ANT-XXVI/2, Weekly Report No. 1

27 November - 4 December 2009

On November 27, 2009, at 10:30pm, it was “all men on deck” aboard R/V Polarstern, marking the begin of the expedition ANT-XXVI/2. The location of departure was the bunker pier Cabo Negro near the Chilean town Punta Arenas. It was here that the Polarstern had been fuelled during the day with 1400m3 of Marine Diesel for the long cruise to New Zealand. The majority of scientists boarded around noon after an exhausting march, loaded with luggage, over the long bunker pier. They had travelled over 30 hours from Europe, the USA, Korea, and New Zealand to arrive in Punta Arenas in time for the departure of the ship. Seven scientists had already boarded a day earlier, when Polarstern was still docked alongside Mardones Pier near the outskirts of Punta Arenas. They helped unpack the expedition goods and started to set up the laboratories. This work continued unabated while the ship was still in the calm waters of the Strait of Magellan. Due to a delayed departure from Cabo Negro of almost 5 hours, we passed the narrow passage of the Strait in the early hours of the 28th. The snow and ice-covered mountains of Patagonia and Terra del Fuego to our sides were one of the few ‘tourist’ highlights of the long cruise we had just begun, on which we would otherwise be seeing only the vast ocean. However, poor visibility, rain and cold winds diminished the view. This was no weather for spectacular pictures. On board are 45 crewmembers and 43 scientists, technicians and helicopter personnel. The science crew, including 17 women, is a multicultural mix of nationals from Chile, Germany, France, India, Italy, Korea, Malaysia, Austria, Switzerland, Spain and the USA.

The focus of expedition ANT-XXVI/2 is marine-geoscientific studies, which for the first time will take the R/V Polarstern across the entire polar South Pacific. This will be complemented by bathymetric and echosounding surveys along the entire cruise track, sampling of atmospheric dust, hydrographic and biological studies in the water column, and gas exchange between atmosphere and ocean. The aim of the studies is to document the role, evolution, and impact of climatically relevant mechanisms such as the biological pump, circulation and stratification of the ocean, water masses, sea ice extent, atmosphere-ocean exchange, atmospheric circulation and the volume and dynamic of the Antarctic ice sheets on geological time scales. At the moment very little information is available about these processes in the Pacific sector of the Southern Ocean, which is an important region of water mass formation, and the key region for understanding of the evolution and dynamics of the Antarctic ice sheets as it collects ca. 70% of the West Antarctic ice sheet drainage.

Immediately after leaving the Strait of Magellan, in the morning of November 28th, the ship began to sway due to 3-4m high waves in the Pacific Ocean. As a result, the number of scientists at mealtimes dropped and the ship’s doctor was busy handing out medication for seasickness. Many people were now seen with pale faces and the well-known patch behind the ear. After leaving Chilean waters (200 mile zone) on November 29th, the acoustic instruments for mapping seafloor topography (swatch echosounder HYDROSWEEP) and sediment distribution (PARASOUND-sediment echosounder), as well as the sea gravimeter were activated and the first sampling station completed. The first piston core was recovered with a length of 18 meters and documents the climate history of the last 600.000 years. A good start! The multi-corer, used to sample the uppermost seafloor sediments, was also successfully deployed.

Problems occurred with the fluorometer on the CTD probe and the multinet, but both could be fixed in the following days. After this test-station for both the instruments and the workflow of the different working groups, it was time to start the hunt for meteorites! Only 24 hours after the first station we reached the area of the Freden Seamounts. An asteroid hit this area ca. 2.5 million years before present at ca. 70,000 km/h, releasing enormous amounts of energy. A 20 km wide water-crater was generated that reached the seafloor at 5,000 m water depth, an ~100 km3 of water together with deep-sea sediments and meteorite debris were ejected at hypervelocity into the atmosphere. Shock waves spread out over the seafloor and a 200-300 m thick sediment layer, that had accumulated over 40 million years on the Freden Seamounts, was literally blown away and the seafloor under the boiling seawater was plowed. At the edge of the water-crater, a wave-ring several kilometres in height developed and travelled at ca. 700 km/h across the globe. In as little as 1-2 hours after the impact, the West Antarctic and South American coastal areas were devastated a tsunami up to 100 m high. Several hours later, the disturbed sediments and meteorite fragments fell back from the atmosphere, started to accumulate on the disturbed seafloor. All this is known from previous studies and model simulations. We wanted to complement these results and locate the exact impact site (‘ground zero’). Model simulations of the impact event have hinted at this location. After surveying the area and sediment sequences using PARASOUND, eight positions were selected. At water depths of 3,000-5,000 m, up to 23m-long sediment cores were ‘punched’ out of the seafloor. Not an easy task to reach the meteorite layer under the 2.5 million year old sediments. We were ultimately successful at three locations and obtained data from an as yet unstudied area. The postulated impact site, however, could not be identified.

Before leaving the Freden Seamounts, an 18-hour seismic survey was conducted, but unfortunately technical problems occurred that disturbed the recording of data. We are now on the way to a new study area. The sediment cores containing meteorite already have been opened. They document enormous destruction of the seafloor and massive meteorite layers deposited above 40 million year old sediments. On Sunday we will have a ‘meteorite show’ in the sediment lab and all participants will be able to touch 4.5 billion year old ‘star dust’. Still another ‘tourist’ highlight! This however, was not without nerve wracking (at least for the chief scientist) and hard work around the clock for everyone. In this first week we recovered 185 meters of sediment core. We are working in two shifts to measure physical properties on all of the cores and open others to take initial samples and document the sediment sequences and stratigraphy.

The weather god has been good to us so far: wave heights of only up to 3-4m and the sun even came out one day. That is, perfect weather in the so-called ‘screaming fifties’. Next week you will hear more from us when we get to the ‘roaring forties’, when Santa Claus will come on board. Hopefully he won’t get seasick. All participants are well and are getting along despite some language barriers.

Rainer Gersonde
(Chief Scientist ANT-XXVI/2)