Showing papers on "Holocene climatic optimum published in 1999"
TL;DR: A new composite δ 18 O record, generated from calcareous fine-fraction and bulk sediments from the Exmouth Plateau, details long-term Cretaceous climatic change at mid-latitudes in the Southern Hemisphere as mentioned in this paper.
Abstract: A new composite δ 18 O record, generated from calcareous fine-fraction and bulk sediments from the Exmouth Plateau, details long-term Cretaceous climatic change at mid-latitudes in the Southern Hemisphere. Assessment of new and previously published δ 18 O data indicates that a mid-Cretaceous global climatic optimum was achieved sometime between the time of the Cenomanian-Turonian boundary and the middle Turonian, when surface-ocean paleotemperatures were the highest of the past 115 m.y. Periods of cooling and warming that reversed the general patterns were superimposed on long-term Aptian-Turonian warming and Turonian-Maastrichtian cooling trends, respectively. Extrapolation of Southern Hemisphere paleotemperature trends to Maastrichtian paleotemperature data from a low-latitude Pacific guyot implies that maximum mid-Cretaceous low-latitude paleotemperatures could have been in excess of 33 °C.
393 citations
TL;DR: The most recent sapropel in the deep eastern Mediterranean Sea has been deposited between 9 and 6 1/p. Climate conditions, as revealed by the pollen records in marine cores, were most favorable for temperate deciduous trees, which is in agreement with the inferences from records of peripheral land pollen sites.
217 citations
TL;DR: The last glacial/interglacial cycle produced a variety of climates and landscape responses in South America as mentioned in this paper, which were coherent with the global climatic changes recorded in other continents.
212 citations
TL;DR: In this article, the authors present a general hypothesis that humans in the Pampa and Patagonia regions evolved from generalists during the Late Pleistocene/Early Holocene to specialists during the Middle Holocene, according to diversity and relative taxonomic richness counts.
130 citations
TL;DR: In this article, a model describing sea ice-climate-ELA relationships in Northern Iceland for this period has been developed, providing a calibrated proxy climate record as a basis for palaeoclimatic reconstruction for the Holocene as a whole.
129 citations
TL;DR: The PASH database has been assembling palaeoclimatic data from the southern hemisphere for a number of years and the results provided insights into probable changes in atmospheric circulation as temperatures across the subcontinent rose by 6-7°C as discussed by the authors.
120 citations
TL;DR: The climate of the Great Plains during the middle Holocene varied considerably, but overall it was marked by a north-south gradient of increasingly warmer and drier conditions, with a reduction in effective moisture, surface water, and resource abundance, and an increase in resource patchiness, sediment weathering, erosion, and aeolian activity as discussed by the authors.
112 citations
TL;DR: In this article, a reconstruction of changes in the W-E stable oxygen isotope gradient in Mediterranean surface waters between the Holocene Climate Optimum and the present, and between the Last Glacial Maximum and the Present.
107 citations
TL;DR: In this article, the authors present results from a cooperative programme grouping several institutes from Turkey and France, on lacustrine, marshy and aeolian sediment sequences of Upper Pleistocene and Holocene age.
106 citations
TL;DR: In this paper, three main stages can be distinguished in the sedimentary development and geomorphological formation of the present delta plains on the Aegean coast of Turkey, and these characteristics can be observed in the same sequence throughout the same region of Turkey.
91 citations
TL;DR: In the southwestern Cape region, the last glacial maximum, in contrast to the situation evident in the summer rainfall region, is suggested to be a period characterised by considerably cooler and wetter conditions in certain parts of the biome as discussed by the authors.
TL;DR: In this article, tephrochronology and 16 AMS14C ages of terrestrial macrofossils are used to date sediment cores from three proglacial lakes in northern Banff National Park, Alberta.
TL;DR: In this paper, the authors analyzed six gravity cores obtained on a deep terrace located on the upper continental slope of the Gulf of Cadiz, between 400 and 700 m water depth.
TL;DR: The lower Carcarana Basin this paper is composed of silty sand and includes two pedogenic levels (Carcarana Fm) and an upper Holocene eolian layer (San Guillermo Fm).
