Biogeochemical Transformations of Silicon Along the Land–Ocean Continuum and Implications for the Global Carbon Cycle¹

Abstract

In the context of a changing Earth, one central interest is an improved understanding of the global carbon cycle and an improved prediction of its likely changes as consequence of global changes. Largescale programs investigated the oceanic cycling of carbon (C) and associated biogenic elements, mainly nitrogen (N) and phosphorus (P), as limiting nutrients of the global production by marine phytoplankton (Falkowski 1997; Tyrrell 1999). However, continental margins play an essential role in the global C cycle, accounting for 14% of global primary production, 80–90% of new production, and 80% of global organic carbon (C_org) burial (Smith and Hollibaugh 1993; Rabouille et al. 2001). Continental margins also represent a filter that removes riverine dissolved and suspended constituents along their path from land to the open ocean (Billen et al. 1991). In order to characterize the C cycle on continental margins, their contribution to carbon dioxide (CO₂) sequestration and to determine horizontal C and associated biogenic element fluxes, some 200 N and P flux budgets have been constructed around the world (cf. Smith et al. 2003b, LOICZ 1998). One biogenic element, silicon (Si) has been largely ignored. Silicon is required by diatoms, (Guillard et al. 1973) which play a critical role in the marine C cycle (e.g., Smetacek 1999).