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Controls on iron(III) hydroxide solubility in seawater: The influence of pH and natural organic chelators
Author(s) -
Kuma Kenshi,
Nishioka Jun,
Matsunaga Katsuhiko
Publication year - 1996
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1996.41.3.0396
Subject(s) - solubility , seawater , chemistry , hydroxide , environmental chemistry , dissolved organic carbon , alkalinity , metal hydroxide , metal , chlorophyll a , inorganic chemistry , geology , oceanography , organic chemistry , biochemistry
Iron solubilities of Fe(III) hydroxide in coastal and oceanic waters and in the ultraviolet (UV)‐irradiated seawaters over a pH range of 5.7–8.2 at 20°C were determined by a simple filtration (0.025 µ m) involving γ ‐activity measurement of 59 Fe. At pH ranges of 5.7–7.2 (coastal water) and of 5.7–7.6 (oceanic water), only the Fe(OH) 2 + species is significant. The calculated solubility products, log* K SO , for coastal and oceanic waters were 4.8–5.0 and 4.4–4.6, respectively. The solubilities within the pH range of 7.8–8.2 are relatively independent of pH and aging time. Solubility in the oceanic water was about one order of magnitude lower than that in the coastal water, and UV irradiation reduced solubility to ≤0.1 nM. The vertical profiles of ambient Fe(III) solubility (pH 8.0–8.2) in oceanic waters have the following features in common: solubility in the surface mixed layer is high and variable (0.3–0.6 nM), generally corresponding with the depth of high chlorophyll a concentrations; solubility minima (0.15–0.2 nM) occur at a depth of 50–200 m. These results suggest that natural organic Fe(III) chelators exist in significant concentrations and control the dissolved iron concentration in seawaters.