PS101 - Weeklý Report No. 1 | 10 - 18 September 2016

PS101 KARASIK

[19. September 2016] 

The aim of POLARSTERN expedition PS101 is to study the geophysical, geological, geochemical and biological processes at seamounts and sources of hydrothermalism at Gakkel Ridge of the Central Arctic. Such integrated studies of ultraslow oceanic spreading zones are rare, because the most extensive of these systems, the Arctic Gakkel Ridge and the Southwest Indian Ridge, lie in poorly accessible areas.

The aim of POLARSTERN expedition PS101 is to study the geophysical, geological, geochemical and biological processes at seamounts and sources of hydrothermalism at Gakkel Ridge of the Central Arctic. Such integrated studies of ultraslow oceanic spreading zones are rare, because the most extensive of these systems, the Arctic Gakkel Ridge and the Southwest Indian Ridge, lie in poorly accessible areas.

We are now returning to the area to assess in an interdisciplinary study how the seamount and vents alter their environment, from hydrographic conditions to the microbial community structure. Allso, our research contributes to assessing the state of the Arctic Ocean system including the sea ice decline and the biogeochemical and biological functions within the central basins. To accomplish this, we will also exchange components of the FRAM Observatory infrastructure. The seamount work contributes to the research program “Geosphere Biosphere Interactions” of the Excellence Cluster MARUM of the University of Bremen. Two different research communities  - the deep-sea and space research communities - are joining forces to better understand how extreme environments under ice could be analogues to distant planetary bodies. Hence, this expedition involves the instrumentation and experience of the ROBEX and PSTAR (“Planetary Science and Technology Through Analog Research Program) NASA/WHOI teams. We are 46 scientists and technicians (Fig. 2) from five different countries during the PS101 mission from 09.09. to 23.10.2016.

We left the port of Tromsø midday of the 09.09.2016 and enjoyed the beautiful Norwegian coastline for a few hours before reaching the open sea. There was much equipment to be unpacked and installed in all the labs of Polarstern. A Major initial piece of work was to install two newly delivered fiber optic cables and to get them to function with our new telemetry-guided instruments, which was a challenge for the crew and scientists alike. The research program started with the deployment of several oceanographic buoys for French colleagues. On 11.09.16 we tested our telemetry-guided equipment at a station East of Svalbard, including the zooplankton recorder LOKI and the Ocean Floor Observation System OFOS.  The latter was delivered just prior to the commencement of the cruise, after having received an upgrade with two sonar systems to map the ocean floor in ice-covered seas. The first images of the seafloor, taken from 250m water depth on the Norwegian shelf, showed abundant benthic life and an undisturbed seafloor, making the mouth water for the potential discoveries to be made at Karasik seamount in the forthcoming days.

We reached the sea ice margin at 81.5°N at midnight of the 11.-12.09.16. A closely spaced oceanography transect was started using underway measurements along 30°E longitude, down the slope into the Nansen Basin. Free falling xCTD probes can be used to sample salinity and temperature in the upper 1000 m while the ship is moving at full speed. On 13.09.16 we reached the deep basin at 4000 m and completed a full-depth CTD-cast with water sampling, of which every milliliter was used by the onboard scientists in analyses. The oceanographers detected a further warming of the deep waters compared to 2015 – an ongoing process they have been monitoring for more than a decade (Fig. 3).

The sea-ice observations made during our missions will contribute to the better assessment of the Arctic change and its ecosystem consequences. We will deploy various autonomous sea ice buoys that will send year-round physical and biogeochemical data to researchers and data archives onshore, even when no research vessel is within the Arctic. The experienced Arctic researchers on board – and also those following us at expedition.awi.de from home – have noticed already, by our speedy course through the ice, that something has changed in the far North. We have an average velocity of 6 knots through the dense autumn ice – a speed made possible by the substantial thinning of the sea ice and the loss of multiyear ice during the past few years. In fact, the sea ice physicists on board estimate that 2016 sets a new record low of sea ice volume in the Arctic since the onset of satellite observations. The new ROV BEAST which we used for the first time at the first ice-station of this mission (Fig .4) transmits images from the melted underside of the ice floes. Also, we encounter vast areas of open water, which are beginning to freeze during the last few days. We find these open regions easily via the the new sea ice geographical information system – short: ICEGIS - we are currently testing onboard (Fig. 5). It displays overlaying  maps of satellite and radar images of the ice, and shows the predictions of computer drift models and wind velocities over our seafloor maps. It is a great tool for way finding and for planning sampling simultaneous research work both on and under ice, and we send grateful thanks to all the programmers involved in realizing this innovation.

During the night of the 14.-15.09.16 we reach the position of our first deep-sea observatory in the Central Arctic basin. It is a mooring of our infrastructure program FRAM packed with physical and biogeochemical sensors and sampling modules, which provide rare year-round observations and samples. Two of these observatory systems were deployed last year in 2015 and will now be recovered. In the morning of the 15.09.16 we retrieved all instruments safely from the first of these and are now looking forward to read out the sensor data. Unfortunately, these are the last year-round interdisciplinary observatories in the Central basins for a few years, as we could not secure reliable shiptime for regular deployment and recovery. Too few ships are capable of reaching these icy locations and carry out such deployment and recovery work.

The station in the deep Nansen basin ends with a dedicated plankton and benthos sampling. The sea ice seems to have already lost its ice algae, the water is deplete of nutrients but full of zooplankton of all sizes and forms – copepods, amphipods and appendicularians are the forms of life we can admire under the microscopes of our colleagues. The seafloor too shows an interesting find, reminiscent of our observations in the last sea ice minimum in 2012: It is littered with greenish clumps of the sea-ice algae Melosira arctica, which sank from the ice. Normally they form thick clumps and long threads in the ice, but warm temperatures and rapid movement of floes rip them off the ice and let them sink to the seafloor. At a second glance we see that something is different. The herds of transparent seacucumbers and brittle stars picking on the algal falls we observed in 2012 are gone, there is still not much life, and we can only see some tiny crawling sea anemones profiting from this food fall phenomenon (Fig. 6).

We then continued further to the Karasik seamount, our main target area. On the way during 16.-17.09., we carried out 2 transects with the so-called T-lance, a giant thermometer to measure the heat flux of the seabed. Ours can penetrate 5 m. The first site showed only cold background values, but the one at the foot of the seamount gave the first indications of some advective flow of porefluids. In the night of 17.-18.09. we have reached the tip of the mount. It has become quite cold but still rarely sunny, outside temperatures are -5°C, and frost flowers are forming on the newly frozen open water zones. Since we have arrived at the seamount we could already fill in a few white spots on the seafloor map, but much remains to be charted, especially with the precision now possible with our high-resolution tools. The next task is the Tow-Yo mapping with the CTD equipped with lots of sensors to find out whether there is any hydrothermal venting nearby. Tow-Yo means the CTD is towed up and down through the water column and along a transect, to be able to discover fluid emissions. But the highlight of Sunday surely was the first OFOS transect across the plateau of the seamount. While I write we are looking at the first images from the OFOS. What we have discovered we will tell in the next weekly report – So stay tuned.

 

All participants are in good health and are sending greetings to families, friends and colleagues.

Antje Boetius

Contact

Science

Antje Boetius
+49(471)4831-1100
Antje.Boetius@awi.de

Scientific Coordination

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

Assistant

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