A 180,000-year pollen record from Owens Lake, CA: terrestrial vegetation change on orbital scales

Pollen from the upper 90 m of core OL-92 from Owens Lake is a climatically sensitive record of vegetation change that indicates shifts in the plant associations representing warm and cold desertscrub, pinyon–juniper woodland, and pine–fir forest during the past 180,000 years. These changes are synchronized with glacial–interglacial cycles. During glacial and stadial climates, juniper woodland expanded downslope and replaced warm desert shrubs while upper montane and subalpine forests in the arid Inyo Mountains also expanded, and those in the Sierra Nevada were displaced by the ice cap and periglacial conditions. Conversely, during interglacial and interstadial climates, warm desert plants expanded their range in the lowlands, juniper and sagebrush retreated upslope, and montane and subalpine forests expanded in the Sierra Nevada. The reconstructed vegetation history demonstrates a regional climatic response, and the congruence of the pollen sequence with marine and ice cap oxygen isotope stratigraphies suggests a link between regional vegetation and global climate change at orbital scales.     

What is a Poor Quality Strong-Motion Record?

Some accelerograms are affected by non-standard recording and digitization problems that mean they are often not used in strong-motion studies. These non-standard problems cannot be corrected by the standard processing techniques that remove low and high-frequency noise from the time-history. Records from analogue instruments are more prone to these problems but even records from digital instruments, which are becoming increasingly common, can be affected by such errors. Since all strong-motion data is valuable it is important to know whether any useful information can be obtained from accelerograms that are affected by such problems. This article examines whether strong-motion records from analogue instruments that are missing their initial part due to late triggering of the instrument and also strong-motion records from digital instruments with low A/D converter resolution can be used for response spectral studies. It is found, by simulating such errors on high-quality strong-motion records, that good response spectral ordinates can be obtained from such `poor-quality' records within the period range of most engineering interest. This revised version was published online in July 2006 with corrections to the Cover Date.     

三门峡地区的红粘土磁性地层及环境记录

位于黄土高原东南缘的三门峡红粘土地层，以陕县指望剖面为其典型代表。厚度为74．3m的指望剖面由上部厚34m的黄土地层和下伏厚40.3m的红粘土沉积组成，黄土为L24－L33的连续风尘沉积，下部红粘土为RS1－RS5的沉积。磁性地层研究显示：M／Ga界线位于33.8m处，黄土与红粘土界线之上20cm，Ga/Gi界线位于56.25m处的RS3中下部。该区红粘土近5Ma至2.6Ma的风尘沉积夹河湖相沉积。指望剖面的红粘土地层磁化率较黄土高原内部偏高，总体特征一致，说明近5Ma来东亚季风在区域演化上的一致性。     

全新世黄土高原塬区植被特征

全新世高分辨率的黄土-古土壤孢粉研究,对于黄土高原历史时期植被的恢复与重建提供了直接的生物学证据.现代遥感数据显示黄土高原主要塬区为农业型生态环境,植被以旱作农作物为主,已无原生植被生长.最近12 000 aBP以来耀县剖面的孢粉记录显示,黄土高原南缘塬区植被经历了干草原-湿润性草原-干草原-湿润草原-草原5个阶段, 表明在黄土高原南缘降水较丰富的半湿润地区,塬区植被仍以草原植被为主,无森林生长.渭南姜村、洛川和富县等塬区剖面的孢粉记录也显示出,全新世以来,即使在全新世高温期水分较现在丰沛的时期,黄土高原塬区植被仍以灌木、草本植物为主,并无森林生长.     

Analysis of macroseismic and instrumental data for the study of the 19 November 1923 earthquake in the Aran Valley (Central Pyrenees)

The 19 November 1923 earthquake in the Aran Valley (Central Pyrenees), with observed maximum intensityI _max = VIII (MSK), has been studied through the compiling and reviewing of macroseismic information and collecting and processing early seismograms. Analysis of macroseismic data gives a focal depth ofh = 5 km and an anelastic attenuation coefficient 10^–3 km^–1. Analysis of early instrumental records allows the computation of estimate of magnitude (M _L = 5.6) and seismic moment (M _o = 1.1 × 10¹⁷ N × m) which are consistent with the values ofI _o andh obtained from macroseismic data.     

