Modern pollen spectra from lake sediments in Finland and Finnmark, north Norway

Absolute (APF) and relative surface pollen spectra from 67 moderate-sized lakes in Finland and Finnmark are presented as pollen diagrams and isopoll maps and analysed by multidimensional scaling. The results are applicable to problems of regional vegetational history through comparisons of pollen spectra and the use of R-values. It is shown that relative spectra can discriminate the major vegetational regions. APFs give better resolution among northern forest regions and low APFs characterize tundra. Gradients of tree-pollen percentages in south and central Finland are related quantitatively to the major forest gradients, which are azonal, mainly related to soils, and affected but not obscured by human influence. Forest clearance is reflected in frequencies of various non-tree pollen types. Non-tree pollen and spores also provide vegetational and climatic information in the far north.     

Contrasting P–T–t paths for Neoproterozoic metamorphism in MacRobertson and Kemp Lands, east Antarctica

Mineral equilibria modelling and electron microprobe chemical dating of monazite in granulite facies metapelitic assemblages from the MacRobertson Land coastline, Rayner Complex, east Antarctica, are consistent with an 'anticlockwise' Neoproterozoic P–T–t path. Metamorphism occurred at c. 990–970 Ma, achieving peak conditions of 850 °C and 5.6–6.2 kbar at Cape Bruce, and 900 °C and 5.4–6.2 kbar at the Forbes Glacier ∼50 km to the east. These peak metamorphic conditions preceded the emplacement of regionally extensive syntectonic charnockite. High temperature conditions are likely to have been sustained for 80 Myr by lithospheric thinning and repeated pluton emplacement; advection was accompanied by crustal thickening to maximum pressures of 6–7 kbar, followed by near-isobaric cooling. This P–T–t path is distinct from that of rocks in adjacent Kemp Land, ∼50 km to the west, where a 'clockwise' P–T–t path from higher- P conditions at c. 940 Ma may reflect the response of a cratonic margin displaced from the main magma flux. In this scenario, crustal shortening was initially accommodated in younger, fertile crust (MacRobertson Land) involving metasediments and felsic plutons with the transfer of strain to adjacent older crust (Kemp Land) subsequent to charnockite emplacement.     

OPTIMAL ESTIMATION OF CRACK-STRIKE1

The accuracy of estimating crack-strike from the algebraic equivalent of a popular technique, the dual source cumulative technique (DCT), for analysing shear-wave splitting in seismic experiments is evaluated for earth models permeated by different alignments of micro-cracks. A complementary analysis is performed using another analysis procedure, the dual-independent source-geophone technique (DIT), to investigate any benefits of the alternative formulation. The investigation considers synthetic vertical seismic profile (VSP) and reflection data for an earth model with two layers over a half-space, and three different classes of crack-strike variation with depth: uniform crack-strike, an abrupt change of crack-strike between the upper and lower layer, and a continuous increase over both layers. The synthetic data for zero-offset and near-offset VSPs and a reflection profile are computed using a full-wave modelling package in which equivalent anisotropic media simulate distributions of aligned vertical, parallel, water-filled microcracks. Estimates from the two techniques agree for the constant crack-strike model, but differ for the VSP data with crack-strike changes. The asymptotic behaviour of the two angular parameters θ_G and θ_S from DIT suggest that it may be used to determine crack-strike under appropriate circumstances in these VSPs, when the time-delay between the split shear-waves for the layer of interest exceeds the peak period of the wavelet. In this limit, θ_G tends to follow the crack-strike change with θ_S tending to a constant value, whereas DCT will give a misleading value between the upper and lower crack-strike. Although the behaviour of DIT is not understood in all cases, θ_G and θ_S values from the VSP data always appear to diverge near the point where an abrupt crack-strike change takes place. This could be used as a qualitative indicator for layer stripping. Both techniques agree for the reflection data as the recorded data matrix is necessarily symmetric, but still give misleading results for deeper layers in the presence of crack-strike changes. This study suggests that more care should be taken when designing and analysing experimental configurations for detecting crack properties in reservoir rocks, to consider the response and resolution limits of the analysis techniques. A note of caution is offered to those who directly interpret polarization estimates as crack-strike.     

Giant flute-like scour and other erosional features formed by the 1929 Grand Banks turbidity current

Erosional features on the floor of Eastern Valley of the Laurentian Fan, in 2800 m water depth, have been mapped with SeaMARC I side-scan sonar images and Seabeam multi-beam echo-soundings, and were directly observed during a dive with the deep submersible Alvin. The most spectacular feature is a 100-m-deep flute-shaped scour, more than 1 km long. The surrounding valley is floored by an unconsolidated coarse conglomerate, which was moulded into transverse bedforms by the turbidity current that was triggered by the 1929 Grand Banks earthquake. Direct observations and seismic-reflection profiles show that the flute-shaped scour cuts through this conglomerate and into Plio-Pleistocene valley-floor sediments, thereby exposing a section through the 1929 deposit. Application of the Allen defect theory suggests that the flute is unusually deep because general channel-floor erosion was inhibited by the conglomerate veneer. Valley-floor channels typically 1 km wide and 10m deep contain series of closed depressions that occasionally deepen to 30 m. These are also interpreted as erosional scours, analogous to pools cut on the beds of bedrock rivers. The large flute was probably formed by detached flow enlarging an initial scour depression. Such scours probably play an important role in channel-floor erosion, increasing the volume of sediment transported by large turbidity currents.     

