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1. Continental flood basalts drive Phanerozoic extinctions

   https://doi.org/10.1073/pnas.2120441119  

   Green, Theodore; Renne, Paul R.; Keller, C. Brenhin (September 2022, Proceedings of the National Academy of Sciences)

   Refinements of the geological timescale driven by the increasing precision and accuracy of radiometric dating have revealed an apparent correlation between large igneous provinces (LIPs) and intervals of Phanerozoic faunal turnover that has been much discussed at a qualitative level. However, the extent to which such correlations are likely to occur by chance has yet to be quantitatively tested, and other kill mechanisms have been suggested for many mass extinctions. Here, we show that the degree of temporal correlation between continental LIPs and faunal turnover in the Phanerozoic is unlikely to occur by chance, suggesting a causal relationship linking extinctions and continental flood basalts. The relationship is stronger for LIPs with higher estimated eruptive rates and for stage boundaries with higher extinction magnitudes. This suggests LIP magma degassing as a primary kill mechanism for mass extinctions and other intervals of faunal turnover, which may be related to CO 2 ,   SO 2 , Cl, and F release. Our results suggest continental LIPs as a major, direct driver of extinctions throughout the Phanerozoic. 

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2. The impact of floating ice on sea level estimates across multiple glacial cycles

   Gasson, E. (December 2018, AGU Fall Meeting)

   Unlike grounded ice sheets, floating ice shelves have minimal direct impact on sea level. However, depending on the method, proxy sea level reconstructions may be affected by the existence of floating ice. Unless ice shelves intercept the seafloor, their former presence is very difficult to detect. The recent discovery of ice erosional features in deep water depths at various locations throughout the Arctic Basin may indicate that extensive ice shelves existed in the Arctic Ocean during glacial maxima. Although dating these features is difficult, the current constraints suggest that a thick ice shelf existed during the penultimate glacial maximum. However, this does not rule out that ice shelves also existed during other glacial stages. Here we use ice sheet and oxygen isotope modeling to explore what impact a former Arctic ice shelf would have on our interpretations of past ice volumes during glacial maxima. We suggest that a former Arctic ice shelf may help to resolve some existing discrepancies between different proxy sea level reconstructions. 

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3. Faunal engineering stimulates landscape-scale accretion in southeastern US salt marshes

   https://doi.org/10.1038/s41467-023-36444-w  

   Crotty, Sinéad M.; Pinton, Daniele; Canestrelli, Alberto; Fischman, Hallie S.; Ortals, Collin; Dahl, Nicholas R.; Williams, Sydney; Bouma, Tjeerd J.; Angelini, Christine (December 2023, Nature Communications)

   Abstract The fate of coastal ecosystems depends on their ability to keep pace with sea-level rise—yet projections of accretion widely ignore effects of engineering fauna. Here, we quantify effects of the mussel , Geukensia demissa , on southeastern US saltmarsh accretion. Multi-season and -tidal stage surveys, in combination with field experiments, reveal that deposition is 2.8-10.7-times greater on mussel aggregations than any other marsh location. Our Delft-3D-BIVALVES model further predicts that mussels drive substantial changes to both the magnitude (±<0.1 cm·yr −1 ) and spatial patterning of accretion at marsh domain scales. We explore the validity of model predictions with a multi-year creekshed mussel manipulation of >200,000 mussels and find that this faunal engineer drives far greater changes to relative marsh accretion rates than predicted (±>0.4 cm·yr −1 ). Thus, we highlight an urgent need for empirical, experimental, and modeling work to resolve the importance of faunal engineers in directly and indirectly modifying the persistence of coastal ecosystems globally. 

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4. Teasing Apart Impacts of Human Activity and Regional Drought on Madagascar’s Large Vertebrate Fauna: Insights From New Excavations at Tsimanampesotse and Antsirafaly

   https://doi.org/10.3389/fevo.2021.742203  

   Godfrey, Laurie R.; Crowley, Brooke E.; Muldoon, Kathleen M.; Burns, Stephen J.; Scroxton, Nick; Klukkert, Zachary S.; Ranivoharimanana, Lovasoa; Alumbaugh, Jamie; Borths, Matthew; Dart, Ryan; et al (September 2021, Frontiers in Ecology and Evolution)

