We are running various systems to carry out flux measurements at the sediment-water interface and the sediment-overlying water. These instruments could either be incorporated in our freefalling systems or handheld by Remotely Operated Vehicles (ROVs).

 

High resolution vertical microelectrode profiles can be measured in situ with an autonomous microprofiler module. The system carries up to 11 sensors for different parameters like O2, H2S, pH, N2O, NO3, temperature, redox and resistivity. A typical vertical resolution is 0.1 mm and once programmed, the instrument operates fully autonomously.

 

Benthic chambers allow determining the total flux of solutes across the sediment water interface by inclosing a known sediment area with some supernatant bottom water. The concentration of oxygen in this water is measured continuously with oxygen sensors. A syringe sampler draws water samples during the incubation period for later analysis of fluxes of dissolved inorganic carbon, nutrients and gases (CH4, H2S).

 

Two-dimensional optical measurements of oxygen and pH distributions in vertical cross-sections of sediments can be performed in high spatial resolution (~ 0.1 mm) with the planar optode module. This tool is especially valuable in highly dynamic and structured systems.

 

The average flux of oxygen across the water-sediment interface is an important measure for benthic remineralization. This flux can be determined completely non-invasive with the Eddy Correlation Sensor by correlating the fluctuations in oxygen concentration with the vertical component of the turbulent water motion.

Seep areas are characterized by advective flow of solutes out of the sediment. To quantify this flow, a fluorescent tracer dye is injected into the sediment and its dispersal is tracked via light-guiding fibres at different sediment depths.

The In-Situ-Incubator (INSINC) is designed to inject radioactively labelled sulphate at the seafloor to measure in situ sulphate reduction rates by sediment-inhabiting bacterial communities. The vertical resolution for the tracer injection is approximately 7 mm.

 

Furthermore, we use different autonomous "handheld" (ROV-operated) microsensor modules to locally characterize the chemical environment in benthic habitats. These modules carry microsensors for temperature, O2, pH, H2S, and CO3.

 

 

Contact: F. Wenzhöfer, R. Hoffmann, F. Janssen

 

 

Literature:

 

Donis, D., McGinnis, D.F., Holtappels, M., Felden, J., Wenzhoefer, F. (2016). Assessing benthic oxygen fluxes in oligotrophic deep sea sediments (HAUSGARTEN observatory). Deep-Sea Research I, 111, 1-10. doi.org/10.1016/j.dsr.2015.11.007.

 

Cathalot, C., Rabouille, C., Sauter, E., Schewe, I., Soltwedel, T. (2015): Benthic oxygen uptake in the Arctic Ocean margins - A case study at the deep-sea observatory HAUSGARTEN (Fram Strait). PLoS ONE, 10 (10) (e01383): 1-23. doi:10.1371/journal.pone.0138339.

 

Boetius, A., Wenzhöfer, F. (2013): Seafloor oxygen consumption fuelled by methane from cold seeps. Nature Geoscience 6: 725-734. doi:10.1038/ngeo1926.

 

Holtappels, M., Glud, R.N., Donis, D., Liu, B., Hume, A., Wenzhöfer, F., Kuypers, M. (2013): Effects of transient bottom water currents and oxygen concentrations on benthic exchange rates as assessed by eddy correlation measurements. Journal of Geophysical Research – Oceans 118: 1–13. doi:10.1002/jgrc.20112.

 

Bue, N.L., Vangriesheim, A., Khripounoff, A., Soltwedel, T. (2011): Anomalies of oxygen measurements performed with Aanderaa optodes. Journal of Operational Oceanography, 4 (2): 27-37.