Large-scale impact of the island mass effect through nitrogen fixation in the western South Pacific Ocean

Abstract

We describe a new mechanism for the island mass effect fueled by nitrogen fixation. The nitrogen fixation activities and δ15N of suspended particles in the surface water in the South Pacific were examined. Active nitrogen fixation and abundant Trichodesmium spp. were observed near islands in the western subtropical region, which was attributable to the material supplied by land runoff. High primary production was extensively centered around the islands and was characterized by low δ15N of suspended particles and a reduction in phosphate concentrations at the surface compared with the subtropical gyre and eastern equatorial upwelling. This suggested that Trichodesmium spp. were advected to areas remote from these islands, and consequently, the elevated primary production fueled by nitrogen fixation extended over a large area around them. Because the proposed island mass effect is triggered by a terrigenous nutrient supply, this ecosystem is potentially vulnerable to human activity on small islands. Key Points A new mechanism for island mass effect fueled by nitrogen fixation is proposed The area of active primary production is >40 times larger than that of islands The occurrence of this oceanic ecosystem is triggered by land runoff ©2014. American Geophysical Union. All Rights Reserved.