The Southern Ocean is the largest high nutrient low chlorophyll (HNLC) oceanic region, where iron limits phytoplankton growth and productivity and ultimately influences the Biological Carbon Pump (BCP). Natural exceptions to the HNLC regime occur where island wakes cause iron to be mixed into surface waters from sediments, enabling large, prolonged phytoplankton blooms and increased carbon drawdown. Interactions between iron and phytoplankton are reciprocal in blooms: with plankton regulating the (re)cycling of iron through cellular uptake and remineralisation. The depth of iron remineralisation then influences either re-supply to the surface mixed layer biota or sequestration into deeper waters. Water column trace metal observations and shipboard experiments, using bioassays and radioisotope (⁵⁵Fe, ³²Si, ¹⁴C) cycling, were undertaken to investigate surface mixed layer phytoplankton iron limitation, iron uptake, and mesopelagic iron remineralisation relative to carbon and silica within the November 2017 bloom downstream of South Georgia. Surface phytoplankton residing in the iron depleted mixed layer were iron limited throughout the four-week sampling period. Experiments designed to investigate particulate water column (re)cycling revealed limited iron remineralisation from freshly produced upper ocean particles. The main pathway of iron transfer from particulates into the dissolved phase was through rapid (<2 d) release of extra-cellular adsorbed iron, which, if occurring in situ, could contribute to observed higher sub-surface dissolved Fe concentrations. This was accompanied by a small loss of cellular carbon, likely through respiration of the fixed ¹⁴C, and limited dissolution of particulate ³²Si to dissolved ³²Si. Decoupling of the remineralisation length scales for Fe, C and Si, with Fe having the fastest turnover, is thus likely in the upper mesopelagic zone beneath the bloom.

南大洋是最大的高营养低叶绿素 (HNLC) 海洋区域，铁限制了浮游植物的生长和生产力，并最终影响生物碳泵 (BCP)。HNLC 制度的自然例外发生在岛屿尾流导致铁从沉积物混入地表水中，从而导致大量、长时间的浮游植物大量繁殖和增加碳吸收。铁和浮游植物之间的相互作用在水华中是相互的：浮游生物通过细胞摄取和再矿化来调节铁的（再）循环。然后，铁再矿化的深度会影响对地表混合层生物群的再供应或对更深水域的封存。水柱痕量金属观察和船上实验，使用生物测定和放射性同位素（⁵⁵ Fe，³² Si, ¹⁴ C) 循环，旨在研究 2017 年 11 月南乔治亚岛下游水华中与碳和二氧化硅相关的表面混合层浮游植物铁限制、铁吸收和中层远洋铁再矿化。在整个 4 周的采样期间，铁贫化混合层中的表面浮游植物铁含量有限。旨在研究颗粒水柱（再）循环的实验表明，新鲜产生的上层海洋颗粒对铁的再矿化有限。铁从颗粒转移到溶解相的主要途径是通过快速（<2 天）释放细胞外吸附的铁，如果发生在原位，可能有助于观察到更高的地下溶解铁浓度。这伴随着细胞碳的少量损失，可能是通过固定^{14 C 的呼吸作用，以及颗粒32} Si有限溶解为溶解的³² Si。因此，Fe、C 和 Si 的再矿化长度尺度的解耦，其中 Fe 具有最快的周转率，因此很可能在大华下方的中远洋上部区域。