WP 6

Observation of carbon fluxes in the deep sea

 

Work Package Leaders

 

Description

Currently we know little about particle transport, carbon export and turnover processes of settling organic aggregates within oxygen depleted eddies. In the oxygenated water column, we typically observe strong flux attenuation in the upper few hundred meters due to efficient microbial degradation and high zooplankton grazing (‘flux feeding’) on settling aggregates. However, strong oxygen depletion might reduce and alter microbial degradation and zooplankton grazing, which potentially decrease the attenuation in the upper water column, finally allowing higher export of organic matter within low oxygen eddies.

This work package intends to study particle dynamics and export fluxes within different types of mesoscale eddies passing the eddy corridor north of the Cape Verde Islands (around site CVOO) on annual and shorter time scales (days to weeks). The project aims at quantifying mass fluxes and size-specific particle abundances within eddies based on short-term observations of fluxes using drifting arrays in the epi- and mesopelagic and classical moored sediment traps in the bathypelagic (CVOO site, cooperation with GEOMAR). We will combine in situ observations with on-board laboratory studies on carbon respiration and settling rates of in situ sampled marine snow aggregates.

 

General Questions and Research topics

The overall research topic is on carbon export and attenuation within low oxygen eddies around CVOO to determine export and attenuation processes.

More specifically, we aim to answer the following questions:

  • What are the seasonal and interannual bathyperlagic carbon fluxes (=carbon sequestration) at CVOO during the passage of different types of eddies with variable oxygen depletions in the upper water column?
  • What is the short-term export processes, e.g. diel variation in export within and outside (sub-) mesoscale eddies around CVOO?
  • What is impact of zooplankton on carbon flux attenuation (‚zooplankton flux feeding‘) within low oxygen eddies?

We will combine field and lab methods. Drifting traps which are equipped with particle preserving gels (see figure 1) will be used for the collection of sinking particles and carbon fluxes. An in situ particle camera will determine particle size-distribution, abundance, and particle type during different oxygen regimes within the eddy (upper 500 m, see figure 2). Multi-nets will be used to quantify zooplankton abundance and species composition. Marine Snow Catchers (MSC, see figure 3) will be deployed for the collection of in situ formed marine snow aggregates below the photic zone. Lab experiments using a flow chamber system (see figure 4) will measure oxygen respiration and settling rates of marine snow particles collected during M160 with the MSC.

Figure 2. Particle camera equipped with a flashlight and underwater battery. Picture credit: Gerhard Fischer Above the aggregate an oxygen micro-sensor is measuring the oxygen gradient towards the aggregate. Picture cr

Figure 4. Flow chamber with a suspended in situ collected marine snow aggregate. Above the aggregate an oxygen micro-sensor measures the oxygen gradient towards the aggregate. Picture credit: Morten Iversen

 

Figure 1. Schematic illustration of a drifting trap array with a surface buoy and three traps located at 100, 200 and 400 m water depths. Each trap has four cyclindrical collectors (see photo to the right), one filled with a particle preserving gel. Picture credit: Gerhard Fischer

Figure 3. Picture of a marine snow catcher device. Picture credit: Gerhard Fischer