The calcite plates, or coccoliths, of haptophyte algae including Emiliania huxleyi are formed in intracellular vesicles in association with water–soluble acidic polysaccharides. These coccolith–associated polysaccharides (CAPs) are involved in regulating coccolith formation and have been recovered from sediment samples dating back to ∼180 Ma. Paired measurements of the carbon isotopic compositions of CAPs and coccolith calcite have been proposed as a novel paleo–pCO2 barometer, but additional proxy validation and development are still required. Here we present culture results quantifying carbon isotopic offsets between CAPs and other cellular components: bulk organic biomass, alkenones, and calcite. E. huxleyi was grown in nitrate–limited chemostat experiments at growth rates (µ) of 0.20–0.62/d and carbon dioxide concentrations of 10.7–17.6 µmol/kg. We find that CAPs are isotopically enriched by 4.5–10.1‰ relative to bulk organic carbon, exhibiting smaller isotopic offsets at faster growth rates and lower CO2 concentrations. This variability suggests that CAPs record a complementary signature of past growth conditions with different sensitivity than alkenones or coccolith calcite. By measuring the isotopic compositions of all three molecules and minerals of self-consistent origin, the ratio µ/[CO2(aq)] may be reconstructed with fewer assumptions than current approaches.

中文翻译：

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Emiliania huxleyi 的与颗石相关的多糖的碳同位素比率作为生长速率和 CO 2 浓度的函数

包括 Emiliania huxleyi 在内的触生藻的方解石板或块石是在与水溶性酸性多糖相关的细胞内囊泡中形成的。这些与颗石相关的多糖 (CAPs) 参与调节颗石的形成，并且已从可追溯到 180 Ma 的沉积物样品中回收。CAPs 和球石方解石的碳同位素组成的配对测量已被提议作为一种新型的古-pCO2 气压计，但仍需要额外的代理验证和开发。在这里，我们展示了量化 CAP 和其他细胞成分之间的碳同位素偏移量的培养结果：大量有机生物量、烯酮和方解石。E. huxleyi 在硝酸盐限制的恒化器实验中以 0.20–0.62/d 的生长速率 (µ) 和 10.7–17 的二氧化碳浓度生长。6 微摩尔/公斤。我们发现，相对于大块有机碳，CAPs 的同位素富集为 4.5–10.1‰，在更快的增长速度和更低的 CO2 浓度下表现出更小的同位素偏移。这种可变性表明 CAP 记录了过去生长条件的互补特征，其敏感性与烯酮或颗石方解石不同。通过测量自洽成因的所有三种分子和矿物的同位素组成，可以用比当前方法更少的假设来重建比率 μ/[CO2(aq)]。这种可变性表明 CAP 记录了过去生长条件的互补特征，其敏感性与烯酮或颗石方解石不同。通过测量自洽成因的所有三种分子和矿物的同位素组成，可以用比当前方法更少的假设来重建比率 μ/[CO2(aq)]。这种可变性表明 CAP 记录了过去生长条件的互补特征，其敏感性与烯酮或颗石方解石不同。通过测量自洽成因的所有三种分子和矿物的同位素组成，可以用比当前方法更少的假设来重建比率 μ/[CO2(aq)]。