Understanding the intricate mechanisms governing soil carbon turnover is critical in our fight against climate change. Recent research conducted by an international team of scientists from MARUM – Center for Marine Environmental Sciences at the University of Bremen and the Alfred Wegener Institute has shed new light on this complex process, emphasizing a predominant influence of temperature on soil carbon dynamics in subtropical and tropical regions. Their groundbreaking study, soon to be published in Nature Communications, unveils that rising temperatures drastically accelerate the decomposition of organic matter in these soils, a phenomenon with profound implications for global carbon budgets and future climate projections.
Soils globally harbor more than twice the amount of carbon stored in Earth’s atmosphere, making them formidable regulators of atmospheric CO₂ concentrations. The balance between carbon uptake and release by soils thereby plays a pivotal role in modulating climate. However, understanding soil carbon sensitivity to environmental changes, particularly in warmer regions, has remained a daunting challenge. This new study unpacks this complexity by focusing on subtropical and tropical ecosystems where vast reservoirs of organic carbon reside, yet the dominant factors influencing their carbon turnover rates have been contested for years.
Previous investigations underscored the importance of permafrost soils in the context of climate change, showing how rising temperatures there induce thawing and the consequent release of trapped carbon. While permafrost feedbacks have gained substantial attention, the behavior of soil carbon under warming in warmer climates remained less defined. Microbial activity in subtropical and tropical soils, known drivers of organic matter decomposition, are known to be sensitive to humidity and temperature, but the relative weight of these factors in controlling carbon release has defied consensus. Some researchers argued that changes in hydroclimatic conditions drive soil carbon dynamics, while others posited temperature as the chief determinant.
In an innovative departure from conventional studies that observe soil processes in situ, the research team adopted a long-term, sedimentary record-based approach. They investigated organic material transported by the Nile River from soils across a vast catchment area spanning subtropical to tropical north-east Africa to its deposition site off the eastern Mediterranean coast. By analyzing marine sediment cores that accumulate land-derived organic carbon over millennia, they accessed a historical archive stretching back 18,000 years, from the terminal stage of the last ice age to present-day conditions. This method allowed them to reconstruct changes in soil carbon turnover rates under varying climatic regimes over geological timescales.
Dr. Vera Meyer, the study’s lead author, explains the reasoning behind the choice of proxy: “Our approach hinges on assessing the age of organic matter delivered by the Nile, which encodes how long carbon spent in soils as well as its downstream transit time. This dual factor record offers an integrative perspective on soil carbon processing beyond the fleeting snapshots afforded by direct soil observation.” Such insights from sedimentary archives provide a window into climate-carbon interactions that modern soil experiments cannot easily achieve.
The researchers’ analysis revealed a striking and unexpected pattern: the age of terrestrial carbon reaching the Mediterranean shifted minimally in response to precipitation variability and runoff fluctuations but changed markedly in alignment with temperature increases. In particular, the warming phase following the last glacial maximum induced a far more pronounced acceleration in soil organic matter decomposition than predicted by prevalent Earth system models. This indicates that microbial-mediated carbon turnover in these subtropical and tropical soils is dominantly controlled by temperature, challenging earlier assumptions that hydrological variations are equally or more influential.
Co-author Dr. Enno Schefuß emphasizes the magnitude of this effect by stating that post-glacial warming triggered a significant surge in soil-derived CO₂ emissions that outpaced existing model projections. The rapid microbial respiration under warmer conditions effectively contributed to the rising atmospheric CO₂ concentrations documented at the end of the ice age, depicting a powerful feedback mechanism between soils and climate. This realization demands urgent re-evaluation and refinement of biogeochemical models to more accurately represent temperature sensitivities in diverse soil ecosystems.
Additionally, as Dr. Peter Köhler from the Alfred Wegener Institute highlights, the underestimation of soil carbon release in climate models not only obscures our understanding of past carbon cycle dynamics but also jeopardizes the reliability of future climate predictions. Current projections may significantly undervalue the extent of positive soil carbon-climate feedbacks that could accelerate global warming, underscoring the importance of integrating empirical paleoenvironmental data into model development.
The implications of these findings extend well beyond academic debate. By confirming that temperature exerts a dominant control over soil organic carbon turnover in (sub-)tropical regions, the study warns of a potentially intensified cycle of carbon release as global temperatures rise in the coming decades. Given the massive carbon stocks stored in these soils, even subtle accelerations in decomposition rates could amplify atmospheric CO₂, thereby fueling further warming in a self-reinforcing loop. This feedback poses an additional challenge to climate mitigation efforts and highlights soils as a critical but vulnerable component of the Earth system.
Moreover, the long-term perspective afforded by sediment core analysis brings to light the evolutionary trajectory of soil carbon responses to natural climate variability. It showcases the intrinsic connection between soil microbial communities and ambient temperatures over millennial timescales, a relationship progressively disrupted by anthropogenic influences. Understanding these temporal dynamics is essential for anticipating how terrestrial carbon reservoirs will fare under unprecedented rates of climate change.
The study was conducted under the auspices of the Cluster of Excellence “Ocean Floor – Earth’s Uncharted Interface” at MARUM, aimed at unraveling the fate of carbon from multiple sources in marine environments. By bridging terrestrial and marine perspectives, researchers are better positioned to map the pathways through which soil carbon exits terrestrial ecosystems and enters the ocean-atmosphere carbon cycle. Such interdisciplinary efforts advance holistic climate science, integrating geochemical, microbiological, and geological viewpoints.
In summary, this research reframes the narrative on tropical and subtropical soil carbon dynamics by unequivocally placing temperature at the helm of controlling organic matter turnover. Its robust evidence from paleoenvironmental archives challenges prevailing models, calls for their recalibration, and raises critical awareness of soil carbon’s role in amplifying ongoing climate change. As global temperatures climb, the findings underscore the urgency of incorporating soil carbon feedbacks into climate policy discussions and environmental management strategies.
Subject of Research: Soil carbon turnover dynamics and the influence of temperature in subtropical and tropical soils over geological timescales.
Article Title: Dominant Control of Temperature on (sub-)tropical soil carbon turnover
News Publication Date: 15-May-2025
Web References:
http://dx.doi.org/10.1038/s41467-025-59013-9
Image Credits: MARUM – Center for Marine Environmental Sciences, University of Bremen; V. Diekamp
Keywords: Earth sciences, Climatology, Earth systems science, Geochemistry, Oceanography, Earth climate, Paleoclimatology
