Water-column data from seven cruises in 2007–2008 reveal pronounced temporal and spatial variations in the distribution of dissolved iron (DFe, <0.4 μm) over the upper 1000 m of the Sargasso Sea near Bermuda, in the western subtropical North Atlantic Ocean. In near-surface waters, DFe exhibits a clear seasonal cycle, increasing from ~0.1–0.3 nM in spring to ~0.4–1.0 nM in summer-early fall. The observed seasonal ranges appear to reflect the extent of winter convective mixing and of summer dust deposition, both of which are closely tied to atmospheric circulation processes. Surface DFe concentrations also show significant (~two-fold) submesoscale lateral variations during summer, perhaps as a result of lateral inhomogeneities in wet deposition and wind-driven mixing. The summer vertical profiles reveal pronounced DFe minima and sometimes deeper maxima in the lower euphotic zone, which likely reflect biological uptake and shallow remineralization, and eddy-driven lateral gradients in these processes. Significant variability is also seen in the mesopelagic zone, with a DFe concentration range of ~0.4–0.7 nM at 1000 m depth, which may reflect mesoscale isopycnal displacements and/or lateral advection of iron-rich waters in the lower thermocline. Physicochemical iron speciation measurements indicate that the major fraction of DFe that accumulates in surface waters of the Sargasso Sea during summer is colloidal-sized Fe(III), which appears to be complexed by strong, iron-binding organic ligands. Concentrations of soluble iron (sFe, <0.02 μm) were considerably lower than DFe in the upper euphotic zone during summer, except over the subsurface DFe minima, where sFe accounts for ~50–100% of the DFe pool. Labile Fe(II), on average, accounted for around 20% of DFe, with maximum concentrations of around 0.1 nM in near-surface waters and in the lower thermocline. The seasonal-scale DFe changes that we have documented near Bermuda are of the same magnitude as basin-scale lateral gradients across the North Atlantic, underscoring the importance of time-series observations in understanding the behavior of trace elements in the upper ocean.

在2007-2008年的7次航行中，水柱数据显示了西亚热带北大西洋百慕大附近Sargasso海上部1000 m的溶解铁分布（DFe，<0.4μm）的明显时空分布。在近地表水域，DFe表现出明显的季节周期，从春季的〜0.1–0.3 nM增加到夏季至初秋的〜0.4–1.0 nM。观测到的季节范围似乎反映了冬季对流混合和夏季尘埃沉积的程度，二者均与大气环流过程密切相关。在夏季，表面DFe浓度也显示出明显的（约两倍）亚中尺度的横向变化，这可能是由于湿沉降和风驱动混合中的横向不均匀性所致。夏季的垂直剖面显示出较低的富营养区明显的DFe最小值，有时甚至更深的最大值，这可能反映了生物吸收和浅层再矿化以及这些过程中由涡流驱动的横向梯度。在中弹性带也观察到显着的变化，在1000 m深度处的DFe浓度范围为〜0.4–0.7 nM，这可能反映了下温跃层中富铁水的中尺度等位位移和/或横向对流。理化铁形态的测量表明，夏季期间在藻类海域的表层水中积累的DFe的主要部分是胶体大小的Fe（III），它似乎与强的，与铁结合的有机配体络合。可溶性铁的浓度（sFe，<0。夏季，在上层富营养区中，Fe2O2的含量要比DFe低得多，但地下DFe的最小值除外，其中sFe约占DFe池的50-100％。平均而言，不稳定的Fe（II）占DFe的20％左右，在近地表水域和下部温跃层中的最大浓度约为0.1 nM。我们在百慕大附近记录的季节尺度DFe变化与整个北大西洋的盆地尺度横向梯度具有相同的幅度，从而强调了时间序列观测对于了解上层海洋中微量元素的行为的重要性。