Historical trends in Hg, Pb and Zn sedimentation in the central shelf area of Portugal

Temporal records of excess 210Pb, and the determination of major (Al and Ca) and trace elements (Zn, Cr, Ni, Pb, Cu and Hg) in two sediment box-cores, collected in the central area of the Portuguese shelf of North of the Nazaré canyon (offshore from the Lis River), allow evaluation of the deposition of various chemical elements normally associated with anthropogenic activities. In order to compensate for the natural sediment variability, heavy metal contents were normalised to Al. Temporal variations of Hg, Pb and Zn (Al-normalised) show an increasing trend since the beginning of the 1920’s, recording the development of industrial activities. Enrichment factors (EF) were calculated to estimate the level of contamination in these sediments. Mercury is the element with the highest average EF values (EF = 3), followed by Pb (EF = 1.5) and Zn (EF = 1.2). The results indicate that since 1991 64% of total Hg, 44% of total Pb and 24% of total Zn are derived from anthropogenic sources. The average anthropogenic fluxes of Hg, Pb and Zn (0.008, 3, 6 μg cm-2yr-1, respectively) for the last 40 years in a ca. 400 km2 deposition area represent a total accumulation of approximately 30, 12000 and 24400 kg per year of Hg, Pb and Zn, respectively. These results indicate that despite the high-energy conditions and the generally sandy nature of the Portuguese shelf sediments, it is possible to identify significant anthropogenic enrichments in some areas of sediment accumulation. These contaminants are not necessarily related to immediate sources but may instead indicate atmospheric and or marine transport from more distant sources.Los registros temporales del 210Pb en exceso, elementos mayores (Al y Ca), y elementos traza (Zn, Cr, Ni, Pb, Cu y Hg) de 2 box-cores procedentes de la plataforma continental al norte del cañón de Nazaré han permitido caracterizar depósitos de elementos químicos asociados a actividades antropogénicas. Los contenidos de metales pesados han sido normalizados con Al para compensar la variabilidad natural. La variación temporal de Hg, Pb y Zn, normalizados con Al, muestran un incremento desde el inicio de la década de 1920 reflejando el desarrollo de la actividad humana. El nivel de contaminación de los sedimentos ha sido calculado en base a Factores de Enriquecimiento (EF). Los valores medios más altos de FE son de mercurio (EF = 3), seguidos de plomo (EF = 1.5) y zinc (EF = 1.2). Los resultados obtenidos indican que a partir de 1991 el 64% del total de Hg, 44% del total de Pb y 24% del total de Zn son de origen antropogénico. La media para los últimos 40 años de los flujos de Hg, Pb y Zn (0.008, 3, 6 μg cm-2 año-1, respectivamente), en un área de deposición de aproximadamente 400 km2, se traduce en la acumulación de 30, 12000 y 24400 kg por año de Hg, Pb y Zn. Sin embargo, a pesar de las condiciones de alta energía y el carácter arenoso de los sedimentos de la plataforma continental portuguesa, se pueden identificar importantes enriquecimientos antropogénicos en depocentros de sedimentos, no relacionados con fuentes antropogénicas próximas pero que pueden indicar transporte marino y atmosférico de fuentes de contaminación distantes

The record of a high-energy event in a mud entrapment on the inner shelf off the Guadiana river

Recent environmental changes associated with high-energy events and human impacts were investigated in a mud entrapment confined in the paleo-Guadiana incised valley. Those changes were recorded in a gravity core during the last 2500 years. An erosional event seems to have occurred at ca. 500 cal yr BP but it is not clear how much sediment was removed. This event was followed by an increase in river discharges until ca. 465 cal yr BP while the benthic foraminiferal faunas were dominated by species associated with shallow-water sandy sediments. Upward, sedimentological and benthic foraminiferal variations indicated environmental changes, promoted by variable sediment supplies to the shelf.info:eu-repo/semantics/publishedVersio

