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Project GB1

Particle Flux, Carbon Turnover and Nutrient Regeneration

 

M. Zabel, G. Fischer, M. Kuypers, G. Mollenhauer
R. Amann, A. Basse, f. Ferdelman, T. Goldhammer, M. Holtappels, M. Iversen, G. Lavik, N. Nowald, V. Ratmeyer

Objectives

The major goal of GB1 is to identify and quantify the controlling processes for transport of organic matter from the ocean surface to and within the sea floor sediment. This involves investigations of the physical transport mechanisms and biological degradation and remineralization processes organic particles in the water column and surface sediments (Fig. 1).

Scientific Background

The relative rates of production and degradation of organic carbon during its transit from productive surface waters to the sediments determine the efficiency of the biological pump. Microbial and zooplankton activities drive high rates of organic consumption and remineralization in the euphotic zone; however, newly-developed imaging techniques suggest a clear spatial separation of net primary production, aggregate formation, and the consumption of organic sinking particles within the euphotic zone. The majority of organic matter recycling and flux attenuation occur in the deep euphotic zone and upper mesopolagic zone (Fig. 2). However, several processes below the euphotic zone may be of importance for the efficiency of biological pump and, hence, the burial of residual organic matter in sediments (see also GB2), e.g. deeper nepheloid layers, the benthic boundary layer, and surface sediments.

It is clear that ecosystem respiration and bacterial abundance are closely linked in particle-rich layers, but the rate-limiting steps in organic matter degradation are poorly understood. Many questions remain concerning the microbial contribution to key processes: redox reactions, chelation, particle formation, sorption and desorption to organic and inorganic particles that are involved in C, Fe, and P regeneration. For example, direct evidence for the participation of bacteria in phosphate sequestration into minerals has only recently become available. The intracellular storage of polyphosphate in large sulfur bacteria and the formation of apatite may be linked to local geochemical conditions (e.g., Ca2+ to Cl- ion balances). The complex interactions between biogeochemical processes and biotic as well as abiotic conditions, their effects on ocean geochemical dynamics, and the magnitude of microbial transfer rates are the main focus of project GB1, which is crosslinked to GB2 and CCP3.

Key Hypotheses

  • The majority of particle-associated carbon turnover and nutrient regeneration in the water column occurs in distinct depth layers.
  • The environmental conditions within distinct layers influence the physiology and/or community composition of key organisms responsible for particle degradation and ultimately the chemical composition of these particles
  • The microbial contribution to the closely coupled cycles of Fe and P during transformations between inorganic and organic pools have been strongly underestimated

Fig. 1. Overview of GB1 project fo key investigations in the water column

Fig. 2. Vertical organic carbon fluxes through the water column (left panel), simultaneous measurements of fluorescence, particle abundance and median diameter (middle panel), and schematic illustration of the processes shaping the particle size spectra and vertical fluxes through the water water (right panel).