Iron fertilization from Asian dust drives tertiary-level productivity of Pacific salmon

Abstract

Iron enrichment in high-macronutrient, low-chlorophyll surface oceans was hypothesized to enhance primary production and carbon sinks that ultimately influence the earth’s climatic system. Although the enhancement of primary production and carbon sinks has been repeatedly verified, the role of iron in upper-level production remained uninvestigated, and thus, our understanding of ecosystem responses is incomplete. In this analysis, paleorecords and modern time series are gleaned to test an extended hypothesis that tertiary-level productivity is also promoted by iron fertilization. Paleoproxies and modern records for the abundance of sockeye salmon returning to an Alaskan lake are related to climatic variables describing the flux of iron-laden Asian dust, its trans-Pacific transport, and its deposition into the iron-limited Gulf of Alaska sockeye salmon feeding ground. The linkage shows that for ∼2,200 years, the productivity of the salmon stock has been driven by this Asian dust supply. Data from modern observations provide more direct support for the linkage between dust-iron input, primary production, and salmon abundance. This analysis indicates that iron from Asian dust drives primary through to sockeye salmon productivity via bottom-up food-web control. This understanding of the role of iron in tertiary-level production provides a basis for the artificial enhancement of ocean living resources, but questions arise regarding the efficiency of iron fertilization in climate mitigation.