Comparison of settling particles and sediments at IMAGES coring site in the northwestern North Pacific — Effect of resuspended particles on paleorecords

In order to understand settling process of particles in high sedimentation area, one mooring of sediment trap was deployed right above the IMAGES coring site in the northwestern North Pacific. In spite of two large maxima of settling particle fluxes in June–July 2002 and October–early January 2003, organic matter (OM) and carbonate showed higher peaks in June–July while lithogenics showed a large peak in October–early January with degraded OM (low aspartic acid/beta-alanine (Asp/Bala) and glutamic acid/gamma-aminobutyric (Glu/Gaba) ratios). Fresh OM production peaked in June–July 2002 and April–May 2003. Thus a large export production occurred in spring–early summer (April–June). Alkenone production was enhanced mainly in June–July. The mean alkenone SST of the settling particles was rather consistent with the observed annual mean SST and alkenone SST determined from the surface sediments. On the other hand, the maximum lithogenic flux along with the degradation of OM indicated that a significant amount of resuspended matter contaminated the bottom sediments. Based upon idealized model, the current and settling speeds make fractionation by size and density of resuspended particles during the settling process. Accumulation rates of lithogenics were ~ 5 times those in the sediment traps, which indicate large contribution of resuspended particles to settling particles especially during October–early January, when the Tsugaru current showed high current speed. These observations call our attention to carefully reconstruct paleo-environments based upon lithogenics and several other proxies such as biogenic silica, which would be biased for example in the record of IMAGES core at Site Shimokita located on the gentle continental slope.