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


Following Expedition 303, Expedition 306 is the second cruise of the North Atlantic paleoceanography study, which aims to generate a late Neogene–Quaternary chronostratigraphic template for North Atlantic climate proxies, allowing their correlation at a sub-Milankovitch scale and their export to other parts of the globe by using a paleointensity-assisted chronology (PAC). The nine primary drilling locations selected for the North Atlantic paleoceanography study (Fig. F1) are known, either from previous Ocean Drilling Program (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 that recovered >4600 m of high-quality Upper Pliocene–Quaternary sediments (Fig. F1): proposed Sites ORPH3A and ORPH2A (Sites U1302 and U1303); GAR2B (Site U1304); LAB6A, LAB7A, and LAB8C (U1305, U1306, and U1307); and IRD1A (U1308) (see the Expedition 303 Preliminary Report [Shipboard Scientific Party, 2005] for additional details).

Results from drilling at proposed Site LAB8C (Site U1307) 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 because of excessive heave when a passing storm system began to affect drilling operations. Based on the results of Expedition 303 (Channell, Stein, Malone, and Expedition Scientists, in press) and the Expeditions 303 and 306 Scientific Prospectus (Channell, Sato, Kanamatsu, Stein, Malone, and the Expedition 303/306 Project Team, 2004), Sites IRD3A and IRD4A and two sites on Eirik Drift were selected to become the primary Expedition 306 sites. The newly proposed Eirik Drift sites offered the unique opportunity to extend the Upper Pliocene–Quaternary record recovered during Expedition 303 back in time to the Miocene (see the Expeditions 303 and 306 Scientific Prospectus Addendum [Kanamatsu, Stein, and Alvarez Zarikian, 2005]).

Continuous weather observations performed throughout Expedition 306 showed, however, that coring operations on Eirik Drift were not possible at any time because of extremely bad weather conditions in the Labrador Sea. Thus, the alternate proposed Site GAR1B was elevated to a primary site instead. In total, we lost 10 days because of severe weather conditions in the first part of the expedition. Therefore, only three of the planned four sites related to the North Atlantic paleoceanography study were drilled during Expedition 306: proposed Sites IRD4A (U1312), IRD3A (U1313), and GAR1B (U1314) (Fig. F1).

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