PS100 - Weekly Report No. 4 | 8 - 14 August 2016
Back at the Greenland Ice Shelf
In sunny weather and light sea ice conditions we find ourselves once again on the shelf of Greenland –this time in Norske Trough. In the beginning of the week we were able to accomplish most of the oceanographic, biological and biogeochemical workload planned along the zonal transect through central Fram Strait along 78°50’N. Subsequently we added to the mooring array deployed along the Greenwich Meridian in the second week of the expedition the southernmost mooring at 78°10’N.
We then left the work area toward the Southwest in the direction of the Greenland shelf. Some days earlier, we had received a request by French colleagues, who had installed a special buoy containing a number of sensors on a drifting ice floe in the central Arctic the year before, in order to continuously observe ocean, sea ice and atmospheric parameters. Meanwhile the buoy had been carried by the Transpolar Drift into the East Greenland Current and had subsequently continued its way toward the south along the shelf break. We were asked to recover the buoy before it might be destroyed. The position data of the buoy transmitted by satellite showed that we should pass by it during our transit to the new work area. As envisioned, in the morning of August 10 the crew of Polarstern were able to recover the buoy from a small ice floe showing signs of decay but also footprints of a polar bear. In addition a second – partly damaged – object was recovered from the same ice floe, which turned out to be a snow buoy from the Alfred Wegener Institute. The East Greenland Current carries polar water covered by the ice formed in the Arctic Ocean toward the Atlantic Ocean. Here we also find presence of the so-called “dirty” ice: ice that is brown to black from its sometimes heavy load of mud. Just like the buoy this muddy ice must have crossed the Arctic Ocean within the Transpolar Drift.
We then continued our way to Norske Trough, along the axis of which we aim at investigating the inflow of warm Atlantic water from Fram Strait to the inner shelf of Greenland. In addition, the geological work programme of this expedition has finally started. From the analysis of sediment cores, the changes of the Greenland ice sheet in the Earth’s past will be investigated.
In this weekly report we would like to focus on the GEOTRACES team – the largest science team on board. GEOTRACES is a worldwide program that investigates the cycling of trace elements and isotopes in the ocean. The importance of studying such elements is that some of them are essential for life and thus their availability (together with the traditional nutrients: nitrogen and phosphorus) may determine the growth of biota, such as for example, algae. The distribution of some other trace elements informs us about the cycling of biological matter in the ocean (e.g. iron or cadmium), about ocean circulation patterns (e.g. natural or artificial radionuclides) and about the interaction of the ocean with the continents (e.g. rare earth elements). In addition to this, by learning and understanding the cycling of trace elements in the ocean we may find some answers related to climate in a way that we can use the chemical signals stored in marine sediments to reconstruct the climate of the past.
In the framework of GEOTRACES many expeditions have been completed already in the world ocean, including an expedition to the Arctic Ocean last year, where Polarstern was one of three ships performing a synoptic study. 15 GEOTRACES scientists take part in this expedition targeting the Fram Strait in order to unravel the links between the Arctic Ocean and the Atlantic (with Fram Strait being the main gateway of waters between the Arctic and the global ocean). The GEOTRACES scientists on board Polarstern measure a wide spectrum of elements in the water column. Some of these elements need to be collected under ultra clean conditions, as the ship itself could be a source of contamination. Iron and mercury are two good examples of this. To this purpose, the GEOMAR team uses its own trace metal clean water sampling system consisting of a CTD-Rosette equipped with 24 trace metal clean Go-Flo bottles that can be closed at desired depths in the water column. Other groups are not so concerned about contamination but they need very large sample volumes for the measurement of isotopes with very low concentrations in the seawater. They use a large-volume CTD-Rosette water sampler consisting of 22 bottles of 25L each. Another group studies the composition of the particles that are suspended in seawater. They need to filter 100s of liters of water that cannot practically be brought on deck by the water samplers and therefore they use the so-called in-situ pumps. These devices are mounted on a wire at different depths and pump water during several hours so that particles are retained on the filters. Other than water samples, atmospheric particles are also collected and several incubation experiments are carried out to determine the limiting nutrients for phytoplankton growth in Fram Strait.
During the first three weeks, in an intensive campaign we collected our samples along the zonal section across the deep part of the FRAM strait between Svalbard and the East coast of Greenland. The output and results of the different parameters will help to determine trace element fluxes into and out of the Arctic Ocean, supported by the physical oceanographers and by the experience from the long time series of current meter observations described in Weekly Report 1.
Best wishes from Polarstern
Torsten Kanzow and the GEOTRACES team
Further information on the GEOTRACES program: www.geotraces.org
GEOTRACES Data and graphics of elemental distributions in the ocean: www.egeotraces.org