The atmospheric abundance of oxalic acid significantly influences the supply of soluble iron (Fe_ws), an essential micronutrient for the phytoplankton growth, to the ocean surface. We used the linear relationship between stable carbon isotopic composition of oxalic acid (δ¹³C_oxalic) and Fe_ws in marine aerosols collected from a coastal ocean, the Bay of Bengal (BoB), to probe the likely photochemical cycling of total aerosol iron (Fe_Tot). In winter, the BoB is influenced by continental pollution from the Indo-Gangetic Plain (IGP) and Southeast Asia (SEA). Despite higher levels of oxalic acid, anthropogenic SO₄^2–, and Fe_Tot in IGP outflow, we observe higher fractional solubility of aerosol iron [Fe_ws (%) = Fe_ws/Fe_Tot × 100] in the SEA outflow (11.4–49.7%). Coincidently, we observe an inverse linear relationship between δ¹³C_oxalic (from −18.4 to −8.8‰) and Fe_ws (3.5–38.0 ng m^–3) in the SEA outflow (slope = −0.18; R² = 0.42; p < 0.05) but not in the IGP outflow. This relationship indicates the catalytic behavior of Fe_Tot in the oxidation of precursor water-soluble organics to oxalic acid, yielding Fe_ws. Unlike the IGP outflow, SEA outflow aerosols (i.e., having excess free inorganic acidity and low aerosol pH) are more acidic and experience higher solar influx over the remote BoB. These findings emphasize the concept that oxalic acid formation from the precursor organics in deliquescent aerosols is catalyzed by Fe_Tot, contributing to an overall increase of Fe_ws (%).

中文翻译：

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涉及铁和草酸的环境光-芬顿反应的¹³ C探测：对海洋生物地球化学的影响

大气中草酸的丰富度显着影响可溶性铁（Fe _ws）的供应，而可溶性铁是浮游植物生长所必需的微量营养素，向海洋表面的供应。我们使用草酸的稳定碳同位素组成之间的线性关系（δ ¹³ C ^_草酸）和Fe _WS在从近海收集海洋气溶胶，孟加拉湾（BOB），以探测总气溶胶铁的可能光化学循环（ Fe _Tot）。在冬季，BoB受印度恒河平原（IGP）和东南亚（SEA）的大陆污染的影响。尽管草酸，人为产生的SO ₄ ^2–和Fe _Tot含量较高在IGP流出中，我们观察到气溶胶铁在SEA流出中的分数溶解度较高[Fe _ws（％）= Fe _ws / Fe _Tot ×100]。巧合的是，我们观察到的逆线性δ之间关系¹³ Ç_草酸（从-18.4至-8.8‰）和Fe _WS（3.5-38.0纳克米^-3）在SEA流出（斜率= -0.18; - [R ² = 0.42; p <0.05），但不在IGP流出中。该关系表明Fe _Tot在前体水溶性有机物氧化为草酸中的催化行为，生成Fe _ws。与IGP流出不同，SEA流出气溶胶（即具有过量的游离无机酸度和较低的气溶胶pH）更酸性，并且比远程BoB的太阳涌量更高。这些发现强调了Fe _Tot催化潮解性气溶胶中前体有机物形成草酸的概念，从而导致Fe _ws（％）的总体增加。