Contrasting variability in foraminiferal and organic paleotemperature proxies in sedimenting particles of the Mozambique Channel (SW Indian Ocean)

Accurate sea surface temperature (SST) proxies are important for understanding past ocean and climate systems. Here, we examine material collected from a deep-moored sediment trap in the Mozambique Channel (SW Indian Ocean) to constrain and compare both inorganic (δ¹⁸O, Mg/Ca) and organic (, TEX₈₆) temperature proxies in a highly dynamic oceanographic setting for application in paleoceanography. High-resolution time-series current velocity data from long-term moorings (2003 - present) deployed across the Mozambique Channel reveal the periodic migration of four to six meso-scale eddies through the channel per year. These meso-scale eddies strongly influence water mass properties including temperature and salinity. Despite the dynamic oceanographic setting, fluxes of the surface-dwelling planktonic foraminifera Globigerinoidesruber and Globigerinoides trilobus follow a seasonal pattern. Temperatures reconstructed from G. ruber and G. trilobus δ¹⁸O and Mg/Ca closely mirror seasonal SST variability and their flux-weighted annual mean SSTs of 28.1 °C and 27.3 °C are in close agreement with annual mean satellite SST (27.6 °C). The sub-surface dwelling foraminifera Neogloboquadrina dutertrei and Globigerinoides scitula recorded high-frequency temperature variations that, on average, reflect conditions at water depths of 50-70 m and 200-250 m, respectively. Concentrations and fluxes of organic compounds (alkenones and crenarchaeol) display no or only moderate seasonality but flux weighted means of the associated temperature signatures, , and of 28.3 °C and 28.1 °C, respectively, also closely reflect mean annual SST. We analyzed all time-series data using multiple statistical approaches including cross-correlation and spectral analysis. Eddy variability was clearly expressed in the statistical analysis of physical oceanographic parameters (current velocity and sub-surface temperature) and revealed a frequency of four to six cycles per year. In contrast, statistical analysis of proxy data from the sediment trap did not reveal a significant coupling between eddy migration and organic compound fluxes or reconstructed temperatures. This is likely a result of the relatively low resolution (21 days) and short (2.5 years) duration of the time series, which is close to the detection limit of the eddy frequency.     

Direct terrestrial-marine correlation demonstrates surprisingly late onset of the last interglacial in central Europe

An interdisciplinary study of a small sedimentary basin at Neumark Nord 2 (NN2), Germany, has yielded a high-resolution record of the palaeomagnetic Blake Event, which we are able to place at the early part of the last interglacial pollen sequence documented from the same section. We use this data to calculate the duration of this stratigraphically important event at 3400 ± 350 yr. More importantly, the Neumark Nord 2 data enables precise terrestrial-marine correlation for the Eemian stage in central Europe. This shows a remarkably large time lag of ca. 5000 yr between the MIS 5e ‘peak’ in the marine record and the start of the last interglacial in this region.     

Implementation of high-order particle-tracking schemes in a water column model

Stochastic differential equations (SDEs) offer an attractively simple solution to complex transport-controlled problems, and have a wide range of physical, chemical, and biological applications, which are dominated by stochastic processes, such as diffusion. As for deterministic ordinary differential equations (ODEs), various numerical scheme exist for solving SDEs. In this paper various particle-tracking schemes are presented and tested for accuracy and efficiency (time vs. accuracy). To test the schemes, the particle tracking algorithms are implemented into a community wide used 1D water column model. Modelling individual particles allows a straightforward physical interpretation of the involved processes. Further, this approach is strictly mass conserving and does not suffer from the numerical diffusion that plagues grid-based methods. Moreover, the Lagrangian framework allows to assign properties to the individual particles, that can vary spatially and temporally. The movement of the particles is described by a stochastic differential equation, which is consistent with the advection–diffusion equation. Here, the concentration profile is represented by a set of independent moving particles, which are advected according to the velocity field, while the diffusive displacements of the particles are sampled from a random distribution, which is related to the eddy diffusivity field.The paper will show that especially the 2nd order schemes are accurate and highly efficient. At the same level of accuracy, the 2nd order scheme can be significantly faster than the 1st order counterpart. This gain in efficiency can be spent on a higher resolution for more accurate solutions at a lower cost.     

