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1. Identifying Temperature and Moisture Controls on Fe Oxide Origins

   https://doi.org/10.1029/2023GL102761  

   Lepre, Christopher (August 2023, Geophysical Research Letters)

   Abstract Magnetism, redness, and Fe oxides are indicators of pedoclimatic conditions. However, uncertainties with observing how Fe oxides form within soils has led to debates about relationships between magnetic mineral assemblages, temperature, and rainfall. To address these issues, Fe oxides from the equatorial tropics of Kenya were examined in Pliocene soils that developed under orbital forcing of the monsoon. Results demonstrate that with warm‐wet monsoons, ferrimagnetic production was increased and correlated with hematite concentrations, in accordance with expectations that ferrimagnetic and hematite minerals codevelop from amorphous Fe oxides. With cool‐dry monsoons, hematite concentrations increased but ferrimagnetic production decreased and decoupled from hematite development. These findings suggest that decreased rainfall rather than temperature change favored the dehydration step required to catalyze hematite enrichment within soils. This study explains Fe oxides origins under variable monsoonal climates and recognizes moisture changes in comparison to temperature as stronger controls on the production of soil‐formed hematite. 

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2. Nitrogen Availability and Changes in Precipitation Alter Microbially Mediated NO and N₂O Emissions From a Pinyon–Juniper Dryland

   https://doi.org/10.1111/gcb.70159  

   Zhao, Sharon; Krichels, Alexander_H; Stephens, Elizah_Z; Calma, Anthony_D; Aronson, Emma_L; Jenerette, G_Darrel; Spasojevic, Marko_J; Schimel, Joshua_P; Hanan, Erin_J; Homyak, Peter_M (March 2025, Global Change Biology)

   ABSTRACT Climate change is altering precipitation regimes that control nitrogen (N) cycling in terrestrial ecosystems. In ecosystems exposed to frequent drought, N can accumulate in soils as they dry, stimulating the emission of both nitric oxide (NO; an air pollutant at high concentrations) and nitrous oxide (N₂O; a powerful greenhouse gas) when the dry soils wet up. Because changes in both N availability and soil moisture can alter the capacity of nitrifying organisms such as ammonia‐oxidizing bacteria (AOB) and archaea (AOA) to process N and emit N gases, predicting whether shifts in precipitation may alter NO and N₂O emissions requires understanding how both AOA and AOB may respond. Thus, we ask: How does altering summer and winter precipitation affect nitrifier‐derived N trace gas emissions in a dryland ecosystem? To answer this question, we manipulated summer and winter precipitation and measured AOA‐ and AOB‐derived N trace gas emissions, AOA and AOB abundance, and soil N concentrations. We found that excluding summer precipitation increased AOB‐derived NO emissions, consistent with the increase in soil N availability, and that increasing summer precipitation amount promoted AOB activity. Excluding precipitation in the winter (the most extreme water limitation we imposed) did not alter nitrifier‐derived NO emissions despite N accumulating in soils. Instead, nitrate that accumulated under drought correlated with high N₂O emission via denitrification upon wetting dry soils. Increases in the timing and intensity of precipitation that are forecasted under climate change may, therefore, influence the emission of N gases according to the magnitude and season during which the changes occur. 

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3. Exploring the Effect of Aspect to Inform Future Earthcasts of Climate‐Driven Changes in Weathering of Shale

   https://doi.org/10.1029/2017JF004556  

   Sullivan, P. L.; Goddéris, Y.; Shi, Y.; Gu, X.; Schott, J.; Hasenmueller, E. A.; Kaye, J.; Duffy, C.; Jin, L.; Brantley, S. L. (April 2019, Journal of Geophysical Research: Earth Surface)

