Hydrochemical and water source variations across a floodplain mire,Insh Marshes,Scotland

Groundwater heads and chemical composition were measured at approximately two week intervals during the summer of 1993 along a 1 km transect across the Insh Marshes floodplain mire in Inverness-shire, Scotland. Groundwater heads were generally higher near the valley side slope, with lower pH values and greater dissolved organic carbon, A1 and C1 concentrations. In the centre of the transect, upward groundwater heads were identified and pH, conductivity and concentrations of base cations were much greater. Near the River Spey, pH and base cation concentrations decreased and A1 and C1 concentrations increased. Deep groundwater followed a similar spatial trend but was generally more base-rich than shallow groundwater. These variations reflect the influence of three major water sources with different chemical signatures. Runoff from the valley side slope increased dissolved organic carbon and A1 in the shallow groundwater, the upward flow of groundwater increased the pH and Ca concentration and inundation near the river decreased the base status and increased C1 and A1.     

Trace elements in speleothems as recorders of environmental change

Speleothems are now established as important palaeoenvironmental archives and contain a number of suitable proxies, although trace elements have been much less widely used than oxygen and carbon isotopes. The complexity of the cave environment helps to explain this since the fluids from which speleothems form vary greatly in composition in space (even within a cave chamber), seasonally, and over longer periods. Understanding the forcing factors for this variability is the key to decoding the significance of the trace element records.A variety of techniques are available for trace element work and it is important to understand the strengths and limitations of each and also to seek an understanding, e.g. by micro-imaging techniques, of whether the elements are associated with inclusions in the CaCO₃, or are isolated within the crystal lattice. For some elements there is a more-or-less predictable relationship between element ratios to Ca in the water and in the calcite. Individual trace elements may be derived from atmospheric deposition, superficial deposits or bedrock and can be recycled in soil processes before being transferred to the cave. Some components show an instantaneous response to water infiltration, whereas others are only leached by slow-flowing seepage waters. Changing in the proportion of water from fracture-fed and seepage-flow aquifer compartments is an important factor in influencing trace element supply. High flows lead to higher fluxes of soil-derived colloidally transported elements. Conversely, under relatively dry conditions, degassing of CO₂ results in “prior calcite precipitation” upflow of the site of speleothem deposition and leads to higher ratios of Sr/Ca and Mg/Ca. Some trace element variations in speleothems over time are induced during crystal growth whereby faster growth leads to a greater departure from equilibrium element partitioning.Despite the demonstrated temperature-dependence of Mg partitioning into calcite, attempts at deriving palaeotemperature records from speleothems have been so far confounded by variations in solution Mg/Ca and/or crystallographic effects. A number of case studies have effectively used trace elements such as speleothem Mg as records of palaeo-aridity, using supporting arguments from modern monitoring or covariations with other parameters such as stable isotopes. Sr and U isotopes can also be indicators of palaeohydrology, although Sr isotope variations can also reflect varying aeolian input. Considerable progress has been made in decoding the meaning of annual trace element variations using criteria for understanding dripwater hydrology and pH. This should lead in the future to more specific interpretations of how seasonality evolves through time.     

Studies in the application of recurrence relations to special perturbation methods

The numerical integration of the differential equations describing dynamical systems has been shown in previous papers of this series to be most effectively accomplished by an explicit Taylor series method.In this paper we show that one explicit Taylor series method, developed earlier in this series and which appears to possess a high degree of versatility, yields considerable gains in efficiency over classical single-step and multi-step methods. (In this context efficiency is a measure of the time taken to carry out a calculation of a specific accuracy).For a given accuracy criterion governing the local truncation error (LTE) it is found that the Taylor series method is generallytwice as fast as the classical multi-step method and up totwenty times faster than the classical single-step method.     

Minor elements in forsterites of Orgueil (C1), Alais (C1) and two interplanetary dust particles compared to C2-C3-UOC forsterites

Abstract— The rare Mg-rich silicate fraction of the C1 meteorites, Orgueil and Alais, is dominated by minute (< 30 μm) forsterite. Twenty three forsterite grains of these meteorites as well as large forsterites in two chondritic porous interplanetary dust particles (IDPs) are characterized by levels of MnO generally, but not always, higher than found in forsterites of C2, C3 and unequilibrated ordinary chondrites (UOC). Forsterite in Orgueil contains 900 to 6200 ppmw MnO while Alais forsterite has less than 2000 ppmw MnO suggesting that the forsterites in the two meteorites are chemically distinct. Alais forsterite shows lower Cr and Al relative to Orgueil forsterite. The C1 forsterites do not show Fe-poor (FeO < 0.3), refractory-rich (Al, Ca, Ti, V) compositions which are relatively common in the C2-C3-UOC meteorites suggesting that the most primitive forsterite compositions are not present in these C1 meteorites. While minor elements in forsterite can not distinguish unambiguously between C1 and C2-C3-UOC sources, the high Mn levels in some IDP forsterites are similar to some C1 forsterites suggesting a possible relation between the forsterites of these two extraterrestrial samples.