Dataset: GP16 Dissolved Manganese
Deployment: TN303

Water-column samples for trace metal analysis were collected in modified 12 L Teflon-lined GO-FLO samplers (General Oceanics Inc.), deployed on the U.S. GEOTRACES clean CTD rosette system with a total of 24 samplers). At each station, the bottles were deployed open and tripped on ascent at 3 m/min. On deck, the bottles were kept in a trace metal clean sampling van over-pressurized with HEPA-filtered air, except immediately prior to and following deployments, in which cases they were covered on both ends with shower caps to avoid deck contamination. All samples were filtered as soon as possible after recovery by GEOTRACES sampling personnel using 0.2 um Supor Acropak filter cartridge (Pall Corp.) inside the U.S. GEOTRACES clean-air laboratory van. Near-surface samples (from ~2 m depth) were collected while underway on approach to or departure from each station using the Bruland-Smith "Geofish" sampling system, which was towed outside of the ship’s wake. Seawater from the Geofish was pumped into a clean-air laboratory van, where it was filtered through 0.2 um Supor Acropak filter cartridges. After sample collection, the exteriors of the bottles were rinsed once with De-ionized water and dried under a laminar flow hood. Samples were acidified within 24 hours with 0.2 mLs of 6N to a pH of ~1.8. Samples were analyzed at sea within 1 month of collection.

Dissolved Mn was determined at sea by flow injection analysis with in-line pre-concentration on resin-immobilized 8-hydroxyquinoline and colorimetric detection. Daily precision of analysis was +/- 0.01 nM or 3.8%, whichever is larger, based on the reproducibility of analytical and internal standards. A conservative estimate of the limit of detection is 0.03 nM based on 3 times the daily precision of analysis, which is consistent with previous work. Two internal reference standards were run over the 57 days of the cruise, with DMn concentrations of 0.42 +/- 0.036 nM (+/- 8.4%; n = 102) and 0.31 +/- 0.041 nM (+/- 13%, n = 69), respectively. The SAFe reference samples were analyzed simultaneously during sample analysis with the following results: for SAFe S, 0.85 +/- 0.026 nM (n = 27; consensus value = 0.79 +/- 0.06 nM); for SAFe D2, 0.40 +/- 0.028 nM (n = 22; consensus value = 0.35 +/- 0.05); and for SAFe D1, 0.36 +/- 0.026 nM (n = 31; no consensus value). 

Intercalibration information:
In addition to the reference standards reported above, we conducted an intercomparisson with three other labs University of California Santa Cruz, University of Southern Mississippi, University of Miami. The stations considered were 1, 17 and 36 (for the UM  group we compare only stations 17 and 36.)

This intercalibration was accepted by the International GEOTRACES Standards and Intercalbration Committee.

Related References:
Resing, J. A. & Mottl, M. J. Determination of manganese in seawater using flow injection analysis with on-line preconcentration and spectrophotometric detection. Anal. Chem. 64, 2682–2687 (1992).