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doi:10.2204/iodp.proc.339.101.2013

Introduction

Integrated Ocean Drilling Program (IODP) Expedition 339 combined IODP Proposal 644-Full2 and ancillary proposal letter (APL)-763. The expedition was primarily paleoceanographic in nature, focusing mainly on the broader significance of Mediterranean Outflow Water (MOW) on North Atlantic Ocean circulation and climate. This expedition offered a rare opportunity to understand the global link between paleoceanographic, climatic, and sea level changes from Messinian to recent time and addressed the importance of ocean gateways in regional and global ocean circulation and climate.

Seven sites (U1385–U1391) were cored and, of those seven, five sites were logged during the expedition in the Gulf of Cádiz and on the West Iberian margin (Figs. F1, F2). Six of the sites, U1386–U1391, were specifically located in order to study the contourite depositional system (CDS) generated by MOW influence and its evolution and environmental implications (Proposal 644-Full2). This CDS has developed at very high rates of sediment accumulation over the past 5 m.y. as the direct result of MOW, providing an expanded sedimentary record that permits detailed examination of paleocirculation patterns linked to past environmental change. One of the sites, U1385, was positioned at the Shackleton site on the Portuguese margin to produce a marine reference section of Pleistocene millennial-scale climate variability and changes in surface and deepwater circulation (APL-763). Climate signals from this reference section will constrain the temporal relationships of abrupt climate change recorded in the northeast Atlantic Ocean, the polar ice cores, and European terrestrial records.

The five principal objectives of Expedition 339 address key elements of the IODP Initial Science Plan (ISP) through targeted drilling of a Neogene and Quaternary continental margin sequence in the Gulf of Cádiz and off West Iberia.

1. Oceanic gateways and their influence: tectonically induced changes are highlighted in the ISP as one of the principal internal forcing mechanisms for environmental change. By drilling in the Gulf of Cádiz, we seek to document the effects of opening the Gibraltar Gateway at ~5.3 Ma and therefore initiating the major influx of warm, saline intermediate water into the North Atlantic Ocean.

2. Paleocirculation and climate: one of the fundamental scientific questions identified in the ISP under Environmental Change, Processes, and Effects is “How did the Earth system respond to climatic change and at what timescales?” A key response of the ocean system to climate forcing is significant reorganization of global circulation and adjustment in the thermohaline conveyor belt model. Hence, the record of paleocirculation and paleoclimate is further identified as a specific target in the ISP. Expedition 339 research will address changes in and effects of MOW as a component of North Atlantic circulation in the post-Miocene time period.

3. Rapid climate change: rapid climate change is highlighted as a special initiative in the ISP under Environmental Change, Processes, and Effects. Future advances in our understanding of the causes of abrupt change will rely on our ability to correlate high-resolution sedimentary archives from oceans, ice cores, and terrestrial sequences and to interpret these records in the context of novel Earth system modeling approaches. A challenge for IODP, and for the broader drilling community, is to identify sequences from appropriate locations with adequate temporal resolution to study processes of the integrated climate system. Expedition 339 recovered sediment records deposited at high accumulation rates containing high-fidelity signals of Pleistocene climate variability and rapid climate change that can be correlated to polar ice-core and terrestrial archives.

4. Sea level change and sediment architecture: the response of sediment architecture, especially along continental margins, to sea level change is highlighted in the ISP as the second principal internal forcing mechanism for environmental change. Whereas considerable attention and several past Ocean Drilling Program (ODP) drilling legs have been directed toward placing turbidites and other downslope systems within a sequence stratigraphic context, there is no generally accepted understanding of how and where the alongslope sedimentary system, driven by bottom water circulation, fits within these models. Fundamental questions regarding the timing and extent of hiatuses and condensed sequences and the corollary periods of alongslope deposition, drift development, and paleodepth reconstruction have yet to be answered. The objectives of Expedition 339 address precisely these aspects of sediment architecture within the Gulf of Cádiz and West Iberian marginal sequences in relation to changes in sea level and other forcing mechanisms.

5. Neotectonic activity: margin evolution anywhere is controlled by complex interactions of many different forcing variables, most importantly sea level and climate, sediment supply, and tectonics. Results from Expedition 339 will be used to reconstruct the timing of neotectonic activity that had a significant impact on submarine topography and, consequently, controlled the flow path of the two branches of MOW and their influence in the North Atlantic.

Expedition 339 was ambitious in scope and scientifically exciting. It was carefully crafted by a broad spectrum of scientists over at least 9 years gestation period. The expedition reflects intense international interest in the region and its global significance, building on a research database accumulated over 35 years. Furthermore, the study of the CDS should be of great interest to the international community not only because of its stratigraphic, sedimentologic, paleoceanographic, and paleoclimatologic significance but also because of its close relationship with possible specific deep-marine geohabitats and/or mineral and energy resources (Rebesco and Camerlenghi, 2008; Hernández-Molina et al., 2011b).

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