Climatic and environmental controls on the occurrence and distributions of long chain alkenones in lakes of the interior United States

Long chain alkenones (LCA) are temperature-sensitive lipids with great potential for quantitative reconstruction of past continental climate. We conducted the first survey for alkenone biomarkers from 55 different lakes in the Northern Great Plains and Nebraska Sand Hills of the United States. Among those surveyed, we found 13 lakes that contain LCAs in the surface sediments. The highest concentrations of alkenones in sediments are found in cold (mean annual air temperature ∼11 °C versus 17 °C in our warmest sites), brackish to mesosaline (salinity = 8.5-9.7 g/L), and alkaline (pH = 8.4-9.0) lakes with high concentrations of sodium and sulfate. The dynamics of stratification and nutrient availability also appear to play a role in LCA abundance, as early spring mixing promotes a bloom of alkenone-producing haptophytes. Four of the alkenone-containing sites contain the C_37:4 alkenone; however, we discovered an unprecedented lacustrine alkenone distribution in a cluster of lakes, with a total absence of C_37:4 alkenone. We attribute this unusual composition to a different haptophyte species and show that the sulfate:carbonate ratio may control the occurrence of these two distinct populations. We created a new in-situ temperature calibration for lacustrine sites that contain C_37:4 using a water-column calibration from Lake George, ND and show that is linearly correlated to lake water temperature (R² = 0.74), but is not. A number of lakes contain an unidentified compound series that elutes close to the LCAs, highlighting the importance of routine GC-MS examination prior to using lacustrine LCAs for paleotemperature reconstructions.     

Alfred E. Bergeat (1866–1924): a distinguished volcanologist and ore deposit researching scientist at the mining academies of Freiberg (Saxony) and Clausthal (Harz mountains) in Germany

Alfred E. Bergeat, originated from a family, who produced gold-glance in a factory (porcelain painting), studied mineralogy and geology at the University of Munich from 1886 to 1892. Due to the results of his habilitation work on the volcanism of island arcs, especially of the Stromboli volcanic island in the Tyrrhenian Sea, he became a recognized volcanologist and specialist in volcanic petrography. He further became an explorer of syngenetic, epigenetic and deuterogenic ore deposits at the mining academies (Bergakademien) of Freiberg (Saxony) and Clausthal (Harz mountains). He described these ore deposits in a two-volume manual (1904–1906) which was summarized again in 1913. After his early death in 1924, the two manuals “Die Vulkane” (1925) and “Vulkankunde” (1927) were posthumously published by his colleague and friend Karl Sapper (1866–1945).     

Lead contents of S-type granites and their petrogenetic significance

An evaluation of Pb and Ba contents in S-type granites can provide important information on the processes of crustal partial melting. Primary low-T S-type granites, which form mainly by fluid-absent muscovite melting, may acquire a significant enrichment in Pb when compared to higher-T S-type granites for a given Ba content. We consider the following factors are responsible for this enrichment: Muscovite is a major carrier of Pb in amphibolite facies metapelites, and thus large quantities of Pb can be liberated upon its breakdown. The typical restite assemblage of Qz?+?Bt?+?Sil?±?Pl?±?Grt?±?Kfsp that forms during low-T, fluid-absent muscovite melting can take up only minor amounts of this Pb. This is because the crystal/melt Pb distribution coefficients for these restite minerals are low to very low. Only K-feldspar is moderately compatible for Pb, with a crystal/melt distribution coefficient of ~3, but its modal content in restites is usually low. At the same time, the restite assemblage will retain much Ba owing to the very high Ba uptake in both biotite and K-feldspar, which is an order of magnitude higher than for Pb. Thus, during a low-T anatectic event involving a low degree of crustal melting, Pb (as an incompatible element) can become strongly enriched in the partial melt relative to Ba and also relative to source rock values. In the case of higher-T anatexis and larger partial melt amounts, the Pb becomes less enriched and the Ba less depleted or even enriched relative to source rock values. During fractional crystallization of a S-type granite magma, Ba behaves strongly compatibly and Pb weakly compatibly. The concentrations of both elements decrease along the liquid line of decent. Owing to this sympathetic fractionation behavior, the primary, source-related Pb–Ba fingerprint (with weak or strong Pb enrichment) remains in evolved S-type granites. This facilitates a distinction between primary low-T S-type granites, which are related to muscovite melting, and secondary low-T S-type granites that evolve through fractional crystallization from a higher-T parental magma. We show in this paper that a simple logarithmic Pb versus Ba diagram can be a valuable aid for interpreting the petrogenesis of S-type granite suites.     

