The second weekly report from this year’s cruise to the deep-sea observatory HAUSGARTEN will present the work carried out by our planktologists and marine chemists.
Plankton comprises all organisms, which float in the water column and cannot swim against currents. It includes (among others) bacteria, unicellular autotrophic algae which are the basis of the marine food web, as well as unicellular organisms which feed on particulate organic matter and are important for the recycling of nutrients. Among the larger organisms in plankton communities the crustaceans are most abundant in our research area. They are an important food source for higher trophic levels, including fishes, whales and seabirds.
Constantly rising water temperatures in Polar Regions promote the invasion of planktonic organisms from warmer regions into areas previously inhabited by cold-adapted species. Besides, increased temperatures in upper water layers will lead to enhanced CO2 uptake, which will cause decreasing pH values and thus ocean acidification. To investigate how the small planktonic organisms respond to changing environmental conditions, we use different types of nets and optical methods to assess plankton samples during our yearly cruises to Fram Strait. In addition we collect water samples in different depths with a rosette water sampler. These samples are filtrated and deep-frozen. Later, in the laboratories at AWI and at the GEOMAR, we will analyse a large set of parameters such as the content, composition, and degradation of particulate and dissolved organic matter (e.g. amino acids, sugars and gel particles), the concentration of algae pigments, and the genetic fingerprints of the bacteria and algae. In addition, we conduct continuous hyperspectral optical measurements using the so-called Ramses radiometer and the AC-S in situ spectrophotometer to assess the transmission and absorption of the sea water.
We also perform a variety of experiments during the cruise. Surface seawater was incubated to study the microbial degradation of so-called “bromocarbons”. These substances are produced by marine cold-water diatoms and arctic ice-algae, possibly as a grazing-defense mechanism. Bromocarbons are, however, also highly reactive, volatile organic compounds and may contribute up to 40% of ozone depletion in the atmosphere in mid latitudes. In another experiment, we test the impact of unicellular heterotrophic organisms (requiring organic compounds of carbon and nitrogen for nourishment) and mixotrophic organisms (able to use a mix of different sources of energy and carbon) on bacterial communities.
Using drifting and moored traps we assess the flux of particulate matter to the seafloor. These particles are, at least partly, of organic origin (dead phyto- and zooplankton) and thus the main food and energy source for deep-sea organisms. The two most important settling particles are “marine snow” and faecal pellets. Marine snow is formed when phytoplankton and other small organic and inorganic particles bump into each other and stick together. Faecal pellets are formed when zooplankton filter the water for small suspended particles and excrete them as small packages surrounded by a membrane. The sinking particles were caught with tubes or outsized funnels that collect the particles in plastic bottles arranged in a loop at the lower end of the cone. A stepper motor exchanges these bottles in pre-programmed time intervals, permitting the recognition of seasonal variations in the food supply to the deep sea.
The downward export of organic matter removes carbon from the surface ocean and enable further uptake of atmospheric carbon dioxide by the ocean. The deeper the organic carbon is exported, the longer it is removed from the atmosphere. However, it is still not know what controls the formation of settling particles, their export to the deep ocean, or how they are degraded and grazed upon during their descent through the water column. During this expedition we quantify the different components of the downward organic flux and identify who is degrading the settling organic particles.
The next weekly report will present the work of our benthologists.
Everybody on board is doing well.
With best wishes from all of us,
Thomas Soltwedel
(with contributions from Barbara Niehoff and Morten Iversen)