Block and boulder accumulations along the coastline between Fins and Sur (Sultanate of Oman): tsunamigenic remains?

The rocky coastline of the Sultanate of Oman between Fins and Sur is decorated by a number of large blocks and boulder accumulations forming ramparts. The blocks occur as individual rocks of up to 40 tons, as imbricated sets and as ??boulder trains.?? Landward, the deposits change into a sand/boulder mixture and distal into sands. The coast is made up of Tertiary folded limestones and beach rock of Quaternary age, both also constitute the megaclasts. The transport distance from the fractured seaward platform of 6?C10?m above mean sea level varies between 20?m and more than 50?m. We found individual blocks of recent corals and overturned blocks with attached oysters and rock pools. Terrestrial laser scanning was used to analyze geomorphologic features as well as for volumetric estimates of the block weights. Tropical cyclones such as Gonu in 2007 or Phet in 2010 are known to have affected Oman??s coastline in the past. The coastal changes during recent cyclones were minor; therefore, we interpret the block deposits as tsunamigenic. However, this interpretation is not unambiguous. The most likely source area for a tsunami is seen in the Makran Subduction Zone situated in the northern Indian Ocean. Here, at least 4?C5 tsunamigenic earthquakes are documented.     

UHP metamorphism recorded by kyanite-bearing eclogite in the Seve Nappe Complex of northern Jämtland,Swedish Caledonides

The first evidence for ultrahigh-pressure (UHP) metamorphism in the Seve Nappe Complex of the Scandinavian Caledonides is recorded by kyanite-bearing eclogite, found in a basic dyke within a garnet peridotite body exposed close to the lake Friningen in northern Jämtland (central Sweden). UHP metamorphic conditions of ~ 3 GPa and 800 °C, within the stability field of coesite, are constrained from geothermobarometry and calculated phase equilibria for the peak-pressure assemblage garnet + omphacite + kyanite + phengite. A prograde metamorphic evolution from a lower P–T (1.5–1.7 GPa and 700–750 °C) stage during subduction is inferred from inclusions of pargasitic amphibole, zoisite and kyanite in garnet cores. The post-UHP evolution is constrained from breakdown textures, such as exsolutions of kyanite and silica from the Ca-Eskola clinopyroxene. Near isothermal decompression of eclogite to lower crustal levels (~ 0.8–1.0 GPa ) led to formation of sapphirine, spinel, orthopyroxene and diopside at granulite facies conditions. Published age data suggest a Late Ordovician (460–445 Ma) age of the UHP metamorphism, interpreted to be related to subduction of Baltoscandian continental margin underneath an outboard terrane, possibly outermost Laurentia, during the final stages of closure of the Iapetus Ocean. The UHP rocks were emplaced from the hinterland collision zone during Scandian thrusting of the nappes onto the Baltoscandian foreland basin and platform. The record of P–T conditions and geochonological data from UHP rocks occurring within the allochthonous units of the Scandinavian Caledonides indicate that Ordovician UHP events may have affected much wider parts of the orogen than previously thought, involving deep subduction of the continental crust prior to final Scandian collision between Baltica and Laurentia.     

Ion transport in porous media: derivation of the macroscopic equations using upscaling and properties of the effective coefficients

In this work, we undertake a numerical study of the effective coefficients arising in the upscaling of a system of partial differential equations describing transport of a dilute N-component electrolyte in a Newtonian solvent through a rigid porous medium. The motion is governed by a small static electric field and a small hydrodynamic force, around a nonlinear Poisson–Boltzmann equilibrium with given surface charges of arbitrary size. This approach allows us to calculate the linear response regime in a way initially proposed by O’Brien. The O’Brien linearization requires a fast and accurate solution of the underlying Poisson–Boltzmann equation. We present an analysis of it, with the discussion of the boundary layer appearing as the Debye–Hückel parameter becomes large. Next, we briefly discuss the corresponding two-scale asymptotic expansion and reduce the obtained two-scale equations to a coarse scale model. Our previous rigorous study proves that the homogenized coefficients satisfy Onsager properties, namely they are symmetric positive definite tensors. We illustrate with numerical simulations several characteristic situations and discuss the behavior of the effective coefficients when the Debye–Hückel parameter is large. Simulated qualitative behavior differs significantly from the situation when the surface potential is given (instead of the surface charges). In particular, we observe the Donnan effect (exclusion of co-ions for small pores).     

