Flood response to rainfall variability during the last 2000 years inferred from the Taravilla Lake record (Central Iberian Range, Spain)   总被引：2，自引：0，他引：2  

Ana Moreno  Blas L. Valero-Garcés  Penélope González-Sampériz  Mayte Rico 《Journal of Paleolimnology》2008,40(3):943-961

A sedimentological, geochemical and palynological study of the Taravilla Lake sequence (Central Iberian Range, NE Spain) provides a detailed record of allochthonous terrigenous layers that intercalate within the lacustrine sediments over the last 2000 years. These terrigenous layers are interpreted as the result of extreme hydrological events that caused higher clastic input to the basin. Anthropogenic influence caused by fires or deforestation is rejected as the main factor generating these layers because human impact, inferred from the pollen reconstruction, was minimal when the terrigenous layers reached their greatest frequency. The reconstructed occurrence of these events in the Taravilla Lake record is coherent with the paleoflood history of the Tagus River, characterized by a notable increase of extreme events at the beginning of the Little Ice Age. The Taravilla record suggests a relationship between the occurrence of extreme hydrological events, solar variability, and the North Atlantic Oscillation for the NE Iberian Peninsula.  相似文献   

EVIDENCES FROM HISTORICAL DOCUMENTS OF LANDSCAPE EVOLUTION AFTER LITTLE ICE AGE OF A MEDITERRANEAN HIGH MOUNTAIN AREA,SIERRA NEVADA,SPAIN (EIGHTEENTH TO TWENTIETH CENTURIES)     

ANTONIO GÓMEZ‐ORTIZ  DAVID PALACIOS  LOTHAR SCHULTE  FERRAN SALVADOR‐FRANCH  JOSEP A. PLANA‐CASTELLVÍ 《Geografiska Annaler: Series A, Physical Geography》2009,91(4):279-289

The Sierra Nevada is the highest mountain system on the Iberian Peninsula (Mulhacén 3482 m; Veleta 3308 m) and is located in the extreme SE region of Spain (lat 37°N, long 3°W). Bibliographic resources, particularly from the eighteenth to twentieth centuries, provide insights into the changing summit landscape as the effects of cold, ice, snow and wind shaped its morphology. The selected references emphasize the Sierra's evolving climate reflected in the glaciers and snow hollows, and in the sparse vegetation above certain altitudes. Scientists had established bioclimatic conditions for the entire range in the early nineteenth century, and their works reflect the progression of ideas, particularly in the area of natural sciences, that influenced the period chosen for this study. This information, in addition to current knowledge about the morphogenetic dynamics of the Sierra Nevada, provides the basis for a comparison of the dominant environments from the Little Ice Age to the present, using the most significant high mountain morphological features as a guide. The most relevant findings indicate that cold climate processes (soli‐gelifluction, frost creep and nivation) were more predominant during the eighteenth and nineteenth centuries than they are today.  相似文献   

Summer temperatures during the Medieval Warm Period and Little Ice Age inferred from varved proglacial lake sediments in southern Alaska     

Michael G. Loso 《Journal of Paleolimnology》2009,41(1):117-128

For the heavily glaciated mountains of southern Alaska, few high-resolution, millennial-scale proxy temperature reconstructions are available for comparison with modern temperatures or with the history of glacier fluctuations. Recent catastrophic drainage of glacier-dammed Iceberg Lake, on the northern margin of the Bagley Icefield, exposed subaerial outcrops of varved lacustrine sediments that span the period 442–1998 AD. Here, an updated chronology of varve thickness measurements is used to quantitatively reconstruct melt-season temperature anomalies. From 1958 to 1998, varve thickness has a positive and marginally significant correlation with May–June temperatures at the nearest coastal measurement stations. Varve sensitivity to temperature has changed over time, however, in response to lake level changes in 1957 and earlier. I compensate for this by log-transforming the varve thickness chronology, and also by using a 400-year-long tree-ring-based temperature proxy to reconstruct melt-season temperatures at Iceberg Lake. Regression against this longer proxy record is statistically weak, but spans the full range of occupied lake levels and varve sensitivities. Reconstructed temperature anomalies have broad confidence intervals, but nominally span 1.1°C over the last 1500+ years. Maximum temperatures occurred in the late twentieth century, with a minimum in the late sixth century. The Little Ice Age is present as three cool periods between 1350 and 1850 AD with maximum cooling around 1650 AD. A Medieval Warm Period is evident from 1000 to 1100 AD, but the temperature reconstruction suggests it was less warm than recent decades—an observation supported by independent geological evidence of recent glacier retreat that is unprecedented over the period of record. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Michael G. LosoEmail:

