Dissolved iron in the Bermuda region of the subtropical North Atlantic Ocean: Seasonal dynamics, mesoscale variability, and physicochemical speciation
Dissolved iron in the Bermuda region of the subtropical North Atlantic Ocean: Seasonal dynamics, mesoscale variability, and physicochemical speciation
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北大西洋副热带百慕大地区的溶解铁：季节动态、中尺度变化和物理化学形态
DOI：
10.1016/j.marchem.2019.103748
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发表时间：
2020
期刊：
影响因子：
3
通讯作者：
Tagliabue, A.
中科院分区：
文献类型：
--
作者：
Sedwick, P.N.;Bowie, A.R.;Church, T.M.;Cullen, J.T.;Johnson, R.J.;Lohan, M.C.;Marsay, C.M.;McGillicuddy, D.J.;Sohst, B.M.;Tagliabue, A.
2007-2008年7次巡航的水柱数据揭示了北大西洋西副热带百慕大附近马尾藻海1000 m以上海域溶解铁（DFe <0.4 μm）分布的明显时空变化。近地表水体DFe呈现明显的季节循环，春季~0.1 ~ 0.3 nM增加到夏秋初秋~0.4 ~ 1.0 nM。观测到的季节变化似乎反映了冬季对流混合和夏季沙尘沉积的程度，这两者都与大气环流过程密切相关。地表DFe浓度在夏季也表现出显著的（~两倍）亚中尺度横向变化，这可能是湿沉积和风驱动混合的横向不均匀性的结果。夏季垂直剖面在低光带显示明显的DFe最小值和有时较深的最大值，这可能反映了生物吸收和浅再矿化过程以及这些过程中涡旋驱动的横向梯度。在中上层区域也有显著的变化，在1000 m深度，DFe浓度范围为~ 0.4-0.7 nM，这可能反映了中尺度等压位移和/或下温跃层富铁水的横向平流。物理化学铁形态测量表明，夏季马尾藻海地表水中积累的DFe的主要部分是胶体大小的Fe(III)，它似乎是由强的铁结合有机配体络合而成。在夏季，除了地表下的DFe最小值（sFe占DFe池的~ 50-100%）外，可溶铁（<0.02 μm）的浓度明显低于DFe。不稳定Fe（II）平均占DFe的20%左右，在近地表水和下温跃层的最大浓度约为0.1 nM。我们在百慕大附近记录的季节尺度DFe变化与横跨北大西洋的盆地尺度横向梯度具有相同的幅度，强调了时间序列观测在理解上层海洋微量元素行为方面的重要性。
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.