The 4GFOR model – Coupling 4G early diagenesis and benthic foraminiferal ecology

Abstract

The 4GFOR model presented in this paper combines the OMEXDIA model of Soetaert et al. (1996) with four theoretical species of benthic foraminifera. The geochemical part of the model simulates the succession of early diagenetic redox reactions in the superficial sediment layers. The four theoretical foraminiferal species, each representing a group of biological species with comparable microhabitats, differ by their limitations with respect to oxygen and nitrate concentration and their ability to feed on different organic matter types. The foraminiferal model is a transformation model in which different proportions of four types of organic matter with different reactivity are attributed to each of the theoretical species. The model has been manually tuned and tested on a large data set from two stations, at 1000 and 550 m depth, in the Bay of Biscay. The model adequately simulates the vertical distribution of shallow, intermediate and deep infaunal species. The 4GFOR model can be used to test several hypotheses concerning foraminiferal ecology. The model has already allowed us to conclude that it is high unlikely that shallow infaunal taxa feed exclusively on the most labile part of the organic matter flux, since it was unable to reproduce the field observations while using this hypothesis. Another important conclusion based on our preliminary model results is that the absence of deep infaunal taxa close to the sediment surface may be explained by their decreasing competitiveness in well oxygenated environments. In the future, the inversion of the 4GFOR model may yield a powerful paleoceanographic tool, enabling us to reconstruct major limiting environmental factors (oxygen and nitrate concentrations; quantity and quality of the organic flux to the ocean floor) from benthic foraminiferal assemblage data.