New constraints on the Pb and Nd isotopic evolution of NE Atlantic water masses

Time series of lead (Pb) and neodymium (Nd) isotope compositions were measured on three ferromanganese crusts recording the evolution of NE Atlantic water masses over the past 15 Ma. The crusts are distributed along a depth profile (∼700–4600 m) comprising the present-day depths of Mediterranean Outflow Water and North East Atlantic Deep Water. A pronounced increase of the 206Pb/204Pb in the two deeper crusts starting at ∼4 Ma and a decrease in 143Nd/144Nd in all three crusts took place between ∼6–4 Ma and the present. These patterns are similar to isotope time series in the western North Atlantic basin and are consistent with efficient mixing between the two basins. However, the changes occurred 1–3 Ma earlier in the eastern basin indicating that the northeastern Atlantic led the major change in Pb and Nd isotope composition, probably due to a direct supply of Labrador Seawater via a northern route. The Pb isotope evolution during the Pliocene-Pleistocene can generally be explained by mixing between two end-members corresponding to Mediterranean Outflow Water and North East Atlantic Deep Water, but external sources such as Saharan dust are likely to have played a role as well. The Pb isotope composition of the shallowest crust that grew within the present-day Mediterranean Outflow Water does not show significant Pb isotope changes indicating that it was controlled by the same Pb sources throughout the past 15 Ma

Cuantifícación de los aportes sedimentarios neogenos y cuaternarios a la Llanura Abisal de Madeira

Cruises Tydeman 80, Tyro 82 and ODP Leg 157 provided 7000 km of single-channel seismic profiles and three d rillin g sites w ith a to ta l o f 11 58 m o f core in the Madeira Abyssal Plain. Merging o f the lithological records and conventional logs into the seismic units and subunits defined, allowed their 3D mapping and calculation of both the sediment volume and approximate accumulation rates in the Great Meteor East area (central subbasin of the Madeira Abyssal Plain) since the Middle Miocene. The total volum e is arou nd 1 9 3 2 7 km3and the accum ulation rates are 2 2 .6 6 m /m y r fo r the U p p er-M id d le Miocene, 68.78 m/myr for the Lower Pliocene, 49.23 m/myr for the Upper Pliocene and 54.93 m/myr for the QuaternaryDurante las campañas Tydeman 80, Tyro 82 y el "leg" 157 del Ocean Drilling Program (ODP), se obtuvieron 7000 km de sísmica de monocanal y tres sondeos de unos 350 m cada uno en la zona central de la Llanura Abisal de Madeira. A partir de los perfiles sísmicos se han diferenciado dos grandes unidades sísmicas y cuatro subunidades. La cartografía 3D de las mismas, junto con el estudio de las columnas litoestratigráficas y las diagrafías de los sondeos, ha permitido calcular el volumen de sedimento depositado en la cuenca desde el Mioceno medio hasta la actualidad. La correlación de las unidades sísmicas con la litoestratigrafía de los sondeos ha posibilitado el cálculo de las tasas de acumulación aproximadas para dicha cuenca. El volumen total depositado desde el Mioceno medio hasta la actualidad es de 19327 km3 y las tasas de acumulación son de 22.66 m/Ma para el Mioceno superior y medio, 68.78 m/Ma para el Plioceno inferior, 49.23 m/Ma para el Plioceno superior y 54.93 m/Ma para el Pleistocen

Sediment instability on the Portuguese continental margin under abrupt glacial climate changes (last 60 kyr)

13 pages, 6 figures, 1 table, appendix supplementary informationIt is well established that orbital scale sea-level changes generated larger transport of sediments into the deep-sea during the last glacial maximum than the Holocene. However, the response of sedimentary processes to abrupt millennial-scale climate variability is rather unknown. Frequency of distal turbidites and amounts of advected detrital carbonate are estimated off the Lisbon-Setúbal canyons (core MD03-2698, at 4602 mwd), within a chronostratigraphy based on radiometric ages, oxygen isotopes and paleomagnetic key global anomalies. We found that: 1) higher frequency of turbidites concurred with Northern Hemisphere coldest temperatures (Greenland Stadials [GS], including Heinrich [H] events). But more than that, an escalating frequency of turbidites starts with the onset of global sea-level rising (and warming in Antarctica) and culminates during H events, at the time when rising is still in its early-mid stage, and the Atlantic Meridional Overturning Circulation (AMOC) is re-starting. This short time span coincides with maximum gradients of ocean surface and bottom temperatures between GS and Antarctic warmings (Antarctic Isotope Maximum; AIM 17, 14, 12, 8, 4, 2) and rapid sea-level rises. 2) Trigger of turbidity currents is not the only sedimentary process responding to millennial variability; land-detrital carbonate (with a very negative bulk δ18O signature) enters the deep-sea by density-driven slope lateral advection, accordingly during GS. 3) Possible mechanisms to create slope instability on the Portuguese continental margin are sea-level variations as small as 20 m, and slope friction by rapid deep and intermediate re-accommodation of water masses circulation. 4) Common forcing mechanisms appear to drive slope instability at both millennial and orbital scales. © 2009The Commission Human Potential Programme Access to Research Infrastructures Activity (ARI) (through the Climate Variability and Abrupt Climate Changes off Portugal application) to support coring of Calypso MD03-2698 during the PICABIA cruise (F.G.A.); the use of XRF Core-Scanner from the University of Bremen (Ocean Drilling Program Repository) also through an ARI Paleostudies proposal (S.M.L.). The funding from ESF-Euromargins projects: SEDPORT – Sedimentation Processes on the Portuguese Margin: The Role of Continental Climate, Ocean Circulation, Sealevel, and Neo-tectonics (Fundaçâo para a Ciência e Tecnologia PDCTM/40017/2003) and SWIM (01-LEG-EMA09F and REN2002-11234E-MAR); and GRICES-CSIC (Cooperaçâo Científica e Técnica Luso-Espanhola). Funding support was also provided by LNEG. A.H.V. acknowledges the postdoctoral fellowship (SFRH/BPD/21691/2005)Peer Reviewe

