High dissolved iron (dFe) concentrations of the order of 10-100 nmol L^-1 are a feature of waters influenced by sedimentary inputs in oxygen minimum zones (OMZ). However, the temporal development of dFe concentrations is poorly defined due to a general reliance on snapshot cross-shelf sections to study marine trace metal dynamics. Multiple cruise campaigns since the 1980s have investigated Fe dynamics over the Peruvian shelf, particularly between 9-17°S where the shelf is broad, extremely productive and known to feature benthic dFe effluxes which are amongst the highest measured globally. This extensive long-term dataset uniquely allows us to study the interannual variability in dFe concentrations and their response to El Niño–Southern Oscillation (ENSO) events. By combining data from 11 cruises during the period 1984-2017 we are able to evaluate dFe dynamics on interannual timescales in a major OMZ. The region where average dFe concentrations are sensitive to variations in ENSO is confined to a subsurface layer at depths between 50-150 m, particularly in the narrow coastal region within 50 km of the coastline. Subsurface dFe concentrations were generally low during El Niño events (0.7-15.4 nmol L^-1) and relatively high with a wider range of variability during the cold ENSO phase (1.1-52.1 nmol L^-1). Inverse relationships between wind speed and surface/subsurface dFe were evident. In the subsurface layer, this may be attributable to enhanced dFe offshore transport along isopycnals when upwelling-favorable winds relax in accordance with previously outlined theories. Surface layer (<40 m) dFe variability was likely associated with a dilution and/or oxidation effect depending on the strength of wind driven water column mixing. Upwelling brings macronutrient-rich water into the euphotic zone, but its intensity had a limited impact on upper layer dFe concentrations possibly due to the influence of an onshore geostrophic flow. Interannual variability in surface chlorophyll-a (Chl-a) was found to correlate with dFe concentration in the offshore zone of northern Peru. This is consistent with bioassay experiments and climatological residual nitrate concentrations which both indicate proximal Fe limitation of phytoplankton growth over and beyond the northern Peruvian shelf. Overall, our work highlights the importance of physical factors driving short-term variations in Fe availability in one of the world’s most economically important fishery regions and suggests that, despite pronounced spatial and temporal variability in dFe concentrations, the ENSO phase has an impact on dFe availability.

^{10-100 nmol L -1}量级的高溶解铁 (dFe) 浓度是受氧最低区 (OMZ) 沉积输入影响的水的一个特征。然而，由于普遍依赖快照跨陆架剖面来研究海洋痕量金属动力学，因此 dFe 浓度的时间发展很难确定。自 20 世纪 80 年代以来的多次巡航活动已经调查了秘鲁大陆架上的铁动态，特别是南纬 9-17° 之间的大陆架，该大陆架广阔、生产力极高，并以海底 dFe 流出量为特征，是全球测得最高的。这个广泛的长期数据集独特地使我们能够研究 dFe 浓度的年际变化及其对厄尔尼诺南方涛动 (ENSO) 事件的响应。通过结合 1984 年至 2017 年期间 11 次航行的数据，我们能够评估主要 OMZ 年际时间尺度上的 dFe 动态。平均 dFe 浓度对 ENSO 变化敏感的区域仅限于 50-150 m 深度的地下层，特别是在海岸线 50 km 以内的狭窄沿海地区。厄尔尼诺事件期间地下 dFe 浓度普遍较低（0.7-15.4 nmol L ^-1），而在冷 ENSO 阶段则相对较高且变化范围较大（1.1-52.1 nmol L ^-1）。风速和地表/地下 dFe 之间的反比关系很明显。在地下层，这可能是由于根据先前概述的理论，当有利于上涌的风减弱时，dFe 沿等密度线的离岸输送增强。表层 (<40 m) dFe 变化可能与稀释和/或氧化效应相关，具体取决于风驱动水柱混合的强度。上升流将富含常量营养素的水带入富光带，但其强度对上层 dFe 浓度的影响有限，可能是由于陆上地转流的影响。研究发现，秘鲁北部近海区域表面叶绿素-a (Chl-a) 的年际变化与 dFe 浓度相关。这与生物测定实验和气候残留硝酸盐浓度一致，两者都表明秘鲁北部陆架上方和以外的浮游植物生长的近端铁限制。总体而言，我们的工作强调了在世界上经济最重要的渔业区域之一推动铁可用性短期变化的物理因素的重要性，并表明，尽管 dFe 浓度存在明显的空间和时间变化，ENSO 阶段仍对 dFe 产生影响可用性。