Complexation of cobalt by natural organic ligands in the Sargasso Sea as determined by a new high-sensitivity electrochemical cobalt speciation method suitable for open ocean work

A seasonal study of dissolved cobalt in the Ross Sea, Antarctica: micronutrient behavior, absence of scavenging, and relationships with Zn, Cd, and P

“…This abundance of labile cobalt is likely important in providing a bioavailable form of Co to eukaryotic phytoplankton (Saito et al, , 2004. Moreover, the presence of measurable labile cobalt throughout the water column of the Ross Sea contrasts with observations in tropical and subtropical regions, where cobalt is often completely bound by strong ligands in the upper euphotic zone (Saito and Moffett, 2001;Saito et al, 2004Saito et al, , 2005Noble et al, 2008). Exceptions to this appear to be related to significant sources of cobalt, such as in the Peru Upwelling Region, where a large flux of cobalt is thought to enter the system as labile cobalt, and where large phytoplankton community shifts occurred concurrently with changes in cobalt speciation (Saito et al, 2004).…”

“…), and 8.3 ± 1.3 pM for the CORSACS-2 dCo and labile Co measurements, (sample set analyst T.J.G.) as determined by running blank seawater as previously described (Saito and Moffett, 2001). Triplicate analysis of a surface sample from the Ross Sea using this automated method yielded 27.8 pM ± 0.7 pM (2.6% RSD).…”

“…After this treatment, 9.25 mL of sample were pipetted into a Teflon sample cup that had been pre-rinsed with a small aliquot of sample; to this was added 50 µL of 0.5 M N-(2-hydroxyethyl)piperazine-N-(3-propanesulfonic acid) buffer (EPPS, Sigma), 30 µL of 0.1 M dimethylglyoxime (DMG; Sigma-Aldrich), and 0.75 mL of 1.5 M sodium nitrite (Fluka). These three reagents were purified as previously described (Saito and Moffett, 2001;Saito et al, 2004Saito et al, , 2005. Instrumentation consisted of two Metrohm 663 hanging mercury drop stands, each interfaced to an Eco-Chemie µAutolab III, IME interface device, and portable Windows XP computer running GPES Electrochemical software (Eco-Chemie).…”

“…Elements such as Co, Fe, Cu, and (at high latitudes) Mn are considered hybrid-type metals, due to their oceanic distributions being strongly affected by both micronutrient uptake and scavenging processes (Bruland and Lohan, 2003;Noble et al, 2008). In addition, organic ligands have been shown to bind Co very strongly and are believed to provide an important control on Co biological availability as well as potentially protecting Co from scavenging in the ocean (Ellwood and van den Berg, 2001;Saito and Moffett, 2001;Ellwood et al, 2005). An experiment that compared Co enrichment incubations with and without the natural phytoplankton and microbial community demonstrated a biological origin of these cobalt ligands in the Costa Rica Dome region .…”

Iron-binding ligands and their role in the ocean biogeochemistry of iron

“…Perhaps, as some results suggest, [58,59] iron binding ligands in deep water are recalcitrant/refractory in nature, and might be analogous to the humic material in terrestrial soil and water that is characteristic of organic matter degradation. The specific nature of iron-binding ligands is also difficult to reconcile with the observation that the chemical speciation of many other transition metals is also dominated by organic complexes, [77,78] including Zn, [79][80][81] Cd, [82] Cu, [83][84][85][86] Ni [85] and Co. [87] As already mentioned, much of this humic material is colloidal in nature in terrestrial environments. This may also be the case in the ocean.…”