch forest limit was not reached until 6300 cal BP (110 m above present pine limit). Warm and dry conditions during the pine forest maximum led to lowering of the water level documented in Lake Badsjön in the Abisko valley about 1-1.5 m lower than today. Pine and mountain birch were growing at the maximum altitude until c. 4500 cal BP. Assuming that land uplift has been in the range of 20-40 m since the mid-Holocene, this implies that the temperature was then c. 1.5-2 °C higher than today. Rising lake-levels and lowering limits of pine and mountain birch since c. 4500 cal BP indicate a more humid and cool climate during the late Holocene.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1008171418429

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7

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Holocene lake sediment records of Arctic hydrology (2000)

MacDonald, Glen ; Felzer, Benjamin ; Finney, Bruce ; [et al.]

Springer

Journal of paleolimnology 24 (2000), S. 1-13

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ISSN: 1573-0417

Keywords: Arctic ; Holocene ; paleohydrology ; paleolimnology ; climate change

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences

Notes: Abstract Although paleoclimatic research in the Arctic has most often focused on variations in temperature, the Arctic has also experienced changes in hydrologic balance. Changes in Arctic precipitation and evaporation rates affects soils, permafrost, lakes, wetlands, rivers, ice and vegetation. Changes in Arctic soils, permafrost, runoff, and vegetation can influence global climate by changing atmospheric methane and carbon dioxide concentrations, thermohaline circulation, and high latitude albedo. Documenting past variations in Arctic hydrological conditions is important for understanding Arctic climate and the potential response and role of the Arctic in regards to future climate change. Methods for reconstructing past changes in Arctic hydrology from the stratigraphic, isotopic, geochemical and fossil records of lake sediments are being developed, refined and applied in a number of regions. These records suggest that hydrological variations in the Arctic have been regionally asynchronous, reflecting the impacts of different forcing factors including orbitally controlled insolation changes, changes in geography related to coastal emergence, ocean currents, sea ice extent, and atmospheric circulation. Despite considerable progress, much work remains to be done on the development of paleohydrological proxies and their application to the Arctic.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1008100714795

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8

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GCM-simulated hydrology in the Arctic duringn the past 21,000 years (2000)

Felzer, Benjamin ; Thompson, Starley ; Pollard, David ; [et al.]

Springer

Journal of paleolimnology 24 (2000), S. 15-28

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ISSN: 1573-0417

Keywords: Last Glacial Maximum ; Arctic ; paleoclimatology ; Holocene ; climate modeling ; hydrology

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences

Notes: Abstract The Paleoclimates from Arctic Lakes and Estuaries (PALE) project has chosen to conduct high resolution data-model comparisons for the Arctic region at 21 and 10 (calendar) ka BP. The model simulations for 21, 10, and 0 ka BP were conducted with the GENESIS 2.0 GCM. The 10 ka BP simulation was coupled to the EVE vegetation model. The primary boundary conditions differing from present at 21 ka BP were the northern hemisphere ice sheets and lower CO2, and at 10 ka BP were the orbital insolation and smaller northern hemisphere ice sheets. The purpose of this article is to discuss the hydrological consequences of these simulations. At the Last Glacial Maximum (21 ka BP) the large ice sheets over North America and Eurasia and the lower CO2 levels produced a colder climate than present, with less precipitation throughout the Arctic, except where circulation was altered by the ice sheets. At 10 ka BP greater summer insolation resulted in a warmer and wetter Beringia, but conditions remained cold and dry in the north Atlantic sector, in the vicinity of the remnant ice sheets. Less winter insolation at 10 ka BP resulted in colder and drier conditions throughout the Arctic. Precipitation - evaporation generally correlated with precipitation except where changes in the surface type (ice sheets, vegetation at 10 ka BP, or sea level at 21 ka BP) caused large changes in the evaporation rate. The primary hydrological differences (from present) at 21 and 10 ka BP correlated with the temperature differences, which were a direct result of the large-scale boundary condition changes.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1008161631633

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9

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Quantitative Holocene climatic reconstruction from Arctic Russia (2000)

Andreev, A.A. ; Klimanov, V.A.

