Chemically and Geographically Distinct Solid-Phase Iron Pools in the Southern Ocean

Abstract

Iron is a limiting nutrient in many parts of the oceans, including the unproductive regions of the Southern Ocean. Although the dominant fraction of the marine iron pool occurs in the form of solid-phase particles, its chemical speciation and mineralogy are challenging to characterize on a regional scale. We describe a diverse array of iron particles, ranging from 20 to 700 nanometers in diameter, in the waters of the Southern Ocean euphotic zone. Distinct variations in the oxidation state and composition of these iron particles exist between the coasts of South Africa and Antarctica, with different iron pools occurring in different frontal zones. These speciation variations can result in solubility differences that may affect the production of bioavailable dissolved iron.

A review of colloidal iron partitioning and distribution in the open ocean

“…Another factor that can affect the %cFe value is the chemical speciation of the Fe phases present, as each different organic and inorganic Fe phase will be associated with differing stability, solubility and dissolution kinetics. Von der Heyden et al (2012) have shown that a variety of Fe enriched phases exist in a single depth profile, with pure Fe(III) phases and two classes of Fe mixed valence phases identified at 2000 m and only pure Fe(III) phases found at 4000 m depth.…”

“…Mass spectrometry combined with chromatographic techniques has been used to precisely characterise Fe binding ligands (Mawji et al, 2011) and direct X-ray probes have been used to understand Fe colloid mineralogy at a particle-by-particle resolution (von der Heyden et al, 2012(von der Heyden et al, , 2014. Techniques such as these seek to understand the chemical and mineralogical considerations that dictate the behaviour of Fe in marine biogeochemical systems.…”

Grand challenges in biogeoscience

“…Powerful methods now exist for examining mineral-organism interactions through numerous advances in microscopy and imaging techniques that can map chemical and other variations on minute scales and can reveal specific microbial metabolisms (e.g., Musat et al, 2008;von der Heyden et al, 2012). Such techniques shed light on processes taking place at the organismal, molecular, and even atomic level, and inform about the spatial disposition between life and its abiotic substrates.…”

Comments on ‘Influence of measurement uncertainties on fractional solubility of iron in mineral aerosols over the oceans’ Aeolian Research 22, 85–92

“…Recent applications of these techniques have been published by Kadar et al (2014), Jeong and Achterberg (2014) and Baddock et al (2013). Synchrotronbased X-ray absorption spectroscopy can also be used to identify iron speciation (von der Heyden et al, 2012;Oakes et al, 2013). All these techniques are suitable for use with the small weights (<0.1 mg) typical of aeolian mineral dust samples.…”