   Madagascar experienced a major faunal turnover near the end of the first millenium CE that particularly affected terrestrial, large-bodied vertebrate species. Teasing apart the relative impacts of people and climate on this event requires a focus on regional records with good chronological control. These records may document coeval changes in rainfall, faunal composition, and human activities. Here we present new paleontological and paleoclimatological data from southwestern Madagascar, the driest part of the island today. We collected over 1500 subfossil bones from deposits at a coastal site called Antsirafaly and from both flooded and dry cave deposits at Tsimanampesotse National Park. We built a chronology of Late Holocene changes in faunal assemblages based on 65 radiocarbon-dated specimens and subfossil associations. We collected stalagmites primarily within Tsimanampesotse but also at two additional locations in southern Madagascar. These provided information regarding hydroclimate variability over the past 120,000 years. Prior research has supported a primary role for drought (rather than humans) in triggering faunal turnover at Tsimanampesotse. This is based on evidence of: (1) a large freshwater ecosystem west of what is now the hypersaline Lake Tsimanampesotse, which supported freshwater mollusks and waterfowl (including animals that could not survive on resources offered by the hypersaline lake today); (2) abundant now-extinct terrestrial vertebrates; (3) regional decline or disappearance of certain tree species; and (4) scant local human presence. Our new data allow us to document the hydroclimate of the subarid southwest during the Holocene, as well as shifts in faunal composition (including local extirpations, large-vertebrate population collapse, and the appearance of introduced species). These records affirm that climate alone cannot have produced the observed vertebrate turnover in the southwest. Human activity, including the introduction of cattle, as well as associated changes in habitat exploitation, also played an important role. 

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5. Multi-proxy record of ocean-climate variability during the last two millennia on the Mackenzie Shelf, Beaufort Sea

   https://doi.org/10.47894/mpal.69.3.04  

   Gemery, Laura; Cronin, Thomas M.; Cooper, Lee W.; Roberts, Lucy R.; Keigwin, Lloyd D.; Addison, Jason A.; Leng, Melanie J.; Lin, Peigen; Magen, Cedric; Marot, Marci E.; et al (January 2023, Micropaleontology)

   A 2,000 year-long oceanographic history, in sub-centennial resolution, from a Canadian Beaufort Sea continental shelf site (60meters water depth) near the Mackenzie River outlet is reconstructed from ostracode and foraminifera faunal assemblages, shell stable isotopes (delta 18O, delta 13C) and sediment biogenic silica. The chronology of three sediment cores making up the composite section was established using 137Cs and 210Pb dating for the most recent 150 years and combined with linear interpolation of radiocarbon dates from bivalve shells and foraminifera tests.Continuous centimeter-sampling of the multicore and high-resolution sampling of a gravity and piston core yielded a time-averaged faunal record of every approximately 40 years from 0 to 1850 CE and every approximately 24 years from 1850 to 2013 CE. Proxy records were consistent with temperature oscillations and related changes in organic carbon cycling associated with the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). Abundance changes in dominant microfossil species, such as the ostracode Paracyprideis pseudopunctillata and agglutinated foraminifers Spiroplectammina biformis and S. earlandi, are used as indicators of less saline, and possibly corrosive/turbid bottom conditions associated with the MCA (approximately 800 to 1200 CE) and the most recent approximately 60 years (1950–2013). During these periods, pronounced fluctuations in these species suggest that prolonged seasonal sea-ice melting, changes in riverine inputs and sediment dynamics affected the benthic environment. Taxa analyzed for stable oxygen isotope composition of carbonates show the lowest delta 18O values during intervals within the MCA and the highest during the late LIA, which is consistent with a 1 degree to 2 degree C cooling of bottom waters. Faunal and isotopic changes during the cooler LIA (1300 to 1850 CE) are most apparent at approximately 1500 to 1850 CE and are particularly pronounced during 1850 to approximately 1900 CE, with an approximate 0.5 per mil increase in delta 18O values of carbonates from median values in the analyzed taxa. This very cold 50-year period suggests that enhanced summer sea ice suppressed productivity,which is indicated by low sediment biogenic silica values and lower delta 13C values in analyzed species. From 1900CE to present, declines in calcareous faunal assemblages and changes in dominant species (Cassidulina reniforme and P. pseudopunctillata) are associated with less hospitable bottom waters, indicated by a peak in agglutinated foraminifera from 1950 to 1990 CE. 

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