What can be deduced from chemical measurement in an open-field raingauge? An example in the Maures Massif,southeastern France

Abstract

The deposition of chemical elements in a catchment occurs through three different processes: wet, dry and cloud deposition. Total deposition cannot be inferred from measurements made with open-field raingauges, and still constitutes a challenge to scientific method. The chemical composition of samples from an open-field raingauge (bulk precipitation) was analysed over a period of several years in a small Mediterranean catchment in the Maures Massif, France. The input of chloride measured in this way was two times lower than the output, despite the fact that this element is reputed to be conservative, which means input and output should roughly balance. This implies that input has previously been underestimated. Analysis of the bulk precipitation data was carried out taking into account both the history of rain events and of sampling. This study allowed the relative parts of the different deposition processes to be quantified. Dry deposition can provide from 20% to more than 80% of the anthropogenic and terrigenic elements (Ca²⁺, Mg²⁺, K⁺, NO₃ ^?, SO₄ ^2-, SiO₂) to the rain samples. The occult deposition of marine elements on the catchment area (50% of total deposition) was found to be mostly due to cloud deposition during wet periods.     

Dinoflagellate cysts reflecting surface-water conditions in Voldafjorden, western Norway during the last 11 300 years

Abundant dinocysts in a high-resolution core from Voldafjorden, western Norway, reflect changes in sea surface-water conditions during the last c. 11 300 BP. The period from c. 11 300 to 10 800 BP (Late Allerφd) was characterized by cool temperate surface-waters, high annual temperature variation and relatively strong stratification of the water column, which is characteristic of fjord environments. Due to the stratification of the surface waters, the uppermost layer may have warmed considerably. This generated a principal difference in temperature conditions between land and sea, with slightly higher temperatures in the marine environments. The period from c. 10 800 to 10 000 BP is characterized by very harsh conditions, with sea surface-water temperatures close to freezing and long lasting seasonal sea-ice cover. Similar temperature changes at the beginning and end of the Younger Dryas are characteristic for NW Europe, but those in Voldafjorden differ from those in the open sea and in the Norwegian Channel by being significantly larger. The stratification of the water column during the Late Allerφd was probably broken down because of incipient inflow of temperate normal saline waters, which caused a marked sea surface-water warming, at c. 10 000 BP. Surface-water conditions close to those of today were gradually established between c. 10000 and 9500 BP. However, these interglacial conditions were abruptly interrupted by a significant drop in winter sea surface-water temperature and salinity occurring around 9700 BP. From c. 9500 to 7000 BP the influence of temperate normal saline water masses increased stepwise until full interglacial conditions were established around c. 7000 BP. The change in the dinocyst assemblage around 7000 BP in Voldafjorden was probably related to the onset of the modern Norwegian Coastal Current, previously documented in cores from the Skagerrak and the Mid-Norwegian Continental Shelf. The last c. 7000 BP is characterized by relatively stable surface-water conditions, possibly interrupted by periods of cooling or decreased inflow of temperate normal saline water. Like several other dinoflagellate cyst records from the Norwegian-Greenland Sea, O. centrocarpum peak values are between 4000 and 5000 BP, suggesting a regional-scale oceanographic change.     

Facies effects on the behaviour of Nd and Sr isotope systems in turbidite mudrocks during diagenesis

A detailed Sm/Nd, epsilon Nd and Rb/Sr profile through a 30-cm thick section of Silurian (Llandovery) interbedded turbiditic and hemipelagic mudrocks from the central Wales Basin shows well-marked chemical and isotopic trends. The variations reflect an interplay of depositional mode and diagenetic fractionation. Sm and Nd values are substantially higher and Sm/Nd ratios tend to be lower in the organic-rich hemipelagite layers due to diagenetic concentration in the hemipelagites. There is a corresponding depletion in the turbidite mudstones. Epsilon Nd values range from −0·8 to −7·1 and this is attributed to diagenetic modification of Sm/Nd ratios causing scatter in back-calculated epsilon values. Rubidium–strontium ratios in this succession fall within a narrow range, due to homogenization during diagenesis. By contrast, data from a hemipelagite-dominated (condensed) succession near the northern margin of the Welsh Basin show a lower range of epsilon Nd values and a higher scatter of Rb/Sr values, consistent with less fluid throughput during burial compaction and hence less diagenetic redistribution in these rocks. These patterns demonstrate the sensitivity of mudrock trace element and isotope compositions to both small-scale sedimentary structure and large-scale basin architecture.     

