Quantitative models for reconstructing catchment ice-extent using physical-chemical characteristics of lake sediments

The physical characteristics of surface sediments from a suite of pristine lakes on Signy Island, maritime Antarctic, were used to develop a quantitative link between catchment ice-extent and lake-sediment response. Percentage dry weight, median particle size, percentage loss-on-ignition and wet density of the lakes' surface sediments were the most significant variables explaining contemporary catchment ice-extent. Two independent reconstruction models – Partial Least Squares (PLS) and a Modern Analog Technique (MAT) – were applied to dated sediment cores at two sites on Signy Island. The validity of the reconstructions was tested against historical information on catchment ice-extent. With sufficiently high sedimentation rates and sampling resolution, the models can predict sub-decadal changes in ice-extent. The model results are best regarded as indicators of erosion resulting from meltwater activity in the catchment. Comparison of results with Twentieth Century climate records affirms the hypothesis that climatic warming is the most likely cause for the ice retreat observed on Signy Island during the last 40 yrs. Similar reconstruction models using these simple sedimentary measures could be developed for analogous locations in the Antarctic and in Arctic and Alpine regions.     

泉州台763长周期地震仪的震相记录特征

76 3长周期地震仪 1 997年起取代基式仪 ,承担我国一类合网对国内外地震的监测和对外观测资料交换任务。本文介绍了我台 76 3长周期地震仪的震相记录特征 ,有利于台站对震相的分析 ,提高对外资料交换和大震速报水平。     

祁连山北坡流域冰川物质平衡波动及其对河西水资源的影响

祁连山北坡各流域发育有现代冰川 2 166条 ,总面积 13 0 8km2 ,冰储量 60km3,冰川融水补给河流约 8× 10 8m3·a-1,占河西地表总径流量的 11% .近 4 0a来 ,东段石羊河流域冰川物质平衡 (Bn)呈较大负平衡 ,Bn在 - 80～ - 12 0mm间 ;西段的讨勒河、疏勒河和党河流域冰川具正物质平衡 ,Bn在+ 5 0～ + 90mm ;黑河流域的冰川处于过渡区 ,其冰川物质平衡多年平均在 - 4 0～ + 4 0mm间 .冰川物质平衡的变化直接影响着河流径流的变化 ,洪水坝河、党河和昌马河的冰川融水补给率达 3 0～ 4 0 %以上 ,东大河、大渚马河、马营河和讨勒河的补给率在 12 %～ 14 %之间 ,而西营河和梨园河仅有 7%左右 .冰川物质平衡逐年变化显示 ,2 0世纪 5 0～ 70年代冰川以负物质平衡为主 ,80年代开始向正的平衡开始转化 ,90年代以正平衡为主 ,主要是冬季气温上升引起的降雪量增加的结果 .在全球气温变暖情景下 ,东段冰川物质平衡将呈增加的趋势 ,西段冰川物质平衡将呈下降的趋势 ,将使西段以冰川融水补给的河流径流增加 ,而东段石羊河流域径流下降明显 .     

Transition of Quaternary glacial cyclicity in deep-sea records at Nansha, the South China Sea

High-resolution oxygen isotope records over the last 2249 ka (MIS 1–86) have been obtained from cores of the upper section (105.08 m) at ODP Site 1143 (water depth of 2772 m) drilled in the Nansha area, southern South China Sea. The sampling resolution is at about 2 ka intervals, resulting in one of the best oxygen isotope records over the global ocean. The oxygen isotope curves, displaying details in the Pleistocene glacial cycles, have revealed a nearly 300 ka long stage of transition from a predominant 40 ka to 100 ka periodicity. Therefore, the “Mid-Pleistocene Revolution” should be considered as a process of transition rather than an abrupt change. Within the 100 ka glacial cycles, the changes in tropical sea surface water were found to lead those in high-latitude ice sheet. Our comparisons show that the ice sheet expansion and the glacial stage extension in the Northern Hemisphere with the 100 ka cycles must have been driven not by ice sheet itself, but by processes outside the high latitudes of the Northern Hemisphere.     

Investigations on the Quaternary Glaciation in the Khumbu Himal (Nepal, East-Himalaya)

Based on geomorphological field work the mapping of former lateral/terminal moraines in the middle segment of the Bhotekoshi Nadi is quite similar to the geomorphological findings of Heuberger (1956: Fig. 2). The deductive calculation of the equilibrium line altitudes is oriented on the reconstructed types of former glaciers. Based on the geomorphological findings of this valley segment the relation of Neoglacial and Late Glacial ice margins of the glaciers of the tributary valleys of the Bhotekoshi Nadi is not conclusive. A post-late glacial maximum snow-line depression of at least 950 m has not obligatory caused an ice fill of the Bhotekoshi Nadi below 3200 m. This revised version was published online in July 2006 with corrections to the Cover Date.     

