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Kim J.-H.,Netherlands Institute for Sea Research | Romero O.E.,Instituto Andaluz Of Ciencias Of La Tierra Csic Ugr | Lohmann G.,Alfred Wegener Institute for Polar and Marine Research | Donner B.,University of Bremen | And 3 more authors.
Earth and Planetary Science Letters | Year: 2012

Millennial-scale Atlantic meridional overturning circulation (AMOC) variability has often been invoked to explain the Dansgaard-Oeschger (DO) events. However, the underlying causes responsible for millennial-scale AMOC variability are still debated. High-resolution U 37 K' and TEX 86 H temperature records for the last 50kyr obtained from the tropical Northeast (NE) Atlantic (core GeoB7926-2, 20°13'N, 18°27'W, 2500m water depth) show that distinctive DO-type subsurface (i.e. below the mixed layer: >20m water depth) temperature oscillations occurred with amplitudes of up to 8°C in the tropical NE Atlantic during Marine Isotope Stage 3 (MIS3). Statistical analyses reveal a positive relationship between the reconstructed substantial cooling of subsurface waters and prominent surface warming over Greenland during DO interstadials. General circulation model (GCM) simulations without external freshwater forcing, the mechanism often invoked in explaining DO events, demonstrate similar anti-phase correlations between AMOC and pronounced NE Atlantic subsurface temperatures under glacial climate conditions. Together with our paleoproxy dataset, this suggests that the vertical temperature structure and associated changes in AMOC were key elements governing DO events during the last glacial. © 2012 Elsevier B.V.


Gonzalez-Munoz M.T.,University of Granada | Martinez-Ruiz F.,Instituto Andaluz Of Ciencias Of La Tierra Csic Ugr | Morcillo F.,University of Granada | Martin-Ramos J.D.,University of Granada | Paytan A.,University of California at Santa Cruz
Geology | Year: 2012

Barite (BaSO4) is found throughout the ocean, yet seawater is undersaturated with respect to barite, and organisms that could account for the abundance of barite have not yet been identified. The mechanism for barite formation in seawater is not fully understood. Here we show that marine bacteria have the ability to precipitate barite through a metabolically mediated biomineralization process. We precipitated barite in laboratory experiments in the presence of several strains of marine bacteria grown on yeast media enriched with barium (Ba); barite did not precipitate under identical conditions in killed-bacteria controls. The crystals develop from amorphous, phosphorous-rich spherical precursors with fibrous internal textures, common in bacterial mineral precipitation. Bacterial mediation of barite precipitation can explain the distribution of barite in the water column and the occurrence of barite crystals in organic-rich sinking aggregates where bacteria are concentrated. This finding has implications for the use of barite and Ba proxies in paleoceanographic research. © 2012 Geological Society of America.


Romero O.E.,Instituto Andaluz Of Ciencias Of La Tierra Csic Ugr | Lopez-Fuerte F.O.,Autonomous University of Baja California Sur
Diatom Research | Year: 2013

Based on light and scanning electron microscopy observations, a detailed description of a new marine alveolate Cocconeis Ehrenberg, C. thalassiana sp. nov., is presented. This large Cocconeis was found in samples collected from a shallow marine coastal lagoon of the Mexican Caribbean, as an epiphyte on the marine seagrass Thalassia testudinum Banks ex König. Among alveolate Cocconeis, the presence of long alveoli for every stria opening into the frustule interior by two long internal apertures of the sternum valve (SV) is a unique character. Other typical frustule features are: bilayered, convex SV thicker than the concave raphe-sternum valve (RSV), the inner face of the SV with hyaline areas between the two apical rows of apertures, the monolayered RSV with a narrow submarginal hyaline area following the valve outline, and the girdle consisting of only two valvocopulae (one for each valve). © 2013 The International Society for Diatom Research.


Romero O.E.,Instituto Andaluz Of Ciencias Of La Tierra Csic Ugr | Jahn R.,Free University of Berlin
Diatom Research | Year: 2013

The nominate varieties of the monoraphid diatoms Cocconeis lineata Ehrenberg and C. euglypta Ehrenberg are typified. Lectotypes of both taxa are preserved at the Ehrenberg Collection, Museum für Naturkunde, Berlin, Germany. The lectotype of C. lineata is a poorly detailed drawing, showing an ovoid valve (or frustule?) with two to three apical lines on each hemivalve. The lectotype of C. euglypta, contained in a mica, shows a unique, broadly elliptical sternum valve with up to five apical striae on each hemivalve, displaying a zigzag pattern. This is roughly consistent with the current concept of C. lineata and C. euglypta and with their usage over the last 160 years. To ensure stabilization of the names and current concepts for these two taxa, culture-based epitypes of C. lineata and C. euglypta are designated. Light and electron microscopy observations, as well as morphometric data from clones for both taxa, are presented and an amended description for each taxon is provided. © 2013 Copyright The International Society for Diatom Research.


