The marine chemistry of platinum is poorly understood, and its oceanic budget remains unconstrained, mainly because of severe analytical artifacts and the paucity of studies on this element of increasing technological interest. Here, we report dissolved and acid-leachable Pt concentrations in the Estuary and Gulf of St. Lawrence (EGSL) under winter conditions, and relate its estuarine geochemical behaviour to that of Cd, an element with similar characteristics and for which we have a more comprehensive knowledge. In contrast to Cd and in many pristine river systems, dissolved Pt concentrations in the EGSL in the winter (0.46 ± 0.09 pM) are significantly higher than the marine endmember (0.26 ± 0.06 pM). This discrepancy could be ascribed to the geology of the EGSL's drainage basins as well as the wet deposition of atmospheric Pt. This observation draws attention to the impacts of anthropogenic Pt emissions on its environmental dispersion, background estuarine concentrations and processes, especially in high-latitude regions. Unlike the results of most studies carried out in estuarine systems under ice-free conditions, we observed a near-conservative mixing behaviour of Pt and Cd in the surface waters of the EGSL during the winter, as is the case for dissolved Mn, Fe and rare earth elements. This observation could be explained by a decreased delivery of colloidal and organic materials to the estuary under ice-covered conditions. We also observed that both the dissolved Pt and Cd concentrations increase in the bottom waters of the EGSL, where the waters are more saline and oxygen-depleted. These higher concentrations may originate from the aerobic mineralization of Pt-bearing organic matter, a decrease of Pt-reactive surface sites on suspended particles, and a change in redox speciation of Pt^II into Pt^IV. Overall, these results highlight that winter and oxygen-depleted conditions can amplify continental Pt fluxes to the oceans and thus should be considered in future Pt oceanic budget calculations.

铂的海洋化学知之甚少，其海洋预算仍然不受限制，主要是因为严重的分析伪影以及对这一日益引起技术兴趣的元素的研究很少。在这里，我们报告了冬季条件下河口和圣劳伦斯湾 (EGSL) 中溶解和酸浸出的 Pt 浓度，并将其河口地球化学行为与 Cd 的行为联系起来，Cd 是一种具有相似特征的元素，我们对此有更多的了解全面的知识。与 Cd 和许多原始河流系统相比，冬季 EGSL 中溶解的 Pt 浓度（0.46 ± 0.09 pM）显着高于海洋端元（0.26 ± 0.06 pM）。这种差异可归因于 EGSL 流域盆地的地质情况以及大气 Pt 的湿沉降。这一观察结果引起了人们对人为 Pt 排放对其环境扩散、背景河口浓度和过程的影响的关注，尤其是在高纬度地区。与在无冰条件下在河口系统进行的大多数研究结果不同，我们观察到冬季 EGSL 地表水中 Pt 和 Cd 的近乎保守的混合行为，溶解的 Mn、Fe 和稀土元素。这一观察结果可以用冰覆盖条件下胶体和有机物质向河口的输送减少来解释。我们还观察到，EGSL 底部水中溶解的 Pt 和 Cd 浓度均有所增加，那里的水含盐量更高且缺氧。^II进入 Pt ^IV。总体而言，这些结果突出表明，冬季和缺氧条件可以放大大陆 Pt 流入海洋的通量，因此应在未来的 Pt 海洋预算计算中予以考虑。