Description: The squat lobster Pleuroncodes monodon is a key species of the highly productive, but oxygen-poor upwelling system of the Eastern Tropical South Pacific. Observations of P. monodon in the water column off Peru have led to the hypothesis that anoxic conditions force this otherwise primarily benthic species to adopt a pelagic lifestyle. Here we show that off Peru, P. monodon can be found in the oxygenated surface water, but also on the anoxic seafloor. Our physiological experiments demonstrate that juvenile and adult specimens have a very low critical respiratory pO2 of 0.5 kPa and that adults survive anoxia for 30.5–70.5 h. Anoxic conditions at the seafloor should therefore force P. monodon to regularly migrate to the oxic surface layer in order to restore energy reserves and recycle metabolic end products of anaerobic metabolism. It was recently estimated that the ammonium supply mediated by diel vertical migrations (DVMs) of zooplankton and nekton considerably fuels bacterial anaerobic ammonium oxidation—a major loss process for fixed nitrogen in the ocean. These estimates were based on the implicit assumption that anoxia does not result in a down-regulation of ammonium excretion. We here show that exposure to anoxia elicits a fourfold reduction in ammonium excretion from 2.1 ± 0.6 µmol h−1 g dry weight−1 under normoxic to 0.5 ± 0.6 µmol h−1 g DW−1 under anoxic conditions in P. monodon. Estimates of ammonium supply to the anoxic core of oxygen minimum zones via DVM therefore are likely too high.

Description: Summary During this cruise a detailed multi-disciplinary research program was conducted at the Peruvian oxygen minimum zone (OMZ) within the framework of the Kiel SFB 754. Investigations were primarily conducted along a depth transect at 12° S. Major aim was to advance understanding of how OMZ´s are maintained and to determine feedbacks of benthic nutrient release on the currently expanding Peruvian OMZ with a major focus on i. variability of benthic nutrient release in response to hydrodynamic forcing and regional differences in bottom water levels of oxygen (O2), nitrate (NO3-), nitrite (NO2-), and sedimentary carbon content, ii. diapycnal and advective fluxes of excess dinitrogen (N2), ammonium (NH4+), phosphorous (P), iron (Fe), silicate (Si), and radium isotopes between the benthic boundary layer, and the stratified interior ocean as well as their entrainment into the surface mixed layer and iii. processes involved in the respective benthic N, Fe, and P cycles. To achieve this goal, physical and biogeochemical measurements were conducted in the water column as well as at the sea floor. For investigations in the water column a total of 84 CTD casts, 41 micro-structure CTD, 20 in situ pump and 12 GoFlo deployments were performed. Sediment samples were obtained during 50 multiple corer casts, 12 gravity corers and 10 benthic chamber lander deployments. Furthermore a profiler lander was used to determine in situ microprofiles of O2, NO3- and nitrous oxide (N2O) in situ. Microprofiles were obtained using glass-microsensors that were pushed into the sediment in 300 μm increments. In order to obtain time series data on the oxygen distribution and the current regime oceanographic moorings were distributed along the 12°S transect in addition to four benthic satellite-landers each equipped with upward looking ADCPs. Lastly, a glider swarm was established at 12°S. These instruments were deployed for the duration of cruise M92 as well as for the subsequent M93 cruise. Deviating from the cruise proposal, more time was spent for station works at the depth transect at 12° S. Major aim of this cruise was to obtain a coherent data set of all involved groups, which however took slightly more time than originally planned, yet bears a high scientific potential. Additionally, it was discovered that at 12° S in shallow waters sulphide was released from the seabed into the bottom water. Furthermore, in water depths from about 120 to 200 m nitrite in addition to nitrate was available in high concentrations which affects the benthic nitrogen cycle to a hitherto unknown extent. Hence these stations were more intensely investigated than originally planned. Weather conditions were fine and all deployments of the scientific gear went very well. It is expected that after analyses and synthesis of the different data sets from the different disciplines the scientific questions above can be addressed to broad extent.

