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1. Volcanic Ash Deposition from Large Eruptions within the Last 150,000 Years Increases Biological Productivity in the Pacific Ocean at Low Latitudes

   Cruz, N; Martinez, V; Wu, J; Abbott, D (February 2024, Proceedings American Geophysical Union)

   Abbott, D (Ed.)

   Known as a bio-limiting metal, high abundances of iron in sea water can amplify biological productivity. The growth of diatoms and other photosynthetic organisms increases, providing more food for grazing organisms like foraminifera. The net result is more organic matter in surface waters and ultimately in surface sediments. Existing satellite data show increases in ocean chlorophyll in areas affected by volcanic eruptions. We infer from this that iron derived from volcanic ash does increase biological productivity. However, the relative increase in productivity is unknown. We examined 3 sediment cores from the Equatorial Western Pacific to analyze the relationship between volcanic ash and biological productivity: RC14-44, RC14-66, and RC14-67. All contain black or dark-colored foraminifera within ash layers and white-shelled foraminifera outside ash layers. We attribute the dark material outside and inside the foraminifera to organic carbon and metals. In our cores, some foraminifera are covered in iron sulfide (FeS), which could be pyrite, and contain large amounts of carbon as well as high abundances of aluminum and silicon. We examined barium concentrations to gain further knowledge of biological productivity at specific core depths as barium is a marker for primary productivity. We found that barium levels within ash layers increased at least ten-fold. Within ash layers, we also noticed that the ashes with higher amounts of fine silt and clay sized material have the greatest increase in barium content, perhaps related to explosion size. This pattern of increases in Ba, metals and organic carbon within ash layers compared to surrounding sediments shows that volcanic ash deposition increases marine productivity. For future research, measuring markers for biological productivity like biogenic silica content and loss on ignition (LOI) within and outside ash layers would further clarify the relationship between volcanic ash deposition and biological productivity. 

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2. Volcanic ash ice nucleation activity is variably reduced by aging in water and sulfuric acid: the effects of leaching, dissolution, and precipitation

   https://doi.org/10.1039/D1EA00071C  

   Fahy, William D.; Maters, Elena C.; Giese Miranda, Rona; Adams, Michael P.; Jahn, Leif G.; Sullivan, Ryan C.; Murray, Benjamin J. (January 2022, Environmental Science: Atmospheres)

   Volcanic ash nucleates ice when immersed in supercooled water droplets, giving it the potential to influence weather and climate from local to global scales. This ice nucleation activity (INA) is likely derived from a subset of the crystalline mineral phases in the ash. The INA of other mineral-based dusts can change when exposed to various gaseous and aqueous chemical species, many of which also interact with volcanic ash in the eruption plume and atmosphere. However, the effects of aqueous chemical aging on the INA of volcanic ash have not been explored. We show that the INA of two mineralogically distinct ash samples from Fuego and Astroni volcanoes is variably reduced following immersion in water or aqueous sulfuric acid for minutes to days. Aging in water decreases the INA of both ash samples by up to two orders of magnitude, possibly due to a reduction in surface crystallinity and cation availability accompanying leaching. Aging in sulfuric acid leads to minimal loss of INA for Fuego ash, which is proposed to reflect a quasi-equilibrium between leaching that removes ice-active sites and dissolution that reveals or creates new sites on the pyroxene phases present. Conversely, exposure to sulfuric acid reduces the INA of Astroni ash by one to two orders of magnitude, potentially through selective dissolution of ice-active sites associated with surface microtextures on some K-feldspar phases. Analysis of dissolved element concentrations in the aged ash leachates shows supersaturation of certain mineral species which could have precipitated and altered the INA of the ash. These results highlight the key role that leaching, dissolution, and precipitation likely play in the aqueous aging of volcanic ash with respect to its INA. Finally, we discuss the implications for understanding the nature and reactivity of ice-active sites on volcanic ash and its role in influencing cloud properties in the atmosphere. 

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3. Evidence for Increases in Biological Productivity from Deposition of Volcanic Ash near Low Latitude Volcanoes Located Outside the Gyres

   Abbott, D; Bostick, B; Wu, J; Cruz, N; Martinez, V (December 2023, Proceedings American Geophysical Union)

   Abbott, D (Ed.)

