Browsing by Author "Lebreiro, Susana"
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- Alterações recentes nas razões isotópicas de Pb em sedimentos do Canhão Submarino de Cascais, PortugalPublication . Mil-Homens, Mário; Caetano, M.; Lebreiro, Susana; Costa, A. M.; Richter, T.; Cesário, R.; Brito, Pedro Oliveira; De Stigter, H.; Boer, Wim; Trancoso, Maria Ascensão; Mouro, F.Temporal variations in lead concentrations and stable lead isotopic ratios in two sediment cores from the Cascais Canyon shows changes in sources of Pb during the last two centuries. The increase of total Pb contents wIth the evolution of Pb ratio recorded in both cores reveals the Increase of Pb from industrial sources. Nevertheless, this increase is lower in deeper core location (252-32) due to dilution and mixing with uncontaminated marine materials. An isotopic shift towards lower Pb/Pb in the shallower core (252-35) during the 1970s may reflect the increasing number of vehicles in the Lisboa area during that time.
- Atlantic circulation changes across a stadial-interstadial transitionPublication . Waelbroeck, Claire; Tjiputra, Jerry; Guo, Chuncheng; Nisancioglu, Kerim H.; Jansen, Eystein; Riveiros, Natalia Vazquez; Toucanne, Samuel; Eynaud, Frédérique; Rossignol, Linda; Dewilde, Fabien; Marches, Elodie; Lebreiro, Susana; Nave, SilviaABSTRACT: We combine consistently dated benthic carbon isotopic records distributed over the entire Atlantic Ocean with numerical simulations performed by a glacial configuration of the Norwegian Earth System Model with active ocean biogeochemistry in order to interpret the observed Cibicides delta C-13 changes at the stadial-interstadial transition corresponding to the end of Heinrich Stadial 4 (HS4) in terms of ocean circulation and remineralization changes. We show that the marked increase in Cibicides delta C-13 observed at the end of HS4 between similar to 2000 and 4200 m in the Atlantic can be explained by changes in nutrient concentrations as simulated by the model in response to the halting of freshwater input in the high-latitude glacial North Atlantic. Our model results show that this Cibicides delta C-13 signal is associated with changes in the ratio of southern-sourced (SSW) versus northern-sourced (NSW) water masses at the core sites, whereby SSW is replaced by NSW as a consequence of the resumption of deep-water formation in the northern North Atlantic and Nordic Seas after the freshwater input is halted. Our results further suggest that the contribution of ocean circulation changes to this signal increases from similar to 40 % at 2000 m to similar to 80 % at 4000 m. Below similar to 4200 m, the model shows little ocean circulation change but an increase in remineralization across the transition marking the end of HS4. The simulated lower remineralization during stadials compared to during interstadials is particularly pronounced in deep subantarctic sites, in agreement with the decrease in the export production of carbon to the deep Southern Ocean during stadials found in previous studies.
- Deep water properties in the North Atlantic's eastern and western basins during the Mid-Brunhes (330-630 ka)Publication . Voelker, Antje H. L.; Lebreiro, Susana
- Os foraminíferos e a história do afloramento costeiro na margem portuguesa durante os últimos 2000 anosPublication . Salgueiro, Emília; Abrantes, Fátima; Loncaric, Neven; Lebreiro, Susana; Moreno, João; Pflauman, Uwe; Oliveira, P.; Moita, T.; Meggers, Helge
- he Mid-latitude North Atlantic ocean during marine isotope stages 10-14Publication . Voelker, Antje H. L.; Lebreiro, Susana
- Higher frequency of turbidites during abrupt climatic "Heinrich" and "Dansgaard-Oeschger events" - evidence for slope instability on the Portuguese MarginPublication . Lebreiro, Susana; Voelker, Antje H. L.; Alt-Epping, Ulrich; Vizcaino, A.; Jung, S.; Abrantes, Fátima; Gràcia i Mont, Eulàlia
- Iberian Margin deep water dynamics : the role of the Mediterranean outflow waterPublication . Voelker, Antje H. L.; Abrantes, Fátima; Martin, Pamela A.; Lebreiro, Susana
- Influence of diagenetic processes and terrestrial/anthropogenic sources in the REE contents of the Cascais submarine canyon (Iberian western coast)Publication . Mil-Homens, Mário; Brito, Pedro Oliveira; Caetano, M.; Costa, A. M.; Lebreiro, Susana; Trancoso, Maria Ascensão; De Stigter, H.ABSTRACT: Temporal variations of rare earth elements (REE) and their fractionation patterns, major elements, Pb and Hg were determined in two multicores collected at 445 and 2100 m water depth (mwd) in the Cascais submarine canyon (CSC). The PAAS-normalized REE patterns suggest mixing of Tagus estuarine and marine sediments, marked by MREE (Nd‐Dy series) enrichment and by positive Eu-anomaly, with marine sediments. The positive Eu/Eu* implies incorporation of detrital feldspar minerals derived from the estuary. Ce/Ce*, (La/Yb)PAAS and (Nd/Yb)PAAS show differences between the two cores. Core 252-35 from the shallower site is enriched in HREE (Ho‐Lu series) over LREE (La‐Pr series), a pattern also found in the Tagus estuary in the vicinity of an abandoned chemical complex, where the environment is affected by the legacy of massive-sulfide ores processing. There seems to be only limited down-canyon sediment transport to the deeper reaches where core 252-32 was collected. This deeper site shows Ce/Ce* peaks coinciding with low (La/Yb)PAAS values suggesting preferential diagenetic remobilization of LREE relative to HREE. Upcore Pb/Al and Hg/Corg trends observed in both cores indicate dispersion of the anthropogenic component from the estuary through the CSC, which is less obvious from the ∑REE/Al trends particularly in the deeper site. This may suggest the influence of diagenetic processes in the REE signal, associated with relatively low sediment accumulation rates.
- Late Holocene climate variability in the Tagus prodelta, Portugal : benthic foraminiferal perspectivePublication . Bartels-Jónsdóttir, Helga B.; Knudsen, Karen L.; Abrantes, Fátima; Eiríksson, J.; Ferreira, A.; Gil, Isabelle M.; Lebreiro, Susana; Rodrigues, Teresa
- Linkages between North Atlantic surface water circulation patterns and Mediterranean outflow variability on the Western Iberian Margin : examples from marine isotope stages 3 and 12 to 10Publication . Voelker, Antje H. L.; Lebreiro, Susana; Rodrigues, Teresa; Abrantes, Fátima; Martin, Pamela A.
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