Expedition 302 summary

• Main Authors: Backman, J., Moran, K., McInroy, D., Brinkhuis, H.K., Clemens, S., Cronin, T., Dickens, G.R., Eynaud, F., Gattacceca, J., Jakobsson, M., Jordan, R.W., Kaminski, M., King, J., Koç, N., Martinez, N.C., Matthiessen, J., Moore, T.C., Onodera, J., O'Regan, M., Pälike, H., Rea, B.R., Rio, D., Sakamoto, T., Smith, D.C., Stein, R., St. John, K.E.K., Suto, I., Suzuki, N., Takahashi, K., Watanabe, M., Yamamoto, M.
• Other Authors: McInroy, D.B., Mayer, L.A.
• Format: Conference Object
• Language: English
• Published: Integrated Ocean Drilling Program Management International, Inc 2006
• Subjects: Arctic; Arctic Ocean; North Pole; Iceberg*; Lomonosov Ridge; Sea ice
• Online Access: https://eprints.soton.ac.uk/41914/; https://eprints.soton.ac.uk/41914/1/302_101.PDF; http://www.ecord.org/exp/acex/vol302/EXP_REPT/CHAPTERS/302_101.PDF

The first scientific drilling expedition to the central Arctic Ocean was completed in September 2004. Integrated Ocean Drilling Program Expedition 302, Arctic Coring Expedition (ACEX), recovered sediment cores to 428 meters below seafloor (mbsf) in water depths of ~1300 m, 250 km from the North Pole. Expedition 302's destination was the Lomonosov Ridge, hypothesized to be a sliver of continental crust that broke away from the Eurasian plate at ~56 Ma. As the ridge moved northward and subsided, marine sedimentation occurred and continues to the present, resulting in what was anticipated from seismic data to be a continuous paleoceanographic record. The elevation of the ridge above the surrounding abyssal plains (~3 km) ensured that sediments atop the ridge were free of turbidites. The primary scientific objective of Expedition 302 was to continuously recover this sediment record and to sample the underlying sedimentary bedrock by drilling and coring from a stationary drillship. The biggest challenge during Expedition 302 was maintaining the drillship's location while drilling and coring in 2–4 m thick sea ice that moved at speeds approaching 0.5 kt. Sea-ice cover over the Lomonosov Ridge moves with one of the two major Arctic sea-ice circulation systems, the Transpolar Drift, and responds locally to wind, tides, and currents. Until now, the high Arctic Ocean Basin, known as "mare incognitum" within the scientific community, had never before been deeply cored because of these challenging sea-ice conditions. Initial results reveal that biogenic carbonate is present only in the Holocene–Pleistocene interval. The upper 198 mbsf represents a relatively high sedimentation rate record of the past 18 m.y. and is composed of sediment with ice-rafted debris and dropstones, suggesting that ice-covered conditions extended at least this far back in time. Details of the ice type (e.g., iceberg versus sea ice), timing, and characteristics (e.g., perennial versus seasonal) await further study. A hiatus occurs at 193.13 mbsf, ...