5. Field report
Alert, 6 April, 2006
A look into the tent with the instruments at the drifting seismic station.Enlarge
The three local inhabitants in the ice camp posed for the photographer during the visit. Greg Middleton to the left, Mike Gorveatt in the middle and Jørgen Skafte to the right.Enlarge
Received from Ron Verral and Trine Dahl-Jensen
Edited by Henrik Højmark Thomsen, GEUS
Visit to Greenland and change of plans
6 April, 2006
Weather in Alert: -26, in the morning, sunny, no wind (mid afternoon -15)
No helicopter flights out on the ice today. The weather was beautiful at Alert, but it was bad at the ice camp. It cleared at noon, and the Twin Otter went out with a load of fuel to the fuel cache at the camp. The Canadian expedition leader Ruth Jackson from Geological Survey of Canada joined the flight to see the "drift seismic station" which has been installed at the camp. This station is sending out sound waves in the water from a couple of airguns, which are mounted in the ocean below the sea ice. The sound waves move down through the water to the bottom of the ocean, where they are reflected from the geological layers below the sea floor. Theses reflected signals are recorded by hydrophones (a kind of microphone), which also are mounted in the ocean below the station. When the station drifts with the ice, we will continuously get data about the geology below the sea floor. However we do not have any control over, how the station is drifting. It is decided by Mother Nature, but we will get data along the random route the station is drifting. The station, which is mounted in a tent on the sea ice, is running, but it is not quit operational yet. The airguns were up for testing and the hydrophones have not been installed. Leaving Ruth at the camp, the Twin Otter went out on the western end of the cross line to look for a landing site. They did land at one spot, but decided against it due to poor ice conditions.
Back in Alert a helicopter took off heading for Greenland, where the weather was better. On board was the Danish expedition leader Trine Dahl-Jensen from GEUS. Trine should visit an earthquake seismic station there and ensure that it was operational. It is located at Frankfield Bay in North Greenland just on the other side of Nares Strait. The station is recording earthquakes and it is one of three new stations, which have been installed in 2004 in North Greenland during an early phase of the LORITA-project. All stations are recording earthquakes from all over the World e.g. in Indonesia or Japan. The waves from the earthquakes will move through the earth and will end up at the stations, and by analysing the signals we will get important information about the earth crust locally around the stations. Trine tapped the data from the station and adjusted the sampling rate, so that the station can follow the frequent shots from the LORITA-1 expedition.
Later on the day the weather had improved on the southernmost inner line with high priority for us, and the forecast for tomorrow was good. As the ice conditions on the cross line were bad, we decided to change our plans again and start on the inner line. As you probably can see, we are very dependent on the weather and ice conditions. However we have very professional support in these matters by the Meteorological Service of Canada, Canadian Ice Service and the Danish Meteorological Institute. All three institutions are working together to deliver the best forecasts of weather and ice conditions to our expedition.
To day four new persons arrived to Alert from Greenland - Morten Sølvsten, Arne Olesen, Søren Rysgaard and Martin Blicker. Morten Sølvsten from Royal Danish Administration of Navigation and Hydrography shall measure the exact water depth along the seismic lines with an echo sounder transmitting sound waves. Arne Olesen from Danish National Space Center shall measure the gravity along the seismic lines, as these data together with the seismic data give important information about the geology under the sea floor. Søren Rysgård and Martin Blicher from Greenland Institute of Natural Resources will carry out a separate research project concerning the importance of sea ice in transporting carbon dioxide from the atmosphere to the ocean. The work will be made in connection with the LORITA-activities, but they are also bringing along a CTD-equipment, which can measure the variations in temperature and salinity in the ocean below the sea ice. The temperature and the amount of salt in the water influences the speed of sound in the water, so the CTD-measurements will be used to translate the echo sounder measurements to exact water depths.
Map with the three new earthquake seismic station installed in North Greenland in 2004. FEB: Frankfield Bay; ASS: Aftenstjerne Sø; CFJ: Citronen Fjord. They supplement the permanent earthquake seismic stations at Station North in Greenland (NOR) and at Alert (ALE).Enlarge
Lay out of the earthquake seismic station at Frankfield Bay in North Greenland. The picture is taken during summer time in 2004. Seismometer to the left. Box with batteries and data storage at the ground. Solar panel and windmill on the mast. Enlarge