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doi:10.2204/iodp.sp.339.2011

Introduction

Integrated Ocean Drilling Program (IODP) Expedition 339, which combines IODP Proposal 644-Full2 and ancillary proposal letter (APL)-763, is primarily paleoceanographic in nature, focusing mainly on the broader significance of Mediterranean Outflow Water (MOW) on North Atlantic circulation and climate. This expedition offers a rare opportunity to understand the global link between paleoceanographic, climatic, and sea level changes from Messinian to recent time and will address the importance of ocean gateways in regional and global ocean circulation and climate by coring and logging seven sites on the Gulf of Cádiz and the West Iberian margin (Figs. F1, F2).

The overarching aims of Expedition 339 are

• To study the contourite depositional system (CDS) generated by MOW influence and its evolution and environmental implications (IODP Proposal 644-Full2). This CDS has been developed with very high rates of accumulation over the past 5 m.y. as the direct result of MOW, which provides an expanded sedimentary record that permits detailed examination of paleocirculation patterns linked to past environmental change; and

• To produce a marine reference section of Pleistocene millennial-scale climate variability and changes in surface and deepwater circulation along the Portuguese margin (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.

Expedition 339 will address the following 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 (Figs. F1, F2).

Oceanic gateways and their influence

Tectonically induced changes are highlighted in the ISP as one of the principal internal forcing mechanisms for environmental change (ISP, pages 36–38). By drilling in the Gulf of Cádiz, we seek to document the effects of opening the Gibraltar Gateway around 5 Ma and therefore initiating the major influx of warm, saline, Intermediate Water into the North Atlantic Ocean.

Paleocirculation and climate

One of the fundamental scientific questions identified in the ISP under Environmental Change, Processes, and Effects (page 35) 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 (pages 35–36). Expedition 339 will address changes in and effects of MOW as a component of North Atlantic circulation in the post-Miocene time period.

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 the 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 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 will recover sediment records deposited at high accumulation rates containing high-fidelity signals of Pleistocene climate variability and rapid climate change, which can be correlated to polar ice core and terrestrial archives.

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 (ISP, pages 40–41). Whereas considerable attention and several past 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. Expedition 339 will 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.

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. Expedition 339 will reconstruct the timing of neotectonic activity that has 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 is certainly ambitious in scope and scientifically very exciting. It has been carefully crafted by a broad spectrum of scientists over an 8 y gestation period. The expedition reflects an intense international interest in the region and its global significance, building on a research database accumulated over 35 y. Furthermore, the study of the CDS should be of great interest to the international community not only because of the 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).

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