The Old Woman,California, IIAB iron meteorite

Abstract– The Old Woman meteorite, discovered in March 1976 by two prospectors searching for a fabled lost Spanish gold mine in mountains ～270 km east of Los Angeles, has achieved the status of a legend among meteorite hunters and collectors. The question of the ownership of the 2753 kg group IIAB meteorite, the second largest ever found in the United States (34°28′N, 115°14′W), gave rise to disputes involving the finders, the Bureau of Land Management, the Secretary of the Department of the Interior, the State of California, the California members of the U.S. Congress, various museums in California, the Smithsonian Institution, and the Department of Justice. Ultimately, ownership of the meteorite was transferred to the Smithsonian under the powers of the 1906 Antiquities Act, a ruling upheld in a U.S. District Court and a U.S. Court of Appeals. After additional debate, the Smithsonian removed a large cut for study and curation, and for disbursement of specimens to qualified researchers. The main mass was then returned to California on long‐term loan to the Bureau of Land Management’s Desert Discovery Center in Barstow. The Old Woman meteorite litigation served as an important test case for the ownership and control of meteorites found on federal lands. The Old Woman meteorite appears to be structurally unique in containing both hexahedral and coarsest octahedral structures in the same mass, unique oriented schreibersites within hexahedral areas, and polycrystalline parent austenite crystals. These structures suggest that different portions of the meteorite may have transformed via different mechanisms upon subsolidus cooling, making the large slices of Old Woman promising targets for future research.     

R. A. BAGNOLD: A BIOGRAPHY AND EXTENDED BIBLIOGRAPHY

1996 is the centenary of the birth of Brigadier Ralph Alger Bagnold, FRS. To mark this important anniversary this paper presents a short biography of Bagnold and an extended bibliography of his published work. The purposes of the paper are firstly, to present a synthesis of the life and significant discoveries made by Brigadier Bagnold, secondly, to communicate something of the character of the man and his work to generations of researchers who have not had the chance to meet him at first hand, and finally, to use this Technical Supplement and Software Bulletin to make summaries of his theories, empirical findings and views on science accessible to students and scholars of physical geography, geomorphology and engineering.     

COMPARISON OF SIGNAL PROCESSING TECHNIQUES FOR ESTIMATING THE EFFECTS OF ANISOTROPY1

Three-component recordings of shear-waves in exploration surveys provide an opportunity to measure crustal anisotropy, which may be important in estimating the geometrical and physical parameters of reservoir rocks. VSPs are particularly important for this purpose as they are less subject to the complex interactions of the shear wavefield with the free surface. The first stage in characterizing the subsurface anisotropy requires that the distinctive phenomenon of shear-wave splitting must be examined for every arrival at each geo-phone. This effect may be defined by two parameters: the polarization of the leading shear-wave and the time-delay between corresponding split shear-waves. A variety of techniques have been designed to estimate these parameters of shear-wave splitting. Here, we classify the published techniques into four main categories and review their properties. Representative procedures from each group are applied to a common synthetic data set contaminated with signal-generated noise. The results allow some general statements to be made about the utility of these methods for processing shear-waves in VSP data.     

Physical characterization of aerosol particles during nucleation events

Particle concentrations and size distributions have been measured from different heights inside and above a boreal forest during three BIOFOR campaigns (14 April–22 May 1998, 27 July–21 August 1998 and 20 March–24 April 1999) in Hyytiälä, Finland. Typically, the shape of the background distribution inside the forest exhibited 2 dominant modes: a fine or Aitken mode with a geometric number mean diameter of 44 nm and a mean concentration of 1160 cm⁻³ and an accumulation mode with mean diameter of 154 nm and a mean concentration of 830 cm⁻³. A coarse mode was also present, extending up to sizes of 20 μm having a number concentration of 1.2 cm⁻³, volume mean diameter of 2.0 μm and a geometric standard deviation of 1.9. Aerosol humidity was lower than 50% during the measurements. Particle production was observed on many days, typically occurring in the late morning. Under these periods of new particle production, a nucleation mode was observed to form at diameter of the order of 3 nm and, on most occasions, this mode was observed to grow into Aitken mode sizes over the course of a day. Total concentrations ranged from 410–45 000 cm⁻³, the highest concentrations occurring on particle production days. A clear gradient was observed between particle concentrations encountered below the forest canopy and those above, with significantly lower concentrations occurring within the canopy. Above the canopy, a slight gradient was observed between 18 m and 67 m, with at maximum 5% higher concentration observed at 67 m during the strongest concentration increases.     

BIBLIOGRAPHIE—BIBLIOGRAPHY

ABSTRACT

With the increasing use of telemetry in the control of water resource systems, a considerable amount of effort is being devoted to the development of models and parameter estimation techniques for on-line use. A variety of models and parameter estimation algorithms have been considered, ranging from complex conceptual models of the soil moisture accounting type, which are traditionally calibrated off-line, to state-space/Kalman filter models which, perhaps, have enjoyed undue popularity in the recent literature due to their mathematical elegance. The fundamental assumptions underlying the various approaches are reviewed, and the validity of these assumptions in the hydrological forecasting context is assessed. The paper draws on some results obtained during a recent workshop at the Institute of Hydrology in making assessments of the relative merits of different models and parameter estimation algorithms; these results have been derived from an intercomparison of a number of real time forecasting models.