Geochemical and palynological analysis of Faiyum Lake sediments, Egypt: Implications for holocene paleoclimate
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Holocene climatic optimum
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About 1397 temperature records during the Holocene are collected to establish a temperature data set of the Holocene in China.1140 of the 1397 records are available after eliminated the abnormal values statistically.There are more than 10 available records in most centuries during the Holocene in China.A synthesis reconstruction method,named the converted single sample from local to regional and averaged by the multiple samples,are designed to quantitatively reconstruct temperature change during the Holocene in China.The synthetically reconstructed Holocene temperature series in China ensures both the quantification and the higher temporal resolution continuously.According to the reconstructed temperature series,the Holocene temperature change in China could be obviously divided into three stages.The early Holocene(11.5-8.9 ka B.P.) was warming period when the temperature rose to near the present with fluctuation.The mid Holocene(8.9-4.0 ka B.P.) was a warmer period named the Holocene Megathermal,when the temperature was 1 ℃ higher than the present in average,with 1.5℃ higher than the present in maximum during 8.0–6.4 ka BP.The late Holocene(after 4.0 ka BP) was a cooling period.
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Inferred mean annual temperatures (Tann) from a radiocarbon-dated fossil pollen stratigraphy obtained from Lake Trehorningen, southwest Sweden, provide evidence of climate variability during the Holocene in the boreal-nemoral zone of Sweden. The record indicates low early Holocene temperatures, followed by a rising trend and maximum temperature values from about 7000 to 4000 cal. yr BP. During the later part of the Holocene until present day, a cooling trend is reflected in the temperature record. At about 8200 cal. yr BP, temperatures temporarily drop, and at 8000 cal. yr BP the rising temperature trend is recovered. Inferred mid-Holocene temperatures are about 2.5-3°C higher than at present, and also higher than other pollen-inferred mid-Holocene temperatures of 1.5-2.5°C further to the north and east in Scandinavia. The reconstructed long-term climate pattern in Trehorningen has an overall consistency with temperature reconstructions from Scandinavia, suggesting a regional climate link for the Holocene variability in Sweden. Holocene climate trends in Trehorningen also show a remarkably similar pattern with the classic work on postglacial climate change by Sernander (1893, Sernander 1909), Andersson (1909) and von Post (1924).
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Six major pollen-spore assemblage zones can be identified showing alternate warm and cool climate fluctuations on a millennial timescale. The early-Holocene optimum at c. 8000-7800 radiocarbon years BP, is marked by a large proportion of evergreen broad-leaf species in Zone I, suggesting the warmest/hottest climate setting of the Holocene. The mid-Holocene optimum ran from c. 7500 to 5000 BP (Zone III), during which many subtropical warmand wet-tolerant species represented by Castanopsis and Cyclobalanopsis glauca occurred, indicating the megathermal trend. The temperature then declined upcore in Zone IV accompanied by a high proportion of Pinus and Cupressaceae. A cooling event occurred at c. 4200 BP, as evidenced by Fagus and Potamogeton in the upper section of Zone IV. Pollen assemblages in Zones V-VI indicate a generally cooler temperature in the late Holocene with a high proportion of Gramineae, indicative of rice cultivation. Onset of the mid-Holocene optimum was associated with sediment deposition of the Holocene delta construction. This promoted the migration of Neolithic settlements onto the delta plain from highlands west of the study area. The cooling event recognized at c. 4200-4000 BP may have triggered the cultural ‘break up’ caused by the climatic transition from early warm-humid to a later cool-wet setting, and lake expansion caused by heavy precipitation.
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Results of a paleolimnological investigated of a well-dated lake sediment section from Shikotan Island (Southern Kurils) showed that from ca 8.0 to 5.8 cal ka BP warm and humid period corresponding to middle Holocene optimum took place. Cooling thereafter corresponds to Neoglacial. A reconstructed from ca 0.9 to ca 0.58 cal ka BP warm period can be correlated to a Medieval Warm Period. Cooling after 0.58 cal ka BP can be correlated with the LIA. Marine regression stages were identified at ca 6.2-5.9, 5.5-5.1 and 1.07-0.36 cal ka BP. The general chronology of major climatic events of Holocene in the island is in accordance with the climate records from the North Pacific region. Revealed spatial differences in timing and magnitude of the Late Holocene climatic episodes (LIA, MWP) within region needs further investigations.
