journal de bord

18/07/2007

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Scientific work during summer

Scientific work during summer

During the drift we are undertaking a great variety of scientific work. Here is a brief summary of the main programmes…



ATMOSPHERE

We have a helium filled balloon that can reach an altitude of 2000 metres. Timo is the specialist of this experiment. Twice a week the balloon is sent up several times during the day to get as much data as possible. This balloon is linked by a line to a small independent winch about a hundred meters from the boat to avoid hitting the masts of Tara. On this line, just bellow the balloon, are secured three sensors measuring altitude, wind direction and strength, temperature, atmospheric pressure and humidity. The data is sent by radio signal to the ground where it is logged on a computer.

Sensors situated on the meteorological mast at different heights between the surface and 10 metres are continuously recording the same parameters as above. We also have automated instruments continuously measuring surface ozone levels.

SNOW

Every week, Hervé and his assistants study snow characteristics at three sites near Tara. This data allows us to look at the evolution of the snow layers. At each site we measure the snow thickness and note the different layers. The temperature, crystal form and density are recorded. This activity requires some experience as observing the snow is not always easy, wind and warm temperatures sometimes complicating the observations.

A radiometer positioned about 100m from Tara also measures the reflectivity (albedo) of the snow continuously. This is an important measurement for calculating the amount of incoming and outgoing solar energy.

ICE

A network of 5 seismometers up to 1km from Tara records the seismic activity of the sea ice. This data is downloaded every week, giving us a good reason to go for a ski tour. Recently we have encountered some problems with these instruments. They have started to float in small pools created by the melting of surrounding snow. They are not endangered as the casing is waterproof but it we have to try to keep the sensors level by drilling the pools to drain the water.

Hervé and Audun are responsible for doing an ice core every week in a specific area. The density and salinity are measured to study the evolution of the ice profile.

The last ice activity, the EM31, is the responsibility of Minh-Ly and Sam. Once a week they cover a distance of 3 kilometres over a specific section of ice to calculate the ice thickness. This instrument measures the ice thickness by way of electromagnetic conductivity, determining the distance between the device and the water. After subtracting the snow thickness, which is measured manually, we are able to get the thickness of the ice.

Other automated ice measurements include an inclinometer measures the ice inclination, an Ice Mass Balance (IMB) measuring the ice thickness at a specific point and two thermistors strings measure the temperature of the ice from the surface to the water. 

BIOLOGY

The biology program is conducted by Marion, studying the water column down to 300 meters under the ice surface. The aim is to study phytoplankton, zooplankton and nutrients to understand the food chain. Once a week we collect water samples at several depths using Nansen bottles. Additional samples are collected with nets, our catch is then preserved for later analysis back in France.

OCEANOGRAPHY

The last program and surely not the least is the oceanography program. The CTD allows us to measure conductivity, temperature and depth down to 3000 metres. Water samples are also taken at various depths in the profile. These activities have not been conducted recently because our large winch has had some technical problems that can not be repaired on board without spares. We are therefore patiently waiting for this part. However, we have managed to put together a system using our small capstans to continue the biology program which does not require the same deep depths.

We also have two automated instruments collected data every day. A POPS (Polar Ocean Profiling System) measures conductivity and temperature to a depth of 1000 meters. While a Microcat collects the same information as the CTD and POPS but at a fixed depth. Finally, an acoustic sonar suspended in the water beside Tara listens to a signal transmitted approximately 120 kilometres away. This experiment is to study the propagation of sound underwater for the future development of underwater remote instrument data transfer.

Keeping all of these instruments running, a challenging task in the harsh conditions of the Arctic, is the responsibility of Jean, our Damocles engineer.

Charles

Tara 2006-2007

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