Microbial biogeography and decomposition of terrigeneous carbon compounds in the gradients of the Baltic Sea - Cruise No. M87/3a - May 29 - June 10, 2012 - Stavanger (Norway) - Rostock (Germany)

• Main Author: Labrenz, Matthias
• Format: Report
• Language: English
• Published: DFG-Senatskommission für Ozeanographie 2015
• Subjects: Earth Science; Earth sciences and geology; Arctic; Norway; Climate change; Zooplankton
• Online Access: https://dx.doi.org/10.2312/cr_m87_3a; https://www.tib.eu/suchen/id/awi:7440f266f6adb09c0324b03b1edfa022e8026c37

The Baltic Sea with its natural gradients and strong reactions to climate change and anthropogenic activity can be used in an ideal way to examine basic ecological processes and their variability in marine ecosystems. The most striking characteristics of the Baltic Sea are the extended gradients in primary (topography, energy, salinity) and secondary (organisms, matter flux, oxygen, nutrients, sediments) environmental properties as a result of different dynamical processes. Leg M87/3a investigated the impact of salinity gradients on degradation of terrestrial dissolved organic matter (tDOC), microbially mediated processes, and on the structure and function of pelagic microbial communities in the Baltic Sea. Following aims were central to this study: (1) Assessment of structure and (selected) functions of pelagic microbial communities (Bacteria, Archaea, Zooplankton) in order to examine whether salinity-related phylogenetic shifts in microbial communities imply relevant functional changes. It provides the general background for the more specific question of decomposition dynamics of imported terrigenous compounds. (1a) Water sampling using the newly developed Automatic Flow-Injection Sampler (AFIS). Traditional water-sampling procedures like Free-flow bottles or Pump-CTD influence the relative abundance of transcripts in microbial transcriptomes, resulting in biased conclusions regarding the relevance of different microbially driven biogeochemical cycles in the studied habitat. The AFIS-system conserves the original microbial expression profile of the environment and by this guarantees a proper assessment of microbial functions based on gene expression analyses. Leg M87/3a provided the opportunity to use it the first time throughout the whole horizontal and vertical Baltic salinity gradient with depths down to 430 m. These samples are the basis for the coming generation of non-biased in situ metabolic fingerprints for the different Baltic Sea environments. (2) Quantification, chemical characterization and decomposition of discharged terrestrial DOC from Northern (arctic) soils in relation to microbial diversity. The aim is to assess the decomposition capacity for organic matter, particularly the degradation potential for introduced terrestrial carbon compounds, along the horizontal salinity gradient of the Baltic Sea. The overall aim of these studies is to gain a comprehensive understanding of the effect of imported terrigenous and autigenous organic material on microbial decomposition processes within the salinity and gradients of the Baltic Sea. To reach these goals, water, fixed water, zooplankton, as well as sediment samples were taken throughout a transect of 27 stations, covering the whole Baltic salinity gradient. Isotopes were analysed continuously. Moreover, microbial decomposition experiments were directly done on board. At the Landsort Deep station TF284, the AFIS-CTD system was successfully used at depths around 430 m. Thus, for the first time it could be demonstrated that this system is robust enough to sample the whole pelagic Baltic Sea. In the morning of May 29th RV METEOR left Stavanger, Norway, towards the first working area. After 26 additional stations RV METEOR reached the harbour Rostock, Germany, where the experiments of the first leg of the cruise M87-3 practically ended on June 10th. : METEOR-Berichte