Seafloor hydrothermal activity may constitute a considerable mercury (Hg) source to the oceans, but the flux from marine shallow-water hydrothermal systems (MSWHS) remains poorly constrained to date. To study the presence of Hg in MSWHS in Paleochori Bay (Milos Island, Greece), sea surface, bottom, pore fluid and hydrothermal gas samples were collected in June of 2017, October of 2018 and July of 2020, and analyzed for Cl, Br, SO₄, As, Ca, Fe, K, Mg, Mn, Na, Si, Sr, H₂S, unfiltered total Hg (THg), and filtered Hg (Hg_diss). Specific sites were selected for the analysis of volatile elemental Hg (Hg^o), dimethylmercury (DMHg), monomethylmercury (MMHg), and Hg in the gas phase (Hg_gas). Concentrations of THg observed in samples collected from the sea surface were elevated compared to surface samples taken outside Paleochori Bay. The highest surface water concentrations (~10 to 15 pM) were measured in samples collected directly above shallow-water hydrothermal discharge areas. Pore fluids outside Paleochori Bay were significantly lower in THg (0.8 to 8.6 pM) than those taken inside (17.4 to 1511 pM). Porewaters collected from areas with visible gaseous or fluid emission were highly variable but generally elevated in THg concentrations (185 to 5066 pM). Concentrations within gases ranged from 0.7 to 2791 nmol/m³. The vast majority of samples with highly elevated THg (> 100 pM) had low Na/K ratios (< 15), indicative of rapidly rising fluid. Concentrations of Hg⁰, DMHg, and MMHg were below detection limits in all samples.

Bottom substrate type (e.g., rocky vs. sediment covered) likely affected infiltration rates of oxygenated seawater below the sediment-water interface, thereby affecting Hg speciation and removal by precipitation. Flux rates from porewaters compared to those with gaseous emission were high (12.56 to 1088 mol THg/year and 0.37 to 1.85 mol THg/year). Sites with slow gaseous emission rates are hypothesized to have extended subsurface reaction times, resulting in lower Hg concentrations emitted to bottom waters. However, increasing rates of gas emission did not necessarily indicate higher Hg concentrations. The scavenging of Hg in the sediments and advective flux out of Paleochori Bay likely prevent significant accumulations of THg in the water column of Paleochori Bay. The total atmospheric flux from Paleochori Bay using average flux calculations over the entire surface area would contribute 6 mmol Hg/year to the atmosphere.

We hypothesize that Hg concentrations within the pore fluids of Paleochori Bay reflect a balance between mixing and precipitation in the subsurface. A three-component mixing system of vapor, brine and seawater determines THg concentrations; however, precipitation due to sulfur cycling, changes in redox conditions and temperature, all play a crucial role in removing Hg from emitted fluids and gases.

海底热液活动可能构成了海洋中大量的汞（Hg）来源，但是迄今为止，来自海洋浅水热液系统（MSWHS）的通量仍然受到限制。为了研究Paleochori湾（希腊米洛斯岛）MSWHS中汞的存在，于2017年6月，2018年10月和2020年7月收集了海面，底部，孔隙流体和热液气体样品，并分析了Cl，Br ，SO ₄，As，Ca，Fe，K，Mg，Mn，Na，Si，Sr，H ₂ S，未过滤的总Hg（THg）和已过滤的Hg（Hg _diss）。选择特定的位点以分析气相中的挥发性元素汞（Hg ^o ），二甲基汞（DMHg），一甲基汞（MMHg）和Hg（Hg_气体））。与从Paleochori湾外采集的水面样品相比，从海面采集的样品中观察到的THg浓度升高。在浅水热液排放区域正上方收集的样品中测量了最高地表水浓度（约10至15 pM）。Paleochori湾外的孔隙液的THg（0.8至8.6 pM）明显低于内层的孔隙液（17.4至1511 pM）。从可见的气体或流体排放区域收集的孔隙水变化很大，但总的THg浓度（185至5066 pM）有所增加。气体中的浓度范围为0.7至2791 nmol / m ³。THg高度升高（> 100 pM）的绝大多数样品的Na / K比低（<15），表明流体迅速上升。汞的浓度⁰，DMHg和MMHg在所有样品中均低于检测极限。

底部基质类型（例如，岩石对沉积物的覆盖）可能影响含氧海水在沉积物-水界面以下的渗透率，从而影响汞的形态和通过沉淀的去除。与具有气体排放的孔隙水相比，孔隙水的通量率较高（12.56至1088 mol THg /年和0.37至1.85 mol THg /年）。假设气体排放速率较低的地点具有较长的地下反应时间，从而导致向底水排放的汞浓度较低。但是，气体排放速率的提高并不一定表明汞的浓度较高。Paleochori湾中沉积物中Hg的清除和对流通量可能阻止了Paleochori湾水柱中THg的大量积累。使用平均通量计算得出的来自Paleochori湾的总大气通量将为大气贡献6 mmol Hg /年。

我们假设Paleochori湾孔隙流体中的Hg浓度反映了地下混合与降水之间的平衡。蒸汽，盐水和海水的三组分混合系统决定了THg的浓度。然而，由于硫循环，氧化还原条件和温度的变化而引起的沉淀，在去除排放的流体和气体中的汞方面都起着至关重要的作用。