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1. What global biogeochemical consequences will marine animal-sediment interactions have during climate change?

   Bianchi, T.S. (June 2021, Elementa)

   Benthic animals profoundly influence the cycling and storage of carbon and other elements in marine systems, particularly in coastal sediments. Recent climate change has altered the distribution and abundance of many seafloor taxa and modified the vertical exchange of materials between ocean and sediment layers. Here, we examine how climate change could alter animal-mediated biogeochemical cycling in ocean sediments.The fossil record shows repeated major responses from the benthos during mass extinctions and global carbon perturbations, including reduced diversity, dominance of simple trace fossils, decreased burrow size and bioturbation intensity, and nonrandom extinction of trophic groups. The broad dispersal capacity of many extant benthic species facilitates poleward shifts corresponding to their environmental niche as overlying water warms. Evidence suggests that locally persistent populations will likely respond to environmental shifts through either failure to respond or genetic adaptation rather than via phenotypic plasticity. Regional and global ocean models insufficiently integrate changes in benthic biological activity and their feedbacks on sedimentary biogeochemical processes. The emergence of bioturbation, ventilation, and seafloor-habitat maps and progress in our mechanistic understanding of organism–sediment interactions enable incorporation of potential effects of climate change on benthic macrofaunal mediation of elemental cycles into regional and global ocean biogeochemical models. 

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2. Coastal Wetland Carbon and Nitrogen Cycles: Recent Advances in Measurements, Modeling, and Syntheses I (Oral session).

   Abdul-Aziz, Omar I.; Tang, Jianwu; Kroeger, Kevin D.; and Windham-Myers, Lisamarie (December 2021, AGU Fall Meeting 2021, held in New Orleans, LA, 13-17 December 2021, id. B21C)

   Coastal marshes, mangroves, and seagrass sequester significant amounts of “blue carbon” in soils, sediments, and biomass. They have potential as a negative emissions technology. With the increasing policy focus on climate change mitigation, we need to understand and accurately predict wetland carbon processes. Complex interactions of climate, land use, sea level, nitrogen pollution, and human management regulate the strength of the carbon sink and the greenhouse gas balance (including CO2, CH4, and N2O). Our ability to measure and model vertical and lateral exchanges, as well as the soil and sediment processes, at the land-ocean interface is limited. We aim to bring together researchers from various disciplines to discuss coastal carbon and nitrogen pools and fluxes, and their roles in global biogeochemical cycling and climate change mitigation. We also aim to report advances in eddy flux, lateral flux, field experiments, remote sensing, modeling, and synthesis that support coastal wetland carbon accounting. 

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3. Coastal Wetland Carbon and Nitrogen Cycles: Recent Advances in Measurements, Modeling, and Syntheses II (Poster).

   Abdul-Aziz, Omar I.; Tang, Jianwu; Kroeger, Kevin D.; and Windham-Myers, Lisamarie (December 2021, AGU Fall Meeting 2021, held in New Orleans, LA, 13-17 December 2021, id. B25C)

   Coastal marshes, mangroves, and seagrass sequester significant amounts of “blue carbon” in soils, sediments, and biomass. They have potential as a negative emissions technology. With the increasing policy focus on climate change mitigation, we need to understand and accurately predict wetland carbon processes. Complex interactions of climate, land use, sea level, nitrogen pollution, and human management regulate the strength of the carbon sink and the greenhouse gas balance (including CO2, CH4, and N2O). Our ability to measure and model vertical and lateral exchanges, as well as the soil and sediment processes, at the land-ocean interface is limited. We aim to bring together researchers from various disciplines to discuss coastal carbon and nitrogen pools and fluxes, and their roles in global biogeochemical cycling and climate change mitigation. We also aim to report advances in eddy flux, lateral flux, field experiments, remote sensing, modeling, and synthesis that support coastal wetland carbon accounting. 

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4. Ediacaran–Cambrian bioturbation did not extensively oxygenate sediments in shallow marine ecosystems

   https://doi.org/10.1111/gbi.12550  

   Cribb, Alison T.; van de Velde, Sebastiaan J.; Berelson, William M.; Bottjer, David J.; Corsetti, Frank A. (July 2023, Geobiology)

   Abstract The radiation of bioturbation during the Ediacaran–Cambrian transition has long been hypothesized to have oxygenated sediments, triggering an expansion of the habitable benthic zone and promoting increased infaunal tiering in early Paleozoic benthic communities. However, the effects of bioturbation on sediment oxygen are underexplored with respect to the importance of biomixing and bioirrigation, two bioturbation processes which can have opposite effects on sediment redox chemistry. We categorized trace fossils from the Ediacaran and Terreneuvian as biomixing or bioirrigation fossils and integrated sedimentological proxies for bioturbation intensity with biogeochemical modeling to simulate oxygen penetration depths through the Ediacaran–Cambrian transition. Ultimately, we find that despite dramatic increases in ichnodiversity in the Terreneuvian, biomixing remains the dominant bioturbation behavior, and in contrast to traditional assumptions, Ediacaran–Cambrian bioturbation was unlikely to have resulted in extensive oxygenation of shallow marine sediments globally. 

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5. Shell Reworking Impacts on Climate Variability Reconstructions Using Individual Foraminiferal Analyses

   https://doi.org/10.1029/2023pa004663  

   Bienzobas_Montávez, Natalia; Thirumalai, Kaustubh; Marino, Gianluca (May 2024, Paleoceanography and Paleoclimatology)

   Abstract Particle mixing by benthic fauna beneath the sediment‐water interface (or bioturbation) fundamentally challenges the proxy based retrieval of past climatic conditions from deep‐sea sediment cores. Previous efforts targeted the impacts of bioturbation on the nature of paleoceanographic changes gleaned from the proxy record, whereas impacts on seasonal and/or interannual variability reconstructions have received less attention. We present TurbIFA (Tracking uncertainty of reworking & bioturbation on IFA), a software that adapts and combines existing algorithms to quantitatively estimate the impact of sediment reworking and other uncertainties and assess significance of ocean and climate variability reconstructions based on individual foraminiferal analyses (IFA). Building upon previous idealized investigations of bioturbation using hydroclimate‐sediment simulations, TurbIFA advances the IFA proxy system modeling such that users may directly assess the sensitivity of their data to various local parameters related to shell reworking across the global ocean. Using the output of state‐of‐the‐art coupled atmosphere‐ocean general circulation models, TurbIFA simulates planktic foraminiferal δ¹⁸O or Mg/Ca‐temperature signal carriers and evaluates uncertainties in the sample size, analytical protocols along with as those arising from bioturbation. Application of TurbIFA to synthetic and existing data sets indicates that the significance of IFA‐based reconstructions can be assessed once the impacts of sediment accumulation rates, sediment mixed layer depths, length of time integrated by the chosen IFA sampling interval, and changes in the amplitude of climate variability (i.e., the targeted environmental signal) are comprehensively evaluated. We contend that TurbIFA can aid quantitative assessments of past seasonal and interannual variability gleaned from the paleoceanographic record. 

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