Escamilla-Roa E.,Institute Astrofisica Of Andalucia Csic | Escamilla-Roa E.,Instituto Andaluz Of Ciencias Of La Tierra Csic Ugr | Sainz-Diaz C.I.,Instituto Andaluz Of Ciencias Of La Tierra Csic Ugr
Journal of Physical Chemistry C | Year: 2014

The interaction of molecules on the mineral surface is interesting in understanding the development of icy mantles on interstellar and interplanetary dust. The ice grains can freeze and cover the silicate cores, growing an amorphous ice mantle. In the interstellar medium, olivine is a silicate that has been found in many places in dust. Previously we have simulated the interaction between amorphous water ice and forsterite surface. In this work we describe a more realistic situation, by adding ammonia molecules in a model of amorphous dirty ice onto forsterite surface. The NH3 is a part of the volatile components of cometary and interstellar ices. We propose models that describe a mixture of amorphous ice (ammonia-water) and forsterite (100) surfaces (dipolar and nondipolar). Our quantum mechanical calculations show that the ammonia has a similar affinity (30 kcal/mol) to the forsterite surface as that of water (31 kcal/mol). We calculated also the infrared frequencies to characterize the most reactive sites in the chemisorption processes. We observed important frequency shifts related to the position of the main vibrational modes of the NH 3 moieties, which react chemically with the mineral surface. © 2014 American Chemical Society.


Escamilla-Roa E.,Institute Astrofisica Of Andalucia Csic | Hernandez-Laguna A.,Instituto Andaluz Of Ciencias Of La Tierra Csic Ugr | Sainz-Diaz C.I.,Instituto Andaluz Of Ciencias Of La Tierra Csic Ugr
American Mineralogist | Year: 2013

Density functional theory (DFT) calculations were performed to study the crystallographic properties of the cis-vacant form of dioctahedral 2:1 phyllosilicates. Samples with different layer charges are studied; only tetrahedrally charged, only octahedrally charged, or mixed octahedrally/ tetrahedrally charged. The isomorphous cation substitutions were explored in different relative positions with substitutions of octahedral Al3+ by Mg2+ or Fe3+, tetrahedral substitution of Si4+ by Al 3+, and different interlayer cations (IC) (Na+, K +, and Ca2+). X-ray diffraction patterns of cis-vacant and trans-vacant forms of phyllosilicates were simulated and compared. The experimental observation of clustering tendency of Fe3+ and dispersion tendency of Mg2+ in the octahedral sheet is reproduced and explained with reference to the relative energies of the octahedral cation arrangements observing the same tendency that in the trans-vacant forms. These energies are higher than those due to the IC/tetrahedral and IC/octahedral cations relative arrangements. The tetrahedral and octahedral substitutions that generate charged layers tend also to be dispersed. The energy difference between the cis-vacant and trans-vacant polymorphs is smaller than that of cation arrangements.


Rodriguez-Liebana J.A.,Instituto Andaluz Of Ciencias Of La Tierra Csic Ugr | Mingorance M.D.,Instituto Andaluz Of Ciencias Of La Tierra Csic Ugr | Pena A.,Instituto Andaluz Of Ciencias Of La Tierra Csic Ugr
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2013

Recovery of mining areas has been encouraged for social and environmental purposes, mainly through revegetation policies, which usually need addition of exogenous organic residues to increase organic matter in soils. At the same time these remediation strategies must establish soil capability of coping with organic pollutants. Therefore two contrasting mining soils from south of Spain, a very acid soil from Nerva (Riotinto area, SW), and a basic soil from Alquife (SE), were evaluated for their retention ability of two pesticides, thiacloprid and fenarimol, in native soils and soils amended with organic residues. Three residues from urban sewage sludges at three concentrations (2-10%) were considered: a stabilized (SSL) and two composted (CLV and CSL) sludges. Results show that pesticide sorption was increased in both soils after amendment, being higher after addition of SSL and CLV and with a strong association between pesticide sorption and soil organic carbon (OC), as revealed by multivariate analysis. Important soil solution properties, not directly related with pesticide sorption, were electrical conductivity and specific UV absorbance which were able to discriminate between both mining soils. Additionally dissolved OC and the humification index separated SSL, a fresh sludge, from the other two composted amendments. Sorption parameters normalized to the organic carbon content (KOC) for both mining soils were generally lower than others reported, a fact maybe related with high soil metal loading. © 2012 Elsevier B.V.


