JR161: Food webs in Antarctica


About the cruise...

JR161 aboard the RRS James Clark Ross (JCR) is the first of a series
of three cruises to the Scotia Sea to study food-wed dynamics in Antarctica

The Challenge

Ocean food webs modify the efficiency with which carbon dioxide (CO2) is absorbed from the atmosphere into the sea, gobbled up by phytoplankton in the surface layers and then transported down into the depths of the ocean. This so-called "biological pump" absorbs about one-third of the CO2 released from all human activities. Our priority is to understand the Southern Ocean ecosystem and how it works well enough to be able to make realistic predictions about how future climate change might affect it. The information we collect on this cruise will also be essential for knowing how to manage this environment and its ecosystems in an environmentally-friendly way.

Our challenge is to understand the structure and functioning of the range of food webs present in the southwest Atlantic Sector of the Southern Ocean, from those in relatively unproductive deep ocean systems to the highly productive, krill-dominated systems elsewhere. We hypothesise that these extremes support fundamentally different types of food web, with the highly productive systems providing an important and efficient transfer of CO2 from the atmosphere into the deep ocean.

Find out more about phytoplankton in the Southern Ocean
Find out more about food webs
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  1. To describe how the distribution of different marine species varies in time and space within each food web. Is the marine food web different in high-productivity and low-productivity waters? What are the limiting factors in low productivity waters?
  2. To quantify the major energy flows.
  3. To understand the key factors controlling energy flow in the food web including a) responses to variable food supply and, b) implications for carbon export.

What we will do

The research cruises aboard RRS James Clark Ross will involve taking samples and making measurements across the range of marine habitats in the Southwest Atlantic sector of the Southern Ocean. In total, 3 cruises will take place so that we can take samples in spring, summer and autumn to see how the data change with the seasons. These cruises are linked to an ongoing research programme on the land-breeding predators, which is co-ordinated from the shore bases on Signy and South Georgia. Our cruise is planned to match the activity timetable for the land stations in Antarctica. 

Key issues include:

1) Investigating the distribution, diet and abundance of poorly known creatures such as baleen whales, king penguins, petrels and myctophids (midwater fish), and collecting extra data on species where data are lacking for nonbreeders, for particular age, sex or size classes, or at certain times of year (usually winter). This will include some laboratory work 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 by which carbon is transportede down into the ocean interior. We will deploy "sediment traps", akin to rain gauges, which collect the material falling out of the productive surface layer.

Above: Simplified picture of the Southern Ocean food web, showing the importance of krill in supporting directly and indirectly (via the fish link in food chains) a diverse and abundant range of higher predators, as well as several major human fisheries. These short food chains (shown in red) link microscopic plants (phytoplankton) at the base of the food chain, via krill to large predator species.

What equipment will we use?

The team will use equipment specially adapted for taking measurements at sea. This includes:

MOCNESS (Multiple Opening/Closing Net and Environmental Sampling System): MOCNESS is made up of 9 nets and sampling devices, and is towed behind the ship at low speed to collect plankton and other cretures living in the water column.

CTD (Conductivity, Temperature, Depth): The CTD measures properties of the seawater. The instrument is tossed over the side of the ship where it submerges, measures the conductivity and temperature of the seawater at given depths and then transmits the data back to a computer on board the ship. The CTD contains a number of sample bottles, so samples of seawater can be brought back onto the ship for further investigations.

Sediment trap: The trap is left to drift a set depths in the coean for up to 5 days. During this time, it collects sediment particles whihc are falling through the water column. When the measuring period is over, the trap is brought back on board and the collected sediment is analysed.

Images courtesy BAS

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October 2006
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