PROBLEM TO BE SOLVED: To provide an iron ion elution material for being integrated in a caisson and capable of effectively eluting bivalent iron ion (Fe) ingestible by photosynthetic organisms (chlorophyll and agar) into sea.SOLUTION: There is provided an iron ion elution material composed of a carbon material, an iron material containing metallic iron, and a floating body, wherein the carbon material and the metallic iron are at least partly made contact with each other.【課題】光合成生物（クロロフィル、藻）が摂取可能な二価の鉄イオン（Ｆｅ２＋）を、効果的に海中に溶出させることができるケーソン組込み用鉄イオン溶出体を提供する。【解決手段】炭素材と、金属鉄を含む鉄材と浮体とからなり、該炭素材と該金属鉄との少なくとも一部を接触させる。【選択図】図１
