MICROBIAL AND MEIOFAUNAL ABUNDANCE, REDOX POTENTIAL, PH AND SHEAR-STRENGTH PROFILES IN DEEP-SEA PACIFIC SEDIMENTS

Vertical profiles of microbial and meiofaunal abundances, and of redox potential, pH, water content and shear strength have been measured in sediment subcores from seven box cores collected in the southern Cent ral Pacific and the findings have been related to potential effects on pelagic fluxes and sedimentation. Microbial and meiofaunal abundance decreased exponentially with sediment depth. Micro-organisms were foun d throughout the depth of the core to 40 cm. Meiofauna were only prese nt in the top 5 cm to 10 cm. Meiofaunal metazoans decreased more rapid ly than foraminiferans. Redox potential was always positive, decreased below the surface and often rose again deeper in the sediment. pH sho wed no clear cut trend with depth. Shear strength increased with sedim ent depth and showed occasional anomalous fluctuations. Water content decreased progressively downwards with the widest scatter in the top 5 -10 cm. The most important implications of these results for the water column above are likely to be biologically mediated organic mineraliz ation and nutrient regeneration into the water column, and biodepositi on of heavy metals and the binding of particulates at and above the se diment-water interface by extracellular polymeric material, which will in turn lead to differential patterns of sedimentation.