Biological Processes Sub-Project

Objectives

To identify the major biological components involved in the vertical and horizontal transport of dissolved and particulate biogenic matter in the shelf/slope region.

To investigate the effect of shelf edge discontinuities on the seasonal primary production, microbial and grazing food webs and the extent of pelagic-benthic coupling along shelf slopes.

To develop numerical ecological and diagenetic models for slope systems and resulting fluxes.

These were investigated through the measurement of vertical fluxes of particulate matter, and the characterisation of this matter. The fluxes were measured using three moorings, instrumented with current meters and transmissometers, with sediment traps at depths of between 600 and 4000 m, deployed for periods in excess of a year. The data showed that the material flux increased with depth, demonstrating the importance of lateral transport in the vicinity of the ocean margin. In addition, process studies were undertaken to investigate the transport and fate of phytoplankton-derived carbon on the European ocean margin.

The Influence of the Shelf Edge on Biology

The relationship between the shelf break and the distribution of the zooplankton community was studied by measuring the strength of acoustic doppler current profiler signal returns. Measurements of this type taken at different times of the day showed large daily movements of several hundred mg of organic carbon into and out of the upper mixed layer that resulted from the vertical migration of the plankton. The supply of organic carbon to deeper waters is not only controlled by the strength and duration of phytoplankton bloom, but also by the dynamics of the zooplankton that graze on them. During OMEX I the relative importance of grazing by the micro and meso-zooplankton in the shelf break area was investigated.

Modelling

Within OMEX I, ecological modelling proved an important tool for integrating the diverse data collected and testing the central questions posed by project. The contribution of modelling was not restricted to running numerical simulations for comparison with field data. Significant additional understanding resulted from the interchange of ideas necessary to develop the models. The various modelling exercises in the Biological Processes Sub-project represented an activity where the investigations from different groups of scientists and from different shelf areas found a common base.