   Some satellite data show an increase in ocean chlorophyll in areas affected by volcanic eruptions. These increases in ocean color are thought to reflect an increase in photosynthetic activity by phytoplankton. These increases in primary production have been attributed to iron (Fe) from volcanic ash, particularly in high-latitude regions where primary productivity is limited by low Fe (the iron fertilization hypothesis). However, photosynthesis also appears to increase in the tropical ocean, for example in the Sunda and Ryukyu arcs and the Bismarck Sea, areas usually not thought to be iron limited. To examine the effects of volcanic ejecta on productivity in other areas, we examine relationships between ash deposition and biological productivity in three cores, RC14-44 (Sunda arc), VM28-309 (Ryukyu arc) and VM33-116 (Bismarck Sea). These cores contain volcanic ash layers with black or dark-colored foraminifera, different from the bright white foraminifera found outside of the ash layers. This dark coloration results primarily from organic carbon. In RC14-44, some foraminifera are coated with FeS and also contain high amounts of internal carbon. In VM28-309 and VM33-116, some foraminifera are filled with organic carbon rich materials, or have coatings rich in carbon. Occasionally, there are local enrichments in Fe within the foraminifera, indicative of extensive redox cycling. We attribute this carbon to increased biological productivity in these intervals. Barium (Ba) concentrations, a proxy for primary productivity because most or all Ba originates from organic matter contained in the sediment, is also enriched by up to 30-fold in the sediments containing ash. The ash layers with the highest amounts of fine material exhibit the largest enrichments in Ba, suggesting ash texture may influence the resulting changes in marine productivity. Overall, we find clear evidence that ash depositions increase both primary production and carbon export to sediments. Loss on ignition (LOI) and biogenic silica contents between and within ash layers, are potentially useful to further examine both the coupling between production and carbon burial, and the influence of ash deposition on phytoplankton community structure. 

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4. Biomass combustion produces ice-active minerals in biomass-burning aerosol and bottom ash

   https://doi.org/10.1073/pnas.1922128117  

   Jahn, Leif_G; Polen, Michael_J; Jahl, Lydia_G; Brubaker, Thomas_A; Somers, Joshua; Sullivan, Ryan_C (August 2020, Proceedings of the National Academy of Sciences)

   Significance Ice-nucleating particles significantly alter cloud properties and lifetime, causing large but poorly constrained climate impacts. Biomass-burning aerosol emitted by wildfires is a major and growing source of atmospheric pollution. Prior work suggested that ice-nucleating particles can sometimes be emitted by biomass combustion, but the production and characteristics of these particles are poorly understood. Here we show that mineral phases are a significant ice-active component of both biomass-burning aerosol and ash particles. These mineral phases are derived from plant inorganic material that decomposes and reforms as ice-active minerals during combustion; they form more commonly from tall grass versus wood fuels. Aerosolized mineral and ash are now understood as a major source of the ice-nucleating particles in biomass-burning smoke. 

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5. Nanoscale silicate melt textures determine volcanic ash surface chemistry

   https://doi.org/10.1038/s41467-024-44712-6  

   Hornby, Adrian J; Ayris, Paul M; Damby, David E; Diplas, Spyridon; Eychenne, Julia; Kendrick, Jackie E; Cimarelli, Corrado; Kueppers, Ulrich; Scheu, Bettina; Utley, James_E P; et al (December 2024, Nature Communications)

   Abstract Explosive volcanic eruptions produce vast quantities of silicate ash, whose surfaces are subsequently altered during atmospheric transit. These altered surfaces mediate environmental interactions, including atmospheric ice nucleation, and toxic effects in biota. A lack of knowledge of the initial, pre-altered ash surface has required previous studies to assume that the ash surface composition created during magmatic fragmentation is equivalent to the bulk particle assemblage. Here we examine ash particles generated by controlled fragmentation of andesite and find that fragmentation generates ash particles with substantial differences in surface chemistry. We attribute this disparity to observations of nanoscale melt heterogeneities, in which Fe-rich nanophases in the magmatic melt deflect and blunt fractures, thereby focusing fracture propagation within aureoles of single-phase melt formed during diffusion-limited growth of crystals. In this manner, we argue that commonly observed pre-eruptive microtextures caused by disequilibrium crystallisation and/or melt unmixing can modify fracture propagation and generate primary discrepancies in ash surface chemistry, an essential consideration for understanding the cascading consequences of reactive ash surfaces in various environments. 

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