SHORT COMMUNICATION THE RELATIONSHIP OF CLOSURE,MEAN CENTERING AND MATRIX RANK INTERPRETATION

This paper describes an investigation into the relationship of closure,a baseline offset and mean centeringto the interpretation of matrix rank.The equivalence of a certain type of closure to a constant baseline(i.e.a simple numerical offset which may vary between response channels but is constant over all samples)is demonstrated.A systematic approach to the interpretation of the rank of a matrix is given.     

Relationships between lithology and diagenesis in a limeston—marl facies transition: an electron microprobe study

A 3 km long lateral facies transition from Oligo-Miocene skeletal grainstones into packstones and mudstones displays systematic variation in carbonate skeletal fragment alteration and secondary carbonate mineral composition. Within the skeletal grainstone end-member all aragonitic grains have dissolved, all Mg-calcite skeletal fragments have altered to calcite, and calcite has been precipitated as both void-filling spar and as syntaxial overgrowths on echinoid fragments. Within the transitional grainstone-packstone lithologies some skeletal fragments show preservation of their original mineralogy, while calcite, ferroan calcite spar and dolomite have precipitated in void spaces. Within the packstone-mudstone end-member of the transition, aragonitic grains have been preserved and Mg-calcite skeletal fragments have retained most of their magnesium. Thin, originally porous grainstone layers within the pack-stone-mudstones contain sideroplesite and ferroan calcite spar in void spaces, and iron has been incorporated in skeletal fragments which were originally Mg-calcite. In these grains iron has been incorporated at the expense of magnesium until the grains approach the composition of the surrounding ferroan calcite cement. The lateral variation in diagenetic alteration across this facies transition is a function of differing groundwater movement and composition, controlled ultimately by the composition, porosity and permeability of the host lithologies.     

Geomorphology of the Sub-Antarctic Australian Territory of Heard Island-McDonald Island

The geomorphology of Heard Island-McDonald Island is primarily the product of close interplay between volcanism, glaciation, and vigorous marine processes in a stormy sub-Antarctic environment. The dominant landform is the strato-volcano Big Ben (2745m), which is the highest mountain on Australian territory outside Antarctica. Other volcanic landforms include scoria cones, domes, open vertical volcanic conduits, lava flows and lava tubes. Volcanic activity is ongoing from the summit of Big Ben, and from Samarang Hill on McDonald Island. Early, but unproven, glacial sediments may exist within the Late Miocene - Early Pliocene Drygalski Formation, which forms a 300m high plateau along the northern coast of Heard Island. Growth of the present glaciers, some of which reach sea level, has been a response to progressive growth of the volcanoes. A variety of erosional and depositional glacial landforms is present, including major lateral moraines and extensive hummocky moraines. Vigorous longshore drift and an abundant sediment supply have produced a large spit at the downdrift end of the island, and formed bars from reworked glacigenic sediment that now impound proglacial estuarine lagoons, some of which have grown rapidly over recent decades as tidewater glaciers have retreated. Integrated study of the volcanic, glacial and coastal sequences offers the possibility of constructing a well-dated record of climate change. Research into the geomorphology, surficial sediments, and contemporary geomorphological processes, including glaciofluvial sediment flux, is also important as an aid to environmental management on land, and to management of the adjacent marine environment.     

MAPPING WISCONSIN

WISCONSIN'S PAST AND PRESENT: A Historical Atlas. By The Wisconsin Cartographers ' Guild , xv and 125 pp.; maps, ills. THE ATLAS OF ETHNIC DIVERSITY IN WISCONSIN. By Kazimierz J. Zaniewski and Carol J. Rosen CULTURAL MAP OF WISCONSIN: A Cartographic Portrait of the State. By David Woodward , Robert C. Ostergren , Onno Brouwer , Steven Hoelscher , and Joshua Hane .