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

Abstract

Abstract. 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.

New insights into upper MOW variability over the last 150kyr from IODP 339 Site U1386 in the Gulf of Cadiz

“…This approach follows Bahr et al (2014) who showed that conditions at the sea surface drive the Br content at Site U1387 which is located in vicinity and similar water depth as Site U1386 (Fig. 1C, Hernández-Molina et al, 2013). It was argued that Br is not distinctly influenced by varying lithology and its variations are not directly linked to other elements, making it an excellent tool for stratigraphic correlation .…”

“…As a water mass, the MOW can be traced within the Gulf of Cadiz in two major flow cores located at 800-1400 m water depth alongside the middle slope (lower MOW core), and at 500-700 m water depth alongside the upper slope including our study area (upper MOW core, Fig. 1B) (Baringer and Price, 1997;Borenäs et al, 2002;Hernández-Molina et al, 2013).…”

Mediterranean Outflow Water variability during the Early Pleistocene

“…Black triangles with numbers indicate biostratigraphic and palaeomagnetic tie points used, as referenced in Table 1. Black and white bar at the top represents core recovery following Hernández-Molina et al (2013). (b) Comparison of the benthic δ 18 O record of Site U1389 on a new timescale according to our tuning, and the benthic δ 18 O MedSea stack on its respective age model (Lourens et al, 2004).…”

“…In the Gulf of Cadiz, MOW follows the topography of the continental shelf in two major flow cores at 800-1400 m water depth (lower MOW core) and 500-700 m water depth including our study area (upper MOW core,Fig. 1a) (Baringer and Price, 1997;Borenäs et al, 2002;Hernández-Molina et al, 2013). After exiting the Gulf of Cadiz, most of MOW flows north along the European continental margin until it mixes with the North Atlantic Current at Rockall Plateau (HernandezMolina et al, 2014b).…”

Stratigraphic variation in ichnofabrics at the “Shackleton Site” (IODP Site U1385) on the Iberian Margin: Paleoenvironmental implications

“…During the IODP Expedition 339, from November 2011 to January 2012, seven sites (Sites U1385-U1391) were drilled in the southwest margin of the Iberian Peninsula (Expedition 339 Scientists, 2013a;Hernández-Molina et al, 2013. IODP Site U1385, located on the West Iberian margin (37°34.285′ N, 10°7.562′ W, Fig.1), was drilled close to core MD01-2444 Voelker and de Abreu, 2011;Channell et al, 2014).…”