Much of the work conducted during PS124 focuses on the deployment and recovery of sensors and equipment designed to allow us a better understanding of the characteristics and dynamics of the water masses and ice in the southern Weddell Sea. This is not the exclusive research aim, however.
To complement the water column and ice research, the seafloor is a focus of study by several groups, including the Ocean Floor Observation and Bathymetry System (OFOBS) team.
Made up of benthic ecologists, technicians and in conjunction with the onboard bathymetry team, the OFOBS device has been deployed during many cruise nights to investigate the diverse seafloors of the southern Weddell Sea.
The OFOBS is a towed device, connected to Polarstern by a special glass fibre and power cable, capable of allowing high data and power connectivity to depth (Fig. 1). The power and data communication is necessary as the OFOBS system is an advanced research platform, supporting high resolution still image camera, video camera, forward and side facing sonar systems, three accurate positioning systems, and a host of other support instruments. By being able to interact with the OFOBS in real time from the ship, the very best data can be collected during deployments. The OFOBS is an updated version of the Ocean Floor Observation System (OFOS), used in Antarctica and the Arctic for a number of years, and is also occasionally deployed from other research vessels, such as the Sonne from Germany and the new Kronprins Hakkon icebreaker from Norway. The device has been used to film the deepest ever observed benthic octopuses in the Pacific and recently, the crawling deep sea sponges of the Arctic.
During PS124, the OFOBS is used to collect data from a range of contrasting seafloors. Not all the seafloor is muddy and unoccupied. We find numerous interesting habitats, which we have mapped with the device… some of which we now introduce based on the following three photos:
- On one of the first dives, the images of the OFOBS reveal many dead ice fish (Fig. 2). Dead cadavers are a welcomed feeding opportunity for many animals as nutrients are often rare in such extreme environments. The octopus clearly enjoys its newly found food source. Some sea stars are also taken advantage of this feast.
- Dive no. 18 has quick changes of habitat at heart (Fig. 3). Different kinds of bryozoans are present throughout, but the megafauna community changes from a few sea stars and sea cucumbers with beautiful feather stars swimming in the water column to a forest of soft corals, sponges and tunicates. Sessile feather stars are also observed.
- On the 20th dive, we encounter a muddy seabed with a benthic community dominated by solitary barrel sponges (Fig. 4). These sponges can reach a height of approximately 50 cm and are often colonized by other benthic organisms such as feather stars, brittle stars, and sea cucumbers as these are not able to settle on very soft sediment. Additionally, as most of these animals are suspension feeders, they benefit from the extent of the sponge into the water column. If you look closely you can also see an ice fish (Channichthyidae) using the hollow sponge as a hiding place.
PS124 sends regards from the passage, only a few nautical miles wide, caused by the break-up of iceberg A74 from the Brunt Ice Shelf.
Hartmut H. Hellmer (Chief Scientist)
