(Table 2) Composition of the deapest pore fluids from ODP Holes 168-1030B and 168-1031A

On the eastern flank of the Juan de Fuca Ridge, reaction between upwelling basement fluid and sediment alters hydrothermal fluxes of Ca, SiO2(aq), SO4, PO4, NH4, and alkalinity. We used the Global Implicit Multicomponent Reactive Transport (GIMRT) code to model the processes occurring in the sediment column (diagenesis, sediment burial, fluid advection, and multicomponent diffusion) and to estimate net seafloor fluxes of solutes. Within the sediment section, the reactions controlling the concentrations of the solutes listed above are organic matter degradation via SO4 reduction, dissolution of amorphous silica, reductive dissolution of amorphous Fe(III)-(hydr)oxide, and precipitation of calcite, carbonate fluorapatite, and amorphous Fe(II)-sulfide. Rates of specific discharge estimated from pore-water Mg profiles are 2 to 3 mm/yr. At this site the basement hydrothermal system is a source of NH4, SiO2(aq), and Ca, and a sink of SO4, PO4, and alkalinity. Reaction within the sediment column increases the hydrothermal sources of NH4 and SiO2(aq), increases the hydrothermal sinks of SO4 and PO4, and decreases the hydrothermal source of Ca. Reaction within the sediment column has a spatially variable effect on the hydrothermal flux of alkalinity. Because the model we used was capable of simulating the observed pore-water chemistry by using mechanistic descriptions of the biogeochemical processes occurring in the sediment column, it could be used to examine the physical controls on hydrothermal fluxes of solutes in this setting. Two series of simulations in which we varied fluid flow rate (1 to 100 mm/yr) and sediment thickness (10 to 100 m) predict that given the reactions modeled in this study, the sediment section will contribute most significantly to fluxes of SO4 and NH4 at slow flow rates and intermediate sediment thickness and to fluxes of SiO2(aq) at slow flow rates and large sediment thickness. Reaction within the sediment section could approximately double the hydrothermal sink of PO4 over a range of flow rates and sediment thickness, and could slightly decrease (by </=10%) the size of the hydrothermal source of Ca.在胡安·德·富卡海岭（Juan de Fuca Ridge）东侧翼部，上升基底流体与沉积物之间的反应会改变钙（Ca）、溶解态二氧化硅（SiO₂(aq)）、硫酸盐（SO₄）、磷酸盐（PO₄）、铵（NH₄）以及碱度的热液通量。本研究采用全局隐式多组分反应输运（Global Implicit Multicomponent Reactive Transport, GIMRT）模型，对沉积物柱内发生的成岩作用、沉积物埋藏、流体平流以及多组分扩散等过程进行模拟，并估算溶质的海底净通量。在该沉积物层段内，调控上述溶质浓度的反应包括：硫酸盐还原介导的有机质降解、无定形二氧化硅溶解、无定形三价铁（氢）氧化物的还原溶解，以及方解石、碳氟磷灰石与无定形二价铁硫化物的沉淀作用。基于孔隙水镁离子剖面估算得到的比流量速率为2~3 mm/yr。本研究站位的基底热液系统是NH₄、SiO₂(aq)与Ca的补给源，同时为SO₄、PO₄以及碱度的消耗汇。沉积物柱内的反应会增强NH₄与SiO₂(aq)的热液补给通量，强化SO₄与PO₄的热液消耗通量，并削弱Ca的热液补给通量。沉积物柱内的反应对碱度的热液通量具有空间异质性影响。 由于本研究所用模型可通过对沉积物柱内生物地球化学过程的机制性描述，复现观测到的孔隙水化学特征，因此可用于探究该研究场景下溶质热液通量的物理控制因素。本研究开展两组模拟实验，分别改变流体流速（1~100 mm/yr）与沉积物厚度（10~100 m）。模拟结果显示，基于本研究中所建模的反应过程，在低流速与中等沉积物厚度条件下，沉积物层段对SO₄与NH₄通量的贡献最为显著；而在低流速与大沉积物厚度条件下，则对SiO₂(aq)通量的贡献最为突出。在一定流速与沉积物厚度范围内，沉积物层段内的反应可使PO₄的热液消耗通量提升约一倍，并可使Ca的热液补给通量小幅降低（≤10%）。