Electromagnetic, rock magnetic, and geochemical properties of surficial sediments in Eckernförde Bay

Submarine groundwater discharge in coastal settings can massively modify the hydraulic and geochemical conditions of the seafloor. Resulting local anomalies in the morphology and physical properties of surface sediments are usually explored with seismo-acoustic imaging techniques. Controlled source electromagnetic imaging offers an innovative dual approach to seep characterization by its ability to detect pore-water electrical conductivity, hence salinity, as well as sediment magnetic susceptibility, hence preservation or diagenetic alteration of iron oxides. The newly developed electromagnetic (EM) profiler Neridis II successfully realized this concept for a first time with a high-resolution survey of freshwater seeps in Eckernförde Bay (SW Baltic Sea). We demonstrate that EM profiling, complemented and validated by acoustic as well as sample-based rock magnetic and geochemical methods, can create a crisp and revealing fingerprint image of freshwater seepage and related reductive alteration of near-surface sediments. Our findings imply that (1) freshwater penetrates the pore space of Holocene mud sediments by both diffuse and focused advection, (2) pockmarks are marked by focused freshwater seepage, underlying sand highs, reduced mud thickness, higher porosity, fining of grain size, and anoxic conditions, (3) depletion of Fe oxides, especially magnetite, is more pervasive within pockmarks due to higher concentrations of organic and sulfidic reaction partners, and (4) freshwater advection reduces sediment magnetic susceptibility by a combination of pore-water injection (dilution) and magnetite reduction (depletion). The conductivity vs. susceptibility biplot resolves subtle lateral litho- and hydrofacies variations.

A time-slice study in Heinrich Stadial 1 and Mid Holocene sediment cores off northern Senegal

Sediment dynamics in limnic, fluvial and marine environments can be assessed by granulometric and rock-magnetic methodologies. While classical grain-size analysis by sieving or settling mainly bears information on composition and transport, the magnetic mineral assemblages reflect to a larger extent the petrology and weathering conditions in the sediment source areas. Here, we combine both methods to investigate Late Quaternary marine sediments from five cores along a transect across the continental slope off Senegal. This region near the modern summer Intertropical Convergence Zone is particularly sensitive to climate change and receives sediments from several aeolian, fluvial and marine sources. From each of the investigated five GeoB sediment cores (494-2956 m water depth) two time slices were processed which represent contrasting climatic conditions: the arid Heinrich Stadial 1 (~ 15 kyr BP) and the humid Mid Holocene (~ 6 kyr BP). Each sediment sample was split into 16 grain-size fractions ranging from 1.6 to 500 µm. Concentration and grain-size indicative magnetic parameters (susceptibility, SIRM, HIRM, ARM and ARM/IRM) were determined at room temperature for each of these fractions. The joint consideration of whole sediment and magnetic mineral grain-size distributions allows to address several important issues: (i) distinction of two aeolian sediment fractions, one carried by the north-easterly trade winds (40-63 µm) and the other by the overlying easterly Harmattan wind (10-20 µm) as well as a fluvial fraction assigned to the Senegal River (< 10 µm); (ii) identification of three terrigenous sediment source areas: southern Sahara and Sahel dust (low fine-grained magnetite amounts and a comparatively high haematite content), dust from Senegalese coastal dunes (intermediate fine-grained magnetite and haematite contents) and soils from the upper reaches of the Senegal River (high fine-grained magnetite content); (iii) detection of partial diagenetic dissolution of fine magnetite particles as a function of organic input and shore distance; (iv) analysis of magnetic properties of marine carbonates dominating the grain-size fractions 63-500 µm.

