Proceedings of the Integrated Ocean Drilling Program 303/306: North Atlantic Climate

Expedition 303 was designed to sample and study strategic sites that record components of North Atlantic Pliocene–Quaternary climate, including the composition and structure of surface or bottom waters and detrital-layer stratigraphy indicative of ice sheet instability. The sites are distributed from the mouth of the Labrador Sea (Eirik Drift and Orphan Knoll) to the central Atlantic in the region of the Charlie Gibbs Fracture Zone. The sites have important climate or paleoceanographic records, adequate sedimentation rates in the 5–20 cm/k.y. range for high-resolution studies, and the potential for stratigraphies based on relative geomagnetic paleointensity and oxygen isotope data. The sites 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 millennial-scale stratigraphies (through geomagnetic paleointensity, oxygen isotopes, microfossils, and regional environmental patterns). They also document the details of geomagnetic field behavior over the last few million years. The ultimate objective is to generate a chronostratigraphic template for North Atlantic climate proxies and to allow their correlation at a sub-Milankovitch scale and their export to other parts of the globe. The lack of such a chronostratigraphic template has been a major obstacle to the study of sub-Milankovitch–scale climate history. A total of 4656 m of high-quality core was recovered from sites with mean sedimentation rates reaching 20 cm/k.y. In the coming years, we expect research on these cores to break new ground in Late Pliocene–Quaternary paleoclimatology, paleoceanography, and paleomagnetism.

The overall aim of the North Atlantic paleoceanography study of Integrated Ocean Drilling Program Expedition 306 is to place late Neogene–Quaternary climate proxies in the North Atlantic into a chronology based on a combination of geomagnetic paleointensity, stable isotope, and detrital layer stratigraphies, and in so doing, generate integrated North Atlantic millennial-scale stratigraphies for the last few million years. To reach this aim, complete sedimentary sections were drilled by multiple advanced piston coring directly south of the central Atlantic "ice-rafted debris belt" and on the southern Gardar Drift. In addition to the North Atlantic paleoceanography study, a borehole observatory was successfully installed in a new 170 m deep hole close to Ocean Drilling Program Site 642, consisting of a CORK (circulation obviation retrofit kit) to seal the borehole from the overlying ocean, a thermistor string, and a data logger to document and monitor bottom water temperature variations through time.