Abstract Several lines of evidence point to low rates of net primary production (NPP) in Archean oceans. However, whether Archean NPP was limited by electron donors or nutrients, particularly phosphorus (P), and how these factors might have changed over a billion years of recorded Archean history, remains contentious. One major challenge is to understand quantitatively the biogeochemical cycling of P on the early Earth. In Part I of this series (Hao et al., 2020), we estimated the weathering flux of P to the oceans as a function of temporally increasing continental emergence and elevation through Archean time. In Part II, we conduct thermodynamic and kinetic simulations to understand key processes of P cycling within the Archean ocean, including seafloor weathering, recycling of organic P, the solubility and precipitation of secondary phosphate minerals, and the burial diagenesis of P precipitates. Our calculations suggest low solubilities of apatite minerals in Archean seawater, primarily due to nearly neutral pH and high levels of Ca. This low solubility, in turn, implies a negligible contribution of apatite dissolution to P bioavailability in Archean seawater. We also simulate the solubility limits of common secondary P-bearing minerals, showing that vivianite would have been the least soluble P mineral in ferruginous Archean seawater (0.1–0.3 µM), even at moderate supersaturation states (Ω = 100 or 1000). If vivianite precipitation was kinetically favorable by microbial activities and mineral adsorption, the sinking flux of P as vivianite in Archean seawater could have reached the modern sinking flux, implying that vivianite precipitation was a potentially major sink for P in Archean oceans. During burial diagenesis, however, vivianite in porewater would have become less stable than Ca-phosphates of lower solubility. At elevated temperatures (>100 °C) associated with burial diagenesis and low-grade metamorphism, vivianite is predicted to react irreversibly with calcite to form apatite. Optimistic assumptions about the recycling efficiency of P on the Archean Earth lead us to estimate that by the end of the eon the total flux of P (continental weathering + recycling) could have supported NPP at levels up to 7% of the modern. The total flux of P would have been much lower on the early and middle Archean Earth, whereas fluxes of electron donors could have been higher, suggesting very low productivity and P-limitation of marine ecosystems during much of the eon. Comparing our estimates of NPP as limited by P supply with the estimate by Ward et al. (2019), in which NPP was limited by electron donors and metabolic efficiency, there could have been a transition between P-limited productivity in the early to middle Archean to electron donor-limitation closer to the eon’s end (assuming no oxygenic photosynthesis). Once oxygenic photosynthesis reached ecological significance, probably near the end of the Archean, our estimated flux of P would allow rapid oxidation of atmosphere.

中文翻译：

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在太古代地球上循环磷：第二部分。太古代生态系统初级生产中磷的限制

摘要 若干证据表明太古代海洋的净初级生产力 (NPP) 率较低。然而，太古代 NPP 是否受到电子供体或营养物质，尤其是磷 (P) 的限制，以及这些因素如何在十亿年的太古代历史记录中发生变化，仍然存在争议。一项主要挑战是定量了解早期地球上磷的生物地球化学循环。在本系列的第 I 部分（Hao 等人，2020 年）中，我们估计了 P 到海洋的风化通量，它是随着太古代时间大陆出现和海拔的时间增加而变化的函数。在第二部分中，我们进行了热力学和动力学模拟，以了解太古代海洋中 P 循环的关键过程，包括海底风化、有机 P 的再循环、次磷酸盐矿物的溶解度和沉淀，以及磷沉淀物的埋藏成岩作用。我们的计算表明，磷灰石矿物在太古代海水中的溶解度低，主要是由于近中性的 pH 值和高水平的 Ca。反过来，这种低溶解度意味着磷灰石溶解对太古代海水中磷生物利用度的贡献可以忽略不计。我们还模拟了常见次生含磷矿物的溶解度极限，表明即使在中等过饱和状态（Ω = 100 或 1000）下，紫云母也是含铁太古宙海水（0.1-0.3 µM）中溶解度最低的磷矿物。如果微生物活动和矿物吸附在动力学上有利于紫云母沉淀，那么太古宙海水中磷作为紫云母的下沉通量可以达到现代下沉通量，这意味着紫云母降水是太古代海洋中 P 的潜在主要汇。然而，在埋藏成岩作用期间，孔隙水中的紫云母会变得不如溶解度较低的磷酸钙稳定。在与埋藏成岩作用和低变质作用相关的高温 (>100 °C) 下，预计紫云母会与方解石发生不可逆反应，形成磷灰石。对太古宙地球上 P 再循环效率的乐观假设使我们估计，到永世末期，P 的总通量（大陆风化 + 再循环）可能支持 NPP 的水平高达现代的 7%。在太古宙早期和中期，P 的总通量会低得多，而电子供体的通量可能会更高，表明在亿万年的大部分时间里，海洋生态系统的生产力和磷限制非常低。将我们对受磷供应限制的 NPP 估计与 Ward 等人的估计进行比较。(2019)，其中 NPP 受到电子供体和代谢效率的限制，在太古宙早期到中期的 P 限制生产力到接近 eon 末期的电子供体限制之间可能存在过渡（假设没有含氧光合作用）。一旦含氧光合作用达到生态意义，可能在太古代末期，我们估计的 P 通量将允许大气快速氧化。在太古宙早期到中期的 P 限制生产力到接近 eon 末期的电子供体限制之间可能存在过渡（假设没有含氧光合作用）。一旦含氧光合作用达到生态意义，可能在太古代末期，我们估计的 P 通量将允许大气快速氧化。太古宙早期到中期的 P 限制生产力可能会在接近 eon 末期的电子供体限制之间发生转变（假设没有含氧光合作用）。一旦含氧光合作用达到生态意义，可能在太古代末期，我们估计的 P 通量将允许大气快速氧化。