Theoretical Studies of the Parameterization of the Non-Neutral Surface Boundary Layer

The parameterization of the non-neutral atmospheric surface layer has been reexamined using the basic principles of small-scale energetics and thermodynamics. On the basis of this more complete treatment, the K- parameterization has been reformulated. It is found that the linear regression laws between fluxes and driving gradient forces of the turbulent heat and humidity exchanges in the surface layer can be derived in a much more comprehensive manner than by using the commonly used K-theory. With respect to stationary conditions and in the context of similarity concepts, a system of algebraic equations has been formulated which provides reasonable estimates of the distributions of the dimension-less rates of viscous energy dissipation as well as turbulent kinetic and thermal-diffusive energy transport as functions of the variable z/L. Quantitative calculations have been performed using the scaling height formulations of Takeuchi and Yokoyama, Prandtl, and von Kármán as closure conditions of the equations.     

Simulation of the nucleation and growth of simple clay minerals in weathering processes: The NANOKIN code

We present a numerical approach which accounts for nucleation, growth and/or resorption of particles of fixed composition in aqueous solutions, and which involves functionalities suited to the formation of simple clay minerals in weathering processes, such as: formation of non-spherical particles, heterogeneous/homogeneous nucleation, several growth laws, precipitation resulting from the dissolution of primary minerals. The overall model is now embedded into a new numerical code called NANOKIN, in which several optimization procedures have been introduced in order to allow long dynamics to be followed. NANOKIN was applied to the precipitation of Al- bearing minerals from aqueous solutions: halloysite, kaolinite and Ca-montmorillonite. It allowed us to propose a stable scheme for the competitive precipitation of halloysite and kaolinite under two different types of initial conditions: (1) a given initial super-saturation state of the aqueous solution; (2) progressive super-saturation resulting from the kinetic dissolution of the minerals from a granitic rock under weathering conditions. Both yield particle sizes in the micron range, but with distinct crystal size distribution functions. The interplay between kinetic and thermodynamic effects is discussed.     

Strontium as a tracer of weathering processes in a silicate catchment polluted by acid atmospheric inputs, Strengbach, France

This paper determines the weathering and atmospheric contributions of Ca in surface water from a small spruce forested silicate catchment (N–E France) receiving acid atmospheric inputs. The bedrock is a granite with K-feldspar and albite as dominant phases. The calcium content in plagioclase is low and the Ca/Na ratio in surface water is high, reflecting other sources of calcium from those expected from the weathering of major mineral phases. The biotite content is low. Only traces of apatite were detected while no calcite was found in spite of a major hydrothermal event having affected the granite. The strontium isotopic ratio ⁸⁷Sr/⁸⁶Sr and Sr content was used as a tracer of weathering and was determined in minerals and bulk bedrock, open field precipitation, throughfall, soil solution, spring and stream water. The Sr isotopic ratio of the reacting weathering end-member was predicted by simulating the alteration of the granite minerals by incorporating strontium into the water–rock interaction kinetic code KINDIS. In the early stages of water–rock interaction, K-feldspar and biotite strongly influence the isotopic composition of the weathering solution whereas, the Na-rich plagioclase appears to be the main long-term reactive weathering end-member. Approximately 50% of dissolved Sr in streamwater are atmospherically derived. The ⁸⁷Sr/⁸⁶Sr ratios of exchangeable Sr in the fine fraction at 1-m depth from a soil profile indicate that the amount of exchangeable Sr seems essentially controlled by atmospheric inputs. The exception is the deep saprolite where weathering processes could supply the Sr (and Ca). Na-Plagioclase weathering obviously control the chemistry and the isotopic composition of surface waters. The weathering of trace mineral plays a secondary role, the exception is for apatite when plagioclase is absent. Our hydrochemical, mineralogical and isotopic investigations show that a major part of the strong Ca losses detected in catchment hydrochemical budgets that result from the neutralization of acid precipitation has an atmospheric origin. Consequently, in the long term, in such areas, the availability of such an exchangeable base cation might be strongly limited and surface waters consequently acidified.