[Translate to English:] Observations of the ocean’s temperature and salinity at different locations and depths – key parameters to assess its state - depended until recently on ship-based expeditions and deep-sea moorings, limiting our ability to monitor oceanic change at adequate resolution and over necessary periods in time and space.  However, with the turn of the century, automated systems gained relevance. The current backbone of the Global Ocean Observing System (GOOS) is the Argo system, which uses an array of >3000 profiling floats (Figure 2).

Until recently, Argo was restricted to ice free oceanic regions, as the floats needed to surface regularly to be localized and to transmit its data.  The Hybrid Antarctic Float Observing System (HAFOS) extends the international Argo array into the seasonally ice covered Weddell Sea (Figure 3) and provides additional deep ocean observation which are of particular relevance in this region.

HAFOS builds on vertically profiling, ice-resilient floats (Figure 4) and a set of multifunctional deep-sea moorings deployed across the Antarctic Circumpolar Current and throughout the Weddell Gyre (Figure 5), serving to

a) obtain hourly oceanographic data at selected sites and depths, including the deep ocean,

b) host sound sources used to track Argo floats under the ice, and

c) host passive hydroacoustic recorders to monitor the presence of Antarctic marine mammals.

HAFOS was first implemented to its full extend in 2012/13 during Polarstern expedition ANT-XXIX/2, yet subsets of the system existed in various configurations since 2002, allowing for the development and testing of components.  HAFOS moorings, due to their battery driven instrumentation, need to be exchanged every second to third year during expeditions with RV Polarstern, which also serve to collect spatially highly resolved CTD sections and to deploy additional ice-resilient floats (Figure 6).