Bioturbation in deep sea Pacific sediments

Abstract

Bioturbation structures have been recorded in sediment cores from 5000 m to 5300 m water depth collected from the Pacific Ocean using subcores from spade box cores. Shear strength and Eh profiles were also taken. The results have been related to pelagic fluxes and sedimentation. Bioturba-tion structures consist of holes and chambers of various sizes running vertically and horizontally, whose abundance, size and shapes have been measured. Values did not decrease exponentially with sediment depth but end abruptly at depths ranging from 30 cm to 45 cm. In many instances there were subsurface peaks of vertical and horizontal burrows. There was also evidence of lateral galleries. Large deep in filled burrows were observed. These consisted of light and dark brown sediment having different shear strengths. Eh profiles showed that the sediment was aerobic, with slightly lower values near the sediment surface, possibly associated with meiofaunal and bacterial activity. The most important implications of this work for pelagic processes are likely to be increased transfer of dissolved and particulate material between the sediment and the water column due to the physical network of burrows within the sediment and increased surface roughness caused by burrow openings. Mucus binding of particulates and faecal pelletization are also likely to be important. All of these effects will be most noticeable at high burrow densities.