Commonly used speleothem-based paleoclimate proxies such as δO, δC, and trace element ratios are capable of high temporal resolution, but their interpretations are often ambiguous due to the conflated effects of multiple forcings. This complexity motivates the development of targeted proxies that can track specific local hydrological conditions. To this end, the concentration of ferromagnetic Fe-oxide particles in speleothem laminae has been suggested as a potential tracer for local precipitation. Here we use the quantum diamond microscope (QDM) to obtain a sub-annual resolution time series of ferromagnetic content in a Brazilian speleothem from a well-ventilated cave environment covering the period between 1913 and 2016 CE. This high resolution allows us to quantify the correlation between speleothem magnetic properties and an instrumental precipitation record for the first time. We find that ferromagnetic content in the central column displays a modest but significant negative correlation with rainfall (, while magnetism in the speleothem flanks shows a weaker, statistically insignificant relationship. Rock magnetic analyses of the speleothem further reveal ultrafine, pedogenic grains to be the dominant ferromagnetic carriers. Combining QDM and electron microprobe data, we show that these pedogenic grains were likely developed in surface soils and delivered into the cave as part of airborne, 10–200 μm silicate-carbonate soil agglomerates. Our results show that speleothem magnetism holds strong potential as a targeted proxy for paleorainfall and demonstrate a method for identifying the mechanism of magnetic enhancement, which sets the necessary foundation for any paleoclimatic interpretations.

中文翻译：

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研究洞穴磁力作为灰尘流动和降雨的代理

常用的基于洞穴的古气候代理（例如 δ18O、δ13C 和微量元素比率）具有较高的时间分辨率，但由于多种强迫的综合影响，它们的解释往往不明确。这种复杂性促使开发能够跟踪特定当地水文条件的目标代理。为此，建议将洞穴层中铁磁性氧化铁颗粒的浓度作为局部降水的潜在示踪剂。在这里，我们使用量子金刚石显微镜 (QDM) 获取了通风良好的洞穴环境中巴西洞穴中铁磁性含量的亚年分辨率时间序列，涵盖了公元 1913 年至 2016 年期间。这种高分辨率使我们能够首次量化洞穴磁性与仪器降水记录之间的相关性。我们发现，中心柱中的铁磁含量与降雨量显示出适度但显着的负相关性（而洞穴侧翼的磁性显示出较弱的、统计上不显着的关系。对洞穴的岩石磁性分析进一步表明，超细的成土颗粒是主要的铁磁载体。结合 QDM 和电子探针数据，我们表明这些成土颗粒很可能是在表层土壤中发育的，并作为空气传播的 10-200 μm 硅酸盐-碳酸盐土壤团聚体的一部分输送到洞穴中。我们的结果表明，洞穴它们的磁性很强潜力作为古降雨的目标代理，并展示了一种识别磁增强机制的方法，这为任何古气候解释奠定了必要的基础。