Distribution and Isotopic Signature of "Ligand-leachable" Particulate Iron in the Eastern Tropical South Pacific: Initial Results from US GEOTRACES EPZT.

Abstract:

Marine particles can act as both a source and sink for dissolved iron and thus play an important role in the biogeochemical cycling of this important micronutrient in the ocean. However, not all particulate iron (pFe) is considered to be biologically available, with some fraction locked away in mineral matrices. As a result, analyses that estimate the bioavailable fraction of pFe are a valuable addition to studies of iron distribution. One such analysis involves the use of an oxalate-EDTA leach at pH 8, with heating, to estimate “ligand-leachable” iron. We will present concentration profiles of ligand-leachable iron associated with suspended (0.8 – 51 μm) particles from the GEOTRACES Eastern Pacific Zonal Transect: a dataset that includes labile particulate iron concentrations measured in the mixed layer, chlorophyll maximum, benthic nepheloid layers, oxygen minimum zones and hydrothermal plume. Where relevant, we compare concentrations to measurements made in similar areas during the US GEOTRACES North Atlantic zonal transect. In addition, we will present initial results from US GEOTRACES EPZT of the stable isotopic composition of iron (δ⁵⁶Fe) in the ligand leachable fraction and discuss the results in terms of biogeochemical cycling of particulate iron.