An intercalibration between the GEOTRACES GO‐FLO and the MITESS/Vanes sampling systems for dissolved iron concentration analyses (and a closer look at adsorption effects)

Abstract

With John Martin's discovery that iron could be a limiting nutrient in phytoplankton growth (Martin and Fitzwater 1988), marine trace metal biogeochemistry has evolved, with more fieldwork devoted to obtaining trace metal samples, more groups participating in trace metal investigations, and increasing inclusion of trace metal parameters in marine models of nutrient and climate cycles. In 2003, the international GEOTRACES program was founded, which aimed to establish global trace element distributions and quantify the fluxes and processes that affect these distributions under variable hydrographic and biogeochemical regimes. The positive international response to this program and the monetary commitment for cruises made by so many countries is a testament to the maturation of the trace metal field.As interest in trace metal biogeochemistry has grown, the technology associated with collecting uncontaminated seawater samples and analyzing low metal concentrations in seawater's complex matrix has developed as well. However, in response to the limited calibration of the now numerous sample collection, handling, and analytical methods used in the community, an intercalibration committee was established from the inception of the GEOTRACES program to lead and oversee these comparison efforts. The power of an international collaboration is the ability to share the manpower and monetary responsibility for collecting and analyzing globally, but the comparison is only as strong as the many methods can intercalibrate.Depending on the measurement and metal of interest, there are many points at which analytical and sampling offsets can occur: precleaning (filters, bottles), sample collection (samplers, hydrowire), sample treatment (filtration, handling, acidification), sample processing (leaching, pre-concentra- An intercalibration between the GEOTRACES GO-FLO and the MITESS/Vanes sampling systems for dissolved iron concentration analyses (and a closer look at adsorption effects) AbstractAn intercalibration of dissolved iron (dFe) concentrations was conducted from samples collected on the GEO-TRACES Pacific Intercalibration cruise using two different sampling devices: the GEOTRACES GO-FLO rosette system and MITESS/Vane samplers. At each depth, the dFe concentrations were identical within analytical error, except at 500 m where contamination in one bottle is suspected. dFe adsorption kinetics to bottle walls was also investigated. Over 29 h, 18% of the dFe adsorbed to the walls of 1 L bottles, whereas over 15 h, 19% adsorbed to the walls of 250 mL bottles, suggesting a relationship between dFe adsorption and sample bottle surface area to volume ratio. Contrary to expectations that refrigeration would slow adsorption, cold 250 mL bottles demonstrated a 29% dFe loss over 15 h compared to 19% loss at room temperature. Finally, we tested the hypothesis that the decreasing dFe observed in successive sub-sampled bottles from the (unacidified) SAFe D1 tank was due not only to adsorption but also to pH-dependent Fe solubility changes ...

Distal transport of dissolved hydrothermal iron in the deep South Pacific Ocean

“…Soluble Fe samples were collected after filtration through a 0.02-μm Anodisc filter. On the Melville BiG RAPA cruise, seawater was collected using the MITESS/Vanes system and filtered through 0.4-μm Nuclepore filters into HDPE bottles (57). Soluble Fe samples were collected using a cross-flow ultrafiltration system in static mode using a 10-kDa nominal molecular weight cutoff regenerated cellulose filter (Pellicon XL, PLCGC; Millipore) after conditioning with 350 mL of filtered sample seawater.…”

The composition of dissolved iron in the dusty surface ocean: An exploration using size-fractionated iron-binding ligands

“…10 rinsed and filled with pH 2 ultrapure acid until use (Fitzsimmons and Boyle, 2012). FLPE bottles were cleaned in 3 M trace metal grade HCl for a month and then were conditioned with ultra clean Milli-Q water for more than a month prior to sample collection in order to remove all acid residue .…”

Intercalibration in chemical oceanography—Getting the right number

“…One outcome from these workshops is the collection of papers found in the special issue of Limnology and Oceanography: Methods, Volume 10, Intercalibration in Chemical Oceanography. These articles include the following: evaluating the performance (hydrographic fidelity, degree of contamination) of the US Sampling system (Cutter and Bruland 2012;Fitzsimmons and Boyle 2012); comparing the composition and elemental concentrations of particles collected via in situ pumping systems and GO-FLO bottles (Bishop et al 2012;Planquette and Sherrell 2012); optimizing the collection and handling, and then intercalibrating samples for neodymium isotopes and rare earth elements Pahnke et al 2012), anthropogenic radionuclides (Kenna et al 2012), 210 Pb and 210 Po (Church et al 2012;Baskaran et al 2013); radium isotopes (Charette et al 2012); the suite of Th and Pa in the dissolved and particulate states Auro et al 2012;Maiti et al 2012); atmospheric aerosols (Buck and Paytan 2012;Morton et al 2013); organic complexation of Fe and Cu ; and a variety of other trace metals and their isotopes Lamborg et al 2012;Sharma et al 2012;Zurbrick et al 2012). …”