Water World

To investigate how algal and bacterial communities respond to changing environmental conditions, we collect water from different depths with a rosette water sampler. These samples are filtrated and deep-frozen. In addition, surface water samples are collected by the automated filtration device AUTOFIM, which is coupled to the seawater circulation system of the ship. Later, in the laboratories of the AWI and the GEOMAR we will measure a large set of parameters such as the nutrient contents, chlorophyll a concentrations, carbon and nitrogen contents, and the genetic fingerprints of the algae and bacteria.

Further to our classical water sampling program, this year we are attempting to implement a range of analytical equipment to measure various biological and chemical properties of surface waters. These devices include an autonomous underway nutrient sampler, a mass spectrometer that can measure the concentrations of argon and oxygen to calculate the amount of production in surface waters, and a device to measure CO₂ in the water. The data will be coupled with those from “Ferrybox” measurements documenting changes in temperature, salinity, chlorophyll, and oxygen. We also applied numerous new biogeochemical sensors to test their performance and accuracy. The information we get from this work will allow us to make choices about which kinds of technology our best suited to our long/term mooring program and help us establish robust infrastructure for sustained observations of Arctic ecosystems into the future.

Ammonia-oxidizing archaea (AOA) are a special group of bacteria that oxidize ammonia into nitrite as their source of electrons and energy and fix carbon dioxide as their main carbon source. Organisms closely related to cultivated AOA account for a large fraction of the microbial community in marine waters, particularly in the deep sea (up to 25% of the bacterioplankton), suggesting that there is a significant ammonia oxidation flux in deep waters. Other bacteria fixate the nitrogen in the water column and thus provide an organic nitrogen source for other organisms, which are not capable of nitrogen fixation. On board we measure the rate at which they photosynthesize and utilize different forms of nitrogen.

Larger organisms such as copepods, amphipods and jellyfish are collected with plankton nets. These samples have been preserved and will be analysed later in the laboratory. In addition, we study the depth distribution of the dominant species with the newly developed LOKI (Light-frame On-sight Key species Investigation). LOKI consists of a high-resolution digital camera, which continuously takes 20 pictures per second while being towed from 1000 m depth to the surface. Salinity, temperature and fluorescence are measured synchronously. This allows directly relating the abundance of different species to hydrography. During this expedition, we attached additional equipment to the LOKI frame – the Aquascat. This acoustical device measures the backscatter of plankton organisms and allows determining the abundance and size of the organisms in the water column.

Besides nutrients, light is another important factor for biological productivity, especially for photosynthetic organisms like phytoplankton. The number of those organisms, other organic and inorganic particles, and dissolved organic matter limit the solar irradiation that is available at different depths in the ocean. The reflected light is used for investigations from satellites (remote sensing) and allows determining the water constituents if in situ measurements for calibration are available. Therefore we also measure optical parameters like absorption and scattering of ocean water. These measurements allow a detailed determination of phytoplankton types, chlorophyll concentration and the amount of dissolved organic carbon in the Arctic Ocean.

The next and last weekly report from RV Polarstern expedition PS99.2 will provide information on the work carried out by our benthic biogeochemists and biologists.

With best regards from all participants,

Thomas Soltwedel

(This weekly report was mainly written by Barbara Niehoff, Ian Salter, Tania Klüver, Stephan Wietkamp, Allison Fong, Sebastian Hellmann and Pierre Offre)