Abstract:
A record of Holocene paleoenvironmental variability from the Antarctic Peninsula has been produced using sediment cores from Site 1098 gathered on Ocean Drilling Project Leg 178. The results provide an accurate and continuous record of biotic and sedimentologic responses to Holocene environmental change. Holes 1098B and 1098C were used to produce the first ultrahigh-resolution record of grain size variability for the past 13,000 years. We utilized samples every 2.5 cm (at 3-5 yr cm (super -1) ) which involved the analysis of 1466 samples from two holes at the site. Particle size was measured on uniform suspensions of dispersed particles using a laser diffraction method. The particles are mainly grains of silt (65-85%) and clay (15-35%) size. The analyses revealed that in most intervals, biotic particles in the form of diatom frustules (mostly spores) dominate the silt component, which is inversely reflected by magnetic susceptibility (MS). In intervals of the core that deviate from this relationship it was found that the MS signal correlated with medium to fine or coarse silt that was dominated by terrigenous rather than a biogenic (diatom) component. Spectral analyses of the variability in clay and medium-fine silt content over the last approximately 9000 calendar years reveal cycles of 1800, 400, 200, 100, 70, 60, and 50 years. The analyses revealed that particle size, specifically medium-fine silt, is an excellent proxy for environmental change in the Palmer Deep region. Such changes may be forced by solar variability (the 200 and 400 year cycles), lunar tidal changes (the 1800 year cycles), and an as yet undetermined multidecadal forcing phenomena that operates in the SE Pacific sector of the Southern Ocean.