Deformation of the radiolarian fossil record: plankton vs. sediment traps vs. surface sediments

BOLTOVSKOY DEMETRIO

Bierville, France

Congreso; INTERRAD VIII; 1997

INTERRAD

The use of radiolarian sedimentary assemblages, for paleoceanographic purposes is hindered by several factors, including the poor state of their taxonomy, the lack of knowledge of the ecological constraints of Recent species, and our poor understanding of the mechanisms that distort the bottom imprint of their planktonic populations. Distortion of the water-column fauna en route to- and on the sea floor is of special importance: most studies that drew close comparisons found very significant qualitative dissimilarities between assemblages recovered from plankton and/or sediment trap samples with those from the surface sediments. In the last years, thanks largely to the advent of new technologies unavailable a decade ago, we are starting to examine these problems in some detail. Time series sediment traps deployed at mid depths in various oceanic regions represent an intermediate step in the formation of the microfossil record, thus allowing interpretation of some of the constraints responsible for the plankton-sediments uncouplings observed. Planktonsediments differences in species makeups and proportions can arise as a consequence of post-mortem processes, of processes associated with traits of the living organisms, or a combination of the two. Post-mortem distorting mechanisms include fragmentation and bulk and selective dissolution en route to the sea-floor and on the bottom, vertical reworking of sediments, and winnowing and lateral advection of displaced sediments. Among the processes associated with traits of the living organisms of special importance are differential seasonal dynamics, differences in species-specific productivity, equatorward subsurface transport, and integration of surface (environment-sensitive) and deep (environment-insensitive) species in the sedimentary record.