Microaggregate-scale heterogeneity as an indicator of initial soil formation in Antarctic cold desert soils

In the context of accelerating climate change, understanding how soil forms in some of the most extreme environments on Earth, such as the cold deserts of Antarctica, is critical. As ice-free areas expand, new substrates are exposed to pedogenesis, a process involving various biogeochemical reactions such as the accumulation of organic matter and the movement of substances within the soil profile. In order to gain a better understanding of these microscale pedogenic processes, it is important to comprehend how and why chemical and biological heterogeneity emerges in such harsh conditions.

In this study, we combined microaggregate fractionation, chemical analyses, and correlative light and electron microscopy (CLEM) to identify early indicators of soil formation and microbial components in Antarctic soils. Bulk soils were fractionated into three microaggregate size classes (53–250 µm, 20–53 µm, < 20 µm), each further separated into free and occluded fractions, yielding six microaggregate fractions in addition to the bulk soil. All fractions underwent chemical analyses to determine elemental composition and key soil properties. CLEM was applied to detect and visualize microbial and organic components within the soil matrix. Energy-dispersive X-ray spectroscopy (EDX) complemented CLEM by revealing the spatial distribution of major elements and mineral phases.

Results showed marked differences among microaggregate classes and between free and occluded fractions, highlighting chemical and biological microscale heterogeneity overlooked by bulk analyses. CLEM revealed organic matter and potential microbial structures within the soil matrix, while EDX highlighted patchy elemental distributions. Notably, the <20 µm fraction displayed distinct chemical characteristics and structural features, suggesting a critical role in early pedogenic differentiation.

These findings indicate that initial soil formation in Antarctic cold deserts emerges at microaggregate-related spatial scales and is closely associated with microbial and organic components. Microscale approaches such as microaggregate analysis combined with CLEM and EDX are therefore essential for understanding the earliest stages of pedogenesis, not only in polar regions but also in other extreme terrestrial environments and analogous extraterrestrial settings, such as Martian cold deserts.

Keywords: Antarctic soils, Early pedogenesis, Soil microaggregates, Soil organics, CLEM