A northwest North American training set: distribution of freshwater midges in relation to air temperature and lake depth     

Erin M. Barley  Ian R. Walker  Joshua Kurek  Les C. Cwynar  Rolf W. Mathewes  Konrad Gajewski  Bruce P. Finney 《Journal of Paleolimnology》2006,36(3):295-314

Freshwater midges, consisting of Chironomidae, Chaoboridae and Ceratopogonidae, were assessed as a biological proxy for palaeoclimate in eastern Beringia. The northwest North American training set consists of midge assemblages and data for 17 environmental variables collected from 145 lakes in Alaska, British Columbia, Yukon, Northwest Territories, and the Canadian Arctic Islands. Canonical correspondence analyses (CCA) revealed that mean July air temperature, lake depth, arctic tundra vegetation, alpine tundra vegetation, pH, dissolved organic carbon, lichen woodland vegetation and surface area contributed significantly to explaining midge distribution. Weighted averaging partial least squares (WA-PLS) was used to develop midge inference models for mean July air temperature (r _boot² = 0.818, RMSEP = 1.46°C), and transformed depth (ln (x+1); r _boot² = 0.38, and RMSEP = 0.58).  相似文献   

Was there ice along the shore of the Sea of Galilee during the last 12,000?—Reply to a comment by Prange et al. (2007) and a comment by Friedman (2007)     

Doron Nof  Ian McKeague  Nathan Paldor 《Journal of Paleolimnology》2007,38(4):597-600

Prange et al. (2007) question our reconstruction of the Sea of Galilee (Lake Kinneret) paleoclimate and argue that a “careful” analysis of the paleoclimatic analysis leads to much smaller cooling events than we have considered. By and large, their “careful” analysis is based on correlating the paleotemperatures of the Lake with those of the northern Red-Sea that (geographically) is much closer to the Lake than the two Mediterranean cores that we used. Ironically, their argument contradicts Friedman’s (2007) statements (the second comment on our original paper), which are based on still-closer cores and support our larger cooling choices. This issue alone would be enough to dismiss the uniqueness of PAL argument but there is another issue with their work that we wish to comment on. In support of their own small cooling argument, PAL present winter correlation maps that indeed show a stronger correlation of the northern Red-Sea SST to the lake SST than the correlation of Mediterranean SST with the lake SST. This seemingly correct correlation argument of PAL is totally false (for both daily and millennial time scales) because it has no climatological basis. On the daily time scale, all the storms that reach the Lake originate in the Mediterranean Sea (to the west of the lake), not the Red-Sea (which lies 700 km south of the lake). Also, although the lake and the Red-Sea are only 700 kilometers apart, their climates are very different because they are subject to two totally different air masses. While the climate of the Red-Sea region is desert-like, the climate of the region surrounding the lake is a typical wet Mediterranean climate. Seasonal correlation maps (and even monthly maps) such as those presented by the authors filter out the storms that control the winter climate in the lake region because these storms occur on a daily scale. With this filtering, all that one is left with is the low frequency first baroclinic mode, which merely reflects the Rossby radius scale (measured from the lake). On the millennial time scale, cold events in the lake regions (from an earlier period) have been attributed to Bond cycles and Heinrich events both of which are global and not local processes. As such, they are probably forced by variability in the solar radiation rather than a local process implied by PAL. Overall, all that the PAL correlation shows for both daily and millennial time scales is that changes in the temperature in the Red-Sea occur at the same time as they do in the Lake. But this does not say anything about the dynamics in question and does not imply that it is better to use records from the Red-Sea (which does not lie within the path of the zonal winds reaching the Lake). Neglecting this issue (as proposed by PAL) distorts the physics and reminds us of the classical statistical example for the limitations involved in the interpretation of correlation—the incidence of lung cancer is strongly correlated with the incidence of carrying matches in ones pocket even though the matches do not cause the cancer and the cancer does not force one to carry matches.  相似文献   

Sedimentology,clay mineralogy and grain-size as indicators of 65 ka of climate change from El’gygytgyn Crater Lake,Northeastern Siberia   总被引：2，自引：0，他引：2  

