Diatom transfer-functions for quantifying past air temperature, pH and total organic carbon concentration from lakes in northern Sweden

The relationships between diatoms (Bacillariophyceae) in surface sediments of lakes and summer air temperature, pH and total organic carbon concentration (TOC) were explored along a steep climatic gradient in northern Sweden to provide a tool to infer past climate conditions from sediment cores. The study sites are in an area with low human impact and range from boreal forest to alpine tundra. Canonical correspondence analysis (CCA) constrained to mean July air temperature and pH clearly showed that diatom community composition was different between lakes situated in conifer-, mountain birch- and alpine-vegetation zones. As a consequence, diatoms and multivariate ordination methods can be used to infer past changes in treeline position and dominant forest type. Quantitative inference models were developed to estimate mean July air temperature, pH and TOC from sedimentary diatom assemblages using weighted averaging (WA) and weighted averaging partial least squares (WA-PLS) regression. Relationships between diatoms and mean July air temperature were independent of lake-water pH, TOC, alkalinity and maximum depth. The results demonstrated that diatoms in lake sediments can provide useful and independent quantitative information for estimating past changes in mean July air temperature (R² _jack = 0.62, RMSEP = 0.86 °C; R² and root mean squared error of prediction (RMSEP) based on jack-knifing), pH (R² _jack = 0.61, RMSEP = 0.30) and TOC (R² _jack = 0.49, RMSEP = 1.33 mg l^-1). The paper focuses mainly on the relationship between diatom community composition and mean July air temperature, but the relationships to pH and TOC are also discussed.     

Vertical distribution of dissolved aluminium in the mediterranean sea

The vertical distribution of dissolved aluminium in the Mediterranean Sea offshore of Corsica has been followed during a period of high biological activity (April–September). In May and August, the concentration of dissolved aluminium is at a relatively low (1.5 μg Al1^?1) and rather constant value in the surface waters, while exhibiting minimum values of about 0.5 and 0.8 μg Al1^?1 in April and September. It increases under the seasonal thermocline to a depth of 150–500 m. The bottom waters are characterized by a constant and relatively high value of 4 μg Al1^?1.The observed concentrations of dissolved aluminium are not compatible with a precipitation-dissolution mechanism of clay minerals.The general distribution pattern and the seasonal changes of dissolved aluminium exhibit strong analogies with those of dissolved silica and nitrogen, suggesting a pre-dominant role of biological activity. It is not possible at this stage to attribute the aluminium uptake in the photic zone solely to the activity of diatoms, as suggested earlier.     

Regional application of a fish yield estimation procedure to lakes in north-east Germany

Primary production and total phosphorus, respectively, have recently been used as the main variables to estimate the fish yield potential of lakes. In order to improve the accuracy of the estimation procedure for regional applications, two major adaptations were implemented. Both the relations between total phosphorus and primary production as well as primary production and corresponding fish yield potential were adjusted to specific regional conditions in north-east Germany and production patterns in shallow lakes, respectively. Applied to 786 lakes, the adapted procedure led to estimated fish yield potentials in the range of 8 … 67 kg/ha · a with shallow lakes showing significantly higher potentials than stratified ones. A comparison of estimated yield potentials with current yield statistics revealed an improved conformity of estimates attained by using the adapted procedure.     

The effects of a variation of the radial viscosity profile on mantle evolution

The present paper describes a set of numerical experiments on the mantle's thermal evolution with an infinite Prandtl number fluid in a compressible spherical shell heated mainly from within. We used the anelastic liquid approximation with Earth-like material parameters. The usual variable-viscosity approach in mantle-convection models is the assumption of a temperature dependence only. The resulting thermal boundary layers are included in our model also, but an additional viscosity profile of the interior mantle was derived: The Birch–Murnaghan equation was employed to derive the Grüneisen parameter and other physical quantities as a function of depth from observational values provided by PREM. We computed the melting temperature and a new mantle viscosity profile, called eta3, using the Grüneisen parameter, Lindemann's law and some solid-state physics considerations. The new features of eta3 are a high-viscosity transition layer with rather high viscosity gradients at its boundaries, a second low-viscosity layer beginning under the 660-km discontinuity, and a strong viscosity increase in the central parts of the lower mantle. The rheology is Newtonian but it is supplemented by a viscoplastic yield stress, σ_y. A viscosity-level parameter, r_n, and σ_y have been varied. For a medium-sized Rayleigh-number–yield-stress area, eta3 generates a stable, plate-tectonic behavior near the surface and simultaneously thin sheet-like downwellings in the depth. Outside this area, three other types of solution were found. Not only the planforms but also the evolution of the Rayleigh number, the reciprocal Urey number, the Nusselt number, the surface heat flow, etc., have been studied. We repeated this investigation with two very different basic viscosity profiles, etaKL5a and etaKM, of other authors. A comparison reveals that eta3 facilitates the generation of surface plates and thin sheet-like downwellings in the depth considerably more than etaKL5a or even etaKM. The presence of two internal low-viscosity layers is obviously conducive for plateness and thin sheet-like downwellings. For an infinite yield stress, the thin cold sheet-like downwellings are reticularly connected. However, the distribution of the downwellings is more Earth-like if a realistic yield stress is added.