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Holocene climatic optimum
Paleosol
Paleoclimatology
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Holocene climatic optimum
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Temperature record
Paleoclimatology
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Shiyang 河排水盆位于亚洲季风区域的西北边缘。以前的研究在盆关于 Holocene 气候的变化得出了不同结论。一些研究建议 Holocene 气候的变化被亚洲季风主要控制并且气候在早 Holocene (11.67.1 cal ka BP ) 期间是相对潮湿的。另外的研究发现 mid-Holocene 气候的最佳(7.05.0 cal ka BP ) ，并且这个气候条件类似于在干旱中亚的 Holocene 西的风模式。现代气候被亚洲季风和西的风在排水盆影响，并且 Holocene 气候的记录显示出二不同 Holocene 气候的 patternsa 西的风模式和 monsoonal 模式。然而，什么引起了二不同 Holocene 气候的模式在这个区域共存，仍然保持不清楚。palynological 记录是为在盆的 Holocene 气候的变化的主要证据。这份报纸为排水盆的不同部分集中于 palynological 记录。在他们之中， QTH02， QTL-03 和 Sanjiaocheng 记录位于终端湖，并且 Hongshuihe 记录位于盆的中间的活动范围。在终端湖， QTH02 和 QTL-03 的 palynological 记录是类似的，但是 Sanjiaocheng 记录不同。差别被可变花粉集合主要在湖盆的不同地点影响。从四个 palynological 记录的比较和合成，我们断定千年规模的 Holocene 气候的变化被亚洲季风和西的风的联合效果在排水盆影响，它在亚洲季风的西北边缘显示出复杂 Holocene 气候的模式。
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More and more intensified dust storms and dust deposition currently over the Loess Plateau of China provide analog for understanding the monsoonal climatic change and reconstruction of the Holocene environment in this semi-arid zone. Thick profiles of the Holocene loess-palaeosol sequence were found on the Zhouyuan loess tableland in the western Guanzhong Basin, Shaanxi Province. Detailed stratigraphic and pedological observations were made in the profile during the filed work. The fragments of the Neolithic cultural remains identified in the profile provide chronological control in the sequence. Multi-disciplinary analyses, including magnetic susceptibility, total Fe, grain-size and total organic carbon, carried out in laboratory show that Holocene climate has been highly variable in this environmental sensitive region. Several important climatic and hydrological events are recorded in this Holocene profile. A flood phase was identified between 9 000～8 800a BP (cal.) during the climatic amelioration in the beginning of the Holocene. The flood was from the uplifted pediment of the Beishan Mountains on the north. The Holocene Megathermal (climatic optimum) was identified between 8 500～3 100a BP,during which policyclic cinnamon soils were developed on the loess tableland. An abrupt climatic shift from humid to dry conditions took place at about 6 000a BP, therefore, a remarkable climatic aridity phase was found between 6 000～5 000a BP. The Holocene Megathermal (climatic optimum) was thus split into two main periods (8 500～6 000a BP and 5 000～3 100a BP) with warm-wet climate. The earlier period was more intensive in its climatic warmness and humidity. This means the Holocene Megathermal was not constant and stable as thought in the past. Another climatic shift was identified at about 3 100a BP. The increase in climatic aridity since then has caused intensified dust storms and acceleration of dust accumulation. Because of the largely decreased precipitation, the deficit soil moisture and intense dust deposit has thus caused soil deterioration on the loess tableland. At the present, a layer of about 0.5～0.8m thick loess has blanketed the landscape on the loess tableland. The present ploughed topsoil is only the top part of this recently accumulated eolian loess sediment. This topsoil is rather poorly developed compared with the Holocene palaeosol S 0 in the middle part of the profile. These results are very important for understanding of the regional response to global change in the semi-humid to semi-arid zone within the middle reaches of the Yellow River drainage basin.
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