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Climate of the Little Ice Age and the past 2000 years in northeast Iceland inferred from chironomids and other lake sediment proxies     

Yarrow Axford  Gifford H. Miller  Peter G. Langdon 《Journal of Paleolimnology》2009,41(1):7-24

A sedimentary record from lake Stora Viearvatn in northeast Iceland records environmental changes over the past 2000 years. Downcore data include chironomid (Diptera: Chironomidae) assemblage data and total organic carbon, nitrogen, and biogenic silica content. Sample scores from detrended correspondence analysis (DCA) of chironomid assemblage data are well correlated with measured temperatures at Stykkishólmur over the 170 year instrumental record, indicating that chironomid assemblages at Stora Viearvatn have responded sensitively to past temperature changes. DCA scores appear to be useful for quantitatively inferring past temperatures at this site. In contrast, a quantitative chironomid-temperature transfer function developed for northwestern Iceland does a relatively poor job of reconstructing temperature shifts, possibly due to the lake’s large size and depth relative to the calibration sites or to the limited resolution of the subfossil taxonomy. The pre-instrumental climate history inferred from chironomids and other paleolimnological proxies is supported by prior inferences from historical documents, glacier reconstructions, and paleoceanographic studies. Much of the first millennium AD was relatively warm, with temperatures comparable to warm decades of the twentieth century. Temperatures during parts of the tenth and eleventh centuries AD may have been comparably warm. Biogenic silica concentrations declined, carbon:nitrogen ratios increased, and some chironomid taxa disappeared from the lake between the thirteenth and nineteenth centuries, recording the decline of temperatures into the Little Ice Age, increasing soil erosion, and declining lake productivity. All the proxy reconstructions indicate that the most severe Little Ice Age conditions occurred during the eighteenth and nineteenth centuries, a period historically associated with maximum sea-ice and glacier extent around Iceland.

Peter G. LangdonEmail:

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A 2000 year record of climatic change at Ongoke Lake,southwest Alaska     

Melissa L. Chipman  Gina H. Clarke  Benjamin F. Clegg  Irene Gregory-Eaves  Feng Sheng Hu 《Journal of Paleolimnology》2009,41(1):57-75

We analyzed sediments of the past 2000 years from Ongoke Lake, southwest Alaska, for organic carbon, organic nitrogen, biogenic silica (BSi), and diatom assemblages at decadal to centennial resolution to infer limnological changes that may be related to climatic variation in southwestern Alaska. The chronology is based on a ²¹⁰Pb profile from bulk sediments and nine AMS ¹⁴C ages from terrestrial plant macrofossils. Four of the ¹⁴C ages span a core depth interval of 60.5 cm but are statistically indistinguishable from one another with a mean of ~1300 AD, which compromises the determination of temporal trends at Ongoke Lake and comparison with other paleoclimate records. The diatom record suggests changes in the duration of ice cover and strength of thermal stratification that are probably related to temperature variation. This variation includes a cold interval around the first millennium cooling (FMC) and a warm interval spanning the medieval climate anomaly (MCA). However, the lake-sediment record shows no clear signals of temperature variation for the period of the Little Ice Age (LIA) or the twentieth century. Climatic changes during these periods may have been manifested through effective-moisture (precipitation minus evapotranspiration) variation in the Ongoke Lake area. We estimate water depths and infer effective-moisture fluctuations by applying a regional transfer function to our diatom record. Together with inferences from diatom autecologies, this water-depth reconstruction suggests that effective moisture increased steadily from 50 BC to 350 AD, which was followed by relatively dry conditions between 550 and 750 AD and relatively wet conditions between 750 and 1450 AD. Effective moisture was low from ~1450 to 1850 AD, coinciding with the LIA; an alternative age model places this interval between ~1315 and 1850 AD. During the past 150 years, effective moisture increased, with estimated water depths reaching peak values in the second half of the twentieth century. This study offers the first paleolimnological record for inferring centennial-scale climatic variation over the past two millennia from southwestern Alaska.

