Browsing by Author "Hernandez-Molina, Francisco J."
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- Climate changes in south western Iberia and Mediterranean Outflow variations during two contrasting cycles of the last 1 Myrs: MIS 31-MIS 30 and MIS 12-MIS 11Publication . Goni, Maria F. Sanchez; Llave, E.; Oliveira, D.; Naughton, F.; Desprat, S.; Ducassou, E.; Hodell, D. A.; Hernandez-Molina, Francisco J.Grain size analysis and physical properties of Sites U1388, U1389 and TJ1390 collected in the Contourite Depositional System of the Gulf of Cadiz during the Integrated Ocean Drilling Program (IODP) Expedition 339 "Mediterranean Outflow" reveal relative changes in bottom current strength, a tracer of the dynamics of the Mediterranean Outflow Water (MOW), before and after the Middle Pleistocene Transition (MPT). The comparison of MOW behavior with climate changes identified by the pollen analysis and 8180 benthic foraminifera measurements of Site U1385, the Shackleton Site, collected in the south western Iberian margin shows that the interval MIS 31-MIS 30,similar to 1.1-1.05 million years ago (Ma), before the MPT, was marked by wetter climate and weaker bottom current than the interval MIS 12-MIS 11 (0.47-0.39 Ma), after the MPT. Similarly, the increase in fine particles from these glacials to interglacials and in coarse fraction from interglacials to glacials was coeval with forest and semi-desert expansions, respectively, indicating the lowering/enhancement of MOW strength during periods of regional increase/decrease of moisture. While these findings may not necessarily apply to all glacial/interglacial cycles, they nonetheless serve as excellent supporting examples of the hypothesis that aridification can serve as a good tracer for MOW intensity. The strongest regional aridity during MIS 12 coincides with a remarkable increase of coarse grain size deposition and distribution that we interpret as a maximum in MOW strength. This MOW intensification may have pre-conditioned the North Atlantic by increasing salinity, thereby triggering the strong resumption of the Meridional Overturning Circulation that could contribute to the great warmth that characterizes the MIS 11c super-interglacial. (C) 2015 Elsevier B.V. All rights reserved.
- Quaternary chronostratigraphic framework and sedimentary processes for the Gulf of Cadiz and Portuguese Contourite Depositional Systems derived from Natural Gamma Ray recordsPublication . Lofi, Johanna; Luise Voelker, Antje Helga; Ducassou, Emmanuelle; Hernandez-Molina, Francisco J.; Sierro, Francisco J.; Bahr, Andre; Galvani, Aurelie; Lourens, Lucas J.; Pardo-Iguzquiza, Eulogio; Pezard, Philippe; Rodriguez-Tovar, Francisco Javier; Williams, TrevorThe Contourite Depositional Systems (CDS) in the Gulf of Cadiz and on the West Iberian margin preserve a unique archive of Mediterranean Outflow Water (MOW) variability over the past 53 Ma. These CDS have been recently drilled in several places during the IODP Expedition 339. These drill sites now offer a new window to the internal Pliocene and Quaternary architecture of the CDS. In this study, we use downhole and core Gamma Ray (GR) data acquired from 5 sites drilled in the CDS along the middle slope and 1 site drilled in the deeper setting of the lower slope, out of the MOW path. The GR data primarily tracks the clay content in the sediment and is the expression of sediment supply and, for sites drilled in the CDS, of the bottom current processes. Both appear astronomically controlled as shown by spectral analysis performed on the GR data. Results also reveal that the GR log patterns correlate well across the sites over the last 1.4 My. Several GR horizons corresponding to drops in GR values were identified, most of which fit with coarse-grained deposits observed in cores and interpreted as contourite beds. The GR horizons are interpreted as isochronous horizons, providing a regional scale chronostratigraphic framework for the CDS depositional records with an accuracy of similar to 20 ky. We further assess the spatial and temporal variability of the CDS hiatuses at the regional scale. (C) 2015 Elsevier B.V. All rights reserved.
- The mediterranean overflow in the Gulf of Cadiz: a rugged journeyPublication . Sanchez-Leal, Ricardo F.; Jesus Bellanco, Maria; Miguel Fernandez-Salas, Luis; Garcia-Lafuente, Jesus; Gasser-Rubinat, Marc; Gonzalez-Pola, Cesar; Hernandez-Molina, Francisco J.; Pelegri, Josep L.; Peliz, Alvaro; Relvas, Paulo; Roque, David; Ruiz-Villarreal, Manuel; Sammartino, Simone; Carlos Sanchez-Garrido, JoseThe pathways and transformations of dense water overflows, which depend on small-scale interactions between flow dynamics and erosional-depositional processes, are a central piece in the ocean's large-scale circulation. A novel, high-resolution current and hydrographic data set highlights the intricate pathway travelled by the saline Mediterranean Overflow as it enters the Atlantic. Interaction with the topography constraints its spreading. Over the initial 200 km west of the Gibraltar gateway, distinct channels separate the initial gravity current into several plunging branches depth-sorted by density. Shallow branches follow the upper slope and eventually detach as buoyant plumes. Deeper branches occupy mid slope channels and coalesce upon reaching a diapiric ridge. A still deeper branch, guided by a lower channel wall marked by transverse furrows, experiences small-scale overflows which travel downslope to settle at mid-depths. The Mediterranean salt flux into the Atlantic has implications for the buoyancy balance in the North Atlantic. Observations on how this flux enters at different depth levels are key to accurately measuring and understanding the role of Mediterranean Outflow in future climate scenarios.