Extraterrestrial dust as a source of bioavailable Fe for the ocean productivity

Abstract. Bioavailable Fe is an essential nutrient for phytoplankton that allows organisms to flourish and drawdown atmospheric CO₂ affecting global climatic condition. In marine locales remote from the continents extraterrestrial-dust provides an important source of Fe and thus moderates primary productivity. Here we provide constraints on partitioning of extraterrestrial Fe between seawater and sediments from observations of dissolution and alteration cosmic spherules recovered from the deepsea sediments and Antarctica. Of the ~ 3000–6000 t/a extraterrestrial dust that reaches Earth surface, ~ 2–5 % material survives in marine sediments whilst the remainder is liberated into seawater. Both processes contributes ~ (3–10) × 10⁻⁸ molFe m⁻² yr⁻¹. Also, Fe contribution due to evaporation of survived particle is estimated to be ~ 10 % of Fe contribution to meteoric smoke. Changes in extraterrestrial-dust flux vary not only the amount of Fe by up to three orders of magnitude, but also the partitioning of Fe between surface and abyssal waters depending on entry velocity and evaporation.