Relative Geomagnetic Paleointensity, Environmental Magnetism, and Cyclicity of Contourites from the West Iberian Margin (IODP Site U1389)
Tuesday, 16 December 2014
The Mediterranean Outflow Expedition provides an outstanding opportunity to address paleoceanographic questions about the evolution of the Mediterranean and North Atlantic climate system over the past 6 million years. As part of the overall project, we present high-resolution paleomagnetic and rock magnetic results from the top ~36 meters composite depth (mcd) of Integrated Ocean Drilling Program (IODP) Site U1389 (36º 25.515’N; 7º 16.683’W, 644 m water depth) located approximately 90 km west of Cádiz. The sedimentary section is represented by a thick, rapidly accumulated (mean sediment accumulation rate of ~40 cm/kyr), and very uniform series of contouritic sediment. The age model was obtained by tuning the planktonic foraminifer oxygen isotope data to the NGRIP ice core record. Paleomagnetic and rock magnetic measurements were collected at 1-cm interval resolution on U-channel samples covering the top ~36 mcd, with the goal of extracting a high-resolution record of paleosecular variation, relative geomagnetic paleointensity change, and the variability of the paleoenvironmental conditions. Detailed demagnetization of the natural remanence (NRM) reveals the successful removal of a secondary magnetization and identification of a stable and strong primary magnetization carried by the sediment samples (average MAD associated with principal component analysis: 0.97º). Isothermal remanent magnetization (IRM) acquisition curves and excellent behavior of the samples during alternating field demagnetization suggest magnetite as the main magnetic remanence carrier. Relative paleointensity estimates were calculated by normalizing NRM with ARM, IRM, as well as magnetic susceptibility. Time-frequency analyses of high-resolution concentration and grain-size dependent paleomagnetic proxy data and other physical properties are in progress and will be presented with the goal of identifying the driver of cyclic changes in the sedimentary section.