The German GEOTRACES GI07 cruise in the Indian Ocean is completed!
By Eric Achterberg, cruise co-chief scientist
The German research cruise SO308 (along the GEOTRACES GI07 section) was completed on the morning of December 22 (2024) as we sailed into the port of Fremantle (Australia). The off loading of containers was conducted swiftly. Getting the biosecurity permissions organised for the airfreight, seafreight and frozen goods transport was a little more challenging and took some negotiating. In the end all was solved and the frozen goods, water and sediment samples are now on their way to the various labs around the world.
We have in total sampled 51 stations along our transect of about 11500 km between Durban and Fremantle (Fig. 1). A total of 16 stations were superstations with an additional CTD deployment with seven in situ pumps. We had planned 51 stations, and we also completed them, with the locations of most stations as initially planned. This is rather unique in my experience as typically there are a range of changes to the station programme on our expeditions. We had to sail somewhat further south in the region south of Reunion and Mauritius, in order to avoid the strongest impacts of an westwards moving hurricane.
The Sonne cruise SO308 was very successful, and we achieved the majority of our objectives. We sampled for aerosols, dissolved and particulate trace elements and isotopes in the water column, sediments using a mini-multi-corer, and particle export including biomarkers for particle degradation. In addition, we conducted an extensive biology programme, aligned with the ambitions of BioGeoSCAPES, which included collection of proteomic and metagenomic samples, assessment of methane producers, (micro)nutrient limitation bioassays of phytoplankton growth, and assessment of diazotrophy. We deployed 19 Argo profiling floats, many of them with biogeochemical sensors, along the transect for the US and German Argo communities.
In the coming months there will be plenty of samples to be analysed, and then manuscripts to be written. The success of the cruise was due to the great international team effort from all involved (Fig. 2), both on land and on the vessel. In particular I would like to mention the captain and crew, who contributed greatly to the success of the cruise.
Eric Achterberg and the SO308 team
