Rocks control the chemical composition of surface water from the high Alpine Zermatt area (Swiss Alps)

The study presents composition data of 87 surface water samples from high alpine catchments of the Zermatt area (Swiss Alps). The investigated area covers 170 km². It was found that the surface runoff acquires the dissolved solids mostly by reaction of precipitation water with the minerals of the bedrock. Total dissolved solids (TDS) vary from 6 to 268 mg L^?1. All collected water shows a clear chemical signature of the bedrock mineralogy. The contribution of atmospheric input is restricted to small amounts of ammonium nitrate and sodium chloride. NH₄ is a transient component and has not been detected in the runoff. Evaporation is not a significant mechanism for TDS increase in the Zermatt area. The chemical composition of the three main types of water can be related to the mineralogy of the dominant bedrock in the catchments. Specifically, Ca-HCO₃ (CC) waters develop from metamorphic mafic rocks and from carbonate-bearing schists. Mg-HCO₃ water originates from serpentinites and peridotites. Ca-SO₄ (CS) waters derive from continental basement rocks such as pyrite-rich granite and gneiss containing oligoclase or andesine. The collected data suggest that, together with reaction time, modal sulfide primarily controls and limits TDS of the waters by providing sulfuric acid for calcite (CC waters) and silicate (CS waters) dissolution. If calcite is present in the bedrock, its dissolution neutralizes the acid produced by sulphide weathering and buffers pH to near neutral to weakly alkaline conditions. If calcite is absent, the process produces low-pH waters in gneiss and granite catchments. The type of bedrock and its mineral assemblage can be recognized in water leaving very small catchments of some km² area. The large variety of water with a characteristic chemical signature is an impressive consequence of the richly diverse geology and the different rock inventory of the local catchments in the Zermatt area.     

Temporal dynamics and persistence of sponge assemblages in a Central Pacific atoll lagoon

Sponges are important components of coral reef fauna, although little is known of their temporal dynamics. Sponges dominate the lagoon system at Palmyra Atoll in the Central Pacific, which may not be its natural state. Here we examined the temporal variability and recruitment rates of these sponge assemblages to determine if they are stable and examined the evidence that a recent transition has occurred from a coral‐ to sponge‐dominated system. We found 24 sponge species in permanent quadrats in the lagoon between 2009 and 2011, and 11 species on our recruitment panels. The sponge assemblage composition and abundance did not vary significantly between years and appear stable. Many sponge recruits were found in both years that the panels were examined although higher rates were recorded in the second year of the study. While it seems very possible that a change to a sponge‐dominated lagoon is associated with declining environmental quality at Palmyra as a result of modifications over 70 years ago, without pre‐modification data on reef assemblage composition this remains speculative. Our observations of short‐term temporal stability in the sponge assemblages at Palmyra highlight the potential for sponge‐dominated reef states to be maintained in degraded reef environments that are seemingly unsuitable for coral survival.     

Changes in Dogger Bank macrofauna communities in the 20th century caused by fishing and climate

The macrofauna communities on the Dogger Bank (North Sea) from the 1920s, the 1950s and the 1980s to the 2000s were compared and identified five communities with similar spatial distribution throughout the 20th century. The abundance of dominant species in the five communities varied with time. Most obvious in the 1950s was the loss of the extensive Spisula and Mactra patches, which covered most of the shallow parts of the Bank in the 1920s. Since the 1980s, they have been found only as juveniles. The biological regime shift in the late 1980s caused an increase in macrofauna abundance, species numbers, diversity and southern species in most of the communities. The climate regime shift in 2001 had opposite effects in which the abundance, species numbers, diversity and southern species decreased in most of the communities. The increase in interface-feeding species and the decrease in sand-licking amphipods in the 2000s especially in the shallow Bank Community give evidence for climate driven changes in water masses, currents, storms, turbidity and food availability via planktonic or benthic primary production. Both fishing impact and climate change are hypothesised as explaining the changes in the Dogger Bank macrofauna communities.     

Export Production in the Subarctic North Pacific over the Last 800 kyrs: No Evidence for Iron Fertilization?

