Instrumentation to conduct flux measurements
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 handled by Remotely Operated Vehicles (ROVs):
Microprofiler
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 Chamber
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).
Planar Optode
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.
Eddy Correlation Sensor
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 by correlating the fluctuations in oxygen concentration with the vertical component of the turbulent water motion.
Deep Flow Sensor
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.
INSINC
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.
Handheld Microsensors
We use different autonomous ROV-operated sensor modules to locally characterize the chemical environment in benthic habitats. These modules carry microsensors for temperature, O2, pH, H2S, and CO32-.
Contact: F. Wenzhöfer
Literature:
Glud, R.N., Wenzhöfer, F., Tengberg, A., Middelboe, M., Oguri, K. & H. Kitazato (2005). Distribution of oxygen in surface sediments from central Sagami Bay, Japan: In-situ measurements by microelectrodes and planar optodes. Deep-Sea research I 52 (10): 1974-1987.
Cook, P.L.M., Wenzhöfer, F., Glud, R.N., Janssen, F. & M. Hüttel (2007). Benthic solute exchange and carbon mineralization in two shallow subtidal sandy sediments: Effect of advective pore-water exchange. Limnology and Oceanography 52 (5): 1943–1963.