Abstract Porewater flow at cold seeps controls methane oxidation and carbonate precipitation rates, and also plays an important role in gas hydrate dynamics. We constrain the porewater flow rates in the upper sediment of Gulf of Mexico cold seeps by fitting measured 226Ra and Cl− profiles. The approach exploits their natural increase with depth through shallow sediments at non-brine (226Ra) and brine (Cl−) seeps. Vertical flow velocities at non-brine and brine seeps are found to be similar in magnitude, typically on the order of 0.1 m y−1. The accuracy of the flow estimates is assessed and shown to depend substantially on uncertainties in both concentrations and sediment tortuosity. Model simulations further reveal that the natural heterogeneity of sediment permeability can cause considerable lateral variability in vertical flow at the scale of a sediment core, which implies that the coring location and core size can have a substantial effect on the estimated porewater velocities. The formation of gas hydrates and calcium carbonates reduce sediment permeability, and decrease the spatial variability in flow over time, as the formation rates are higher along preferential flow paths. This analysis of the effect of spatiotemporal variability on chemical profiles improves the assessment of uncertainties in the estimated magnitude of flow, and is important for the evaluation of benthic-pelagic coupling at seeps.

中文翻译：

---

从保守示踪剖面和早期成岩模型推断出的地表冷渗沉积物中的孔隙水流动模式

摘要 冷泉孔隙水流控制甲烷氧化和碳酸盐沉淀速率，在天然气水合物动力学中也起着重要作用。我们通过拟合测量的 226Ra 和 Cl− 剖面来限制墨西哥湾冷渗流上部沉积物中的孔隙水流速。该方法利用非盐水 (226Ra) 和盐水 (Cl−) 渗漏处的浅层沉积物随深度自然增加。发现非盐水和盐水渗漏处的垂直流速在量级上相似，通常在 0.1 my-1 的数量级。流量估计的准确性被评估并显示在很大程度上取决于浓度和沉积物曲折的不确定性。模型模拟进一步表明，沉积物渗透率的自然非均质性会导致沉积物核心尺度上垂直流的相当大的横向变化，这意味着取心位置和核心尺寸会对估计的孔隙水速度产生重大影响。天然气水合物和碳酸钙的形成降低了沉积物的渗透率，并随着时间的推移降低了流动的空间变异性，因为沿着优先流动路径的形成速率更高。这种时空变化对化学剖面影响的分析改进了对估计流量大小的不确定性的评估，并且对于评估渗漏处的底栖-远洋耦合很重要。这意味着取心位置和岩心尺寸会对估计的孔隙水速度产生重大影响。天然气水合物和碳酸钙的形成降低了沉积物的渗透率，并随着时间的推移降低了流动的空间变异性，因为沿优先流动路径的形成速率较高。这种时空变化对化学剖面影响的分析改进了对估计流量大小的不确定性的评估，并且对于评估渗漏处的底栖-远洋耦合很重要。这意味着取心位置和岩心尺寸会对估计的孔隙水速度产生重大影响。天然气水合物和碳酸钙的形成降低了沉积物的渗透率，并随着时间的推移降低了流动的空间变异性，因为沿着优先流动路径的形成速率更高。这种时空变化对化学剖面影响的分析改进了对估计流量大小的不确定性的评估，并且对于评估渗漏处的底栖-远洋耦合很重要。