01 Jan 1999
TL;DR: In this paper, detailed palynological investigations were carried out on two long sediment cores (106 and 224 m) from the lakes Lama and Levinson-Lessing, which reveal continuous information concerning the vegetation and climate histories of the unglaciated southern and northern Taymyr Peninsula since probably Late and Middle Weichselian times, respectively.
Abstract: Within the scope of the Taymyr Project, detailed palynological investigations were carried out on two long sediment cores (106 and 224 m) from the lakes Lama and Levinson-Lessing The results reveal continuous information concerning the vegetation and climate histories of the unglaciated southern and northern Taymyr Peninsula since probably Late and Middle Weichselian times, respectively The Weichselian was characterized by a cold and dry climate leading to strongly reduced vegetation The stadial setting was interrupted at least twice by relatively short, warm interstadials recorded in the lower part of the core from Levinson-Lessing Lake These interstadials may represent parts of the Middle Weichselian The Pleistocene/Holocene transition in both cores is characterized by a climatic warming trend during the Bolling, Allerod, and Preboreal periods, with interruptions during the Older (post-Bolling) and Younger Dryas events The Holocene climatic optimum occurred during the late Preboreal and Boreal periods During this time interval only, larch forests dominated at Lama Lake, and birch and later dense alder boscages at Levinson-Lessing Lake Starting in the Atlantic period, a climatic deterioration took place, which favoured sedge and sweet grass communities at Levinson-Lessing Lake but did not significantly influence the forest vegetation at Lama Lake The climatic deterioration continued up to the middle Subboreal period, when present climate and vegetation conditions were probably established A comparison of these results with preliminary palynological data from the lakes Changeable, Severnaya Zemlya Archipelago, and Kokora, central Taymyr Peninsula, yields new information concerning Weichselian and Holocene zonal vegetation shifts in northern Central Siberia
TL;DR: Pollen stratigraphy of an extrazonal palsa bog in the middle taiga of the West Siberian plain is dated by radiocarbon at five levels as mentioned in this paper, which is the basis for palaeogeographical reconstructions.
Abstract: Pollen stratigraphy of an extrazonal palsa bog in the middle taiga of the West Siberian Plain is dated by radiocarbon at five levels. Local pollen assemblage zones (LPAZ) are the basis for palaeogeographical reconstructions. Tundra-steppe plant communities with shrub birch (Betula nana) dominated in the latest Pleistocene. Warming after 10 000 14C yr BP caused the local thawing of permafrost, forming shallow lakes. Larixand then Picea spread along river valleys and depressions. Steppe plant communities existed on the dry interfluves. Further climatic warming and drying caused Picea to retreat, and Betula forest-steppe dominated 9500–8900 yr BP. Dense Pinus sylvestris and Pinus sibirica forests then spread over the whole area, and steppe communities decreased about 8300 yr BP. The Holocene climatic optimum (6000–5000 yr BP) was characterized by warm and wet conditions and Abies was widespread. Cooling then caused retreat of Abiesforests to the south and the expansion of Pinus sibirica forests on clay soils...
TL;DR: In the geologically recent past, the warmest period in Earth's history was the Miocene Climatic Optimum (14.5-17 million years ago), when temperatures at high latitudes were as much as 6 oC higher than they are now as mentioned in this paper.
Abstract: In the geologically recent past, the warmest period in Earth's history was the Miocene Climatic Optimum (14.5-17 million years ago), when temperatures at high latitudes were as much as 6 oC higher than they are now. According to new molecular isotopic studies, levels of atmospheric CO2were comparatively low during this time. So mechanisms other than CO2may have been the main factors driving and maintaining the warming.
Journal Article•
TL;DR: In this article, the late Holocene sedimentary record of Falasarna Harbour, western Crete, includes detailed evidence of tsunamis and serves as an independent dataset to evaluate the magnitude and timing of coastal tectonic movements in an area affected by contrasting Tectonic regimes.
