A High-Resolution Late Pleistocene Sediment Record From the Central Lomonosov Ridge, Arctic Ocean

During the 2005 Healy-Oden Trans-Arctic Expedition (HOTRAX) piston and gravity cores were taken from the central Lomonosov Ridge in a >1000 m deep depression in the ridge morphology forming a local "Intra basin" (Bjork et al., 2007) . Core HLY0503-18TC was retrieved from the deeper parts of this Intra basin at a water depth of 2598 m where sedimentation appears to be focused and accumulation rates, thus, are higher. The core top sediment composition with only some shell material without manganese coating and no gravel clasts suggests a calm depositional environment at this coring site. The uppermost 70 cm of core HLY0503-18TC contains low content of coarse grains (grain size fraction >63 μm) but high abundances of well preserved planktonic and benthic foraminifera and calcareous nannofossils. The planktonic foraminifera assemblage consists of 95- 99% Neogloboquadrina pachyderma (sinistral) in the >150 μm size fraction. Stable isotope measurements performed on N. pachyderma (s) show distinct δ13C minimum values around 40 cm core depths associated in previous studies by e.g. Stein et al. (1994) and Norgaard-Pedersen et al. (1998) with a major meltwater anomaly at the beginning of Termination I. This interval coincides with low number of foraminifera and a reversal in the calcareous nannofossil assemblage from Geophyrocapsa to Emiliana huxleyi (Fornaciari et al., 2006). The total length of this uppermost part of the brown cycle containing abundant foraminifera is more than double compared to what usually is found in the central Arctic Ocean. Nine samples have been submitted for 14C-dating in order to constrain the chronostratigraphy of this, possibly, first high- resolution sediment record from the central Arctic Ocean. References: Bjork, G. et al., 2007, Deep-Sea Research I, 54. Fornaciari, E. etal., 2006, AGU Fall Meet. Suppl., Abstract OS53B-1110. Norgaard-Pedersen, N. et al., 1998, Paleoceanography, 13(2). Stein, R. et al., 1994, Marine Geology, 119.