Simulation models for ocean nutrients cycling
Much research is currently being undertaken into understanding the global carbon system since it is now generally accepted that the large increase in atmospheric carbon dioxide is influencing our climate. Despite the ocean being the largest active carbon reservoir, the forces that govern organic sediment and gas transformations in the ocean's water column are yet not fully understood. Through project ORFOIS research was carried out in this area, particularly examining the origin and fate of biogenic particle fluxes in the ocean and their interaction with atmospheric carbon dioxide concentrations. A sediment module was set up to describe Particulate Organic Carbon (POC) remineralisation, by oxide degradation and sub-oxide nitrate reduction. Model PISCES was used to provide bottom water conditions for chemical parameters such as oxygen, phosphate, alkalinity, nitrate and Dissolved Inorganic Carbon (DIC), which allowed realistic simulations to be set up. Stable distributions of dissolved and sediment tracers were established and sediment composition then calculated to provide initial conditions for the simulation model. The model requires a steady state be reached between water column and sediment and as such is still running. Annual fluxes for SiO2 and CaCO3 were also assessed using two different versions of the PISCES model. However neither model was found to be in total agreement with determined levels, yielding lower values of CaCO3 than those observed in some cases. The models were also used to assess benthic oxygen fluxes. One of the models in particular gave good results for flux distributions. Since oxygen flux is linked to mineralisation activity and aerobic metabolism it is essential to be able to accurately monitor this system. Further development of these models is necessary for the successful simulation of the water column-sediment environment. Understanding the system is essential to accurately predict nutrient cycling and climatic change, and interested parties are invited to join in the search for answers.