![]() ![]() Vertically resolved diagenetic models finally represent the most mechanistically oriented alternative to represent ocean–sediment exchange fluxes. ![]() Although termed “vertically integrated” not all of the schemes that fall into this category can be traced back to some actual vertically resolved model that was vertically integrated. Mass balances of some, if not all, constituents of this single-layer sediment can be traced. The vertically integrated dynamic category 3 encompasses ocean–sediment exchange schemes that explicitly include a single-box representation of the surface sediment. They do not, however, allow us to take into account the complexities of the actual remineralisation pathways of the various biogenic components in the surface sediments, nor can they represent the temporary storage of such materials in the surface sediment or delayed return of nutrients, dissolved inorganic carbon or silica to the ocean bottom waters. be linked to the degree of saturation with respect to one carbonate mineral or another, and organic carbon fractions remineralised can be linked to the degree of oxygenation of the bottom waters.īoth schemes are attractive because of their convenient computational efficiencies. The fraction remineralised can be made to vary in space and time and can also be different for different materials.Ĭarbonate fractions remineralised can e.g. Here, only some of the remineralisation products (nutrients, dissolved inorganic carbon, silica, etc.) of the solids reaching the sea floor are returned to the bottom water the remainder is returned to the surface, mimicking riverine input and once again allowing for global mass conservation. This unrealistic behaviour can to some extent be alleviated with the semi-reflective or conservative scheme. Global mass conservation is obviously guaranteed with this approach, but the approach may be unrealistic in some places: calcite gets dissolved even if the sea floor bathes in waters that are strongly supersaturated with respect to calcite or organic matter oxidised even if oxygen levels are low. the deepest layer in the model water column) is unconditionally remineralised (oxidised, dissolved) there. Reflective boundary conditions are the simplest of these: material reaching the model sea floor (i.e. ( 2000):Ĭategories 3 and 4 respectively correspond to their level 3 and 4 descriptions category 1 fits their level 2 description, while category 2 generalises the latter. These categories are similar but not identical to the levels in the classification of Soetaert et al. (3) vertically integrated dynamic models and (4) vertically resolved diagenetic models. (1) reflective boundary conditions (2) semi-reflective or conservative These can be classified into four major categories ( Hülse et al., 2017): Ocean biogeochemical cycle models call upon a variety of schemes of different complexity levels to represent ocean–sediment exchange fluxes. ![]() MEDUSA can also be run in parallel computing environments using the Message Passing Interface (MPI).ġ.1 Ocean–sediment exchange schemes: an overview The composition of the two phases, the processes (chemical reactions) and chemical equilibria between solutes are not fixed any more, but get assembled from a set of XML-based description files that are processed by a code generator to produce the required Fortran code.ġD, 2D and 2D ×2D interfaces have been introduced to facilitate the coupling to common grid configurations and material compositions used in biogeochemical models. MEDUSA has been extensively modified since its first release from 2007. Gradually, as solid material gets transferred here from the overlying reactive layer, it is buried and preserved in a stack of layers that make up a synthetic sediment core. Solids that get transported deeper than the bottom boundary of the reactive mixed layer enter the second zone underneath, where reactions and mixing are neglected. The classical coupled time-dependent early diagenesis equations (advection–diffusion reaction equations) are used to describe the evolutions of the solid and solute components here. Solids are transported by bioturbation and advection, and solutes are transported by diffusion and bioirrigation. This is where chemical reactions take place. Solids (biogenic, mineral, etc.) raining down from the surface of the ocean are collected by the reactive mixed layer at the top. In the vertical, the sediment is subdivided into two different zones. MEDUSA is a time-dependent one-dimensional numerical model of coupled early diagenetic processes in the surface sea-floor sediment. ![]()
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