The late Quaternary development of three ancient tarns on southwestern Cumberland Peninsula, Baffin Island, Arctic Canada: paleolimnological evidence from diatoms and sediment chemistry

Sediment diatom and chemical analyses of cores from three poorly buffered extra-glacial lakes on the northeastern margin of the Canadian Shield (Cumberland Peninsula, Baffin Island) record interactions between aquatic and terrestrial spheres that were influenced by late Quaternary climatic conditions. Although differences exist between each of the lakes, notably with regards to the intensity of pre-Holocene catchment erosion and the timing of the onset of organic sedimentation, an underlying pattern of lake ontogeny, common to all three lakes, is identified. Although intensified watershed erosion characterized the Late Wisconsinan and Neoglacial cold periods, the lakes nonetheless remained viable ecosystems at these times. Sudden catchment stabilization during the late-glacial to earliest Holocene is associated with incipient organic sedimentation. Lake-water pH increased at this time, likely in response both longer base cation residence times as lake flushing rates decreased, and enhanced alkalinity production from sediment biogeochemical reactions. Subsequently, as the catchments remained stable during the productive early Holocene (c.9–7 ka BP), then gradually received a renewed increase of minerogenic sedimentation, the breakdown of sources of lake alkalinity resulted in natural acidification. Burial of cation-rich mineral sediments and the loss of permanent sedimentary sinks for the products of microbial reduction likely impeded within-lake alkalinity production, and catchment-derived base cations appeared ineffective in curtailing pH declines. The general nature of the Holocene development of these lakes is similar to that observed elsewhere on crystalline terrains, following deglaciation. Our data therefore suggest that catchment glaciation is not a necessary precursor for models of lake development characterized by initial base cation enrichment and subsequent gradual acidification.     

中国数字地震台网（CDSN）数据文件系统：—CDSN应用系列论文一

中国数字地震台网(CDSN)观测并生成的数字地震资料是开展数字地震学研究必不可少的高质量数据源。为了使科学家们更好地使用这些数据,本文主要从数字地震资料产生出的各个环节、数据结构与格式、数据物理量之间的换算向读者作概括的介绍.希望读者对数字化地震资料的数据文件、数据记录、数据字均能有透彻的理解,从而节省时间和精力,提高资料的使用率。     

冰期与间冰期在第四纪地层与岩性上的作用

论述了冰期与间冰期的气候变化与海平面升降的关系以及冰期与间冰期的古地貌，全面系统地阐述了上海地面沉降之后的地质环境，并提出了控制地面沉降的５条建议。     

Spectral magnitude and seismic radiated energy computed from CDSN records

We have employed 10 digital records and computed the spectral magnitude and the seismic radiated energy for 18 large earthquakes (M _s≥6) occurred in Eur-asian belt during 1986–1989. The nine digital stations (CD-SN) distribute all over China and one in Germany. The spectral magnitudes of various period have different stability among stations. The stability is better for maximum spectral magnitudemi and seismic radiated energyE, their differences among stations are smaller, especially for the stations where the ray path main penetrates the low mantle. But the stability of corner period is usually not good. The relation between seismic radiated energy and seismic moment magnitudeM _w is lg (E)=1.5Mw+c, wherec is a constant. The maximum spectral magnitudemi=M _w+0.1, it is consistant with theoretical prediction. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 418–426, 1993. This work supported by the Deutsche Forschungsgemeinschaft, Bonn, F. R. Germany. The support is grateful acknowledge.     

Environmental transformation of the Bilbao estuary,N. Spain: microfaunal and geochemical proxies in the recent sedimentary record

The distribution and abundance of benthic foraminifera and a range of elements have been analysed in six long cores (up to 10 m long) from the Bilbao estuary, N. Spain, to document environmental transformation of this estuarine ecosystem and to determine sediment contamination levels. Three different environmental zones could be distinguished in the recent sedimentary record based on its microfaunal and geochemical contents. Initially, a pre-industrial zone containing very abundant and diverse foraminiferal assemblages together with baseline metal levels. Secondly, an older industrial zone exhibiting co-existence of abundant and diverse foraminiferal assemblages with high concentrations of metals. Finally, a younger industrial zone with extreme concentrations of metals and barren of indigenous foraminifera. This environmental transformation has been caused by the discharge of untreated domestic and industrial effluents during the last 150 years. The occurrence of foraminifera in the two industrial zones and along the estuary is not related to defined levels of metals, and this seems to confirm oxygen limitation as the key factor to explain complete estuarine defaunation during deposition of the younger industrial zone (period 1950-2000). Effectiveness of current regeneration schemes could be assessed using microfaunal and geochemical proxies as environmental quality indicators.