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doi:10.2204/iodp.proc.303306.109.2006

Part A: Ice sheet–ocean atmosphere interactions on millennial timescales during the late Neogene–Quaternary using a PAC for the North Atlantic

Introduction

Following Expedition 303, Expedition 306 is the second cruise of the North Atlantic paleoceanography study that aims to generate a late Neogene–Quaternary chronostratigraphic template for North Atlantic climate proxies and allow for their correlation at a sub-Milankovitch scale and their export to other parts of the globe by using a PAC. The nine primary drilling locations selected for the North Atlantic paleoceanography study (Fig. F1) are known, either from previous ODP/Deep Sea Drilling Project (DSDP) drilling or from conventional piston cores, to have the following attributes:

• They contain distinct records of millennial-scale environmental variability (in terms of ice sheet–ocean interactions, deep circulation changes, or sea-surface conditions).

• They provide the requirements for developing a millennial-scale stratigraphy (through geomagnetic paleointensity, oxygen isotopes, microfossils, and regional environmental patterns).

• They document the details of geomagnetic field behavior.

Expedition 303, carried out in October–November 2004, occupied seven precruise sites recovering over 4600 m of high-quality upper Pliocene–Quaternary sediments (Fig. F1): Sites U1302/U1303 (proposed sites ORPH3A and 2A), U1304 (proposed site GAR2B), U1305, U1306, and U1307 (proposed sites LAB6A, 7A, and 8C), and U1308 (proposed site IRD1A) (see Expedition 303 Preliminary Report [Shipboard Scientific Party, 2005] for additional details).

Results from drilling at Site U1307 (LAB8C) during Expedition 303 established the feasibility of recovering the Pliocene sedimentary section on the Eirik Drift using the advanced piston corer (APC) system. Two holes were drilled at Site U1307 (LAB8C) reaching a maximum depth of 162 meters composite depth (mcd) in the uppermost Gilbert Chronozone (~3.6 Ma). Coring was terminated due to excessive heave when a passing storm system began to affect drilling operations. Proposed Expedition 306 sites on Eirik Drift would have offered the unique opportunity to extend the upper Pliocene–Quaternary record recovered during Expedition 303, back in time to the Miocene (see Expedition 303/306 Scientific Prospectus Addendum [Kanamatsu et al., 2005]).

Based on the Expedition 303/306 Scientific Prospectus (Channell et al., 2004) and the results of Expedition 303, Sites IRD3A and IRD4A and two sites on Eirik Drift were selected to become the primary Expedition 306 sites. Continuous weather observations performed throughout Expedition 306 showed, however, that coring operations on Eirik Drift were not possible at any time due to extremely bad weather conditions in the Labrador Sea. Thus, the alternate Site GAR1B was a primary site instead. In total we lost 10 days due to severe weather conditions during the first part of the expedition. Therefore, only three, instead of the planned four sites related to the North Atlantic paleoceanography study, could be drilled during Expedition 306 (Sites U1312, U1313, and U1314) (Fig. F1).

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