Abstract: Abstract The late Holocene sedimentary record of Falasarna Harbour, western Crete, includes detailed evidence of tsunamis and serves as an independent dataset to evaluate the magnitude and timing of coastal tectonic movements in an area affected by contrasting tectonic regimes. Analysis of a foraminiferal assemblage makes it possible to identify suites of tsunami-deposited sediments within normal sedimentary sequences. The palaeo-environmental record is then complemented with a sequence of raised fossil marine notches. The transitional boundary between marine and terrestrial sedimentation indicates tectonic uplift at c. ad 63–75 ± 90 radiocarbon years bp, which is in conflict with previously published interpretations. No sedimentary evidence can be found for a tsunami believed to be associated with a large uplift event during ad 365.
01 Sep 1999
TL;DR: Bodri et al. as mentioned in this paper reconstructed the regional patterns of the respective climate change in the Czech Republic using the temperature-depth logs of borehole logs, and compared the obtained maps with the meteorological observations and proxy climatic reconstructions.
Abstract: Accurate temperature–depth profiles may help to assess the temperature variations associated with the climate changes in the past. Ninety-eight ground surface temperature histories inverted from the temperature–depth borehole logs drilled on the territory of the Czech Republic [Bodri, L., Cermak, V., 1995. Climate changes of the last millennium inferred from borehole temperatures: results from the Czech Republic — Part I. Global Planet. Change 11, pp. 111–125; Bodri, L., Cermak, V., 1997. Climate changes of the last two millennia inferred from borehole temperatures: results from the Czech Republic — Part II. Global Planet. Change 14, pp. 163–173.] are used to reconstruct the regional patterns of the respective climate change. The climate was mapped for the following periods: 1100–1300 A.D. (Little Climatic Optimum), 1400–1500 A.D., 1600–1700 A.D. (main phase of the Little Ice Age), and for the most recent climate trend after year 1960. Comparison of the obtained maps with the meteorological observations and proxy climatic reconstructions confirmed good applicability of the “geothermal” paleoclimatic reconstructions for the regional studies.
TL;DR: A synthesis of the two contrasting climates of the upper Quaternary in the Southern Hemisphere, based on continental geological indicators, suggests that the Antarctic Anticyclone is the most important climatic system in the hemisphere as discussed by the authors.
01 Jan 1999
TL;DR: In this article, the Tepsankumpu site was revisited, and the till-covered thick freshwater gyttja deposit was studied in detail for pollen in order to search for signals of rapid climatic fluctuations postulated for the earlier part of the Eemian on the basis of Greenland ice core studies.
Abstract: Several till-covered organic deposits, principally lake gyttja, in Finnish Lapland have been correlated with the last (i.e. Eemian) interglacial on the basis of their lithostratigraphic position and pollen stratigraphy. Most of the sequences are short, but together with three longer sequences from Finnish Lapland and one from Swedish Lapland (Leveaniemi) they provide a complete picture of Eemian vegetational and climatic development. The Tepsankumpu site was revisited, and the till-covered thick freshwater gyttja deposit was studied in detail for pollen in order to search for signals of rapid climatic fluctuations postulated for the earlier part of the Eemian on the basis of Greenland ice core studies. The Eemian pollen stratigraphy in Finnish Lapland closely resem- bles the Holocene pollen stratigraphy of the area. The abundance of spruce and alder pollen suggests, how- ever, more northerly limits for forest vegetation zones during the Eemian than during the Holocene. Oak also grew closer to Lapland, indicating a warmer climate than during the Holocene climatic optimum. The Tepsan- kumpu pollen stratigraphy indicates climatic stability over the entire time-span it covers, i.e. the major part of the interglacial. This finding is in conflict with results from Greenland GRIP ice core studies and interpreta- tions of some Continental European Eemian pollen diagrams.
TL;DR: Several till-covered organic deposits, principally lake gyttja, in Finnish Lapland have been correlated with the last (i.e. Eemian) interglacial on the basis of their lithostratigraphic position and pollen stratigraphy as mentioned in this paper.
