A comparison of biogenic iron quotas during a diatom spring bloom using multiple approaches

[摘要] Biogenic Fe quotas were determined using three distinct techniques onsamples collected concurrently in the subtropical Pacific Ocean east of NewZealand. Fe quotas were measured using radioisotope uptake experiments (24 hincubation), bulk filtration and analysis by inductively-coupled plasma massspectrometer (ICPMS), and single-cell synchrotron x-ray fluorescence (SXRF)analysis over a sixteen-day period (year days 263 to 278 of 2008) during aquasi-Lagrangian drifter experiment that tracked the evolution of the annualspring diatom bloom within a counter-clockwise open-ocean eddy. Overall,radioisotope uptake-determined Fe quotas (washed with oxalate reagent toremove extracellular Fe) were the lowest (0.5–1.0 mmol Fe:mol P;4–8 μmol Fe:mol C), followed by single-cell Fe quotas (2.3–7.5 mmol Fe:mol P;17–57 μmol Fe:mol C), and the highest and most variable quotas werefrom the bulk filtration ICPMS approach that used the oxalate reagent wash,corrected for lithogenic Fe using Al (0.8–21 mmol Fe:mol P; 4–136 μmol Fe:mol C). During the evolution of the spring bloom within the eddy (yeardays 263 to 272), the surface mixed layer inventories of particulatebiogenic elements (C, N, P, Si) and chlorophyll increased while Fe quotasestimated from all three approaches exhibited a general decline. After theonset of the bloom decline, the drogued buoys exited the eddy center (days273 to 277). Fe quotas returned to pre-bloom values during this part of thestudy. Our standardized and coordinated sampling protocols reveal thegeneral observed trend in Fe quotas: ICPMS > SXRF > radioisotope uptake.We discuss the inherent differences between the techniques and argue thateach technique has its individual merits and uniquely contributes to thecharacterization of the oceanic particulate Fe pool.

[学科分类] 地球化学与岩石