Expedition 302 summary

Abstract

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-

Rhizon Sampling of Pore Waters on Scientific Drilling Expeditions: An Example from the IODP Expedition 302, Arctic Coring Expedition (ACEX)

“…The in 1206-1288 m water depth (Backman et al, 2006). The 1206-1288 m water depth (Backman et al, 2006).…”

“…IODP Expedition 302 was designed to reconstruct the Cenozoic oceanographic history of the central Arctic Ocean (Backman et al, 2006) One specific aim within this broad goal was an understanding of the sedimentary manganese record in the first 10-50 m below seafloor (mbsf). Piston cores from the central Arctic Ocean show a series of solidphase manganese spikes, which may record past changes in bottom water redox conditions (Li et al, 1969;Jakobsson et al, 2000).…”

“…The methodology and results of these analyses are presented by Backman et al (2006), although we briefly note the analytical technique for the two sets of measurements presented here. Dissolved ammonium (NH 4 + ) was determined on 0.5-mL aliquots at sea using the "Teflon tape gas -mL aliquots at sea using the "Teflon tape gas mL aliquots at sea using the "Teflon tape gas Teflon tape gas eflon tape gas separator method" (Hall and Aller, 1992); dissolved Mn 2+ detailed dissolved Mn 2+ profile in shallow sediment was therefore incompatible with Expedition 302 operations using traditional means for collecting IW samples.…”

“…IODP Expedition 302 drilled five holes at four sites on the Lomonosov Ridge at ~88.5°N latitude, 136-140°E longitude, and in 1206-1288 m water depth (Backman et al, 2006). The in 1206-1288 m water depth (Backman et al, 2006).…”

“…The in 1206-1288 m water depth (Backman et al, 2006). The 1206-1288 m water depth (Backman et al, 2006). The five holes (M0002A, M0003A, and M0004A-C) have been and M0004A-C) have been M0004A-C) have been grouped together as a single drill site because they are proximal, and because seismic reflection profiles show the same basic stratigraphy at each hole (Backman et al, 2006).…”