Springer

Journal of paleolimnology 24 (2000), S. 81-91

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ISSN: 1573-0417

Keywords: fossil pollen ; climate reconstruction ; Holocene ; Arctic Russia

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences

Notes: Abstract Vegetation changes reflected in fossil pollen spectra are a primary source of information about climate fluctuations in the past. A statistical-information (transfer function) method based on the correlation of recent pollen spectra with modern climate conditions has been used to reconstruct Holocene climatic changes from fossil pollen. Climatic variables used for the reconstructions are the mean annual, January, July temperatures and annual precipitation. Peat sections with pollen and 14C data from the Arctic Russia were used for the reconstructions. The reconstructed climate fluctuations are similar to the climate changes obtained from many sites in the former USSR. A clear signal for Younger Dryas cooling, 11,000-10,000 yr BP and early Preboreal warming is apparent. The early Preboreal (10,000-9000 yr BP) was the warmest time for sites from modern coastal and island areas. The warm interval occurred in the Boreal period, about 8500 yr BP. According to the reconstructions the warmest time for non-coastal areas was the last half of Atlantic period, 6000-4500 yr BP. Other warm intervals were reconstructed about 3500 and 1000 yr BP. Reconstructions show that warming periods are primarily defined as times of increased summer temperatures, and cooling periods as time of decreased winter temperatures. The precipitation followed the temperatures: during the warming periods precipitation increased and during the cooling periods it decreased. Precipitation maximum, about 100 mm higher than present, are reconstructed for the warmest interval, 6000-4500 yr BP at all sites.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1008121917521

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10

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A paleoclimate record for the past 250,000 years from Summer Lake, Oregon, USA. 1. chronology and magnetic proxies for lake level (2000)

Negrini, Robert ; Erbes, Daniel ; Faber, Karin ; [et al.]

Springer

Journal of paleolimnology 24 (2000), S. 125-149

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ISSN: 1573-0417

Keywords: paleolimnology ; paleoclimate ; Great Basin ; environmental magnetism ; paleomagnetic secular variation ; pleistocene ; quaternary

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences

Notes: Abstract This study presents the age control and environmental magnetism components of a new, late Pleistocene paleoclimate record for the Great Basin of western North America. Two new cores from the Summer Lake sub-basin of pluvial Lake Chewaucan, Oregon, USA are correlated to basin margin outcrops on the basis of tephrochronology, lithostratigraphy, sediment magnetism and paleomagnetic secular variation. Eleven tephra layers were found in the cores that correlate to tephra identified previously in the outcrop. The Olema ash was also found in one of the cores; its stratigraphic position, relative to 3 dated tephra layers, indicates that its age is 50-55 ka, somewhat younger than has been previously reported. The Summer Lake sediments are divided into deep and shallow lake lithosomes based on sedimentary features. The stratigraphic position of these lithosomes support the tephra-based correlations between the outcrop and the cores. These sediments contain a well resolved record of the Mono Lake Excursion (MLE) and an earlier paleomagnetic excursion as well as a high quality replication of the paleosecular variation immediately above the MLE. Relative sedimentation rates increased dramatically toward the depocenter during intervals of low-lake level. In contrast, during intervals of high-lake level, relative sedimentation rates were comparable along the basin axis from the basin margin to the depocenter. The magnetic mineralogy of the Summer Lake sediments is dominated by pseudo-single domain (titano)magnetite and intervals of high/low magnetite concentration coincide with lithosomes that indicate high/low lake levels. Magnetic grain size also varies in accord with bulk sediment grain size as indicated by the silt/clay ratio. To a first order, variations in magnetic parameters, especially those attributable to the concentration of magnetic minerals, correlate well with global glacial/interglacial oscillations as indicated by marine oxygen isotope stages. This relationship can be explained by increased dissolution of (titano)magnetite minerals as lake level dropped and the lake became more productive biologically. This inference is supported by a correspondence between lower concentrations of magnetite with higher levels of total organic carbon and vice-versa.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1008144025492

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