| Summary: | Maintenance and Update Frequency: notPlanned Statement: Particulate trace metal samples were collected from a combination of in situ pump (ISP) profiles at 8 of the TMR stations (super-stations) and 4 L subsamples taken from the TMR Niskin bottles at 19 of the TMR stations (sampling locations given in Figure 3b). Full details of ISP particulate trace metal preparation, sampling and analytical techniques can be found in van der Merwe et al. (2019). 4 L subsamples from the TMR Niskin bottles were filtered onto paired, 25 mm, 0.8 µm Supor polyethersulfone (PES) membrane filters giving an effective pore diameter of 0.45 µm (Bishop et al., 2012) and matching the filters used on the ISPs. Due to the low volume of the Niskin filtrations, these filters were only subjected to a complete acid digestion using trace-metal grade (Seastar Baseline) concentrated hydrofluoric (HF), hydrochloric (HCl) and nitric acids (HNO3), while the 42 mm diameter subsamples of the 142 mm diameter ISP filters were subjected to a weak chemical leach (Berger et al., 2008) to separate the chemically labile from the refractory particulate fractions prior to a total digestion. To make these fractions comparable here, we summed the labile and refractory Fe fractions collected using the ISPs to give total pFe. The extra processing step required to determine the labile fraction completed on the ISP samples can lead to errors. However, comparison between the sum of these fractions and coincident total digestions on ISP subsamples from the same filter revealed recoveries of 101 ± 9.3 % (n = 3) for pFe, indicating that the methods are comparable. Certified reference material BCR-414 (Plankton for trace element analysis, European Commission – Joint Research Centre) was analysed to assess method accuracy. Results for pFe were 1.80 ± 0.009 g/kg (n = 3) while the certified value is 1.85 ± 0.19 g/kg giving a recovery of 97%. References: Berger, C. J. M., Lippiatt, S. M., Lawrence, M. G., & Bruland, K. W. (2008). Application of a chemical leach ...
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