Effect of ENSO events on sediment production in a large coastal basin in northern Peru

Although the importance of ENSO on hydrological anomalies has been recognized, variations in sediment fluxes caused by these extreme events are poorly documented. The effect of ENSO is not limited to changes in sediment mobilization. Since ENSO events can affect terrestrial ecosystems, they may have important effects on sediment production and transport in river basins over time spans that are longer than the duration of the event itself. The Catamayo‐Chira basin is an interesting casestudy for investigating these geomorphic implications. The objectives were: (i) to study the effect of ENSO on stream flow and sediment yields in the basin, (ii) to investigate if ENSO events affect sediment yields in the post‐ENSO period and (iii) to understand which factors control the ENSO and post‐ENSO basin response. During strong negative ENSO periods, mean annual stream flow discharge at the inlet of the Poechos reservoir in the lower basin was 5.4 times higher than normal annual discharges, while average sediment fluxes exceeded those of normal years by a factor of about 11. In two heavily affected periods, 45.9% of the total sediment yield in the 29 years observation period was generated. Sediment fluxes in the post‐ENSO period are lower than expected, which proves post‐ENSO event dynamics are significantly different from pre‐event dynamics. Our analysis indicates the increase of vegetation growth in the lower basin is not the main reason explaining considerable sediment flux decrease in post‐ENSO periods. During strong ENSO events, sediment in alluvial stores in the lower part of the basin is removed due to enlarging and deepening of channels. In post‐ENSO periods, normal discharges and persisting sediment supplies from the middle/upper basin lead to river aggradation and storage of large amounts of sediment in alluvial plains. The decrease in sediment export will last for several years until the equilibrium is re‐established. Copyright © 2011 John Wiley & Sons, Ltd.     

Universe models with negative bulk viscosity

The concept of negative temperatures has occasionally been used in connection with quantum systems. A recent example of this sort is reported in the paper of S. Braun et al. (Science 339:52, 2013), where an attractively interacting ensemble of ultracold atoms is investigated experimentally and found to correspond to a negative-temperature system since the entropy decreases with increasing energy at the high end of the energy spectrum. As the authors suggest, it would be of interest to investigate whether a suitable generalization of standard cosmological theory could be helpful, in order to elucidate the observed accelerated expansion of the universe usually explained in terms of a positive tensile stress (negative pressure). In the present note we take up this basic idea and investigate a generalization of the standard viscous cosmological theory, not by admitting negative temperatures but instead by letting the bulk viscosity take negative values. Evidently, such an approach breaks standard thermodynamics, but may actually be regarded to lead to the same kind of bizarre consequences as the standard approach of admitting the equation-of-state parameter w to be less than ?1. In universe models dominated by negative viscosity we find that the fluid’s entropy decreases with time, as one would expect. Moreover, we find that the fluid transition from the quintessence region into the phantom region (thus passing the phantom divide w=?1) can actually be reversed. Also in generalizations of the ΛCDM-universe models with a fluid having negative bulk viscosity we find that the viscosity decreases the expansion of the universe.     

Assessment of the ecological quality status of soft-bottoms in Reunion Island (tropical Southwest Indian Ocean) using AZTI marine biotic indices

The ability of the two synthetic marine biotic indices, AMBI and M-AMBI, to account for changes in the ecological quality of coastal soft bottoms of Reunion Island according to disturbances was assessed from macrobenthic samples collected in five sectors between 1994 and 2004. Samples were collected under non-perturbed conditions and at two sites subjected to heavy organic enrichment. Both indices are based on a classification of macrofauna into ecological groups (EG), and their transfer to tropical waters required some adaptations. These indices proved efficient in detecting a degradation of habitat quality. Their use resulted in the classification of all sites sampled between 1996 and 1998 as "good" or "high". M-AMBI nevertheless tended to result in the attribution of a slightly worse ecological quality status than AMBI. Together with an update of the EG species list for the Indian Ocean area, our results support the extension of both indices for the assessment of tropical soft bottoms.