In the geological record, fossil phosphatic stromatolites date back to the Great Oxidation Event in the Paleoproterozoic, but living phosphatic stromatolites have not been described previously. Here, we report on cyanobacterial stromatolites in a supratidal freshwater environment at Cape Recife, South African southern coast, precipitating Ca carbonate alternating with episodes of Ca phosphate deposition. In their structure and composition, the living stromatolites from Cape Recife closely resemble their fossilized analogues, showing phosphatic zonation, microbial casts, tunnel structures and phosphatic crusts of biogenic origin. The microbial communities appear to be also similar to those proposed to have formed fossil phosphatic stromatolites. Phosphatic domains in the material from Cape Recife are spatially and texturally associated with carbonate precipitates, but form distinct entities separated by sharp boundaries. Electron Probe Micro‐Analysis shows that Ca/P ratios and the overall chemical compositions of phosphatic precipitates are in the range of octacalcium phosphate, amorphous tricalcium phosphate and apatite. The coincidence in time of the emergence of phosphatic stromatolites in the fossil record with a major episode of atmospheric oxidation led to the assumption that at times of increased oxygen release the underlying increased biological production may have been linked to elevated phosphorus availability. The stromatolites at Cape Recife, however, form in an environment where ambient phosphorus concentrations do not exceed 0.28 μM, one to two orders of magnitude below the previously predicted minimum threshold of >5 μM for biogenic phosphate precipitation in paleo‐systems. Accordingly, we contest the previously proposed suitability of phosphatic stromatolites as a proxy for high ambient phosphate concentrations in supratidal to shallow ocean settings in earth history.

中文翻译：

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低磷环境中的活性磷酸叠层石：在古系统中使用磷替代磷含量的含义

在地质记录中，磷化石叠层石的历史可以追溯到古元古代的大氧化事件，但是以前没有描述过活的磷石叠层石。在这里，我们报告了南非南部海岸累西腓海角上层淡水环境中的蓝藻岩层间辉石，沉淀出碳酸钙与磷酸钙沉积交替出现的现象。在结构和组成上，来自累西腓角的活层叠层岩与它们的化石类似物极为相似，显示出磷化带，微生物铸件，隧道结构和生物成因的磷化壳。微生物群落似乎也与提议形成化石磷叠层石的微生物群落相似。累西腓角（Cape Recife）材料中的磷酸盐区域在空间和质地上与碳酸盐沉淀有关，但形成了由尖锐边界隔开的不同实体。电子探针显微分析表明，磷沉淀物的Ca / P比和整体化学成分在磷酸八钙，无定形磷酸三钙和磷灰石的范围内。在化石记录中出现的磷酸叠层石与大气氧化的一次主要事件的发生时间相吻合，从而得出这样的假设：在氧气释放量增加的时候，潜在的生物产量增加可能与磷的利用率增加有关。但是，累西腓角的叠层石形成于环境磷浓度不超过0.28μM的环境中，比先前预测的古生物系统中磷酸盐磷酸盐的最低阈值> 5μM低一到两个数量级。因此，我们对先前提出的磷酸叠层石作为地球历史上浅海环境中高环境磷酸盐浓度的替代品提出了质疑。