Archive of News and Press Releases

PS94 Weekly Report No. 5 | 15. till 20. September 2015

Searching for suitable ice

[20. September 2015] 

On Friday evening we spent three hours searching for an ice floe. Not that there was no ice – just as during the whole cruise so far, also now our progress is hampered by huge ice floes that we have to circumvent, and ridges that we have to pass by ramming.

But at least here, in the Siberian Arctic, some of the ice is a bit weaker than further north. But since strong ice floes, mushy ice and even thin new ice is equally covered by a thick layer of snow and since, in addition to that, the visibility is reduced in the dim light of the night hours it is hardly possible to distinguish between the different ice types from the bridge. However, for a combined station, with access to an ice floe on the port side and operation of the water instruments on the starboard side, we need the following: an ice floe that is large enough to achieve a representative ice thickness survey; that is strong enough not to break when the ship is pushing against it; the ship must be able to go alongside with the wind from starboard side and in the same time there must be a fair area of open water on the starboard side; and this situation must foreseeably remain so for the next 20 hours. Eventually, this combination was found and the work could begin.

Despite it was late in the evening, all ice groups were ready to enter the ice floe with their equipment to conduct their various tasks for the next 6, some groups for the next 12 hours at temperatures around -13°C and at snow drifting with wind of Beaufort 6. The biogeochemistry group, for example, marked a small area to take ice samples at nearly the same spot. Using a tube-shaped drill they drilled 15 ice cores. The cores were cut into slices representing the ice layers from top to bottom. Thoroughly documented, the slices went into bags and were transported onboard to be analyzed by the various groups. For example, one core will, after melting, be filtered for ice algae. Here they are typically dominated by the diatom Melosira arctica which forms long chains and which we see often from the bridge coloring the ice with large brown clots.

Another core was taken for determination of methane content. On earlier cruises we found unexpectedly high levels of methane in the sea ice. Now we want to understand how repeated freezing and melting is influencing this high methane content. There might be a relationship between the methane in the ice and the formation of DMS (Dimethylsulfid). DMS is a climate relevant gas in the atmosphere formed during degradation of DMSP (Dimethylsulfoniopropionat) which is produced by ice algae for frost protection.

All other cores were distributed to a growing group of „customers“, since the GEOTRACES group is increasingly interested in also investigating sea ice for capturing the full budgets of the various trace elements in the marine Arctic.

One of the key GEOTRACES stations during our cruise was, however, the crossover station conducted earlier this week in the Makarov Basin. This summer, altogether three expeditions are designed to map different regions of the Arctic Ocean for getting a pan-Arctic view of the distribution of trace elements and isotopes (TEIs). To ensure a quasi-synoptic view we have to make sure that each parameter can be directly compared to the one measured in the American and Canadian regions. To do so the different cruise transects intercept at so called crossover stations. The crossover stations are located in regions with small temporal variation, i.e. where no currents lead to fast water exchange. The German-American crossover station was in the Makarov Basin right in the middle of the Arctic Ocean - not affected by boundary currents and remote from shelf seas with their variable supply of trace elements.

Exactly at 87°30 N, 179°59 E, we have been conducting a long suite of water sampling casts with our two rosettes, about two weeks after the GEOTRACES colleagues on the USCGC Healy have conducted exactly the same sampling. The parameters to be compared to the different counterparts are natural and artificial radionuclides (i.e. 129I, 230Th/231Pa, 210Pb/210Po, 236U, Pu-isotopes), rare earth elements (i.e. Nd), dissolved and particulate trace metals (i.e. Fe, Zn, Co, Ni, Cu, Hg, Pb) and their stable isotopes. Every parameter is measured as a full water column profile, targeting the same sampling depths. In addition to sampling for our own analysis, we took extra samples to send them out to partner laboratories to organize a broader intercalibration for some key elements. The challenge of such a practice is not only reaching the exact location and probing the same depths, but also measuring the entire suite of parameters some of which are present only at extremely low concentrations (i.e. Hg concentrations are only a few picomoles per liter and only one million atoms of 129I can be found in one liter of seawater). After successful intercalibration the datasets of all three Arctic cruises will be merged into the GEOTRACES Intermediate Data Product 2017 (to be released in Goldschmidt Conference in Paris). Let’s keep fingers crossed that the differences between the different labs’ analyses remain small!

With our best regards from Polarstern,

Ursula Schauer

 

With contributions by Nuria Casacuberta and Ellen Damm

Contact

Scientific Coordination

Rainer Knust
+49(471)4831-1709
Rainer Knust

Assistant

Sanne Bochert
+49(471)4831-1859
Sanne Bochert