To establish a link between the marine carbon and sulfur cycles.
Both cycles are relevant to climate change studies, carbon being the main contributor to the greenhouse effect, and sulfur as an important source of cloud condensation nuclei, thereby regulating cloud albedo. Greenhouse effect and cloud albedo are two opposing mechanisms. The former results in global warming, the latter in cooling of the earth's climate. Both cycles meet intimately in the ubiquitous marine phytoplankton taxon Phaeocystis sp.. This colony-forming alga is an important source of the volatile organic sulfur compound dimethyl sulfide (DMS), and its dense blooms can act as a carbon sink.
A thorough inventory of the carbon and sulfur cycles will be made during two blooms of Phaeocystis in two different geographical areas: in northern Norwegian coastal waters and in the Southern Bight of the North Sea. These field campaigns will be preceded and followed by well defined laboratory experiments in order to study isolated processes relevant for the field situation.
In many coastal areas a stereotype pattern of algal succession during the spring bloom is observed in which Phaeocystis outcompetes other algal species. Due to the time development of various processes influencing the wax and wane of a phytoplankton bloom, sedimentation of organic material as well as the flux of DMS to the atmosphere can be highly variable. Mapping of the horizontal and vertical distribution (in water and atmosphere) of the different sulfur and carbon compounds in the two different geographical areas will give information on the dynamics of these systems.
Field data on sulfur and carbon compounds will be combined with data from incubation and process studies. A possible competitive advantage of Phaeocystis over other relevant spring bloom species in the uptake of CO2 will be linked to the metabolism of dimethylsulfoniopropionate (DMSP), the precursor of DMS, using axenic cultures. Biological removal processes of Phaeocystis-derived sulfur and carbon compounds will be studied in laboratory as well as on-board incubation experiments. The role of grazers as an intermediate in the degradation of a bloom and, thus, in the fate of carbon and sulfur, will be studied in experiments in the lab and in incubation studies in the field. During the course of a plankton bloom, stimulation of the bacterial community may result from the excretion of organic compounds or from cell rupture. A changing bacterial community structure will have implications for the degradation rate of Phaeocystis-derived organic material. In on-board incubation experiments, removal rates of various carbon and sulfur compounds will be measured. A differentiation between metabolic routes will be examined using specific inhibitors. With the development and application of molecular probes a differentiation of bacterial and algal DMSP-lyases (enzymes that are responsible for the conversion of DMSP into DMS and acrylic acid) can be established.
Process studies and field campaigns are expected to result in a better understanding of the role of Phaeocystis blooms in the escape of DMS to the atmosphere and of carbon from the photic zone. A conceptual model which mirrors the processes described in the study will allow an estimation of the impact of Phaeocystis dominated ecosystems on global climate.
Funding SchemeCSC - Cost-sharing contracts
PL1 3DH Plymouth