Search the data

Dissolved iron concentrations and isotopes on GEOTRACES process cruises GPpr01 (TAN0811) and GPpr10 (TAN1212)

Responsible investigator

Dr Michael Ellwood
email: michael.ellwood@anu.edu.au
Research School of Earth Sciences
Australian National University
61 Mills Road, Acton, Canberra, 0200
Australia

Data contributors

Dr Michael Ellwood
email: michael.ellwood@anu.edu.au
Research School of Earth Sciences
Australian National University
61 Mills Road, Acton, Canberra, 0200
Australia

Laboratory of analysis

Australian National University

Dataset brief description

Dissolved iron concentrations and isotopes on GEOTRACES process cruises GPpr01 (TAN0811) and GPpr10 (TAN1212)

Acquisition description

Sampling methodology

Samples were collected using acid-cleaned 5 L, Teflon coated, externally sprung, Niskin bottles attached to an autonomous rosette. Upon retrieval, bottles were removed from the rosette and transferred to a "clean container" with HEPA filtered air. Seawater samples were drained from the Niskin bottles, filtered through acid-cleaned 0.2 µm capsule filters (Supor AcroPak 200, Pall) and acidified to pH 1.8 with distilled nitric acid.

Analytical methodology

Dissolved iron concentrations were determined by ICPMS following pre-concentration and matrix separation using a similar procedure to that outlined by Bruland et al. (1979) and Danielsson et al. (1982). Briefly, 100 g of seawater was buffered to a pH of 4.5 with 0.5 mL of purified ammonium acetate (6.5 mol L ^-1 ) buffer. Purified ammonium pyrrolidinedithiocarbamate (APDC) and sodium diethyldithiocarbamate (DDC) were added (0.5 mL, 1% w/w of each) to the sample, which was then extracted twice following the addition of ~ 8 mL of purified chloroform. The two chloroform extracts were then combined, acidified with 0.1 mL of 16 mol L ^-1 nitric acid, shaken for 1 min and then diluted to 1 mL with deionised water (Millipore, Australia). Trace metal concentrations were determined by ICP-MS (820-MS Varian, Australia) with hydrogen introduced into the collision reaction interface to reduce the interference of ⁴⁰ Ar ¹⁶ O on ⁵⁶ Fe (Ellwood et al., 2008). As a check on the analytical method used, shallow and deep Sampling and Analysis of Iron (SAFe) standards were analysed in conjunction with seawater samples (Johnson et al., 2007). The results for analysis of SAFe standards were 0.09 ± 0.02 nmol kg ^-1 and 0.90 ± 0.05 nmol kg ^-1 for surface and deep standards, respectively. These values are within the accepted range of 0.09 ± 0.007 nmol kg ^-1 and 0.90 ± 0.02 nmol kg ^-1 surface and deep standards, respectively.

The δ ⁵⁶ Fe composition of Fe was made on samples purified using the anion exchange procedure described by Poitrasson and Freydier (2005). Before purification, DFe samples were preconcentrated by dithocarbamate extraction. Iron isotopes were determined using a Neptune Plus multicollector Inductively Coupled Plasma Mass Spectrometer (ICPMS) (Thermo Scientific) with an APEX-IR introduction system (Elemental Scientific) and with X-type skimmer cones. Samples were measured in high-resolution mode with ⁵⁴ Cr interference correction on ⁵⁴ Fe and with instrumental mass bias correction using nickel

References cited

Bruland, K.W., Franks, R.P., Knauer, G.A., Martin, J.H., 1979. Sampling and analytical methods for the determination of copper, cadmium, zinc and nickel at the nanogram per liter level in sea water. Anal. Chim. Acta. 105, 233-245

Danielsson, L., Magnusson, B., Zhang, K., 1982. Trace metal determinations in estuarine waters by electrothermal atomic adsorption spectroscopy after extraction of dithiocarbamate complexes into freon. Anal. Chim. Acta. 144, 183-188

Ellwood, M.J., Boyd, P.W., Sutton, P., 2008. Winter-time dissolved iron and nutrient distributions in the Subantarctic Zone from 40-52S; 155-160E. Geophys. Res. Lett. 35 (L11604).

Johnson, K.S., Elrod, V., Fitzwater, S., Plant, J., Boyle, E., Bergquist, B., Bruland, K., AguilarIslas, A., Buck, K., Lohan, M., Smith, G.J., Sohst, B., Coale, K., Gordon, M., Tanner, S., et al., 2007. Developing standards for dissolved iron in seawater. EOS 88 (11), 131-132

Poitrasson, F., Freydier, R., 2005. Heavy iron isotope composition of granites determined by high resolution MC-ICP-MS. Chem Geol 222(1-2):132-147

BODC Data Processing Procedures

The mapping between the originator's channels and the BODC parameter codes are detailed in the table below.

Data Quality Report

None.