Machine learning identifies ecological selectivity patterns across the end-Permian mass extinction

The end-Permian mass extinction occurred alongside a large swath of environmental changes that are often invoked as extinction mechanisms, even when a direct link is lacking. One way to elucidate the cause(s) of a mass extinction is to investigate extinction selectivity, as it can reveal critical information on organismic traits as key determinants of extinction and survival. Here we show that machine learning algorithms, specifically gradient boosted decision trees, can be used to identify determinants of extinction as well as to predict extinction risk. To understand which factors led to the end-Permian mass extinction during an extreme global warming event, we quantified the ecological selectivity of marine extinctions in the well-studied South China region. We find that extinction selectivity varies between different groups of organisms and that a synergy of multiple environmental stressors best explains the overall end-Permian extinction selectivity pattern. Extinction risk was greater for genera that had a low species richness, narrow bathymetric ranges limited to deep-water habitats, a stationary mode of life, a siliceous skeleton, or, less critically, calcitic skeletons. These selective losses directly link the extinctions to the environmental effects of rapid injections of carbon dioxide into the ocean-atmosphere system, specifically the combined effects of expanded oxygen minimum zones, rapid warming, and potentially ocean acidification

A lithium-isotope perspective on the evolution of carbon and silicon cycles

The evolution of the global carbon and silicon cycles is thought to have contributed to the long-term stability of Earth's climate. Many questions remain, however, regarding the feedback mechanisms at play, and there are limited quantitative constraints on the sources and sinks of these elements in Earth's surface environments. Here we argue that the lithium-isotope record can be used to track the processes controlling the long-term carbon and silicon cycles. By analysing more than 600 shallow-water marine carbonate samples from more than 100 stratigraphic units, we construct a new carbonate-based lithium-isotope record spanning the past 3 billion years. The data suggest an increase in the carbonate lithium-isotope values over time, which we propose was driven by long-term changes in the lithium-isotopic conditions of sea water, rather than by changes in the sedimentary alterations of older samples. Using a mass-balance modelling approach, we propose that the observed trend in lithium-isotope values reflects a transition from Precambrian carbon and silicon cycles to those characteristic of the modern. We speculate that this transition was linked to a gradual shift to a biologically controlled marine silicon cycle and the evolutionary radiation of land plants

Marine anoxia linked to abrupt global warming during Earths penultimate icehouse.

Piecing together the history of carbon (C) perturbation events throughout Earth’s history has provided key insights into how the Earth system responds to abrupt warming. Previous studies, however, focused on short-term warming events that were superimposed on longer-term greenhouse climate states. Here, we present an integrated proxy (C and uranium [U] isotopes and paleo CO2) and multicomponent modeling approach to investigate an abrupt C perturbation and global warming event (∼304 Ma) that occurred during a paleo-glacial state. We report pronounced negative C and U isotopic excursions coincident with a doubling of atmospheric CO2 partial pressure and a biodiversity nadir. The isotopic excursions can be linked to an injection of ∼9,000 Gt of organic matter–derived C over ∼300 kyr and to near 20% of areal extent of seafloor anoxia. Earth system modeling indicates that widespread anoxic conditions can be linked to enhanced thermocline stratification and increased nutrient fluxes during this global warming within an icehouse

Response of Siliceous Marine Organisms to the Permian-Triassic Climate Crisis Based on New Findings From Central Spitsbergen, Svalbard

Siliceous marine ecosystems play a critical role in shaping the Earth's climate system by influencing rates of organic carbon burial and marine authigenic clay formation (i.e., reverse weathering). The ecological demise of silicifying organisms associated with the Permian-Triassic mass extinction is postulated to have elevated marine authigenic clay formation rates, resulting in a prolonged greenhouse climate during the Early Triassic. Yet, our understanding of the response of siliceous marine organisms during this critical interval is poor. Whilst radiolarians experienced the strongest diversity loss in their evolutionary history and perhaps also the greatest population decline of silica-secreting organisms during this event, only a small number of Griesbachian (post-extinction) localities that record siliceous organisms are known. Here, we report newly discovered latest Changhsingian to early Griesbachian (Clarkina meishanensis - Hindeodus parvus Zone) radiolarians and siliceous sponge spicules from Svalbard. This fauna documents the survival of a low-diversity radiolarian assemblage alongside stem-group hexactinellid sponges making this the first described account of post-extinction silica-secreting organisms from the Permian/Triassic boundary in a shallow marine shelf environment and a mid-northern paleolatitudinal setting. Our findings indicate that latitudinal diversity gradients for silica-secreting organisms following the mass extinction were significantly altered, and that silica productivity was restricted to high latitude and deep water thermal refugia. This result has potential to further shape our understanding of changes in marine dissolved silica levels and in turn rates of reverse weathering, with implications for our understanding of carbon cycle dynamics during this interval

