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The first scientific drilling expedition to the central 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, spanning a 25 m.y. interval from the early Miocene to the middle Eocene betweeñ 18 Ma and 43 Ma. The sediment record during the middle Eocene is of dark, organic-rich biosiliceous composition. Isolated pebbles, interpreted as ice-rafted dropstones, are present down to 239 mbsf, well into this middle Eocene interval. Around the lower/middle Eocene boundary an abundance of Azolla spp. occurs, suggesting that a fresh and/or low-salinity surface water set-

A 2 m-long sediment core from the siliceous ooze domain in the Central Indian Ocean Basin (CIOB; 13 • 03 S: 74 • 44 E; water depth 5099 m) is studied for calcium carbonate, total organic carbon, total nitrogen, biogenic opal, major and few trace elements (Al,

Depth profile and inventory of fallout 237 Np in sediment cores from the Mikata Five Lakes and Nyu Bay located in the coastal area of the Sea of Japan have been studied together with those of Pu isotopes ( 238 Pu, 239 -24°P u and 241 Pu), 241 Am and 137 Cs to understand the sedimentation behaviors of these elements under different aquatic environments. Mikata Five Lakes has different water salinity levels in a narrow area: fresh water (Lake Mikata), brackish water (Lakes Kugushi, Suigetsu and Suga) and sea water (Lake Hiruga).The inventory of 239,240 Pu estimated from measured depth profiles ranged from 109 to 347 MBq/km 2 . The depth profiles of 237 Np and 241 Am in sediment cores were similar to that of 239,240p u Gn the basis of a comparison of the 237 Np/ 239 -240 Pu inventory ratio obtained in sediment cores with that in surface soils, Np is considered to be more soluble than Pu in an aquatic environment. The 241 Am depth profile observed can well be explained by the ingrowth from parent 241 Pu by assuming the USA nuclear tests during the late 1950's as a substantial source of this nuclide and the immobilization of Pu and Am in the sediment. The 239,240 Pu/ 137 Cs inventory increased from 0.027 to 0.38 with the increase of salinity of the water.