DISCOVERY-FOOD-WEBS: Scotia Sea FOOD-WEBS

We hypothesise that these extremes support fundamentally different types of food web, with the latter effecting an efficient transfer of CO2 from the atmosphere into the deep ocean. Much data have already been collected by various nations on the distribution and diets of the major species within the food web. We will firstly synthesise these data, for example with construction of databases, and target field sampling at some key unresolved issues.

The research cruises aboard James Clark Ross will involve large scale transecting across the range of habitats in the Southwest Atlantic sector of the Southern Ocean. We plan three such cruises, sampling in spring, summer and autumn to incorporate elements of seasonal change. These cruises are linked to an ongoing research programme from the shore bases on Signy and South Georgia on the land-breeding predators.

Key issues include: 1) Investigating the distribution, diet and abundance of poorly known taxa such as baleen whales, king penguins, petrels and myctophids (midwater fish), and gap-filling for species where data are lacking for nonbreeders, for particular age, sex or size classes, or at certain times of year (usually winter). Where appropriate this will include indirect approaches such as fatty acid, trace metal and stable isotope analysis in order to construct comprehensive models of food web operation and energy flow. 2) Understanding the role of iron, which is a critical nutrient but is in short supply over much of the Southern Ocean.

Where it fertilises the upper ocean (for example in wind-blown dust) it can generate outbursts or &blooms& of phytoplankton which support the food web. 3) Determining the rate of vertical export of carbon to the ocean interior. We will deploy "sediment traps", akin to rain gauges, which collect the material falling out of the productive surface layer.