   Abstract Projections of future conditions within the critical zone—earthcasts—can be used to understand the potential effects of changes in climate on processes affecting landscapes. We are developing an approach to earthcast how weathering will change in the future using scenarios of climate change. As a first step here, we use the earthcasting approach to model aspect‐related effects on soil water chemistry and weathering on hillsides in a well‐studied east‐west trending watershed (Shale Hills, Pennsylvania, USA). We completed model simulations of solute chemistry in soil water with and without the effect of aspect for comparison to catchment observations. With aspect included, aqueous weathering fluxes were higher on the sunny side of the catchment. But the effect of aspect on temperature (0.8 °C warmer soil on sunny side) and recharge (100 mm/year larger on shaded side) alone did not explain the magnitude of the observed higher weathering fluxes on the sunny side. Modeled aspect‐related differences in weathering fluxes only approach field observations when we incorporated the measured differences in clay content observed in augered soils on the two hillslopes. We also had to include a biolifting module to accurately describe cation concentrations in soil water versus depth. Biolifting lowered some mineral dissolution rates while accelerating kaolinite precipitation. These short‐duration simulations also highlighted that the inherited differences in particle size on the two sides of the catchment might in themselves be explained by weathering under different microclimates caused by aspect—over longer durations than simulated with our models. 

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4. Geochemical phosphorus sequestration in tundra soils limits primary production in Arctic headwater streams and rivers. Upper Kuparuk River, North Slope, Alaska, 2020-2023.

   https://doi.org/10.18739/A2348GJ1Z  

   Sutor, Frederick (January 2024, NSF Arctic Data Center)

   Climate warming in the Arctic region is thawing previously frozen soil (permafrost). Permafrost thaw alters landscape hydrology, increases weathering rates, and thus increases the delivery of solutes to adjacent waters. Long-term monitoring of the Kuparuk River (North Slope, Alaska) confirms significant increases in many solutes that are indicative of thawing permafrost. However, there is no evidence of an increase in phosphorus (P), the nutrient that most often limits primary production in tundra streams. Here, we show that soils in the upper Kuparuk River watershed have a high biogeochemical sorption capacity that can limit P mobility and use published data to show that this may be a pan-Arctic characteristic. While P bioavailability is restricted by vegetative cycling, we found that concentrations of Mehlich-3 extractable iron (Fe) and aluminum (Al) also impart a very high P geochemical sorption capacity across our study sites. Analysis of a pan-Arctic soils database suggests that this high P sorption capacity could be a ubiquitous feature of Arctic soils. Therefore, we conclude that while warming-induced permafrost thaw may increase P mobility, simultaneous increases in pedogenic secondary Fe/Al minerals will continue to retain P in tundra soils and limit biological productivity in adjacent aquatic systems. 

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5. Reviews and syntheses: Changing ecosystem influences on soil thermal regimes in northern high-latitude permafrost regions

   https://doi.org/10.5194/bg-15-5287-2018  

   Loranty, Michael M.; Abbott, Benjamin W.; Blok, Daan; Douglas, Thomas A.; Epstein, Howard E.; Forbes, Bruce C.; Jones, Benjamin M.; Kholodov, Alexander L.; Kropp, Heather; Malhotra, Avni; et al (January 2018, Biogeosciences)

   null (Ed.)

   Abstract. Soils in Arctic and boreal ecosystems store twice as much carbon as the atmosphere, a portion of which may be released as high-latitude soils warm. Some of the uncertainty in the timing and magnitude of the permafrost–climate feedback stems from complex interactions between ecosystem properties and soil thermal dynamics. Terrestrial ecosystems fundamentally regulate the response of permafrost to climate change by influencing surface energy partitioning and the thermal properties of soil itself. Here we review how Arctic and boreal ecosystem processes influence thermal dynamics in permafrost soil and how these linkages may evolve in response to climate change. While many of the ecosystem characteristics and processes affecting soil thermal dynamics have been examined individually (e.g., vegetation, soil moisture, and soil structure), interactions among these processes are less understood. Changes in ecosystem type and vegetation characteristics will alter spatial patterns of interactions between climate and permafrost. In addition to shrub expansion, other vegetation responses to changes in climate and rapidly changing disturbance regimes will affect ecosystem surface energy partitioning in ways that are important for permafrost. Lastly, changes in vegetation and ecosystem distribution will lead to regional and global biophysical and biogeochemical climate feedbacks that may compound or offset local impacts on permafrost soils. Consequently, accurate prediction of the permafrost carbon climate feedback will require detailed understanding of changes in terrestrial ecosystem distribution and function, which depend on the net effects of multiple feedback processes operating across scales in space and time. 

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