“Groundwork”

The sediments are partly processed to assess how much organic matter from primary production at the sea surface has settled down to the deep-sea floor, thereby supplying a food input to the benthic organisms. For this we analyse the concentration of algal pigments (chlorophyll and its degradation products) in the sediments. Another parameter immediately analysed on board is the activity of bacteria living in the sediments. To determine this, we nourish the bacterial community with a special substrate and measure how much of this is cleaved by the bacteria over a certain time span. All remaining sediments are either deep frozen or fixed with formalin for later investigations at the home lab.

For the sampling of smallest sediment-inhabiting organisms at the deep seafloor, we are using the Multiple Corer (MUC). The MUC is able to retrieve up to eight sediment cores of 10 cm in diameter and approx. 40 cm in length during a single haul. Individual cores were subsequently subsampled for bacteria and the so-called meiofauna, which consists of invertebrates of up to 1 mm in size. Of primary interest to us are the bacterial communities in the sediment surface layers. Bacteria are very susceptible to environmental changes, such as fluctuations in food availability or in temperature and can therefore be used as first indicators of changes in the ecosystem. Horizontal and vertical meiofauna distribution patterns will be examined as part of doctoral dissertation, thereby continuing a unique time-series started in the year 2000.

Larger sediment-inhabiting organisms, the so-called macrofauna, are sampled by a Box Corer (BC). This gear retrieves one large block of sediments covering an area of 50 x 50 cm and 50 - 60 cm in height per haul. BC samples are sieved through 1 mm and the macrofaunal organisms remaining on the sieve are subsequently preserved for later counting and taxonomic analysis.

A Sediment Profiling Imagery (SPI) camera is used to take a “look into the sediments”. Once the frame of the camera system is set on ground, the middle part of the gear, carrying the camera penetrates into the sediment. The SPI camera takes pictures of the uppermost sediment-layers and could unveil e.g. vertical alterations within surface sediments or, by chance, burrowing organisms in tunnels and chambers, in their natural environment.

To assess spatial patterns in the large epibenthic fauna (e.g. sessile sea lilies and mobile sea cucumbers, sea urchins and crustaceans), we use the so-called Ocean Floor Observation and Bathymetry System (OFOBS). The OFOBS is equipped with a downward-looking camera and is towed for four hours at about 0.5 knots by the ship one and a half meters above the seafloor, along the same course tracks every year. Changes in the bottom-dwelling fauna (densities and composition) can be deduced through comparison with images from previous years.

Benthic invertebrates dominate seafloor communities in both abundance and biomass. Still, very little is known about how these organisms reproduce. The most abundant species reproduce via planktotrophic larvae, i.e. larvae that could easily be transported by bottom currents, thereby enhancing their geographical distribution. During our cruise we try to collect invertebrate larvae with pumping systems attached to Bottom Landers moored at the deep seafloor for a few days at a time. It would be an exciting result to match the larvae we collect to the adults that are common at HAUSGARTEN and describe the larval forms of some Arctic deep-sea species for the first time.

More than two decades of long-term investigations at HAUSGARTEN have also enabled us to (regrettably) show that the amount of man-made litter in the Fram Strait has increased markedly. In the next (and final) weekly report, we will describe the work of our colleagues assessing anthropogenic impacts (microplastics and marine litter) in the area.

Everybody on board is doing well.

Best wishes from all of us,

Thomas Soltwedel