El Proceso de precarización en el mercado de trabajo del Gran La Plata. Principales características y tendencias actuales (2003-2004)

El objetivo del presente artículo es identificar las principales características y tendencias del trabajo precario en el Gran La Plata considerando la dinámica económica nacional actual. Tomando como parámetro el empleo pleno, pueden identificarse distintos grados de precariedad según la carencia de los atributos que caracterizan dicha plenitud. Existiría así una gradación de situaciones, con una referencia máxima en el empleo pleno hasta una mínima en el desempleo absoluto. El análisis partió de procesamientos propios de datos brindados por la Encuesta Permanente de Hogares (EPH). Abarca el período comprendido entre el segundo semestre de 2003 y el primero del 2004, debido a que tras la reformulación EPH sólo se dispone a la fecha de información específica de ese período. Los resultados del trabajo realizado dan cuenta de que, en la región, los trabajadores precarios representan el 39,3 de la PEA en el primer semestre de 2004. Si se suma el sector de los desocupados, la Población con Problemas de Empleo supera el 50 y muestra la presión que ejercen sobre el mercado laboral los subocupados demandantes. En el sector estatal, el 16,4 de los empleados están precarizados. Si se suman los beneficiarios de planes de empleo la cifra se eleva al 34. En el sector privado, el empleo precario comprende al 54 de sus trabajadores. Respecto a la evolución de los ingresos aun en los grupos de ocupados que mejoraron su capacidad de consumo entre 2003 y 2004, los niveles de ingresos alcanzados se hallan muy por debajo de los que percibían antes de la devaluación de 2002. Los principales aportes del trabajo consisten en la identificación, cuantificación y caracterización del empleo precario en la región en la etapa post-devaluación, sobre el análisis de la Base Usuaria de la EPH.

Susceptibility, conductivity and porosity along a GEM-SHARK profile

The coastal systems, are often subjected to high anthropogenic pressure, which makes it necessary to develop new techniques to assess the environmental impacts caused by such human activity. This paper presents the first results obtained during the development and implementation of a new equipment of submarine geophysics survey oriented to integrated coastal zone management (ICZM). It is based on the drag of a submarine in contact with the sea-bottom. The submarine is equipped with an electromagnetic sensor which allows the measurement of the magnetic susceptibility and electrical conductivity of the surface sediments continuously and to a depth of sediment of 40 cm. This system, once improved, will allow us to obtain valuable information for monitoring the environmental quality of coastal areas.

El Proceso de precarización en el mercado de trabajo del Gran La Plata. Principales características y tendencias actuales (2003-2004)

El objetivo del presente artículo es identificar las principales características y tendencias del trabajo precario en el Gran La Plata considerando la dinámica económica nacional actual. Tomando como parámetro el empleo pleno, pueden identificarse distintos grados de precariedad según la carencia de los atributos que caracterizan dicha plenitud. Existiría así una gradación de situaciones, con una referencia máxima en el empleo pleno hasta una mínima en el desempleo absoluto. El análisis partió de procesamientos propios de datos brindados por la Encuesta Permanente de Hogares (EPH). Abarca el período comprendido entre el segundo semestre de 2003 y el primero del 2004, debido a que tras la reformulación EPH sólo se dispone a la fecha de información específica de ese período. Los resultados del trabajo realizado dan cuenta de que, en la región, los trabajadores precarios representan el 39,3 de la PEA en el primer semestre de 2004. Si se suma el sector de los desocupados, la Población con Problemas de Empleo supera el 50 y muestra la presión que ejercen sobre el mercado laboral los subocupados demandantes. En el sector estatal, el 16,4 de los empleados están precarizados. Si se suman los beneficiarios de planes de empleo la cifra se eleva al 34. En el sector privado, el empleo precario comprende al 54 de sus trabajadores. Respecto a la evolución de los ingresos aun en los grupos de ocupados que mejoraron su capacidad de consumo entre 2003 y 2004, los niveles de ingresos alcanzados se hallan muy por debajo de los que percibían antes de la devaluación de 2002. Los principales aportes del trabajo consisten en la identificación, cuantificación y caracterización del empleo precario en la región en la etapa post-devaluación, sobre el análisis de la Base Usuaria de la EPH.