Abstract: Several till-covered organic deposits, principally lake gyttja, in Finnish Lapland have been correlated with the last (i.e. Eemian) interglacial on the basis of their lithostratigraphic position and pollen stratigraphy. Most of the sequences are short, but together with three longer sequences from Finnish Lapland and one from Swedish Lapland (Leveaniemi) they provide a complete picture of Eemian vegetational and climatic development. The Tepsankumpu site was revisited, and the till-covered thick freshwater gyttja deposit was studied in detail for pollen in order to search for signals of rapid climatic fluctuations postulated for the earlier part of the Eemian on the basis of Greenland ice core studies. The Eemian pollen stratigraphy in Finnish Lapland closely resembles the Holocene pollen stratigraphy of the area. The abundance of spruce and alder pollen suggests, however, more northerly limits for forest vegetation zones during the Eemian than during the Holocene. Oak also grew closer to Lapland, indicating a wanner climate than during the Holocene climatic optimum. The Tepsankumpu pollen stratigraphy indicates climatic stability over the entire time-span it covers, i.e. the major part of the interglacial. This finding is in conflict with results from Greenland GRIP ice core studies and interpretations of some Continental European Eemian pollen diagrams.
TL;DR: In this article, the authors divided the Tarim River basin into four stages based on the analyses of sedimentary phase, the features of some climatic and environmental biomarks in the sedimentary strata and desert evolution.
Abstract: Climatic changes in the Tarim River basin since 12 kaBP were divided into four stages based on the analyses of sedimentary phase, the features of some climatic and environmental biomarks in the sedimentary strata and desert evolution. During the Holocene, cool-dry and temperate-dry climates resulted in apparent alluvial-fluvial and weak aeolian activities. During 10–8 kaBP, the climate was dry and cold, large-scale sand dunes activities led to regional deeert expansion. During the hypsithermal (8–3 kaBP), the climate was dry and warm, shifting sand areas decreased and a lot of sand dunes were fixed along the banks of the Tarim River and its tributaries, lowlands and lakes. As a result, fluvial-alluvial areas increased. Since 3 kaBP, the aeolian activity and sandstorms have been enhancing due to the combined influences of climatic warming and illogicill exploitation of land and water resources. The climate in the Tarim River basin have been persistently dry and alternated by warm and cold periods. Consequently, the sedimentary environments have varied fmm desert steppe to desert, and strongly influenced by periphery mountains and global climatic fluctuations.
TL;DR: In this paper, a 10.4 m sediment core from Harris Lake, southwestern Saskatchewan, is reconstructed from the ostracode stratigraphy of the sediment core, and the mean and variance of chemical, climatic and physical variables were inferred from modern analogues of the fossil assemblages, using existing autecological data from 6720 sites, mostly in western Canada.
Abstract: Holocene paleoenvironments of Harris Lake, southwestern Saskatchewan, are reconstructed from the ostracode stratigraphy of a 10.4 m sediment core. Twenty three taxa, representing nine genera, were identified and counted from 113 samples. At each depth, a theoretical faunal assemblage was derived from the raw counts. The mean and variance of chemical, climatic and physical variables were inferred from modern analogues of the fossil assemblages, using existing autecological data from 6720 sites, mostly in western Canada. These data suggest four paleoenvironments: an early-Holocene (9240–6400 years BP) variable climate supporting aspen parkland vegetation; the warm dry hypsithermal (6400–4500 years BP); a short transitional period of ameliorating climate and expanding subboreal forest (4500–3600 years BP); and the present environment since 3600 years BP. A change in regional climate with the draining of Glacial Lake Agassiz (ca. 8500 years BP) and landsliding in the watershed (ca. 4000 years BP) caused relatively rapid environmental change. The ostracode record generally corroborates the interpretations of other proxy data previously published for Harris Lake. Most of the discrepancy involves the timing and severity of maximum Holocene warmth and aridity. Peak aridity interpreted from the pollen data is earlier than in the other proxy records. Both the diatoms and ostracodes indicate highest paleosalinity between ca. 6500 and 5000 years BP, but maximum salinity in the diatom record occurs between ca. 6000–5700 years BP, whereas the ostracode-inferred salinity is relatively low at this time and peaks later at ca. 5000 years. Neither of these reconstructions suggests the short episodes of hypersalinity interpreted from the mineralogy.
TL;DR: A well-defined Late Pleistocene and Holocene dune fields are present on the surface of the Purisima-Iray Magdalena sedimentary basin and on the top of barrier islands of the Lagoonal Complex in Baja California Sur, Mexico as mentioned in this paper.
