Modeling the modern marine δ30Si distribution

Abstract

The silicon isotopic composition of opal sediments can be used as a proxy for past Si utilization, and hence paleoproductivity for a fixed ocean circulation. Interpretation of this Si utilization proxy is limited by our understanding of the present marine Si isotope distribution. Observations show significant isotopic variations is silicic acid between deep‐water masses that are not captured by a previous global climate model (GCM). Here, simple box models of the global oceans for the Si cycle are presented, which can account for the observed 0.3‰ difference between Atlantic and Pacific deep‐water δ30Si values, using typical opal export fluxes. The δ30Si gradient results from both a high δ30Si of dissolved Si overturning in the North Atlantic and the dissolution of low δ30Si of opal in the deep waters around the Southern Ocean that feed into the Pacific.