Solis-Calero C.,University of the Balearic Islands | Ortega-Castro J.,University of the Balearic Islands | Hernandez-Laguna A.,Instituto Andaluz Of Ciencias Of La Tierra Csic Ugr | Munoz F.,University of the Balearic Islands
Journal of Physical Chemistry C | Year: 2013

Mechanisms for Amadori rearrangements from Schiff bases from reactions between d-erythrose and ethylamine, glycine, and phosphatidylethanolamine (PE) based on Dmol3/DFT calculations were realized. For the case of PE, calculations were done under periodic boundary conditions (PBCs), in an amine-phospholipid monolayer model with two molecules of PE by cell. In the three cases, the reaction started with a neutral Schiff base, having in the case of PE surface model a positive charged amine group belonging to the adjacent PE molecule. The catalytic role of PE surface components such as amine and phosphate groups is highlighted. All models included water molecules forming hydrogen bond networks, these networks were involved in the reactions by stabilizing reaction intermediates and transition states and performing as proton-transfer carriers, important in all steps of reactions. In all the studied reactions, they take place in two steps, namely, (1) formation of a 1,2-enaminol intermediate and (2) ketonization to the Amadori rearrangement product, having the last step clear lower values for relative free energies in the case of stationary points of the reaction on PE surface. An alternative pathway in the first step of Amadori rearrangement above PE surface, starting since positive charged Schiff base, was also evaluated, obtaining values for the free energy barrier similar to the step, starting from neutral Schiff base form. On the basis of our results, it is possible then to hypothesize that the cell membrane phospholipid surface environment modifies the kinetic behavior of some biological reactions, enhancing some of them through a catalyst effect. © 2013 American Chemical Society.


Comparison of the stratigraphic distribution of major and trace elements, used as proxies for palaeoproductivity and redox conditions, and benthic foraminifera from Oxfordian shelf deposits of the External Prebetic (Betic Cordillera, South Spain) allows us to recognise two sedimentary cycles, both characterised by initial enhanced productivity and decreasing oxygen availability in the seabottom, and a subsequent decreasing productivity with a recovering in oxygenation during the second half of each cycle. Dysoxic conditions appear to coincide with maximums in marine surface productivity, thus suggesting that oxygen depletion may be linked to greater consumption rather than restricted circulation. The boundary between the two cycles is characterised by low contents of redox-sensitive elements and lower TOC content and Sr/Al, P/Ti, Ca/Al and Ba/Al ratios, indicating well oxygenated sea-bottom, lower productivity and lower organic matter accumulation. The geochemical proxies have also revealed as a valuable tool for interpreting the stratigraphic fluctuations of benthic foraminiferal assemblages, as well as for evaluating the palaeoecology of the main genera. Spirillina is adversely influenced by oxygen depletion independently of food availability. Ophthalmidium presents very good correspondence with palaeoproductivity fluctuations, and tolerated low oxygen levels in the sediment-water interface. Reophax was an opportunist that proliferated after adverse conditions when oxygenation and food availability were limiting factors. The variability in the microhabitat depth inside the sediment of Reophax favoured adaptation to adverse conditions. Lenticulina shows behaviour similar to Reophax. Finally, Ammobaculites shows a low degree of relation with the palaeoproductivity proxies, and is intolerant with respect to low oxygen values in shallow infaunal microhabitats.


Holbourn A.,University of Kiel | Kuhnt W.,University of Kiel | Lyle M.,Texas A&M University | Schneider L.,Texas A&M University | And 2 more authors.
Geology | Year: 2014

During the Middle Miocene, Earth's climate transitioned from a relatively warm phase (Miocene climatic optimum) to a colder mode with reestablishment of permanent ice sheets on Antarctica, thus marking a fundamental step in Cenozoic cooling. Carbon sequestration and atmospheric CO2 drawdown through increased terrestrial and/or marine productivity have been proposed as the main drivers of this fundamental transition. We integrate high-resolution (1-3 k.y.) benthic stable isotope data with X-ray fl uorescence scanner- derived biogenic silica and carbonate accumulation estimates in an exceptionally well preserved sedimentary archive, recovered at Integrated Ocean Drilling Program Site U1338, to reconstruct eastern equatorial Pacifi c productivity variations and to investigate temporal links between high- and low-latitude climate change over the interval 16-13 Ma. Our records show that the climatic optimum (16.8-14.7 Ma) was characterized by high-amplitude climate variations, marked by intense perturbations of the carbon cycle. Episodes of peak warmth at (Southern Hemisphere) insolation maxima coincided with transient shoaling of the carbonate compensation depth and enhanced carbonate dissolution in the deep ocean. A switch to obliquity-paced climate variability after 14.7 Ma concurred with a general improvement in carbonate preservation and the onset of stepwise global cooling, culminating with extensive ice growth over Antarctica ca. 13.8 Ma. We fi nd that two massive increases in opal accumulation ca. 14.0 and ca. 13.8 Ma occurred just before and during the fi nal and most prominent cooling step, supporting the hypothesis that enhanced siliceous productivity in the eastern equatorial Pacifi c contributed to CO2 drawdown. © 2013 Geological Society of America.

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