The ferrimagnetic (FM) and antiferromagnetic (AFM) particles of iron oxides are considered pedogenic and climatic indicators due to their enrichment with comparable increasing in rainfall and temperature. However, the opposite changes in rainfall and temperature result in rapid change of relative humidity (RH), which could lead to their competition and transformation. We examined two soil sequences undergone contrary climate development on the eastern edge of the Tibetan Plateau. The dry and warm climate with low RH favors the coordinative enrichment of AFM hematite and FM particles, while the wet and cool climate with high RH mainly produces goethite but leads to competition between low content AFM hematite and FM particles. The outcome well interprets the changing relationship between color and magnetism in soils and sediments, and suggests that temperature is as important as precipitation in paleoclimate reconstruction based on iron oxides, especially during strong dry-wet cycles and climate pattern shifts.

Magnetic particles including ferrimagnetic (FM) and antiferromagnetic (AFM) particles are ubiquitous in the surface of Earth and Mars. The FM particles dominating soil magnetism usually coexist or compete with AFM hematite due to their comparable thermodynamic stability. The uncertain correlation can be modulated by phosphorous (P) absorption during aging of precursor amorphous iron (Fe) oxides. We investigated two Ferralsol sequences around a P mining field with comparable content of hematite but contrasting P/Fe ratio. The FM particles accompanying the formation of hematite are enriched stably at accelerating rates under high P/Fe but at unstably even rates under low P/Fe. The FM particles became less abundant and coarser while the iron oxide crystallinity increased monotonically as P/Fe decreased. We attribute it to more rapid grain growth of FM particles and transformation into hematite without P retarding the crystallization of iron oxides.

Magnetic particles associated with iron (Fe) oxides are widespread on the surface of Earth and Mars and serve as reasonable climatic indicators. Ferrimagnetic maghemite (Mgh) and antiferromagnetic hematite (Hm), which dominate magnetism and redness, often coexist or compete with each other in soils and sediments. The formation efficiency of Mgh relative to Hm could be modulated by geochemical background in addition to climate, especially by phosphate (P), which has a high affinity on the surface of precursor iron oxides in natural systems. We investigated two Ferralsol sequences around a P mining field with comparable climate but contrasting P/Fe ratios. High P/Fe retards iron oxide crystallization as well as grain growth and transformation into Hm, which thereby promotes more effective accumulation of ferrimagnetic Mgh as intermediate products. The ligand-protected effect well interprets asynchronous changes in magnetism and redness in soils and sediments across large spatial and temporal scales.

Pedogenic carbonates document a wealth of environmental information, but their seasonal variations may obscure long-term trends. Here we report evidence of changing seasonality of pedogenic carbonate growth from the Chinese Loess Plateau during the Quaternary glacial cycles, using the d18O of pedogenic carbonates (d18Oc). The glacial and interglacial d18Oc show negative and positive correlations with proxy-inferred rainfall amount, respectively. We explain this pattern using modern observations and modeling results, which show opposite correlations between d18Oc and rainfall amount in growing versus non-growing seasons. In glacial episodes under weak monsoon, pedogenic carbonate growth occurred within the growing season, inheriting a negative d18Oc-rainfall correlation. Conversely, pedogenic carbonate growth likely extended into the non-growing season during interglacials due to intensified monsoonal rainfall, incorporating a positive d18Oc-rainfall correlation. Our work links seasonal fluctuations of pedogenic carbonates with their long-term records, shedding new light on interpreting this paleoarchive.

The “dolomite problem” is a long-standing puzzle in sedimentology and mineralogy. Previous studies have shown that some dolostones are formed by microbes or in hydrothermal-burial environments. Here, we provide a different case in which an abiotic and Ca-rich proto-dolomite layer with weak cation ordering precipitated in Lake Sayram, Central Asia, during the Early Holocene. The 12-cm-thick layer, with abundant proto-dolomite (mean 50 wt% and maximum=81 wt%), consists of euhedral and rhombohedral grains. The similarδ18O values of proto-dolomites and ostracods at the same depth demonstrate that the former are authigenic. Morphologic and isotopic features of these proto-dolomites are distinct from those of microbial dolomites, suggesting an abiotic origin. We infer that this proto-dolomite layer is the product of a warming and arid climate, which is supported by regional climatic records. This study provides evidence for previous studies that dolomite can precipitate directly in “dolomite seas” at ambient temperature.