THE EFFECT OF SYNOPTIC SCALE WEATHER SYSTEMS ON SUB‐SURFACE SOIL TEMPERATURES IN A DIURNAL FROST ENVIRONMENT: PRELIMINARY OBSERVATIONS FROM SUB‐ANTARCTIC MARION ISLAND

Marion Island in the South Indian Ocean has a maritime climate dominated by diurnal frost processes in the landscape. We test the hypothesis that synoptic time‐scale measurements are essential in understanding the drivers of diurnal frost processes. Preliminary results from automated microclimate measurements in a polar desert habitat show that diurnal soil surface temperatures on Marion Island are influenced by a complex interaction of radiation balance, air mass circulation, cloud cover and snow. The passage of synoptic scale weather systems influences soil thermal characteristics through changes in dominance of the radiation budget. Soil frost on Marion appears to be dependent on clear skies, while synoptic weather systems affect the duration and intensity of soil frost processes and non‐radiative heat fluxes. Air circulation patterns at Marion Island influence diurnal scale temperature fluctuations and its direct and indirect interactions with ecosystem processes. The data suggest that in a maritime sub‐Antarctic environment the climatic drivers of soil frost occur at a finertemporal resolution than for seasonal and permafrost environments and needs to be measured at a diurnal time‐scale to be meaningful.     

A Periglacial Palaeoenvionment in the Upper Carboniferous–Lower Permian Tobra Formation of the Salt Range, Pakistan

The Upper Carboniferous—Lower Permian(Upper Pennsylvanian-Asselian) Tobra Formation is exposed in the Salt and Trans Indus ranges of Pakistan.The formation exhibits an alluvial plain(alluvial fan-piedmont alluvial plain) facies association in the Salt Range and Khisor Range.In addition,a stream flow facies association is restricted to the eastern Salt Range.The alluvial plain facies association is comprised of clast-supported massive conglomerate(Gmc),diamictite(Dm)facies,and massive sandstone(Sm) Hthofacies whereas the stream flow-dominated alluvial plain facies association includes fine-grained sandstone and siltstone(Fss),fining upwards pebbly sandstone(Sf),and massive mudstone(Fm) Hthofacies.The lack of glacial signatures(particularly glacial grooves and striatums) in the deposits in the Tobra Formation,which are,in contrast,present in their timeequivalent and palaeogeographically nearby strata of the Arabian peninsula,e.g.the AI Khlata Formation of Oman and Unayzah B member of the Saudi Arabia,suggests a pro-to periglacial,i.e.glaciofluvial depositional setting for the Tobra Formation.The sedimentology of the Tobra Formation attests that the Salt Range,Pakistan,occupied a palaeogeographic position just beyond the maximum glacial extent during Upper Pennsylvanian-Asselian time.     

Experimental Study of Sand Bed Configurations in Front of a Vertical Wall Under Wave Action

—When a 2-D progressive wave train normally or obliquely approaches a vertical wall and thenis normally or obliquely reflected from it,the combination of the approaching and reflected waves may re-sult in a standing wave or a short-crested wave in front of the wall.This paper presents the experimentalobservations of sand bed configurations under the action of these water waves in front of the wall.The ge-ometry of sand ripples under these water waves in front of the vertical wall is presented as a function offlow parameters,such as the water particle semi-excursion and the mobility number.     

Summary findings of the fourth international radiocarbon intercomparison (FIRI)(1998–2001)

Interlaboratory comparisons have been widely used in applied radiocarbon science. These are an important part of ongoing quality assurance (QA) programmes, which are vital to the appropriate interpretation of the evidence provided by the ¹⁴C record in Quaternary applications (including climate change and environmental reconstruction). International comparisons of laboratory performance are an essential component of the quality assurance process in radiocarbon dating. If the user community is to have confidence in radiocarbon results, it needs to be assured that laboratories world wide are producing measurements that are reliable and in accordance with ‘good practice’. The findings from the most recent (completed in 2001) and extensive (more than 90 participating laboratories) radiocarbon intercomparison (FIRI) are reported here. This study was designed (i) to assess comparability, or otherwise, of the results from different laboratories and (ii) to quantify the extent and possible causes of any interlaboratory variation. The results demonstrate that there are no significant differences amongst the main measurement techniques (gas proportional counting, liquid scintillation counting and accelerator mass spectrometry (AMS)) but there is evidence of small laboratory offsets relative to known age samples for some laboratories. There is also evidence in some cases of underestimation of measurement precision. Approximately 10% of all results were classified as extreme (outliers) and these results were generated by 14% of the laboratories. Overall, the evidence supports the fact that radiocarbon laboratories are generally accurate and precise but that, notwithstanding internal QA procedures, some problems still occur, which can best be detected by participation in independent intercomparisons such as FIRI, where the results allow individual laboratories to assess their performance and to take remedial measures where necessary. The results from FIRI are significant in that they show a broad measure of agreement between measurements made in different laboratories on a wide range of materials and they also demonstrate no statistically significant difference between measurements made by radiometric or AMS techniques. Copyright © 2002 John Wiley & Sons, Ltd.     