Calcareous nannofossil stratigraphy, nannofossil events and carbon isotopic ratios of ODP Leg 183 sites

Cores from Sites 1135, 1136, and 1138 of Ocean Drilling Program Leg 183 to the Kerguelen Plateau (KP) provide the most complete Paleocene and Eocene sections yet recovered from the southern Indian Ocean. These nannofossil-foraminifer oozes and chalks provide an opportunity to study southern high-latitude biostratigraphic and paleoceanographic events, which is the primary subject of this paper. In addition, a stable isotope profile was established across the Cretaceous/Tertiary (K/T) boundary at Site 1138. An apparently complete K/T boundary was recovered at Site 1138 in terms of assemblage succession, isotopic signature, and reworking of older (Cretaceous) nannofossil taxa. There is a significant color change, a negative carbon isotope shift, and nannofossil turnover. The placement of the boundary based on these criteria, however, is not in agreement with the available shipboard paleomagnetic stratigraphy. We await shore-based paleomagnetic study to confirm or deny those preliminary results. The Paleocene nannofossil assemblage is, in general, characteristic of the high latitudes with abundant Chiasmolithus, Prinsius, and Toweius. Placed in context with other Southern Ocean sites, the biogeography of Hornibrookina indicates the presence of some type of water mass boundary over the KP during the earliest Paleocene. This boundary disappeared by the late Paleocene, however, when there was an influx of warm-water discoasters, sphenoliths, and fasciculiths. This not only indicates that during much of the late Paleocene water temperatures were relatively equable, but preliminary floral and stable isotope analyses also indicate that a relatively complete record of the late Paleocene Thermal Maximum event was recovered at Site 1135. It was only at the beginning of the middle Eocene that water temperatures began to decline and the nannofossil assemblage became dominated by cool-water species while discoaster and sphenolith abundances and diversity were dramatically reduced. One new taxonomic combination is proposed, Heliolithus robustus Arney, Ladner, and Wise.

El Proceso de precarización en el mercado de trabajo del Gran La Plata. Principales características y tendencias actuales (2003-2004)

El objetivo del presente artículo es identificar las principales características y tendencias del trabajo precario en el Gran La Plata considerando la dinámica económica nacional actual. Tomando como parámetro el empleo pleno, pueden identificarse distintos grados de precariedad según la carencia de los atributos que caracterizan dicha plenitud. Existiría así una gradación de situaciones, con una referencia máxima en el empleo pleno hasta una mínima en el desempleo absoluto. El análisis partió de procesamientos propios de datos brindados por la Encuesta Permanente de Hogares (EPH). Abarca el período comprendido entre el segundo semestre de 2003 y el primero del 2004, debido a que tras la reformulación EPH sólo se dispone a la fecha de información específica de ese período. Los resultados del trabajo realizado dan cuenta de que, en la región, los trabajadores precarios representan el 39,3 de la PEA en el primer semestre de 2004. Si se suma el sector de los desocupados, la Población con Problemas de Empleo supera el 50 y muestra la presión que ejercen sobre el mercado laboral los subocupados demandantes. En el sector estatal, el 16,4 de los empleados están precarizados. Si se suman los beneficiarios de planes de empleo la cifra se eleva al 34. En el sector privado, el empleo precario comprende al 54 de sus trabajadores. Respecto a la evolución de los ingresos aun en los grupos de ocupados que mejoraron su capacidad de consumo entre 2003 y 2004, los niveles de ingresos alcanzados se hallan muy por debajo de los que percibían antes de la devaluación de 2002. Los principales aportes del trabajo consisten en la identificación, cuantificación y caracterización del empleo precario en la región en la etapa post-devaluación, sobre el análisis de la Base Usuaria de la EPH.