Feng Sheng HuEmail:

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A 2000 year record of climate variations reconstructed from Haukadalsvatn,West Iceland     

Áslaug Geirsdóttir  Gifford H. Miller  Thorvaldur Thordarson  Kristín B. Ólafsdóttir 《Journal of Paleolimnology》2009,41(1):95-115

The sediment fill of Haukadalsvatn, a lake in northwest Iceland, preserves a record of environmental change since deglaciation, 13 ka ago. The rapid sedimentation rate over the past 2 ka (ca. 4 m ka⁻¹) provides a high-resolution archive of late Holocene environmental change. Physical and chemical environmental proxies extracted from cores from the Haukadalsvatn sediment fill provide a reconstruction of sub-decadal-scale climate variability in Iceland over the past 2 ka. Over this interval biogenic silica (BSi) reflects warm April–May temperatures, whereas total organic carbon (TOC) peaks represent an increased flux of carbon to the lake from eolian-derived soil erosion following periods of cold summers accompanied by dry, windy winters. The proxy-based temperature reconstructions show a broad interval of warmth through Medieval times, but this warmth is punctuated by multi-decadal cold intervals. The transition into the Little Ice Age occurred in two steps, with initial summer cooling 1250–1300 AD, and a more severe drop in summer temperatures between 1450 and 1500 AD; both are periods of severe explosive volcanism. Multi-decadal patterns of cold and warm conditions have some characteristics of a North Atlantic Oscillation (NAO)-like signal, but instrumental records and proxy-based reconstructions of the NAO index contain little power in the frequencies most strongly expressed in our data set. Although severe soil erosion in Iceland is frequently equated with settlement, our reconstructions indicate that soil erosion began several centuries before settlement, whereas for several centuries after settlement, when summer temperatures were relatively high, there was little or no soil erosion. Only during the transition into and during the Little Ice Age did soil erosion become a major feature of the record. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Kristín B. ólafsdóttirEmail:

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Interelement relationships and age-related variation of trace element concentrations in liver of striped dolphins (Stenella coeruleoalba) from Japanese coastal waters     

Tetsuro Agusa  Kumiko Nomura  Takashi Kunito  Yasumi Anan  Hisato Iwata  Nobuyuki Miyazaki  Ryo Tatsukawa  Shinsuke Tanabe   《Marine pollution bulletin》2008,57(6-12):807

Concentrations of 19 trace elements (V, Cr, Mn, Fe, Co, Cu, Zn, Se, Rb, Sr, Mo, Ag, Cd, Sb, Cs, Ba, Tl, Hg, and Pb) were determined in the liver of the striped dolphins (Stenella coeruleoalba) collected around Japan during 1977–1982 to examine the sex difference, age dependence, and interrelationships among trace elements. Tissue distribution of trace elements was also investigated in one adult and one fetus specimens. Generally, concentrations of Se, Sr, Ag, Cd, Cs, Ba, Hg, and Pb were higher in the tissues of adult than those of fetus, whereas the opposite trend was observed for Cr and Tl. There were no significant sex differences in the trace element levels in the liver. Significant positive correlations between age (0–26.5 years) and hepatic concentrations were found for Ag, Se, Hg, V, Fe, Pb, and Sr, suggesting their age-dependent accumulation in the liver. In contrast, hepatic concentrations of Mn and Zn decreased with age. Significant positive relationships were observed between Se, and Hg, Ag, V, Fe, and Sr in the liver.  相似文献   