Celeste A. Asikainen  Pierre Francus  Julie Brigham-Grette 《Journal of Paleolimnology》2007,37(1):105-122

El’gygytgyn Crater Lake, NE Siberia was investigated for sedimentological proxies for regional climate change with a focus on the past 65 ka. Sedimentological parameters assessed relative to magnetic susceptibility include stratigraphy, grain size, clay mineralogy and crystallinity. Earlier work suggests that intervals of high susceptibility in these sediments are coincident with warmer (interglacial-like) conditions and well-mixed oxygenated bottom waters. In contrast, low susceptibility intervals correlate with cold (glacial-like) conditions when perennial ice-cover resulted in anoxia and the dissolution of magnetic carrier minerals. The core stratigraphy contains both well-laminated to non-laminated sequences. Reduced oxygen and lack of water column mixing preserved laminated sequences in the core. A bioturbation index based upon these laminated and non- laminated sequences co-varies with total organic carbon (TOC) and magnetic susceptibility. Clay mineral assemblages include illite, highly inter-stratified illite/smectite, and chlorite. Under warm or hydrolyzing conditions on the landscape around the lake, chlorite weathers easily and illite/smectite abundance increase, which produces an inverse relationship in the relative abundance of these clays. Trends in relative abundance show distinct down-core changes that correlate with shifts in susceptibility. The mean grain-size (6.92 μm) is in the silt-size fraction, with few grains larger than 65 μm. Terrigenous input to the lake comes from over 50 streams that are filtered through storm berms, which limits clastic deposition into the lake system. The sedimentation rate and terrigenous input grain-size is reduced during glacial intervals. Measurements of particle-size distribution indicate that the magnetic susceptibility fluctuations are not related to grain size. Lake El’gygytgyn’s magnetic susceptibility and clay mineralogy preserves regional shifts in climate including many globally recognized␣events like the Younger Dryas and Bolling/Allerod. The sedimentary deposits reflect the climatic transitions starting with MIS4 through the Holocene transition. This work represents the first extensive sedimentological study of limnic sediment proxies of this age from Chukotka (Fig. 1). This is the tenth in a series of eleven papers published in this special issue dedicated to initial studies of El'gygytgyn Crater Lake and its catchment in NE Russia. Julie Brigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue.  相似文献   

Sieve mesh size and quantitative chironomid paleoclimatology     

Dirk Verschuren  Hilde Eggermont 《Journal of Paleolimnology》2007,38(3):329-345

The minimum sieve mesh size for fossil chironomid analysis is usually set at 100 μm, to ensure adequate recovery of small species. Yet taking into account the labor intensity of sorting and identifying fossil chironomid remains, the large numbers of samples requiring processing in paleoclimate studies with high temporal resolution, and the increasing need to engage non-specialist analysts in this work, it seems appealing to sieve samples through a larger mesh size that would mainly retain easier-to-see, easier-to-extract and easier-to-identify fossil specimens. In this study we evaluated the influence of sieve mesh size on chironomid-based quantitative paleoenvironmental reconstructions in African lakes. We developed two chironomid-salinity calibration data sets based on either the >100 μm or >150 μm size fractions of surface-sediment fossil assemblages, and compared the performance of salinity-inference models derived from them. We find that, despite ∼35% additional fossil loss, restriction to >150 μm data did not appreciably affect individual taxon optima or tolerances, and resulted in only a modest reduction of mean taxon richness per lake. Parameters of statistical model performance were as good, or better than those of models based on the >100 μm data, albeit only after excluding two atypically dilute (<100 μS/cm) lakes from the calibration. Application of inference models based on >150 μm or >100 μm data to a 200-year fossil record from Lake Abiyata, Ethiopia, produced very similar trends, amplitudes and uncertainty ranges of inferred past salinity change. Restriction to >150 μm data reduced the mean fossil yield of core samples by ∼20% on average, i.e. fossil loss was markedly lower than in surface-sediment samples. Using the larger mesh size reduced sample processing time by up to 50%, partly by removing a significant proportion of visually obstructive organic debris, and partly by allowing a greater fraction of chironomid fossils to be identified directly in the sorting tray. The fraction of 1st instar group taxa in surface-sediment samples was reduced from 13% to 3%, increasing the mean taxonomic resolution of fossil assemblages, and thus their ecological specificity.  相似文献   

