Punta Arenas – Las Palmas – Bremerhaven
11 April – 24 May 2009

On 22 April POLARSTERN reached the southern end of the Vema Channel after leaving the Patagonean shelf and crossing the Argentine basin. This submarine canyon measures several hundred kilometers. It enables Antarctic Bottom Water to flow equatorwards across the Rio Grande Rise. Its sill depth amounts to approximately 4600 meters. Two nearby CTD stations were occupied. Revisits to the channel entrance since 1972 have revealed a slide tendency towards higher temperatures. This trend was confirmed by our latest observations.
All underway instruments and probes for vertical soundings are in operational conditions. Intermediate problems with the ADCP and a pump system could be solved in short time. At the beginning of the cruise we agreed to introduce weekly the various research activities on group-by-group base. Today it’s the turn of Björn Fiedler and Inga Piller from the division of the Chemistry Research Unit of IFM-GEOMAR in Kiel:

One of the goals during this transit is to evaluate a broad range of different sensors for the exchange of matter between the ocean and the atmosphere. Here, we are focusing on carbon dioxide as a greenhouse gas for which different analytical methods are available, in order to determine its concentration in the ocean and in the atmosphere, respectively. Novel sensor techniques and measurement systems are partly in use on different applications. Therefore a much better coverage of observations in the oceans in terms of spatial and temporal distributions might be possible in future (e.g. on profiling Argo floats).
On our long journey from Chile to Germany we are passing a broad range of climatic and oceanic regimes in the whole Atlantic. This facilitates a perfect situation for our sensor evaluation project. While steaming, we are pumping seawater through our instruments for testing our sensor setup constantly.

Our main focus lies on a new CO2 sensor, which can be used on many applications due to its small size. First comparisons with classical instruments have pointed to a good accordance with those. As a reference for our field tests we are collecting water samples on a regular basis. Analyses will be carried out later in Kiel.
During the upcoming weeks we are going to carry out further tests with the sensor, mounted on the CTD rosette frame. First vertical profiles of this sensor, combined with water sampling, will be utilized for a better characterisation of the sensor’s behaviour in the water column.

Furthermore, a novel optical nutrient sensor, which is also included in our setup, is monitoring the nitrate concentration in the ocean surface. To evaluate precision and accuracy of the sensor, nitrate concentrations are determined by a classical wet chemical method. First results of our measurements are showing a quite good accordance between both methods.

All are doing well on board. We are looking forward leaving autumn in the south in exchange for spring beyond the equator.

Greetings from a lonesome spot called Vema Channel far in the east of Brazil’s secret capital Rio de Janeiro.

Walter Zenk (Chief Scientist)
24 April 2009