Unified modeling of contrasting basin-scale dissolved Al distributions using dissolution kinetics of diatom aggregates: Implication for upwelling intensity as a primary factor to control opal burial rate

Distribution of dissolved aluminum is strongly coupled with dissolution of diatom frustules, since opal is the main scavenger of dissolved oceanic Al. Given Al has a much shorter residence time compared with silicic acid, vertical processes affecting Al must be much more important. It may therefore be possible to understand dissolution behavior of diatom frustules indirectly via Al distribution. In this paper, we explore the features that dissolution kinetics of diatom frustule aggregates would provide with respect to vertical profiles of silicic acid, opal and dissolved Al. This dissolution kinetics has merits to understand 1) the elemental composition of siliceous fraction of settling particles and 2) limited occurrence of opal deposition. The dissolution kinetics of diatom frustule aggregates describes dissolution as a function of aggregate size, which depends on diatom productivity. To heighten our understanding, a unidimensional model has been developed incorporating the dissolution kinetics. This model reproduces basin-scale Al vertical profiles in the Atlantic and Pacific Oceans and Arctic and Mediterranean Seas with the identical parameter of Al absorption by opal as well as maximum Si concentration and minimum Al concentration at increasing depths with increasing Si concentrations. The distribution of opal predicted by this model may be useful and may explain discrepancies between the observed and previously-modeled depth profiles for dissolved Al. This model predicts the effective dissolution/burial of frustules during periods of smaller/greater production. Because upwelling triggers the production of diatoms, we propose that increase in upwelling intensity may be most important parameters to reduce the oceanic silicic acid inventory.