R&D PROJECTS
Environmental Significance of the Mediterranean Outflow Water and its Global Implications (“GUCADRILL”- IODP Full Proposal-644)
Stow, D.A.V.1, Hernández-Molina, F.J.2, Cacho, I.3; Escutia, C.4; Gardner, J.5; Ito, M.6; Lebreiro; S.7; Martin, P.8; Mulder, T. 9; Rebesco, M.10; Roberts, A.11; Schoenfeld, J.12; Sierro, F.13; Somoza, L.7; Terrinha, P.14; Voelker, A.14; Weaver, P.11
This is a paleoceanographic proposal involved 44 researchers from 11 different countries focusing on the broader significance of Mediterranean Outflow Water (MOW) on North Atlantic circulation and climate (Stow et al., 2006). It addresses important questions highlighted in the IODP Initial Science Plan related to paleocirculation and climate, the influence of oceanic gateways, and sea-level control on sediment architecture along continental margins. In order to answer these questions, we propose targeted drilling of a Neogene continental margin sequence in the Gulf of Cadiz and off West Iberia. The high rates of accumulation associated with Contourite Depositional System (CDS) deposits in this region provide an expanded sedimentary record that permits detailed examination of paleocirculation patterns linked to past environmental change. This proposal offers a unique opportunity to understand the global link between paleoceanographic, climatic and sea-level changes from Messinian to recent time. The Gulf of Cadiz and off West Iberia CDS is an extensive compound sedimentary body, which has been developing along the mid-slope over the past 5 million years, under the direct influence of MOW (Fig. 1). It therefore holds an unmistakable signal of MOW through the Gibraltar Gateway, re-opened following tectonic adjustments at the end of the Messinian Salinity Crisis, and hence a clear record of Mediterranean Sea and MOW influence on the North Atlantic Ocean.
Figure 1. Regional bathymetric map indicating the general circulation patterns...
Figure 2. Regional map of the Contourite Depositional System
An extensive array of high quality data exists for the region and a detailed seismic stratigraphic framework has recently been proposed, which can only be confirmed by drilling. Seven primary sites have therefore been identified (Fig. 2) that will allow us to identify and calibrate the third and fourth order depositional units and associated widespread erosive discontinuities across the CDS (Stow et al., 2006). This is of great significance, both regionally and globally, for: (1) monitoring the long-term variability of MOW and its global climatic significance; (2) constraining the main paleoceanographic events through late Miocene to Recent time, including high-resolution focus on late Pleistocene and Holocene rapid climate events; (3) evaluating the influence of opening of the Gibraltar gateway on North Atlantic oceanography and climate, and monitoring the effects of sea-level change on MOW flux; (4) understanding the architecture of a complex contourite depositional system, and the nature of its unit stacking pattern related to allogenic and autogenic controls and (5) investigating the dramatic large-scale asymmetric cycles of seismic character evident on high-resolution records, thereby identifying their occurrence onto Quaternary-Pliocene climate/sea-level and paleoceanographic changes.
An extensive Contourite Depositional System (CDS) has been developing within the Gulf and the West Iberian Margin over the past 5 million years as the direct result of the Mediterranean Outflow Water (MOW). The high rates of accumulation and expanded sedimentary records of drift deposits permit high-resolution examination of past environmental change. The CDS deposits, therefore, hold the very best signal of MOW flow through the Gibraltar gateway, and a clear record of its influence on the oceanography and climate of the North Atlantic Ocean and on North Atlantic Deep Water (NADW) variability (Fig. 3).
The importance of the Gulf of Cadiz is clearly reflected in the large number of regional studies and multinational interest shown over the past 30 years. But, despite such extensive surveying, the region has not yet been drilled for scientific purposes, even though the Gibraltar gateway clearly has major implications for global climate and oceanography. We have identified the following four broad scientific objectives, which require a total of seven drill sites (Fig. 2) through the Pliocene to Quaternary sedimentary record (Stow et al., 2006): 1) Influence of the Gibraltar Gateway; 2) MOW paleoceanography and global climate significance; 3) Sea-level changes and sediment architecture of the Cadiz CDS and Iberian margin; and 4) Synsedimentary neotectonic control on architecture and evolution of the CDS. To achieve theses major scientific objective, it is essential to integrate the results of the proposed drill sites with a dense network of existing high-resolution seismic reflection profiles. Interpretation of this seismic network is already well established, although the inferred ages require drilling confirmation.
Acknowledgements
We thanks to REPSOL, TGS-NOPEC and the Spanish company for the Morocco-Spain connection trough the Strait of Gibraltar (SECECSA) for their fully co-operation and support for the drilling proposal and permission to use some data and figures. This research proposal is supported by the Spanish “Comisión Interministerial de Ciencia y Tecnología (CYCIT)” through the Project CTM 2008-06399-C04/MAR (CONTOURIBER).
References
Hernández-Molina, F.J., Llave, E., Somoza, L., Fernández-Puga,M.C., Maestro, A., León, R., Barnolas, A., Medialdea, T., García, M., Vázquez, J.T., Díaz del Río; V., Fernández-Salas, L.M., Lobo, F., Alveirinho Dias, J.M., Rodero, J., Gardner, J., 2003. Looking for clues to paleoceanographic imprints: a diagnosis of the gulf of Cadiz contourite depositional systems. Geology, 31 (1): 19-22.
Hernández-Molina, F.J., Llave, E., Stow, D.A.V., García, M., Somoza, L., Vázquez, J.T., Lobo, F.J., Maestro, A., Díaz del Río, V., León, R., Medialde, T., Gardner, J., 2006. The contourite depositional system of the Gulf of Cádiz: A sedimentary model related to the bottom current activity of the Mediterranean outflow water and its interaction with the continental margin. Deep-Sea Research II, 53: 1420-1463.
Llave, E., Hernández-Molina, F.J., Somoza, L., Díaz-del-Río, V., Stow, D.A.V., Maestro, A., Alveirinho Dias, J.M., 2001. Seismic stacking pattern of the Faro-Albufeira contourite system (Gulf of Cadiz): a Quaternary record of paleoceanographic and tectonic influences. Marine Geophysical Researches, 22: 487-508.
Stow, Hernández-Molina, et al., 2006. Proposal -644 GUCADRILL “ENVIRONMENTAL SIGNIFICANCE OF THE MEDITERRANEAN OUTFLOW WATER AND ITS GLOBAL IMPLICATIONS”). Propuesta del Integrated Ocean Drilling Program (IODP).