ENSO-coupled precipitation records (1959–2004) based on shells of freshwater bivalve mollusks (<Emphasis Type="Italic">Margaritifera falcata</Emphasis>) from British Columbia

We present the results of sclerochronologically calibrated growth and stable isotope analyses of the freshwater bivalve Margaritifera falcata collected from an agricultural, suburban setting near Vancouver, BC. The oxygen isotope range of shell aragonite can be explained by the temperature range during the growing season, assuming the water δ ¹⁸O composition remained constant. However, shell growth is strongly influenced by local summer precipitation and potentially runoff of nutrient-rich stormwater. About 44% of the variability of annual shell growth can be explained by amounts of local summer (June–September) rainfall. Local winter precipitation and El Niño–Southern Oscillation (ENSO) strength during the preceding year exert a weak, but significant control on shell growth. In combination, summer and winter precipitation can explain up to 50% of the variability in annual shell growth. Spectral analyses substantiate the effect of precipitation on shell growth and demonstrate that shell growth and ENSO are coupled by precipitation. Common spectral density was found at periods of 6.5–9 years, particularly between 1985 and 2004. Higher frequency oscillation corresponding to periods of 3–5 years occurred during the early 1970s, early to mid 1980s, and later 1990s. These results suggest that skeletal records of bivalve mollusks provide suitable archives of ENSO-coupled precipitation in areas where other climate proxies such as tree-rings and speleothems may not be available.     

辽东湾古近系震积岩特征及其时空分布规律研究

辽东湾古近系地层中发育大量与古地震有关的震积岩,通过岩芯观察识别出包括:微褶皱、阶梯状断层、震塌岩、内碎屑副角砾、液化卷曲构造、串珠状构造、震积砂球-枕状构造、火焰构造、砂泥岩脉、震裂缝、自碎屑角砾共11种震积标志,主要分布于三角洲前缘斜坡和与前三角洲相邻的坡脚。依据塑性与脆性变形建立了震积序列,将其分为I,II,III单元,其所示古地震强度为I< II< III。通过地质统计学的方法,对辽东湾震积岩时空分布规律及其所反映的古地震强度研究认为:古近纪时期郯庐断裂在辽东湾呈NNE向展布,其构造活动分为三个阶段:第一阶段为E₂s3,第二阶段为E₃s2~E₃s1,第三阶段为E₃d,其中第一、三阶段为强构造活动时期。E₂s3构造活动主要分布于辽西凸起北端,E₃s2与E₃s1主要分布于辽中凹陷A油田附近,E₃d则主要分布于辽中凹陷南端、北端和A油田,辽西凸起中部靠近A油田附近区域。结果表明:通过震积岩时空分布规律反演构造活动是可行的,该方法为今后进行盆地分析提供了新的思路。     

深圳湾北岸新民孔的Q_3~3-Q_4~1气候记录

对深圳湾北岸新民钻孔岩心沉积物中铁、钒元素、矿物鉴定的伊利石以及生物指标贝类介壳揭示的环境特征资料进行了分析,研究初步表明,该钻孔岩心沉积物理深12．12～10．91m层段的杂色花斑粘土中存有晚更新世晚期至早全新世气候波动的记录。钒元素和伊利石分析也得到了相应的证实。所记录的短期降温和升温事件可能表明,在第四纪末次冰期-冰消期中,气候曾强烈波动,并逐渐由晚冰期向冰后期过渡。这对研究晚武木冰期最低海面时期以来,海面回升及晚更新世晚期／早全新世的古环境方气候影响提供有价值的资料。     

Rotifers (Rotifera) from four natural water bodies of central Mexico

Faunistic analysis from the Iakes Zirahuen, El Bordito, Cuitzeo and Zacapu (State of Michoacan, Mexico) revealed the presence of 110 rotifer taxa. 9 genera and 29 species are new to Mexico. The new records are: Cephalodella megalocephala (Glascott, 1893); C. globata (Gosse, 1887); Cupelopagis vorax (Leidy, 1857); Eothinia elongata (Ehrenberg, 1832); Lecane bifurca (Bryce, 1892); L. decipiens (Murray, 1913); L. elegans Harring, 1914; L. leontina (Turner, 1892); L. monostyla (Daday, 1897); L. nodosa Hauer, 1938; L. ruttneri Hauer, 1938; L. ungulata (Gosse, 1887); Lepadella astacicola (Hauer, 1926); L. benjamini Harring, 1916; L. ehrenbergi (Perty, 1850); Lindia ecela Myers, 1933; Macrochaetus subquadratus (Perty, 1850); Monommata diaphora Myers, 1930; Notommata cerberus (Gosse, 1886), N. copeus Ehrenberg, 1834; Proales sordida Gosse, 1886; Resticula gelida Harring & Myers, 1922; R. nyssa Harring & Myers, 1924; Sinantherina ariprepes Edmonson, 1939; S. semibullata (Thorpe, 1889); Sphyrias lofauna (Rousselet, 1910); Testudinella incisa (Tarnetz, 1892); Tetrasiphon hydrocera Ehrenberg, 1840 and Trichocerca musculus (Hauer, 1935). Notommata tripus Ehrenberg, 1838 earlier observed from Mexico, but not illustrated, has been depicted in the present study. Comments to diagnostic characteristics and the zoogeographical distribution of the new rotifer taxa are given. All new records have been illustrated.