Enhanced phosphorus weathering contributed to Late Miocene cooling

Late Miocene climate evolution provides an opportunity to assess Earth’s climate sensitivity to carbon cycle perturbation under warmer-than-modern conditions. Despite its relevance for understanding the climate system, the driving mechanisms underlying profound climate and carbon cycle changes – including the enigmatic Late Miocene cooling from 7 to 5.4 million years ago – remain unclear. Here, we present magnetic and geochemical paleoceanographic proxies from a hydrogenetic ferromanganese crust retrieved in the northwestern Pacific Ocean. Our results indicate a striking 50% surge in deep ocean phosphorus concentrations occurred 7 – 4 million years ago, synchronous with enhanced deep ocean oxygen consumption. Employing a global biogeochemical model, we show that increased continental phosphorus weathering, without a concurrent rise in silicate weathering, contributed to the decline in atmospheric CO2 and associated cooling over the Late Miocene. This suggests a prominent decoupling of phosphorus and silicate weathering during a major carbon cycling event over the last 10 million years

Acceleration of phosphorus weathering under warm climates

The release of phosphorous (P) via chemical weathering is a vital process that regulates the global cycling of numerous key elements and shapes the size of the Earth’s biosphere. It has long been postulated that global climate should theoretically play a prominent role in governing P weathering rates. Yet, there is currently a lack of direct evidence for this relationship based on empirical data at the global scale. Here, using a compilation of temperature and P content data of global surface soils (0 to 30 cm), we demonstrate that P release does enhance at high mean annual surface temperatures. We propose that this amplification of nutrient supply with warming is a critical component of Earth’s natural thermostat, and that this relationship likely caused expanded oceanic anoxia during past climate warming events. The potential acceleration of phosphorus loss from soils due to anthropogenic climate warming may pose threats to agricultural production, terrestrial and marine ecosystems, and alter marine redox landscapes

Enhanced phosphorus weathering contributed to Late Miocene cooling

Late Miocene climate evolution provides an opportunity to assess Earth’s climate sensitivity to carbon cycle perturbation under warmer-than-modern conditions. Despite its relevance for understanding the climate system, the driving mechanisms underlying profound climate and carbon cycle changes – including the enigmatic Late Miocene cooling from 7 to 5.4 million years ago – remain unclear. Here, we present magnetic and geochemical paleoceanographic proxies from a hydrogenetic ferromanganese crust retrieved in the northwestern Pacific Ocean. Our results indicate a striking 50% surge in deep ocean phosphorus concentrations occurred 7 – 4 million years ago, synchronous with enhanced deep ocean oxygen consumption. Employing a global biogeochemical model, we show that increased continental phosphorus weathering, without a concurrent rise in silicate weathering, contributed to the decline in atmospheric CO2 and associated cooling over the Late Miocene. This suggests a prominent decoupling of phosphorus and silicate weathering during a major carbon cycling event over the last 10 million years

Is Earth special?

Peculiar conditions may be required for the origin of life and/or the evolution of complex organisms. Hence, Earth attributes—such as plate-tectonics, oceans, magnetism and a large moon—may be necessary preconditions, for our own existence, that are rare in the general population of planets. The unknown magnitude of this observational bias undermines understanding of our planet. However the discovery and characterization of exoplanets, along with advances in mathematical modelling of Earth systems, now allow this “anthropic selection” effect to be more thoroughly evaluated than before. This paper looks at a number of properties of our Solar System and our planet. It examines their possible benefits for life, whether these properties might be rare, whether they required fine-tuning and whether they have an associated habitability-lifetime. It also discusses additional data likely to become available in the near future.None of the individual properties considered show convincing evidence for anthropic bias. However, the time-scales associated with habitability— in particular, those associated with solar-warming, with axial stability and with planetary-cooling—are surprisingly similar and this provides tentative support for the view that Earth may be special

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