Description: Summary A detailed multi-disciplinary research program was conducted at the Mauritanian oxygen minimum zone (OMZ). Investigations were primarily performed along a depth transect at 18°20’ N. In this area upwelling of cold, nutrient-rich deep water is strongly seasonal, predominating from April until December. Major aim was to advance understanding of how OMZs are maintained and to determine feedbacks of benthic nutrient release on the currently expanding Mauritanian OMZ under such conditions. Major focus was on (i) variability of benthic nutrient release in response to hydrodynamic forcing and regional differences in geochemistry, (ii) diapycnal and advective fluxes of nutrients, trace metals, and radio-tracer between the sediments and the stratified interior ocean as well as their entrainment into the surface mixed layer and (iii) processes involved in the respective benthic and pelagic N, Fe, and P cycles. The working program in the water column comprised a total of 73 CTD casts, 38 microstructure CTD- and 17 in situ pump deployments. Moorings and Glider were deployed at 18°20’ N and 19°50’ N. Furthermore, in the northern working area ADCP-transects and casts of Underway CTDs were conducted to follow upwelling-induced frontal systems. In situ benthic fluxes of nutrients and oxygen were conducted using the Biogeochemical Observatories BIGO I and BIGO II comprising a total of 9 deployments. Further sediment samples for biogeochemical, investigations were obtained during the deployment of 22 casts of a video guided Multiple Corer (MUC). All deployments were successful and the envisaged data and samples were collected.

Description: The magnitude of nutrient and trace metal release from oxygen minimum zone (OMZ) sediments as well as their fate in the water column is of utmost importance for the pelagic nutrient budget and consequently for the ongoing expansion of OMZs. The major aim of this research cruise that was conducted within the framework of the Kiel collaborative research center SFB 754 (Climate – Biogeochemistry Interactions in the Tropical Ocean), was to study the effects of variable environmental conditions on benthic element turnover and exchange with the bottom water under natural conditions of austral fall/winter but also during experiments. This allows the quantitative simulation of benthic-pelagic nutrient- and trace metal budgets over longer time periods. The experimental investigations aimed to specifically resolve the contribution of sulfur bacteria and denitrifying foraminifera controlling benthic N, P and S fluxes. The investigation of mixing processes in the bottom boundary layer (BBL) and quantification of diapycnal and advective fluxes across the BBL and the stratified water column will be used to resolve the fate of these substances. The multidisciplinary study mainly focused on a depth transect at 12°S and is scientifically closely linked to the METEOR cruises M135, M136 and M138. In order to achieve the scientific goals an intense physical, biogeochemical and biological working program was conducted in the water column and at the seafloor accompanied by shipboard experiments. Studies in the water column comprised 92 CTD, 65 microstructure CTD, 18 TM-CTD and 14 in situ pump deployments. Sediment samples were obtained during 47 mulitple-corer and 12 Lander deployments. Additionally, lander deployments were performed to obtain time series of physical parameters and the current regime in water depths of 76 and 128m. The deployment of these instruments covered the time period of cruises M136 and M137. We slightly deviated from the cruise proposal and spent a minor amount of the station time along a zonal transect at 12.3°S in order study the biogeochemistry during eddy formation. Eddy formation cannot be predicted and hence planned in a cruise proposal, however their study bears a high scientific potential and is a central part of the SFB745 research activities. Due to the good weather conditions all deployments were successful, hence all the data and sample material aimed for has been achieved. It is to expect that as planned all scientific questions can be addressed. Especially, the joined synthesis including the data of the other recent SFB cruises M135, M136 und M138 and their comparison with the earlier SFB-cruises M77, M92 harbor a high scientific potential.

Description: Rotifers, one of the smallest metazoans, are only seldom found in marine environments. Surprisingly, we discovered high abundances of at least two new species of rotifers settling in anoxic and highly sulphidic sediments associated with shallow gas hydrates (GH) at the southern crest of Hydrate Ridge off Oregon, NE Pacific, in a water depth of about 780 m. At basins adjacent to Hydrate Ridge, 1,285–2,304 m deep, we found rotifers co-occurring with the sulphide-oxidising bacteria Thioploca sp.

Description: FS MARIA S. MERIAN - MSM114, Las Palmas - Mindelo, 15. - 21. Januar 2023 „MOSES Eddy Study IV“

Description: FS MARIA S. MERIAN - MSM114, Las Palmas - Mindelo, 16. - 21. Januar 2023 „MOSES Eddy Study IV“