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Particle interactions and shelf sediments

To­gether with the RE­CEIVER unit, we want to de­term­ine how the in­ter­ac­tions and feed­backs between the mar­ine biogeo­chem­ical cycles and the shelf-sea and open ocean cir­cu­la­tion de­term­ine the fluxes of car­bon and nu­tri­ents, as well as their budgets. To this end, a re­gional mod­el­ing system was newly designed (see Figure 1). The MIT general circulation model (MITgcm), which simulates the physical ocean circulation, was set up for the Northwest African upwelling system.

Currently we are working on implementing the different remaining modules that can be seen in Figure 1. The biogeo­chem­istry mod­ule (green in Fig. 1) is a Nutrient-Phytoplankton-Zooplankton-Detritus model. Phytoplankton and detritus form together the pool for biogenic particle aggregation. The particle ag­greg­a­tion/​dis­ag­greg­a­tion modeling (blue in Fig. 1) follows the approach of Kriest and Evans (1999) and Barkmann et al. (2010). Biogenic particles collide among each other and with lithogenic particles and form aggregates that sink to the ocean floor with a prognostic sink­ing velocity. The particles are represented by a con­tinu­ous size spec­trum, which is assumed to follow a certain power law, making it possible to model the entire range of particle sizes by only two prognostic variables. As a last step we plan to incorporate an early dia­gen­esis model of pela­gic sed­i­ments (MEDUSA, Munhoven 2007, brown in Fig. 1), which models the exchange of organic material and carbonates between the sediments and the ocean above.

The re­gional mod­el­ing sys­tem will be ap­plied first to the North­w­est African up­welling sys­tem, which is char­ac­ter­ized by high pro­ductiv­ity and high sed­i­ment­a­tion rates, in­flu­enced by changes in the large-scale at­mo­spheric and ocean cir­cu­la­tion and at­mo­spheric dust de­pos­ition.

Fig1_modeling_enabler_receiver
Planned set-up of the modeling framework for the Northwest African upwelling system

Literature:
Barkmann W, Christian Schäfer-Neth C, Balzer W (2010) Modelling aggregate formation and sedimentation of organic and mineral particles. Journal of Marine Systems 82:81–95

Kriest, I., and G. T. Evans (1999), Representing phytoplankton aggregates in biogeochemical models, Deep Sea Research Part I: Oceanographic Research Papers, 46 (11), 1841–1859.

Munhoven G (2007) Glacial interglacial rain ratio changes: Implications for atmospheric CO2 and ocean sediment interaction, Deep Sea Research Part II: Topical Studies in Oceanography 54:722–746