Inorganic geochemistry of El’gygytgyn Lake sediments (northeastern Russia) as an indicator of paleoclimatic change for the last 250 kyr     

P. S. Minyuk  J. Brigham-Grette  M. Melles  V. Ya. Borkhodoev  O. Yu. Glushkova 《Journal of Paleolimnology》2007,37(1):123-133

The inorganic geochemistry of sediments from El’gygytgyn Lake shift in phase with interpreted paleoclimatic fluctuations seen in the record over the past 250 ka. Warm periods, when the lake was seasonally ice free and fully mixed, are characterized by increased concentrations of SiO₂, CaO, Na₂O, K₂O, and Rb, by decreased contents of TiO₂, Fe₂O₃, Al₂O₃, and MgO, and by a lower chemical index of alteration (CIA). Increased levels of SiO₂ reflect increases in limnic productivity whereas many of the other elements and the CIA likely reflect increased hydrological activity coincident with an increase in coarser sand and silt content and a decrease in clay mineral content. For cold/cooler periods when perennial lake ice cover lead to a stratifed water column and anoxic bottom waters, the opposite is generally observed suggesting a decrease in hydrological activity and an increase in post-depositional chemical alteration. Peaks in P₂O₃ and MnO, coincident with an increased abundance of vivianite, suggest possible linkages to the paleoproductivity of local fish fauna regardless of climate change across the region surrounding Lake El’gygytgyn. Strontium is high in concentration during warmer intervals and may also be linked to paleoproductivity. Enrichment of the post-Eemian portion of the sediment record in niobium, and yttrium appears independent of glacial–interglacial change; rather it may reflect a gradual shift in the geomorphology of the catchment, particularly the hydrology of large alluvial fans along the western side of the lake. In contrast to some lake records, changes in Zr concentration over time suggests only a weak, if any, increase in eolian sediment supply during colder periods. This is the first in a series of eleven papers published in this special issue dedicated to initial studies of El'gygytgyn Crater Lake and its catchment in NE Russia. Julie Brigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue.  相似文献   

Late Quaternary palaeohydrology of Lake Pergusa (Sicily,southern Italy) as inferred by stable isotopes of lacustrine carbonates     

Giovanni Zanchetta  Alessandra Borghini  Anthony E. Fallick  Francesco P. Bonadonna  Gabriello Leone 《Journal of Paleolimnology》2007,38(2):227-239

Ten meters of lacustrine deposits retrieved from Lake Pergusa (Sicily, southern Italy) were investigated through stable isotope composition (carbon and oxygen) of authigenic carbonate (calcareous muds) and freshwater shells. The core chronology was established through three AMS dates, and by correlation with a previously dated nearby core. Stable isotope data show that the lake water evolution was mainly dominated by evaporation. Between ca. 20 and 28 ka the recovered sediments have very high δ¹⁸O values, likely corresponding to very dry climatic conditions. The observed rapid oscillations in the δ¹⁸O of the recovered sediments during this period also suggest important climatic fluctuations. More humid conditions dominated during the Holocene period, with the wettest interval occurring between ca. 9000 and 3000 years BP. Late Holocene sediments represent a substantial return to drier conditions. The available pollen data from a nearby core substantially confirm this general climatic trend during the Holocene. The positive correlation between δ¹³C of the calcareous muds and carbonate content suggests that biological activity played a key role in the carbon isotope evolution of dissolved inorganic carbon. However, a clear climatic signal is not evident from the δ¹³C record.  相似文献   