SPIRITUAL PILGRIMS AT MOUNT SHASTA,CALIFORNIA*     

Lynn Huntsinger  María Fernndez‐Gimnez 《Geographical review》2000,90(4):536-558

ABSTRACT. Even the casual visitor cannot fail to notice unusual activity on the slopes of Northern California's Mount Shasta. Prayer flags, altars, and crystals are found in the meadows; drumming, chanting, and meditation are commonplace. Non‐indigenous spiritual pilgrims have found Mount Shasta a sacred place. An amorphous group of spiritual seekers, these are sometimes referred to as “New Age” adherents or “Crystal People.” Within the Shasta‐Trinity National Forest, the situation of this sacred site exemplifies the difficulties of reconciling nonsecular claims to public lands with secular management mandates. Spiritual activism at Mount Shasta includes recently successful opposition to development of a Forest Service‐endorsed ski area. Using a questionnaire survey and interviews, we compare the characteristics, activities, and attitudes toward resource management of spiritual pilgrims and others who visit Mount Shasta's meadows. Conclusions are drawn about the environmental values and concerns of all visitors and of spiritual pilgrims in particular, including some that bear on pilgrim activities and ecological restoration efforts.  相似文献   

North Atlantic climate variability since AD 1350 recorded in δ 18O and skeletal density of Bermuda corals     

S. Draschba  J. Pätzold  G. Wefer 《International Journal of Earth Sciences》2000,88(4):733-741

The reconstruction of the climatic history during the past several hundred years requires a sufficient geographical coverage of combined climate proxy series. Especially in order to identify causal connections between the atmosphere and the ocean, inclusion of marine records into composite climate time series is of fundamental importance. We present two skeletal δ ¹⁸O chronologies of coral skeletons of Diploria labyrinthiformis from Bermuda fore-reef sites covering periods in the nineteenth and twentieth centuries and compare them with instrumental temperature data. Both time series are demonstrated to display sea-surface temperature (SST) variability on inter-annual to decadal time scales. On the basis of a specific modern δ ¹⁸O vs instrumental SST calibration we reconstruct a time series of SST anomalies between AD 1350 and 1630 covering periods during the Little Ice Age. The application of the coral δ ¹⁸O vs temperature relationship leads to estimates of past SST variability which are comparable to the magnitude of modern variations. Parallel to δ ¹⁸O chronologies we present time series of skeletal bulk density. Coral δ ¹⁸O and skeletal density reveal a strong similarity during Little Ice Age, confirming the reliability of both proxy climate indicators. The past coral records, presented in this study, share features with a previously published climate proxy record from Bermuda and a composite time series of reconstructed Northern Hemisphere summer temperatures. The coral proxy data presented here represent a valuable contribution to elucidate northern Atlantic subtropical climate variation during the past several centuries. Received: 9 November 1998 / Accepted: 13 September 1999  相似文献   

陕南镇巴筇竹寺期的海绵骨针化石     

郑亚娟  李勇  郭俊锋 《地球科学与环境学报》2012,(2):24-30

在陕南镇巴下寒武统西蒿坪段和水井沱组下段的碳酸盐地层中含有大量保存完好、类型多样的海绵骨针化石。基于形态描述法,对海绵骨针化石进行了详细的形态描述及产地与层位判断。结果表明:根据与其共生的小壳化石和三叶虫等生物地层学资料,发现这些海绵骨针化石属于筇竹寺期;该区海绵骨针类型不仅包含有形态规则的二轴四射骨针、三轴六射骨针、三轴五射骨针,而且还有形态不规则的四轴四射骨针、五轴五射骨针、尖头星状骨针、二歧分叉式骨针等;其中的四轴四射骨针、五轴五射骨针、五刺尖头星状骨针、二歧分叉二射式骨针为本次发现的新类型,极大地丰富了海绵骨针的类型。陕南镇巴筇竹寺期海绵骨针化石的数量以及分异度快速增加,充分说明海绵动物在陕南地区寒武纪早期开始大量繁盛并且迅速演化。  相似文献