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I. MARIANNE LAGERKLINT GUNHILD ROSQVIST OTTO HERMELIN KIRK MAASCH 《Geografiska Annaler: Series A, Physical Geography》2005,87(1):111-124
ABSTRACT. A new high-resolution, alkenone-de-rived record of sea-surface temperature (SST) change covering the last 26000 years was obtained from the east-equatorial Atlantic off the Congo River. Temperature fluctuations correspond to climate change recorded in other marine and terrestrial archives of the region. The maximum temperature difference between 26000 years BP ago and the Holocene climate optimum around 6000 years BP was 4.3°C, corroborating other SST estimates from the same area. The coldest conditions were followed by a warming that began at 24000 calendar years BP, a time when Northern Hemisphere ice sheets were still at their maximal position. This comparatively early warming is in agreement with previous findings from the east-equatorial South Atlantic. After a relatively stable period between 21500 and 14500 calendar years BP, a second warming began at 14500 calendar years BP which coincides with the onset of the African Humid Period. A cool period at 11500 calendar years BP halted this warming but the trend of increasing temperatures began again at 10000 calendar years BP, this time through large-scale oscillations. The warmest time, around 6000 calendar years BP, was followed by a modest cooling that coincides with the end of the African Humid Period and the onset of Neoglaciation on the African continent. Following this the record shows two distinct warming-cooling cycles during the late Holocene. 相似文献
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V.A. POHJOLA J. COLE-DAI G. ROSQVIST A.P. STROEVEN L.G. THOMPSON 《Geografiska Annaler: Series A, Physical Geography》2005,87(1):259-270
ABSTRACT. We have studied a 33.7 m deep ice core from a small polythermal Scandinavian ice cap to determine whether it is possible to recover pre-20th century climatic information from the glacier. Ice structural studies show a significant change from clear ice above 11 m depth (superimposed ice indicating refreezing) to bubbly ice below 11 m depth, indicating this is the transition between Little Ice Age (LIA) and 20th century ice. Calculations with a Nye-age model, along with a mass balance reconstruction, show that this structural boundary likely formed in the last part of the LIA, which in this region ended about 1910. The ice below this boundary was sampled and analysed for stable isotopic composition and ionic content, which both show significant variations with depth. The stable isotope record likely contains cycles of annual duration during the LIA. The chemistry in the ice core indicates that the information is useful, and can be used to interpret climatic and environmental variables during the LIA. A comparison of Riukojietna ion chemistry and oxygen isotope records with similar records from other glaciers in this region reveals a clear continental-maritime gradient. Changes in this gradient with time may be possible to resolve using such ice core records. Results from this study demonstrate that ice cores from glaciers in this climatic environment can be useful in revealing environmental conditions from climatically colder periods and yield pre-industrial benchmark values for chemical loading and oxygen isotopes, but that hiatuses complicate the depth-age relationship. 相似文献
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PETER JANSSON GUNHILD ROSQVIST THOMAS SCHNEIDER 《Geografiska Annaler: Series A, Physical Geography》2005,87(1):37-50
ABSTRACT. In order to perform inverse modelling of climate variability based on palaeoclimate proxy records, the complexity of intermediate steps in the chain of processes from the climate forcing to the responding proxy has to be considered. In reconstructing climate-forced glacier fluctuations from proglacial lacustrine sediments it is important to understand how climate affects glacier dynamics. A glacier system is complex with many factors influencing sediment production, transport and deposition. Fluvial and mass movement processes in the proglacial environment may affect lake sedimentation substantially. We argue that it is easy to over-interpret glaciolacustrine sediment variability by ignoring these complications. The sediment records may contain individual layers resulting from single precipitation or melt events, as well as persistent changes in climate-forced glacier dynamics. We conclude that it is necessary to consider all possible influencing factors in order to derive reliable palaeoclimate data from lacustrine sediment sequences. 相似文献
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