古ENSO的研究进展   总被引：1，自引：0，他引：1       下载免费PDF全文

闻新宇  王绍武  朱锦红 《地球物理学报》2007,50(2):387-396

本文对20世纪90年代后期逐渐在古气候学、古海洋学、地质学和古生物学等跨学科交叉领域中崭露头角的热点问题——古ENSO研究的前沿进展做了系统的总结和回顾.从观测和气候模拟两方面对集中于不同时间尺度的焦点问题进行展开，主要包括如下几个时段：早-中全新世的厄尔尼诺的减弱；末次冰期中的ENSO循环及其与高纬气候的联系；以及末次间冰期的ENSO现象.其中对早-中全新世时期的ENSO减弱的相对成熟的“岁差”机制做了详细总结，而对另两个时段的矛盾和问题做了简要整理和概括.建议在今后的古ENSO研究中，除观测外，要注意提高对古ENSO进行动力模拟研究的比重，两者相互配合来增加对ENSO循环和气候背景之间相互作用机理的理解，从而为今后全球变暖背景下的ENSO预测提供有意义的借鉴.  相似文献   

Quaternary glaciation and hydrologic variation in the South American tropics as reconstructed from the Lake Titicaca drilling project     

Sherilyn C. Fritz  Paul A. Baker  Geoffrey O. Seltzer  Ashley Ballantyne  Pedro Tapia  Hai Cheng  R. Lawrence Edwards 《Quaternary Research》2007,68(3):410-420

A 136-m-long drill core of sediments was recovered from tropical high-altitude Lake Titicaca, Bolivia-Peru, enabling a reconstruction of past climate that spans four cycles of regional glacial advance and retreat and that is estimated to extend continuously over the last 370,000 yr. Within the errors of the age model, the periods of regional glacial advance and retreat are concordant respectively with global glacial and interglacial stages. Periods of ice advance in the southern tropical Andes generally were periods of positive water balance, as evidenced by deeper and fresher conditions in Lake Titicaca. Conversely, reduced glaciation occurred during periods of negative water balance and shallow closed-basin conditions in the lake. The apparent coincidence of positive water balance of Lake Titicaca and glacial growth in the adjacent Andes with Northern Hemisphere ice sheet expansion implies that regional water balance and glacial mass balance are strongly influenced by global-scale temperature changes, as well as by precessional forcing of the South American summer monsoon.  相似文献   

延怀盆地晚更新世中晚期湖泊发育与气候变化   总被引：1，自引：0，他引：1       下载免费PDF全文

郑荣章  计凤桔  李建平 《地震地质》2001,23(1):55-62

延怀盆地晚更新世发育湖相沉积。根据 4个中晚期湖相层剖面的孢粉分析鉴定结果 ,结合区内晚更新世湖相层的年代测定及湖泊发育的分期 ,恢复了发育于 55～ 2 6和 2 0～ 8kaB .P .时间段内的第 2 ,3期湖泊发育期间的古气候环境。延怀盆地晚更新世中晚期湖泊沉积反映了潮湿气候的特征  相似文献   

Paleoecology and high-resolution paleohydrology of a kettle peatland in upper Michigan     

Robert K Booth  Stephen T Jackson 《Quaternary Research》2004,61(1):1-13

We investigated the developmental and hydrological history of a Sphagnum-dominated, kettle peatland in Upper Michigan using testate amoebae, plant macrofossils, and pollen. Our primary objective was to determine if the paleohydrological record of the peatland represents a record of past climate variability at subcentennial to millennial time scales. To assess the role of millennial-scale climate variability on peatland paleohydrology, we compared the timing of peatland and upland vegetation changes. To investigate the role of higher-frequency climate variability on peatland paleohydrology, we used testate amoebae to reconstruct a high-resolution, hydrologic history of the peatland for the past 5100 years, and compared this record to other regional records of paleoclimate and vegetation. Comparisons revealed coherent patterns of hydrological, vegetational, and climatic changes, suggesting that peatland paleohydrology responded to climate variability at millennial to sub-centennial time scales. Although ombrotrophic peatlands have been the focus of most high-resolution peatland paleoclimate research, paleohydrological records from Sphagnum-dominated, closed-basin peatlands record high-frequency and low-magnitude climatic changes and thus represent a significant source of unexplored paleoclimate data.  相似文献