Browsing by Author "B. Li"

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IODP Expedition 339 in the Gulf of Cadiz and off West Iberia: Decoding the environmental significance of the Mediterranean outflow water and its global influence
(2013) F.J. Hernández-Molina; D. Stow; C. Alvarez-Zarikian; G. Acton; A. Bahr; B. Balestra; E. Ducassou; R. Flood; J.-A. Flores; S. Furota; P. Grunert; D. Hodell; F. Jimenez-Espejo; J.K. Kim; L. Krissek; J. Kuroda; B. Li; E. Llave; J. Lofi; L. Lourens; M. Miller; F. Nanayama; Naohisa Nishida; C. Richter; C. Roque; H. Pereira; M. Goñi Fernanda Sanchez; F.J. Sierro; A.D. Singh; C. Sloss; Y. Takashimizu; A. Tzanova; A. Voelker; T. Williams; C. Xuan
IODP Expedition 339 drilled five sites in the Gulf of Cadiz and two off the west Iberian margin (November 2011 to January 2012), and recovered 5.5 km of sediment cores with an average recovery of 86.4 %. The Gulf of Cadiz was targeted for drilling as a key location for the investigation of Mediterranean outflow water (MOW) through the Gibraltar Gateway and its influence on global circulation and climate. It is also a prime area for understanding the effects of tectonic activity on evolution of the Gibraltar Gateway and on margin sedimentation. We penetrated into the Miocene at two different sites and established a strong signal of MOW in the sedimentary record of the Gulf of Cadiz, following the opening of the Gibraltar Gateway. Preliminary results show the initiation of contourite deposition at 4.2-4.5 Ma, although subsequent research will establish whether this dates the onset of MOW. The Pliocene succession, penetrated at four sites, shows low bottom current activity linked with a weak MOW. Significant widespread unconformities, present in all sites but with hiatuses of variable duration, are interpreted as a signal of intensified MOW, coupled with flow confinement. The Quaternary succession shows a much more pronounced phase of contourite drift development, with two periods of MOW intensification separated by a widespread unconformity. Following this, the final phase of drift evolution established the contourite depositional system (CDS) architecture we see today. There is a significant climate control on this evolution of MOW and bottom-current activity. However, from the closure of the Atlantic-Mediterranean gateways in Spain and Morocco just over 6 Ma and the opening of the Gibraltar Gateway at 5.3 Ma, there has been an even stronger tectonic control on margin development, downslope sediment transport and contourite drift evolution. The Gulf of Cadiz is the world's premier contourite laboratory and thus presents an ideal testing ground for the contourite paradigm. Further study of these contourites will allow us to resolve outstanding issues related to depositional processes, drift budgets, and recognition of fossil contourites in the ancient record on shore. The expedition also verified an enormous quantity and extensive distribution of contourite sands that are clean and well sorted. These represent a relatively untapped and important exploration target for potential oil and gas reservoirs. © Author(s) 2013.
Planktic foraminiferal responses to orbital scale oceanographic changes off the western Iberian margin over the last 900kyr: Results from IODP site U1391
(Elsevier B.V., 2015) A.D. Singh; K. Verma; S. Jaiswal; M. Alonso-Garcia; B. Li; F. Abrantes
This paper presents planktic foraminiferal assemblage records of the last 900 kyr from the SW Iberian margin (IODP Site U1391). The faunal records show the history of surface oceanographic changes on glacial/interglacial scales before and after the Mid-Brunhes Event (MBE), a period when a major shift in the climate pattern was recorded in other regions. Temporal variations in relative abundances of characteristic species/groups are used to infer changes in the latitudinal position of the polar/Arctic water (% Neogloboquadrina pachyderma sinistral and Turborotalita quinqueloba), influence of the transitional subpolar water mass (% N. pachyderma dextral), and subtropical water (% tropical/subtropical species/group). Past changes in the upwelling intensity and productivity pattern associated with seasonal trade wind strength are inferred from the abundance variations of Globigerina bulloides and G. bulloides+. Globigerinita glutinata, respectively. Faunal data reveal the influence of cold water masses (polar/subpolar) at the examined site was more pronounced during glacial stages except for marine isotope stage (MIS) 14 and 16. The magnitude of the polar/subpolar water mass invading the study area was at maximum before the MBE during MIS 18, 20 and 22, resulting in a situation like the present day Arctic Front. Interglacial periods prior to the MBE were also relatively colder than those of the post-MBE. Our faunal based inferences are in agreement with the ice-rafted debris (IRD) concentration and N. pachyderma sinistral records of the subpolar North Atlantic sites. Based on faunal proxies, we recorded major and rapid changes in upwelling intensity and related productivity during glacial Terminations. Both the upwelling intensity and productivity significantly increased after the MBE, particularly during the interglacials MIS 7, 9 and 11. Our productivity record parallels the EPICA CH4 record suggesting teleconnections between trade winds induced productivity and the tropical climate through oceanic-atmospheric processes. © 2015 Elsevier B.V.