TL;DR: In this paper, the Red Dunes of Guadalupe Mountains National Park are examined for correlating evidence of aeolian deposition, which in this basin is taken as an indication of arid conditions.
Abstract: The Red Dunes of Guadalupe Mountains National Park are quartzose sand sheets and dunes stabilized by sparse plant cover. Stratigraphy, radiocarbon dating, and δ13C analysis were examined in two of the larger arroyos for correlating evidence of aeolian deposition, which in this basin is taken as an indication of arid conditions. Four quartz-sand lithostratigraphic units, representing intervals of aeolian activity, are identified. Radiocarbon dates provide constraint on the timing of the three youngest quartz-sand units. A mid-Holocene aeolian interval, represented by a single radiocarbon date of 6350± 70 BP, is interpreted as transitional to an altithermal regime. A neopluvial period, dated at 3370± 70 BP, separates mid-and late-Holocene aeolian activity. Late-Holocene time is characterized by generally drier conditions than present and almost continuous aeolian activity from 1690± 80 BP to 350± 0 BP. Stable carbon isotope analysis suggests an abrupt shift to generally cooler summer temperatures during thi...
TL;DR: In this article, it was shown that complete dune activation occurred either continuously or sporadically between approximately 8.2 ka and 5.9 ka in tropical northern Australia, which coincides with a brief period of global climate change recognized in 18 O records from Antarctica, methane records of the Greenland Summit ice cores, changes to deep-sea benthic foraminferal composition and atmospheric 14 C variations.
Abstract: Thermoluminescence ages from a longitudinal dunefield in tropical northern Australia suggest that complete dune activation occurred here either continuously or sporadically between approximately 8.2 ka and 5.9 ka. This period, in Australia, is normally ascribed to one of increasingly warm and wet conditions towards the Holocene Climatic Optimum. However, elsewhere, this time (| 8 ka) coincides with a brief period of global climate change recognized in 18 O records from Antarctica, methane records of the Greenland Summit ice cores, changes to deep-sea benthic foraminferal composition and atmospheric 14 C variations. In tropical Africa two distinct phases of aridity have been dated at approximately 8 ka and 6 ka. The coincidence of aeolian reacti- vation episodes in this north Australian dunefield with brief phases of early-Holocene climate change elsewhere suggests possible global climatic teleconnections at this time.
TL;DR: In this article, the results reported are from three sedimentary sections bordering the Rio Grande and its tributary in San Salvador de Jujuy and surrounding areas, and they are used to recognize two Holocene dry phases and two humid phases.
TL;DR: In order to evaluate the sensitivity of aquatic and terrestrial ecosystems to climatic changes, lithological (sediment structure and color, grain size, physical properties) and biochemical (TOC, TOC/TN, δ13C of TOC and carbonates) investigations were carried out on an 11.12 m-long sediment core from Lama Lake (Central Siberia, Putorana Plateau) as discussed by the authors.
Abstract: In order to evaluate the sensitivity of aquatic and terrestrial ecosystems to climatic changes, lithological (sediment structure and color, grain size, physical properties) and biochemical (TOC, TOC/TN, δ13C of TOC and carbonates) investigations were carried out on an 11.12 m-long sediment core from Lama Lake (Central Siberia, Putorana Plateau). According to the pollen data, the sequence represents the termination of the Pleistocene, and the entire Holocene. It is composed of highly terrigenous and stratified clays and silts. Sediment structure, grain-size distribution, carbonate contents and physical properties of the sediment indicate that glaciers were present in the catchment area of Lama Lake during the period Oldest Dryas to AllerOd. For the same time period, δ13C values of TOC give indications of a perennial ice cover. Since the AllerOd, organic matter accumulation has increased, caused by an increasing input of land vegetation and aquatic primary production as revealed by relations TOC contents, TOC/TN ratios and δ13C values of TOC. During the Holocene climatic optimum, in late Preboreal and Boreal times, biogenic primary production in Lama Lake reached its maximum and the vegetation in the catchment area changed from grassy tundra to a dense forest. From the Atlantic period to the present, small variations in δ13C values of TOC and TOC contents are probably related to the location of Lama Lake on the border between grass and wooded steppe, leading to responses of environmental conditions to even small changes in climate.