Dr. Oliver Schmale
Scientist (Senior scientist)
- chemical oceanography
- pelagic methane cycle with focus on redox-gradients
- methane gas exchange between surface water and atmosphere
- benthopelagic transport mechanisms at methane seeps
- mechanisms controlling subsurface methane anomalies (“ocean methane paradox”)
- gaschemistry of hydrothermal systems and its influence on the surrounding water column
- areal examinations of nitrogen fixation in surface waters
- Bubble Shuttle II – Bentho-pelagic transport of methanotrophic microorganisms via gas bubbles, DFG SCHM 2530/7-1
Gas bubble releasing seep sites are relevant methane sources in aquatic systems. In the vicinity of these sites, methanotrophic microorganisms in the sediment and water column play a key role in controlling the methane flux into the atmosphere. Recent studies in the water column surrounding hydrocarbon seeps indicated an elevated abundance and activity of methanotrophic microorganisms in the near field of gas bubble plumes. During our pilot studies conducted at the Coal Oil Point Seep region in California (DFG project “Transport of methane oxidizing microorganisms from the sediment into the water column (Bubble Shuttle)” (SCHM 2530/3-1), we could show for the first time that methanotrophic bacteria were transported by gas bubbles from the sediment into the water column. Within this follow-up project we aim to support these first indications by conducting comprehensive studies on a variety of gas bubble releasing seep sites. The fundamental goal of our project is to evaluate the importance of such a transport mechanism on the pelagic methane turnover at these seep sites. Multidisciplinary studies at different seep locations located in the Coal Oil Point seep field and the North Sea will help us to discuss the different environmental factors, which control the transport efficiency of the bentho-pelagic gas bubble mediated exchange process. By integrating lab-based incubation experiments we will study the activity of seep-associated benthic methanotrophic bacteria in the pelagic environment. Additional phylogenetic analyses will be used to test our hypothesis that the gas bubble transport mechanism impacts the diversity of pelagic methanotrophic bacteria at seep sites. Field studies at a Blowout location in the North Sea and the integration of oceanographic measurements and models will be used to establish a budget for pelagic methanotrophic bacteria in the near field of seep sites. Overall, this approach will help us to discuss the impact of the bubble transport mechanism on the abundance of methanotrophic bacteria and the pelagic methane sink.
Methane is a known greenhouse gas that severely enhances climate change on earth, yet not all methane sources into atmosphere have been identified. A process that might be of importance is the production of methane by microorganisms within the anoxic guts of certain zooplankton species and their fecal pellets. This production takes place in the upper oxygenated water column and thus could have a direct impact on the methane flux between ocean and atmosphere. We hypothesize that highly productive regions like marginal seas, which have never been studied in detail in this context before, are areas of enhanced zooplankton-mediated methane production, which most probably causes the subthermocline methane anomaly that have been sporadically identified in the oxygenated water column of the Baltic Sea. In the ZooM project, we will combine methane chemistry, microbiology, and zooplanktology in a multidisciplinary approach to investigate zooplankton-associated methanogenesis in detail using the Baltic Sea as a model system. We plan to investigate the following key questions: (1) Is the subthermocline methane anomaly a widespread phenomenon in the Baltic Sea, which shows a temporal and spatial variability? (2) Does zooplankton-associated methane production have the potential to support the methane anomaly in the shallow water and how are copepod species and environmental factors like food composition influencing methane production? (3) Which microbes are involved in zooplankton-associated methane production and can we detect differences in methanogenic assemblages and their activities between copepod guts and their fecal pellets?
Methane is an important atmospheric trace gas with a relevant impact on earth’s climate. Although aquatic systems represent the most significant source of atmospheric methane, the importance of the marine system seems to be marginal. One effective mechanism that is limiting the flux of methane from the sedimentary reservoir into the atmosphere is the microbial oxidation of methane in the sediment. Compared to the number of studies on the microbial processes of methane oxidation in sediments, water column studies are scarce. Long-time stagnation periods within the deep basins of the central Baltic Sea (Gotland- and Landsort-Deep) have caused anoxic conditions in the deep water with strongly elevated methane concentrations. The transition zone between the oxic and anoxic water bodies (redoxcline) allows a systematic sampling of the water depth that is relevant for the turnover of methane. Thus, the detailed study of the microbial methane oxidation in the Gotland- and Landsort-Deep enables us to get new insights into the cycle of methane in the Baltic Sea that may can be used for a better understanding of the methane turnover in other anoxic/oxic basins in the world. In our multidisciplinary approach we (1) quantify the processes of the turnover of methane in the water column of the Gotland- and Landsort-Deep, (2) identify the organisms which are relevant for the turnover of methane in the water column and study their footprint in the sedimentary geological record, (3) integrate our results into hydrodynamic-biochemical numerical model.
The process of microbial methane oxidation in the water column is only insufficiently investigated. Water column studies in the vicinity of gas bubble releasing seep sites show, that the majority of dissolved methane is immediately oxidized by microbes after its injection into the water body, and that only a small fraction of methane is reaching the surface water and the atmosphere. In this project, our multidisciplinary approach is investigating the link between sedimentary and pelagic methanotrophy at gas bubble releasing seep sites (study area: Coal Oil Point, Santa Barbara Basin, California). We hypothesize that at these sites methane oxidizing microbes are transport by gas bubbles from the sediment into the water column. In detail we use gas chemistry and molecular biology to (1) identify the zone of methane oxidation and the organisms responsible for the turnover of methane in the sediment, (2) prove the process of methane oxidation within the surrounding water column, and (3) verify the transport of sedimentary methane oxidizing microbes by gas bubbles through the collection of gas bubbles in different water depths.
Recently ended projects
Our objective in the third phase of the SPP is to determine the transport of methane, hydrogen and 3-helium in the plumes originating from the Logatchev vent field on the Mid Atlantic Ridge. We (IFM-GEOMAR and IOW) intend to conduct Tow-yo CTD surveys of these dissolved gases within a distance of a few kilometers from these vents. We will combine this information with long-term current monitoring measurements that will be carried out by Fischer and Visbek (IFM-GEOMAR). The Tow-yo surveys will be conducted at the beginning and at the end of the moored profiler/current meter monitoring, on F/S MERIAN cruises 06/2 and 10/3, in order to provide cross-sectional snap shots of the gas distributions in conjunction with these time-series records. Additional vertical CTD-rosette sampling stations will be placed along the 100 km length of the rift valley axis that starts from the 15°20’N Fracture Zone in order to obtain an estimate of the inventories of these gases in this segment. Methane and hydrogen will be measured on board these expeditions; helium isotope measurements will be conducted at the University of Bremen subsequently. We will measure dissolved methane and hydrogen concentrations in the vent fluids collected during these expeditions, and we shall measure the methane 13C/12C ratio in all gas samples collected on these expeditions.
BALTIC GAS aims to understand how climate change and long-term eutrophication affect the accumulation of shallow gas and the emission of methane and hydrogen sulfide from the seabed to the water column and atmosphere. The outcome of the project will be a new understanding and quantitative synthesis of the dynamics and budget of methane in the seabed, an important but poorly understood component of the Baltic ecosystem response to natural and human- induced impacts. The project aims to develop a predictive model of gas accumulation and emission under realistic scenarios of climate change and eutrophication, which will improve the knowledge base for necessary future policy actions. The multidisciplinary project will involve 12 partner institutions from 5 nations and will apply modern advanced technology and novel combinations of approaches.