Diffusion transport of water in basalts

Studying diffusive transport in porous rocks is of fundamental importance in understanding a variety of geochemical processes including: element transfer, primary mineral dissolution kinetics and precipitation of secondary phases. Here we report new findings on the relationship between diffusive transport and textural characteristics of the pore systems on the example of mid-oceanic ridge basalts having different degree of alteration but very similar bulk pore volume. Diffusion processes in porous basalts were studied in situ using H2O -> D2O exchange experiments. The effective diffusion coefficients of water molecules increase systematically from 5.05*10**-11 to 1.19*10**-10 m**2/s for fresh and moderately altered basalts and from 2.40*10**-11 to 6.72*10**-11 m**2/s for completely altered basalt as temperature increases from 5 to 50 °C. The activation energy of the diffusion process increases from 12.29 ± 0.71 kJ/mol for fresh and moderately altered basalts to 14.3 ± 1.33 kJ/mol for completely altered basalt. The results indicate that neither the bulk porosity nor the degree of alteration can be used as proxies for the efficiency of element transport during MORB-water interaction. The formation of secondary phases that replace primary minerals and fill the pore space in the rock leads to the formation of tiny pores and phases with large specific surface area. These factors might have a dominant control on the transport properties of altered basaltic rocks.

Element concentration and GDGT fractional abundances of sediment core GeoB3910-2

In dieser Arbeit wurde das Zeitintervall zwischen 20 und 10 ka vor heute einschließlich des Heinrichevent 1 und der Younger Dryas am Kern GeoB 3910-2 neu untersucht. An organischen Parametern, basierend auf der Verteilung von bakteriellen GDGTs, und Elementkonzentrationen wurde eine Rekonstruktion der klimatischen Bedingungen und Veränderungen im Hinterland von NO Brasilien durchgeführt. Es zeigt sich, dass sich die durchschnittliche Landtemperatur gleich der Oberflächenwassertemperatur verhält und im Gegensatz zu den Phasen von H6 bis H2 dem antarktischen Erwärmungstrend ab 17 ka vor heute folgt. Weiterhin konnte gezeigt werden, dass durch die südwärts Verlagerung der ITCZ während H1 und der YD die Niederschläge in NO Brasilen intensiviert wurden, was eine Ausbreitung der Flüsse und Änderung der Erosionsgebiete zur Folge hatte.

Oxygen concentration at time series station DYNAPROC

Continuous measurements between 0 and 200 m depth were performed every 2 h over two separate periods of four days at a station in the open northwestern Mediterranean Sea (Dyfamed Station) during the Dynaproc cruise in May 1995. Estimates of the daily variations in profiles of temperature, partial pressure of CO2, oxygen, chlorophyll a and nutrients were obtained. The distributions of the various physical and chemical properties were clearly different during the two time series, which were separated by a period of 11 days during which a wind event occurred. The mean daily utilization or production due to biological processes of dissolved inorganic carbon (DIC), nitrate+nitrite and oxygen were calculated along isopycnals using a vertical diffusion model. Between the surface and about 20 m depth, DIC was consumed and O2 released during the two time series while the nitrate+nitrite concentrations as well as supplies were zero. After the wind event, the O2 : C : N ratios of consumption (or production) were, on average, near the Redfield ratios, but during the first time series, the C : N utilization ratio between 20 and 35 m was two to three times that of Redfield stoichiometry and the oxygen release was low. The integrated net community production (NCP) in terms of carbon was equivalent during the two time series, whereas the chlorophyll a biomass was twice as high, on average, during the first time series but did decrease. These results imply that the production systems were different during the two periods. The first time series corresponds to a period at the end of production, due to the nutrient depletion in the euphotic layer. The formation of degradation products of the living material in dissolved organic form is probably important as indicated by the high C : N utilization ratios. The second time series corresponds to a reactivation of the primary production due to the upward shift of nutrients after the wind event.

