Contribution of riverine nutrients to the silicon biogeochemistry of the global ocean – a model study

C. Y. Bernard,C. Heinze,H. H. Dürr,E. Maier-Reimer,J. Segschneider

doi:10.5194/bg-8-551-2011

Abstract

Abstract. Continental shelf seas are known to support a large fraction of the global primary production. Yet, they are mostly ignored or neglected in global biogeochemical models. A number of processes that control the transfer of dissolved nutrients from rivers to the open ocean remain poorly understood. This applies in particular to dissolved silica which drives the growth of diatoms that form a large part of the phytoplankton biomass and are thus an important contributor to export production of carbon. Here, the representation of the biogeochemical cycling along continents is improved by coupling a high resolution database of riverine fluxes of nutrients to the global biogeochemical ocean general circulation model HAMOCC5-OM. Focusing on silicon (Si), but including the whole suite of nutrients – carbon (C), nitrogen (N) and phosphorus (P) in various forms – inputs are implemented in the model at coastal coupling points using the COSCAT global database of 156 mega-river-ensemble catchments from Meybeck et al. (2006). The catchments connect to the ocean through coastal segments according to three sets of criteria: natural limits, continental shelf topography, and geophysical dynamics. According to the model the largest effects on nutrient concentrations occur in hot spots such as the Amazon plume, the Arctic – with high nutrient inputs in relation to its total volume, and areas that encounter the largest increase in human activity, e.g., Southern Asia.

Highlights

Continental shelf seas play a crucial role in biogeochemical fluxes from the continents to the open ocean
Global biogeochemical models partly fail to integrate processes taking place on the continental margins such as benthic/pelagic coupling, tidal currents mixing, coastal upwelling driven by wind forcing or general circulation and the land/ocean interaction; they reproduce only crudely the nutrient enrichment supported by coastal upwelling
In this work we demonstrate the importance of riverine inputs of dissolved silica (DSi) to the global biogeochemical cycles on the global scale by adding the riverine fluxes of nutrients to a global scale biogeochemical general circulation model (BGCM)

Summary

Introduction

Continental shelf seas play a crucial role in biogeochemical fluxes from the continents to the open ocean. They are known to support a large part of the global primary production (Conley et al, 1993; Rabouille et al, 2001): they make up for only 8% of the ocean surface but 25% of the ocean primary production (Ver et al, 1999). Global biogeochemical models partly fail to integrate processes taking place on the continental margins such as benthic/pelagic coupling, tidal currents mixing, coastal upwelling driven by wind forcing or general circulation and the land/ocean interaction; they reproduce only crudely the nutrient enrichment supported by coastal upwelling

Results

Discussion

Conclusion