Geochemistry of serpentinized peridotites from ODP Holes 207-1272A and 207-1274A

Despite the key importance of altered oceanic mantle as a repository and carrier of light elements (B, Li, and Be) to depth, its inventory of these elements has hardly been explored and quantified. In order to constrain the systematics and budget of these elements we have studied samples of highly serpentinized (>50%) spinel harzburgite drilled at the Mid-Atlantic Ridge (Fifteen-Twenty Fracture zone, ODP Leg 209, Sites 1272A and 1274A). In-situ analysis by secondary ion mass spectrometry reveals that the B, Li and Be contents of mantle minerals (olivine, orthopyroxene, and clinopyroxene) remain unchanged during serpentinization. B and Li abundances largely correspond to those of unaltered mantle minerals whereas Be is close to the detection limit. The Li contents of clinopyroxene are slightly higher (0.44-2.8 µg/g) compared to unaltered mantle clinopyroxene, and olivine and clinopyroxene show an inverse Li partitioning compared to literature data. These findings along with textural observations and major element composition obtained from microprobe analysis suggest reaction of the peridotites with a mafic silicate melt before serpentinization. Serpentine minerals are enriched in B (most values between 10 and 100 µg/g), depleted in Li (most values below 1 µg/g) compared to the primary phases, with considerable variation within and between samples. Be is at the detection limit. Analysis of whole rock samples by prompt gamma activation shows that serpentinization tends to increase B (10.4-65.0 µg/g), H2O and Cl contents and to lower Li contents (0.07-3.37 µg/g) of peridotites, implying that-contrary to alteration of oceanic crust-B is fractionated from Li and that the B and Li inventory should depend essentially on rock-water ratios. Based on our results and on literature data, we calculate the inventory of B and Li contained in the oceanic lithosphere, and its partitioning between crust and mantle as a function of plate characteristics. We model four cases, an ODP Leg 209-type lithosphere with almost no igneous crust, and a Semail-type lithosphere with a thick igneous crust, both at 1 and 75 Ma, respectively. The results show that the Li contents of the oceanic lithosphere are highly variable (17-307 kg in a column of 1 m * 1 m * thickness of the lithosphere (kg/col)). They are controlled by the primary mantle phases and by altered crust, whereas the B contents (25-904 kg/col) depend entirely on serpentinization. In all cases, large quantities of B reside in the uppermost part of the plate and could hence be easily liberated during slab dehydration. The most prominent input of Li into subduction zones is to be expected from Semail-type lithosphere because most of the Li is stored at shallow levels in the plate. Subducting an ODP Leg 209-type lithosphere would mean only very little Li contribution from the slab. Serpentinized mantle thus plays an important role in B recycling in subduction zones, but it is of lesser importance for Li.

Controls of sediment dynamics on the Galician slope reconstructed from three sediment cores (GeoB11035-1, GeoB130206-1, GeoB13071-1)

Controls of sediment dynamics at the Galician continental slope (NW Iberia) during the past 30 ka were reconstructed from three new gravity cores (GeoB11035-1, 130206-1, 13071-1) based on sedimentological (e.g. sortable silt, IRD), micropalaeontological (e.g. coccoliths), geochemical (AMS 14C, XRF) and geophysical (e.g. magnetic susceptibility) diagnostics. The data are consistent with existing regional knowledge that, during marine isotope stages 3-1, variations in detrital input, marine productivity and sea level were the essential drivers of sediment availability on the slope, whereas deep-water current velocities controlled sediment deposition: (1) the period prior to 30 cal ka BP is characterized by minor but systematic variations in various proxies which can be associated with D-O cycles; (2) between 30 and 18 cal ka BP, high detrital input and steady slope-parallel currents led to constant sedimentation; (3) from the LGM until 10 cal ka BP, the shelf-transgressive sea-level rise increased the detrital particle flux; sedimentation was influenced by significantly enhanced deep-water circulation during the Bølling/Allerød, and subsequent slowing during the Younger Dryas; (4) an abrupt and lasting change to hemipelagic sedimentation at ca. 10 cal ka BP was probably due to Holocene warming and decelerated transgression; (5) after 5 cal ka BP, additional input of detrital material to the slope is plausibly linked to the evolution of fine-grained depocentres on the Galician shelf, this being the first report of this close shelf-slope sedimentary linkage off NW Iberia. Furthermore, there is novel evidence of the nowadays strong outer shelf Iberian Poleward Current becoming established at about 15.5 cal ka BP. The data also demonstrate that small-scale morphologic features and local pathways of sediment export from the neighbouring shelf play an important role for sediment distribution on the NW Iberian slope, including a hitherto unknown sediment conduit off the Ría de Arousa. By implication, the impact of local morphology on along- and down-slope sediment dynamics is more complex than commonly considered, and deserves future attention.