High-resolution imaging of active structures offshore on the Southwest Iberian Margin: implications for paleoseismic studies

1 pageThe Southwest Iberian Margin is affected by large earthquakes in Western Europe as it hosts the boundary beween Eurasian and African plates. We identified several active faults which are potential sources of large magnitude earthquakes and tsunamis (Mw > 6). We have acquiered giant piston cores and TOBY mosaics, which allow us to investigate on the past activity of the faults, which has implications for seismic hazard assessment on the southwest Iberian MarginPeer reviewe

CT-images of contourite cores: An onset to processing and data interpretation

2nd Deep-Water Circulation Congress: The Contourite Log-book, 10-12 September 2014, Ghent, BelgiumPeer Reviewe

A Middle Pleistocene Northeast Atlantic coccolithophore record: Paleoclimatology and paleoproductivity aspects

Changes in paleoclimate and paleoproductivity patterns have been identified by analysing, in conjunction with other available proxy data, the coccolithophore assemblages from core MD03-2699, located in the Portuguese margin in the time interval from the Marine Isotope Stage (MIS) 13/14 boundary to MIS 9 (535 to 300 ka). During the Mid-Brunhes event, the assemblages associated with the eccentricity minima are characterised by higher nannoplankton accumulation rate (NAR) values and by the blooming of the opportunistic genus Gephyrocapsa. Changes in coccolithophore abundance are also related to glacial-interglacial cycles. Higher NAR and numbers of coccoliths/g mainly occurred during the interglacial periods, while these values decreased during the glacial periods. Superimposed on the glacial/interglacial cycles, climatic and paleoceanographic variability has been observed on precessional timescales. The structure of the assemblages highlights the prevailing long-term influence of the Portugal (PC) and Iberian Poleward (IPC) Currents, following half and full precession harmonics, related to the migration of the Azores High (AH) Pressure System. Small Gephyrocapsa and Coccolithus pelagicus braarudii are regarded as good indicators for periods of prevailing PC influence. Gephyrocapsa caribbeanica, Syracosphaera spp., Rhabdosphaera spp. and Umbilicosphaera sibogae denote periods of IPC influence. Our data also highlights the increased percentages of Coccolithus pelagicus pelagicus during the occurrence of episodes of very cold and low salinity surface water, probably related to abrupt climatic events and millennial-scale oscillations of the AH/Icelandic Low (IL) System. (c) 2012 Elsevier B.V. All rights reserved

Medical CT-images of contourite cores: An onset to processing and data interpretation

2nd Deep-Water Circulation Congress: The Contourite Log-book, 10-12 September 2014, Ghent, Belgium.-- 2 pages, 2 figuresAlthough CT scans are being used in scientific research since the late 1970's, they are only recently being used in contourite research. Mostly a vertical slice through or an X-radiograph of the sediment core is shown, not displaying the three-dimensional variations within the sediment core. These can be very important however. This research attempts to discern components within the entire core based on their radio-density values, using the 3D analysis sofware >Morpho+>, developed by the UGCT (Ghent University Centre for X-Ray Tomography). The abundance of each component is desplayed throughout the sediment core and will be compared to MSCL, XRF and grainsize data in order to derive what information is held within CT scans. By scanning muddy, silty and sandy contourite cores (both compacted and not), a non-exhaustive reference set of CT scans for contourite cores will be createdThe authors acknowledge FWO grant >Contourite-3D> for financing this projectPeer Reviewe