系外海洋中多种碳酸盐促进了Carbon Cycle的形成
Diverse Carbonates in Exoplanet Oceans Promote the Carbon Cycle
摘要：
海洋中的碳酸盐沉淀对于碳酸盐-硅酸盐循环（无机碳循环）维持温带气候至关重要。通过考虑碳酸盐化学的热力学，我们表明，海洋pH值下降约0.5的系数增加10的大气中的二氧化碳含量。海洋pH值的上限和下限在1-4之间，其中上限受到碳酸盐沉淀的缓冲，并定义了碳循环运行时的海洋pH值。如果碳酸盐补偿深度（CCD）位于洋底之上，那么碳酸盐沉淀和碳循环停止运作。由于海洋温度高和大气中二氧化碳含量高，CCD位于深海（>40公里）。镁、钙和铁的关键二价碳酸盐产生越来越宽的深度CCD参数空间，表明化学多样性促进了碳循环。从系外行星寻找生命将受益于包括化学上比地球双胞胎更多样化的目标。
英文摘要：
Carbonate precipitation in oceans is essential for the carbonate-silicate cycle (inorganic carbon cycle) to maintain temperate climates. By considering the thermodynamics of carbonate chemistry, we demonstrate that the ocean pH decreases by approximately 0.5 for a factor of 10 increase in the atmospheric carbon dioxide content. The upper and lower limits of ocean pH are within 1-4 of each other, where the upper limit is buffered by carbonate precipitation and defines the ocean pH when the carbon cycle operates. If the carbonate compensation depth (CCD) resides above the ocean floor, then carbonate precipitation and the carbon cycle cease to operate. The CCD is deep (>40 km) for high ocean temperature and high atmospheric carbon dioxide content. Key divalent carbonates of magnesium, calcium and iron produce an increasingly wider parameter space of deep CCDs, suggesting that chemical diversity promotes the carbon cycle. The search for life from exoplanets will benefit by including chemically more diverse targets than Earth twins.
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