Fractional abundance and indices for brGDGTs and crenarchaeol in dust samples, surface water samples and surface sediment samples

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are membrane lipids produced by soil bacteria and occur in near coastal marine sediments as a result of soil organic matter input. Their abundance relative to marine-derived crenarchaeol, quantified in the BIT index, generally decreases offshore. However, in distal marine sediments, low relative amounts of brGDGTs can often still be observed. Sedimentary in situ production as well as dust input have been suggested as potential, though as yet not well constrained, sources. In this study brGDGT distributions in dust were examined and compared with those in distal marine sediments. Dust was sampled along the equatorial West African coast and brGDGTs were detected in most of the samples, albeit in low abundance. Their degree of methylation and cyclisation, expressed in the MBT' (methylation index of branched tetraethers) and DC (degree of cyclisation) indices, respectively, were comparable with those for African soils, their presumed source. Comparison of DC index values for brGDGTS in global soils, Congo deep-sea river fan sediments and dust with those of distal marine sediments clearly showed, however, that distal marine sediments had significantly higher values. This distinctive distribution is suggestive of sedimentary in situ production as a source of brGDGTs in marine sediments, rather than dust input. The presence of in situ produced brGDGTs in marine sediments means that caution should be exercised when applying the MBT'-CBT palaeothermometer to sediments with low BIT index values, i.e. < 0.1, based on our dataset.

Diffusion boundary layers ameliorate the negative effects of ocean acidification on the temperate coralline macroalga Arthrocardia corymbosa

Anthropogenically-modulated reductions in pH, termed ocean acidification, could pose a major threat to the physiological performance, stocks, and biodiversity of calcifiers and may devalue their ecosystem services. Recent debate has focussed on the need to develop approaches to arrest the potential negative impacts of ocean acidification on ecosystems dominated by calcareous organisms. In this study, we demonstrate the role of a discrete (i.e. diffusion) boundary layer (DBL), formed at the surface of some calcifying species under slow flows, in buffering them from the corrosive effects of low pH seawater. The coralline macroalga Arthrocardia corymbosa was grown in a multifactorial experiment with two mean pH levels (8.05 'ambient' and 7.65 a worst case 'ocean acidification' scenario projected for 2100), each with two levels of seawater flow (fast and slow, i.e. DBL thin or thick). Coralline algae grown under slow flows with thick DBLs (i.e., unstirred with regular replenishment of seawater to their surface) maintained net growth and calcification at pH 7.65 whereas those in higher flows with thin DBLs had net dissolution. Growth under ambient seawater pH (8.05) was not significantly different in thin and thick DBL treatments. No other measured diagnostic (recruit sizes and numbers, photosynthetic metrics, %C, %N, %MgCO3) responded to the effects of reduced seawater pH. Thus, flow conditions that promote the formation of thick DBLs, may enhance the subsistence of calcifiers by creating localised hydrodynamic conditions where metabolic activity ameliorates the negative impacts of ocean acidification.

Model of interactive visualization of diffusion processes from different strains, and source routes and spatial diffusion of capuchin monkeys over the past 6 million years

Source routes and Spatial Diffusion of capuchin monkeys over the past 6 million years, rebuilt in the SPREAD 1.0.6 from the MCC tree. The map shows the 10 different regions to which distinctive samples were associated. The different transmission routes have been calculated from the average rate over time. Only rates with Bayes factor> 3 were considered as significantly different from zero. Significant diffusion pathways are highlighted with color varying from dark brown to red, being the dark brown less significant rates and deep red the most significant rates.

Water level time series and sediment grain size model

The environment of ebb-tidal deltas between barrier island systems is characterized by a complex morphology with ebb- and flood-dominated channels, shoals and swash bars connecting the ebb-tidal delta platform to the adjacent island. These morphological features reveal characteristic surface sediment grain-size distributions and are subject to a continuous adaptation to the prevailing hydrodynamic forces. The mixed-energy tidal inlet Otzumer Balje between the East Frisian barrier islands of Langeoog and Spiekeroog in the southern North Sea has been chosen here as a model study area for the identification of relevant hydrodynamic drivers of morphology and sedimentology. We compare the effect of high-energy, wave-dominated storm conditions to mid-term, tide-dominated fair-weather conditions on tidal inlet morphology and sedimentology with a process-based numerical model. A multi-fractional approach with five grain-size fractions between 150 and 450 µm allows for the simulation of corresponding surface sediment grain-size distributions. Net sediment fluxes for distinct conditions are identified: during storm conditions, bed load sediment transport is generally onshore directed on the shallower ebb-tidal delta shoals, whereas fine-grained suspended sediment bypasses the tidal inlet by wave-driven currents. During fair weather the sediment transport mainly focuses on the inlet throat and the marginal flood channels. We show how the observed sediment grain-size distribution and the morphological response at mixed-energy tidal inlets are the result of both wave-dominated less frequent storm conditions and mid-term, tide-dominant fair-weather conditions.