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Dissolved iron in the tropical North Atlantic Ocean

机译：在热带北大西洋中溶解的铁

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Seawater from 27 stations was sampled in a zig-zag transect across the tropical North Atlantic from Barbados to the Cape Verde Islands, 7-20°N and 21 -58°W. Under the Northwest African dust plume, surface dissolved Fe (dFe) was elevated, averaging 0.55 ± 0.29 nmol/kg (1SD), but showed a wide range from 0.12 to 1.31 nmol/kg with no clear longitudinal or latitudinal gradients. A subsurface dFe maximum in excess of 1 nmol/kg was evident coincident with the oxygen minimum zone. Our goal was to determine whether this maximum occurred as a result of remineralization of high Fe:C organic material formed in the dust-laden (Fe-rich) surface ocean or as a result of lateral mixing of a coastal Fe signal from the African margin. We found that dFe is directly related to apparent oxygen utilization (AOU) with the same slope across all depths sampled, which implies a remineralization source throughout the water column. A continental margin dFe supply was discounted because a modeled margin Fe source should cause curvature in the Fe-AOU relationship that was not observed. We also did not see a significant dissolved manganese (dMn) plume emanating from the margin. Regenerated Fe:C ratios calculated from the dFe:AOU relationships ranged from 9.6 to 12.4 μmol Fe/mol C, which is much higher than ratios found in HNLC and dust-poor regions. Deep waters measured at one station in the eastern tropical North Atlantic reflected typical NADW concentrations until 4000 m, where the dFe increased to 0.82 nmol/kg in four discrete samples down to 5000 m. We propose that this increase in dFe may reflect dFe inputs to deep waters as they traverse the Mid-Atlantic Ridge and enter the eastern basin.
机译：在从北巴巴多斯到北佛得角群岛，北纬7-20°和西经21 -58°的热带北大西洋的锯齿形样带中对27个站点的海水进行了采样。在西北非洲的尘埃羽流下，表面溶解的Fe（dFe）升高，平均为0.55±0.29 nmol / kg（1SD），但显示范围为0.12至1.31 nmol / kg，没有明显的纵向或横向梯度。超过1 nmol / kg的亚表面dFe最大值明显与最小氧区一致。我们的目标是确定该最大值是否是由于在充满尘埃（富铁）的表层海洋中形成的高Fe：C有机物质的再矿化或来自非洲边缘的沿海铁信号的横向混合而发生的。我们发现，dFe与表观氧气利用率（AOU）直接相关，在所有采样深度上斜率都相同，这意味着整个水柱中都有一个矿化源。大陆边际dFe供应被打折，因为模型化的边际铁源会引起未观察到的Fe-AOU关系中的曲率。我们也没有看到边缘有明显的溶解锰（dMn）羽流。根据dFe：AOU关系计算得出的再生Fe：C比值介于9.6至12.4μmolFe / mol C之间，这比HNLC和灰尘少的地区的比例高得多。在北大西洋东部热带地区一站所测得的深水反映了典型的NADW浓度，直到4000 m，在四个不超过5000 m的离散样品中，dFe均增加到0.82 nmol / kg。我们认为，dFe的增加可能反映了dFe穿过深大西洋中脊并进入东部盆地时对深水的投入。

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