Our wonderful cruise is now definitely coming to an end. We are nearly on our way back home, heading for one last station where we will cast a final CTD and send an ARGO float on its journey. These floats are part of a giant international project and basically drift with the water currents, all the while consistently measuring the salinity, temperature and pressure of different water layers. While writing these lines, there are about 4000 floats deployed in the world’s oceans. Tonight, it’ll be 4001. The floats are able to adjust themselves to maintain a certain depth and take measurement profiles along vertical transects. Every now and then (approximately every 10 days) they dive up to the surface and send the acquired data to a central data base. Being equipped with a SIM card, the communication between the ARGO on the sea surface and the data centre happens via satellite – this is the only stable and reliable way to transmit data, especially when being so far from land and away from any network reception. Once transferred, the raw data are processed and quality flagged automatically. This data freely and publicly available – if you are interested in the project and its data, you can visit the German hydrographic office website, who provide a platform for the ARGO program as well as regular updates on the whereabouts of active floats.
All of those measurements, data handover, and their publication happen within minutes to very few hours – hence anyone can observe the ocean parameters in near real-time. Scientists all over the world use these data to compute and predict currents, temperature variations, and weather and climate forecasts – they can even be used as tsunami early warning systems.
The life span of an ARGO float is about 4-5 years which is, compared to their small size (~ 2 x 0.3 m), a very long time – considering constant data recording, as well as large temperature and pressure variations, is battery intensive. When their expiry date has almost arrived, they travel to the surface one last time to send an EOL (end-of-life) message saying goodbye to the operators and then dive down to 1000 m to die. Unfortunately, there is no effective procedure yet for retrieval and re-use which is why all the ex-ARGOS gather in the water column at -1000m. However, efforts are being made to design a recovery method and involve recyclable material for the ARGO construction process. Once in a while, dead ARGO floats are being caught by accident. Last week, one was retrieved by a Portuguese fishing vessel – it is now on land and back in the hands of the operator. Its final words are not yet spoken and maybe it gets a chance to live a second life!
From my side, unfortunately these are the final words on this blog. It has been a true pleasure writing it and I would like to say thank you to you, dear readers. I hope you keep an eye on the iAtlantic homepage and on the Senckenberg website – our mission goes on and so does ocean research! At the end of an expedition, we scientists always have the ideas for the next one. The story will be continued…