Premiere for Eddy: in situ measurements at REGAB

The author Antje Boetius has introduced herself in the BLOG of 25 July.

After several delays due to necessary repairs on the ROV we have deployed the lift with lots of instruments: the microprofiler measuring sulfide and oxygen fluxes as well as pH and temperature with microsensors (see BLOG of 26 July for further explanation), and the Eddy system for integrated benthic community respiration. This system is composed of an instrument measuring the bottom current velocity and an oxygen sensor measuring even tiny variations in oxygen concentrations. From these measures, the total benthic community respiration can be calculated, integrated over 10-100 square meters of ocean floor. Benthic community respiration is an important measure for the activity of a benthic community, and can be converted to CO₂ fluxes. We will try here for the first time if this measure is useful in deep-sea habitats, and we try to calibrate it with parallel benthic chamber incubations, a classical method for measuring benthic respiration.

Today’s dive also provided us with the first in situ measures of microbial activity at the REGAB seafloor. We used the in situ incubation system INSINK to assess microbial respiration of sulfate in the highly gassy sediments associated with mussel beds (Figure 1). Especially with gassy sediments, measurements on board are problematic because the gas expands dramatically upon pressure release during core recovery.

Also we deployed the Eddy system on three different locations to measure integrated benthic oxygen consumption: 1) on the central pockmark site comprising hilly carbonate layers overgrown by mussels associated with outcropping hydrates and surrounded by tubeworm bushes (Figure 2), 2) in the south of the carbonate platform facing a flat sedimentary area with patches of vesicomyid bivalves (Figure 3), and 3) in the same area but facing mussel beds on highly gassy sediments. In addition, we deployed the microprofiler close to and away from a larger patch of vesicomyid clams.

It was possible to collect two sets of push cores, one ca. half a meter away from the mussel bed (Figure 4), and a second one on the vesicomyids, including the recovery of those cores we had left over from dive 221 because of an arm failure. Tonight the navigation worked really well and we were surprised how simple it was to find back the left over cores. Also, we sampled the mussels growing on the gassy seabed with a net for further analyses of the symbiotic mussels of REGAB (also see BLOG of 04 August).

The third new instrument to be deployed, the xy-profiler measuring multiple microsensor profiles could not be started, and hence was collected early back into the lift (Picture 5). So far, this was our longest dive during this expedition and it was great to complete so many different tasks during one deployment. The problem with the oil leaks seems to have improved considerably, so we hope for a bit more luck for the remaining 10 days.

With many greetings

Antje Boetius