A high resolution Late Glacial and Postglacial record from the central Lomonosov Ridge, Arctic Ocean
2008 (English)In: Second Conference on Arctic Palaeoclimate and its Extremes (APEX), 2008Conference paper (Other academic)
Core HLY0503-18TC used for this study was taken during the 2005 Healy-Oden Trans-Arctic Expedition (HOTRAX) on the central Lomonosov Ridge. The coring site is located in a local “Intra Basin”, a >1000 m deep depression in the ridge morphology, where sedimentation appears to be focused and accumulation rates, thus, are higher (Björk et al., 2007). The uppermost 70 cm of core HLY0503-18TC contains high abundances of well preserved planktonic and benthic foraminifera and calcareous nannofossils. The planktonic foraminifera assemblage in the >125 μm size fraction is monospecific and consists of Neogloboquadrina pachyderma, of which >95% are of the left-coiling variety. Stable isotope measurements of the >150 μm size fraction on N. pachyderma (s) show a distinct δ13C minimum at 35-40 cm depth. Similar changes in δ13C in previous studies have been associated with a major melt water anomaly at the beginning of Termination I (Nørgaard-Pedersen et al., 1998; Stein et al., 1994). We also see other signs for a significant shift at this depth, such as low foraminifera abundance and a change in the coccolith assemblage (Fornaciari et al., 2006). To establish an age model for core HLY0503-18TC radiocarbon dating was performed on nine very small planktonic and benthic foraminifera samples at Lund University Radiocarbon Dating Laboratory. The results indicate Holocene/Late Glacial ages for the samples in the upper half of the core. The oldest non-infinite 14C-dating provided an age of ~14 cal ka BP on a sample at 32 cm depth (Marine04 calibration data set). However, the highly incoherent ages of planktonic and benthic foraminifer at 12 cm depth imply high reservoir ages for at least deeper Arctic waters, showing that caution is needed when a 14C based chronology is established on Arctic marine sediments. All 14C measurements below 42 cm core depth yielded infinite ages (>44 ka). This large shift of more than 30 kyr over a few centimeters suggests a hiatus, either in form of no/low sedimentation or erosion due to changes in the paths or strength of the bottom currents. The abundance of foraminifera and the nannofossil composition of the sediments between 40 and 70 cm core depth suggests that this part of the core belongs to either marine isotope stage 3 or 5 (Fornaciari et al., 2006). This implies that at least entire MIS 2 may be missing in the core.
Place, publisher, year, edition, pages
Earth and Related Environmental Sciences
IdentifiersURN: urn:nbn:se:su:diva-15019OAI: oai:DiVA.org:su-15019DiVA: diva2:181539