Stormy and icy seas - Antarctica: Global Science from a Frozen Continent - page 159

sediment traps and the vocalisations of marine mammals can also be recorded.
Bottom pressure recorders indicate variations of the sea surface height and in
combination with inverted echosounders the change of water mass properties.
Drifting instruments, which transmit their data and positions, can be applied at
the sea surface or deployed on ice

floes and move with the water masses. Vertically

pro les of temperature and salinity every couple of days,

when they leave their parking depth at about 1000m, and descend to 2000m
depth. Normally every 10 days they come to the surface where they use satellite
communication to determine their position and to transmit the recorded data. If the
ocean is covered by sea ice, they cannot reach the surface and they avoid hitting the
ice by detecting when the temperature is close to freezing and terminating the
ascent. Data are stored until the

ling oats measure pro

float reaches the surface the next time.
Recently marine mammals, e.g. elephant seals, have been used to carry
sensors, which transmit their data via satellites. The animals migrate over long
distances and reach areas that are dif cult to reach by ship or buoy. Since they need

air to breathe they search actively for open water and in consequence are able to
transmit data rather frequently. The instruments provide not only the physical
environmental data, but also tell us about the foraging behaviour of the animals
and their physiological performance.
Whereas in-situ instruments can only cover a very limited area and time
period, satellites have the potential to obtain regional data rather rapidly. Data now
include sea surface temperature, salinity and colour, roughness (from which wind
and waves can be derived) and sea surface height (which also allows ocean currents
to be determined). Satellites can also measure sea ice concentration and extent,
sea ice drift and to some extent sea ice thickness.
The combination of satellites and in-situ data allows an increasingly detailed
description of the present state of the Southern Ocean and the detection of changes,
but compared with other oceans the data from the Southern Ocean are still very limited.
The new international initiative Southern Ocean Observing System is intended to collect
many types of data from all over the Southern Ocean throughout the year. Signi cant

efforts are needed to obtain data sets that are suf ciently dense in space and time to

support or reject hypotheses on changes. Here, numerical models can help to fill the gaps

by covering the Southern Ocean and its variability over longer times and on a complete
grid. Since they are based on physical laws, they can give answers to the question
of the origin of the observed fluctuations and help to predict future development.

Conclusions

The Southern Ocean is a major part of the global climate system. Due to the
harsh natural conditions it is, in spite of a century of exploration, still poorly known.