Big relief! As of last Sunday our “Large Rosette” is finally working. The Large Rosette is just another device we use for measuring vertical casts of temperature and salinity and taking a series of water samples at the same time. In the very moment when our Dutch colleague Sven Ober finished repairing the malfunctioning “Ultra-Clean Rosette”, the next rosette signaled troubles and needed repair. What do we need all the different “rosettes” (which is the name of a ring of water samplers) for?

Each drop of ocean water has a certain temperature and a salinity. Temperature is a fairly simple parameter. Salinity is a more complex parameter as there are many types of salts dissolved in the ocean. Furthermore, the ocean contains many different substances. All the elements in the period table are present along with many of their different isotopes. Isotopes are atoms of the same element that all weigh a little different because they have a different number of neutrons. Taking just iron for an example: Iron is present in the ocean in four forms: as tiny particles, as even tinier particles (called colloids), dissolved in the water, and attached to organic material. All of these can exist in four isotope varieties. These sixteen variations of iron behave differently in the ocean. We want to determine the spatial distribution of all the different forms of iron, because they and their differences can tell us a lot about the ocean currents, about the exchange between ocean and atmosphere and about the chance of the ecosystem to adapt to changes in the Arctic Ocean.

However, our biogeochemists do not only analyse iron, but altogether more than 100 different substances. For this purpose we collect hundreds of liters of water from all depths of the ocean. Our “normal rosette” carries 24 bottles of 12 liters. So we can sample 24 depth levels. But this is in no way sufficient to satisfy all demands – particularly not when the biologists also want water for their investigations of phytoplankton. We could then do one or more additional casts, but this takes a lot of time (which on a ship is precious). So our Dutch colleagues built an extra “Large Rosette” which carries 24 bottles of 25 liters. With this device we bring 600 Liters of water on deck with one cast. For comparison: this amount of water contains just 0.00001 grams of iron.

Anyway, the samples for iron determination are not taken with the “Large Rosette”. It is not clean enough, since there is metal on the ship everywhere. This would contaminate the samples immediately unless severe hygienic precautions were taken. Therefore, we use for the sampling of trace metals an “Ultra-clean Rosette”. This rosette is not lowered with the usual 6000 m long steel cable, but with an extra carbon fiber line. Once the ultra-clean rosette is on deck it is moved into an ultra-clean container. Only the cleanest of us are allowed to enter while wearing protective clothing (protecting the samples, not the scientists). While hardly being allowed to breath they draw the water from the bottles.

Hidden by the bottles, in the very cores of the various sampling rosettes, are electronic sensors, called CTD, that measure temperature and electric conductivity and thus salinity. These properties determine the density of sea water which is closely linked to a large part of ocean currents, among them the Atlantic-wide overturning circulation. At the same time, the wide-spread temperature measurements provide us with information on whether the Arctic Ocean has continued warming since our last survey 4 years ago. Last week, we had used (and described here) the underway-CTD; now we use the CTD in the various rosettes. But every now and then we make ourselves independent from them and measure temperature and salinity with an expendable CTD, or XCTD. Here, a small probe falls from a launcher that is connected through a thin wire that spools off. The data are stored in real time on a laptop connected to the launcher. At ca. 800 m depth, the wire breaks and no more data is received and the sensor is lost forever. We can easily take this XCTD system into a helicopter, fly to an ice floe some distance from the ship and take a CTD cast, and save even more ship time!

The study of the many substances contained in the water are a contribution to the international program GEOTRACES. Two more ships are operating in the central Arctic this summer for conducting the same analyses: the US Coast Guard ship Healy works in the Pacific sector of the Arctic, and the Canadian Coast Guard ship Amundsen covers the straits in the Canadian Arctic Archipelago. Thus, we will obtain an Arctic-wide pattern of the distribution of the individual substances and can determine budgets (the amount) and fluxes (the rate of flow across an area). Will we meet the Healy? We don’t know yet, since the very dense ice cover makes any steaming progress unpredictable.

During the last days, temperatures have been around -5°C which is pretty cold even with respect to being in the Arctic. Every lead is refrozen and all melt ponds that we remember from other years as beautiful turquoise pools in the white landscape are covered with 10 centimeters of new ice and blown over with nearly as much snow. This makes working on the ice easier in some respects and more challenging in others. We had two ice stations last week and next weekend we will report on our research related to sea ice.

For today, all the best, regards!    

Ursula Schauer