Links between bulk sediment particle size and magnetic grain‐size: general observations and implications for Chinese loess studies

Using a combination of particle size analysis, magnetic measurements, scanning electron microscopy and transmission electron microscopy imaging, this study shows that in a wide range of depositional environments, there is a strong link between particle size classes and magnetic response, especially below the upper limit of stable single domain magnetic behaviour. Ferrimagnetic grain assemblages dominated by stable single domain magnetosomes regularly have peak susceptibility and remanence values in coarser grades than do those containing finer‐grained, viscous and superparamagnetic secondary magnetic minerals formed during pedogenesis. This effect is despite the fact that there is a one to two orders of magnitude size difference between the particle size boundaries (at 1 or 2 μm) and key domain state transitions (mostly below 0·05 μm). The implications of these results are explored using samples spanning 22 Myr of loess accumulation on the Chinese Loess Plateau. The results from the loess sections, complemented by data from low‐temperature magnetic experiments, show that there are subtle distinctions in mean ferrimagnetic grain‐size between the Pleistocene and Miocene parts of the record, thus allowing more refined rock magnetic interpretations of the fine‐grained ferrimagnetic mineral assemblages arising from the effects of weathering, pedogenesis and possibly diagenesis in the sections studied.     

A Melt Inclusion Record of Volatiles, Trace Elements and Li-B Isotope Variations in a Single Magma System from the Plat Pays Volcanic Complex, Dominica, Lesser Antilles

Glass inclusions in plagioclase and orthopyroxene from daciticpumice of the Cabrits Dome, Plat Pays Volcanic Complex in southernDominica reveal a complexity of element behavior and Li–Bisotope variations in a single volcanic center that would gounnoticed in a whole-rock study. Inclusions and matrix glassesare high-silica rhyolite with compositions consistent with about50% fractional crystallization of the observed phenocrysts.Estimated crystallization conditions are 760–880°C,200 MPa and oxygen fugacity of FMQ + 1 to +2 log units (whereFMQ is the fayalite–magnetite–quartz buffer). Manyinclusion glasses are volatile-rich (up to 6 wt % H₂O and 2900ppm Cl), but contents range down to 1 wt % H₂O and 2000 ppmCl as a result of shallow-level degassing. Sulfur contents arelow throughout, with <350 ppm S. The trace element compositionof inclusion glasses shows enrichment in light rare earth elements(LREE; (La/Sm)_n = 2·5–6·6) and elevatedBa, Th and K contents compared with whole rocks and similaror lower Nb and heavy REE (HREE; (Gd/Yb)_n = 0·5–1·0).Lithium and boron concentrations and isotope ratios in meltinclusions are highly variable (20–60 ppm Li with ⁷Li= +4 to +15 ± 2; 60–100 ppm B with ¹¹B = +6 to+13 ± 2) and imply trapping of isotopically heterogeneous,hybrid melts. Multiple sources and processes are required toexplain these features. The mid-ocean ridge basalt (MORB)-likeHREE, Nb and Y signature reflects the parental magma(s) derivedfrom the mantle wedge. Positive Ba/Nb, B/Nb and Th/Nb correlationsin inclusion glasses indicate coupled enrichment in stronglyfluid-mobile (Ba, B) and less-mobile (Th, Nb) trace elements,which can be explained by fractional crystallization of plagioclase,orthopyroxene and Fe–Ti oxides. The ⁷Li and ¹¹B valuesare at the high end of known ranges for other island arc magmas.We attribute the high values to a ¹¹B and ⁷Li-enriched slabcomponent derived from sea-floor-altered oceanic crust and possiblyfurther enriched in heavy isotopes by dehydration fractionation.The heterogeneity of isotope ratios in the evolved, trappedmelts is attributed to shallow-level assimilation of older volcanicrocks of the Plat Pays Volcanic Complex. KEY WORDS: subduction; volcanic arcs; igneous processes; melt inclusions; SIMS; trace elements; lithium and boron isotopes; diffusion     

Palaeomagnetic records from two varved clay sequences in the Middle Swedish ice marginal zone

Two varved clay sequences, at Rystad and Tottnäs, situated in the Middle Swedish ice marginal zone were analysed palaeomagnetically. Two parallel profiles were sampled and analysed at each site. The varved clay at Rystad was dated by floating varve chronology. The varves at Tottnäs can be linked to Swedish time scale, expressed in calendar years B.P. Due to the distance between the sites they cannot be correlated by means of varve diagrams. Palaemagnetic methods were used as an alternative. Based an AF demanetization of pilot samples, the palaeomanetic to be too low, in the order of15, compared to the site latitude. At Tottnäs the inclination records are very close to the expected inclination with respect to the site latitude. Because of a systematic inclination error in the Rystad profiles the correlation was based on the declination records. Statistical comparisons of these records between the two sites indicate that the sediment successions are partly synchronous. It is concluded that the deglaciation at Tottnäs started c. 130 years earlier than at Rystad. This mean that the Swedish ice marginal zone east of Rystad will have a more northeasterly extension than previously thought.