Pore water data of thallium (Tl) in marine environments are scarce. It has been suggested that anoxic sediments are a sink for dissolved Tl likely due to its incorporation into Fe sulfides. However, recent studies indicated that Tl is removed from solution prior to the onset of sulfidic conditions and that Tl is involved in biological cycles in coastal seawater. To assess the Tl behavior in marine sediments, pore waters of a high energy beach (Spiekeroog Island, Germany) were sampled during different seasons and on different spatial scales. The study site provides a perfect set of samples to assess trace metal behavior under various redox conditions.

Samples were analyzed for dissolved trace metals Tl, molybdenum (Mo), uranium (U), and rhenium (Re). Additionally, sediments were incubated to monitor trace metal removal or release under controlled conditions. On-site redox conditions were characterized using dissolved oxygen (O₂), manganese (Mn), and iron (Fe) concentrations.

Our results indicated high enrichments of Tl in pore waters concurrently to aerobic organic matter (OM) degradation, exceeding seawater concentrations up to 6-fold. In contrast, Tl was completely removed in weakly reducing pore water characterized by more than 1 µM Mn or Fe. The spatial Tl distribution in intertidal pore waters responded to the present dissolved Mn and Fe level, which varied in space and with season. We suggest, Tl release to be attributed to OM degradation, particle desorption, or reoxidation, whereas Tl removal is likely related to the presence of traces amounts of dissolved sulfide.

In conclusion, the fast reaction kinetics of Tl led to fast and complete removal in comparison to Mo, U, and Re and we suggest the following order of removal: Tl>Re>U>Mo. The removal behavior as well as the high enrichments of Tl in pore waters implicate that sinks and sources in the marine environment are not yet fully understood. Although the intertidal sediments form an overall sink for Tl (U and Re), especially under mostly anoxic conditions in summer, sediments turn into a Tl net source in winter, when sediments are more oxic.

For global marine Tl balances, Tl fluxes have been estimated based on pore water Tl/Mn ratios. Contrastingly, Tl removal from pore waters at low threshold concentrations of Mn at our site indicates that these Tl flux estimations may not be applicable in permeable sandy beach sediments and in many other types of sediments, which host mildly sulfidic conditions.

海洋环境中th（Tl）的孔隙水数据很少。已经提出，缺氧沉积物可能是溶解的T1的汇，这可能是由于其掺入了Fe硫化物中。然而，最近的研究表明，T1在硫化物条件发生之前就从溶液中除去，并且T1参与沿海海水中的生物循环。为了评估海洋沉积物中的T1行为，在不同的季节和不同的空间尺度上对高能海滩（德国Spiekeroog岛）的孔隙水进行了采样。该研究地点提供了一套完美的样品，以评估各种氧化还原条件下的痕量金属行为。

分析样品中的痕量金属T1，钼（Mo），铀（U）和rh（Re）。另外，将沉淀物温育以监测痕量金属在受控条件下的去除或释放。使用溶解氧（O ₂），锰（Mn）和铁（Fe）浓度来表征现场氧化还原条件。

我们的结果表明，Tl在孔隙水中的高度富集与需氧有机物（OM）降解同时发生，超过了海水浓度的6倍。相反，在特征为大于1μM的Mn或Fe的弱还原孔隙水中完全除去了T1。潮间带孔隙水的空间T1分布对当前溶解的Mn和Fe含量有反应，该含量随空间和季节而变化。我们建议，T1的释放归因于OM降解，颗粒解吸或再氧化，而T1的去除可能与痕量溶解的硫化物的存在有关。

总之，与Mo，U和Re相比，Tl的快速反应动力学导致快速，完全去除，我们建议以下去除顺序：Tl> Re> U> Mo。孔隙水中T1的去除行为以及高度富集意味着海洋环境中的水槽和水源尚未得到充分了解。尽管潮间带沉积物形成了T1的总体汇（U和Re），尤其是在夏季大部分为缺氧条件下，但在冬季，当沉积物的含氧量更高时，沉积物变成Tl的净水源。

对于全球海洋T1平衡，已经基于孔隙水T1 / Mn比估算了T1通量。相反，在我们的站点中，在低阈值的Mn浓度下从孔隙水中去除T1表示，这些T1通量估算值可能不适用于渗透性沙滩沉积物和许多其他类型的沉积物，这些沉积物具有轻度的硫化条件。