The subarctic North Pacific is a high nitrate-low chlorophyll (HNLC) region, where phytoplankton growth rates, especially those of diatoms, are enhanced when micronutrient Fe is added. Accordingly, it has been suggested that glacial Fe-laden dust might have increased primary production in this region. This paper reviews published palaeoceanographic records of export production over the last 800 kyrs from the open North Pacific (north of ∼35°N). We find different patterns of export production change over time in the various domains of the North Pacific (NW and NE subarctic gyres, the marginal seas and the transition zone). However, there is no compelling evidence for an overall increase in productivity during glacials in the subarctic region, challenging the paradigm that dust-born Fe fertilization of this region has contributed to the glacial draw down of atmospheric CO₂. Potential reasons for the lack of increased glacial export production include the possibility that Fe-fertilization rapidly drives the ecosystem towards limitation by another nutrient. This effect would have been exacerbated by an even more stable mixed layer compared to today. This revised version was published online in July 2006 with corrections to the Cover Date.     

How contact metamorphism can trigger global climate changes: Modeling gas generation around igneous sills in sedimentary basins

Large volumes of greenhouse gases such as CH₄ and CO₂ form by contact metamorphism of organic-rich sediments in aureoles around sill intrusions in sedimentary basins. Thermogenic gas generation and dehydration reactions in shale are treated numerically in order to quantify basin-scale devolatilization. We show that aureole thicknesses, defined as the zone of elevated metamorphism relative to the background level, vary within 30-250% of the sill thickness, depending on the temperature of the host-rock and intrusion, besides the sill thickness. In shales with total organic carbon content of >5 wt.%, CH₄ is the dominant volatile (85-135 kg/m³) generated through organic cracking, relative to H₂O-generation from dehydration reactions (30-110 kg/m³). Even using conservative estimates of melt volumes, extrapolation of our results to the scale of sill complexes in a sedimentary basin indicates that devolatilization can have generated ∼2700-16200 Gt CH₄ in the Karoo Basin (South Africa), and ∼600-3500 Gt CH₄ in the Vøring and Møre basins (offshore Norway). The generation of volatiles is occurring on a time-scale of 10-1000 years within an aureole of a single sill, which makes the rate of sill emplacement the time-constraining factor on a basin-scale. This study demonstrates that thousands of gigatons of potent greenhouse gases like methane can be generated during emplacement of Large Igneous Provinces in sedimentary basins.     

Stabilisation of soil organic matter by interactions with minerals as revealed by mineral dissolution and oxidative degradation

Soil organic matter is known to contain a stable fraction with an old radiocarbon age. Size and stabilisation processes leading to the formation of this old soil carbon pool are still unclear. Our study aims to differentiate old organic matter from young and labile carbon compounds in two acid forest soils (dystric cambisol, haplic podzol). To identify such fractions soil samples were exposed to oxidation with Na₂S₂O₈ and to dissolution by hydrofluoric acid (HF). A negative correlation between ¹⁴C activity and carbon release after dissolution of the mineral matrix by HF indicates a strong association of stabilised carbon compounds with the mineral phase. A negative correlation between the ¹⁴C activity and the relative proportion of carbon resistant to oxidation by Na₂S₂O₈ shows that young carbon is removed preferentially by this treatment. The fraction remaining after oxidation represents a certain stabilised, long residence time carbon pool. This old fraction comprises between 1 and 30% of the total soil organic carbon in the surface horizons, but reaches up to 80% in the sub-surface horizons. Old OC is mainly stabilised by organo-mineral associations with clay minerals and/or iron oxides, whereas intercalation in clay minerals was not found to be important.     

The out of ecliptic distribution of interplanetary dust and its relation to other bodies in the solar system

We discuss the out-of-ecliptic component of the interplanetary dust cloud and its relation to the other small bodies in the solar system. The determination of the mass loss of comets, so far is quite uncertain and doesn't allow a finite study of the mass input to the dust cloud. However it is shown, that the dust particles in the inner solar system, i.e. within the earth orbit are most probable produced from a collisional evolution of larger, meteoroid, fragments of cometary origin. A further component of interstellar dust is especially important in the outer solar system and perhaps for the collisional evolution of the small bodies.