Alexandre Pohl

• PhD
• CNRS Researcher at Biogéosciences Dijon

The early evolutionary and much of the extinction history of marine animals is thought to be driven by changes in dissolved oxygen concentrations ([O2]) in the ocean1–3. In turn, [O2] is widely assumed to be dominated by the geological history of atmospheric oxygen (pO2)4,5. Here, by contrast, we show by means of a series of Earth system model expe...

The geological record of marine animal biodiversity reflects the interplay between changing rates of speciation versus extinction. Compared to mass extinctions, background extinctions have received little attention. To disentangle the different contributions of global climate state, continental configuration, and atmospheric oxygen concentration (p...

Geochemical redox proxies indicate that seafloor anoxia occurred during the latest Ordovician glacial maximum, coincident with the second pulse of the Late Ordovician mass extinction. However, expanded anoxia in a glacial climate strikingly contrasts with the warming-associated Mesozoic anoxic events and raises questions as to both the causal mecha...

Marine ecosystems with a diverse range of animal groups became established during the early Cambrian (~541 to ~509 Ma). However, Earth’s environmental parameters and palaeogeography in this interval of major macro-evolutionary change remain poorly constrained. Here, we test contrasting hypotheses of continental configuration and climate that have p...

Global cooling has been proposed as a driver of the Great Ordovician Biodiversification Event, the largest radiation of Phanerozoic marine animal Life. Yet, mechanistic understanding of the underlying pathways is lacking and other possible causes are debated. Here we couple a global climate model with a macroecological model to reconstruct global b...

A global carbonate prediction method with computer support

Stable oxygen isotopes (δ18O) are routinely used to reconstruct sea-surface temperatures (SSTs) in the geological past, with mineral δ18O values reflecting a combination of the temperature and oxygen isotope composition of seawater (δ18Osw). Temporal variation of mean-ocean δ18Osw is usually accounted for following estimates of land-ice volume. Spa...

The global ocean circulation plays a pivotal role in the regulation of the Earth’s climate. The specific pattern and strength of circulation also determines how carbon and nutrients are cycled and via the resulting distribution of dissolved oxygen, where habitats suitable for marine animals occur. However, evidence from both geological data and mod...

Throughout the Phanerozoic (538.8 Ma to present), climate change is demonstrably linked to radiations, extinctions, and turnovers in the biosphere. Here, we show that this connection existed in the late Ediacaran (~579 to 538.8 Ma), the first interval in Earth’s history to host complex macro-organisms, including early metazoans. Current correlation...

An ostracod assemblage from the Late Ordovician (Katian) Phu Ngu Formation of northern Vietnam, South China paleoplate, yields typical Baltic and Laurentian-­ affinity genera together with some endemic forms. Detailed paleontological and sedimentary analysis of the Phu Ngu Formation suggests it was deposited in a deeper marine forearc setting, belo...

The Devonian is a warmer-than-present geological period spanning from 419 to 359 million years ago (Ma) characterized by multiple identified ocean anoxic/hypoxic events. Despite decades of extensive investigation, no consensus has been reached regarding the drivers of these anoxic events. While growing geological evidence has demonstrated a tempora...

The end-Triassic mass extinction was among the most severe biotic crises of the Phanerozoic. It has been linked with the global expansion of marine anoxia, and the prolongation of these conditions within epeiric seas has been proposed as a cause for the suppression of biodiversity during the early Jurassic Hettangian Stage. Testing this interpretat...

The Devonian is a warmer-than-present geological period spanning from 419 to 359 million years ago (Ma) characterized by multiple identified ocean anoxic/hypoxic events. Despite decades of extensive investigation, no consensus has been reached regarding the drivers of these anoxic events. While growing geological evidence has demonstrated a tempora...

Recurrent global marine anoxia marked the Early Triassic in the aftermath of the Permian-Triassic mass extinction. Growing evidence suggests contrasting redox histories across regions, with differing durations and intensities of anoxic conditions, but proposed climate-induced mechanisms for marine anoxia cannot fully explain these contrasting redox...

Nature News and Views Scientists have long sought to understand what drives biodiversity changes. A study unifies ideas about marine and terrestrial biodiversity in one explanatory framework, pointing to physical geography as dictating life’s trajectory. Writing in Nature, Salles et al. present numerical simulations of changing continental lands...

The end-Triassic mass extinction was among the most severe biotic crises of the Phanerozoic. It has been linked with the global expansion of marine anoxia, and the prolongation of these conditions within epeiric seas has been proposed as a cause for the suppression of biodiversity during the Hettangian. Testing this interpretation is complicated by...

Global cooling during the Ordovician (485 Ma to 443 Ma) has long been considered as a possible driver of the Great Ordovician Biodiversification Event (GOBE), the largest radiation of Phanerozoic marine animal Life. Yet, this hypothesis exclusively relies on temporal correlations. Mechanistic understanding of the underlying pathways is lacking and...

Surface currents constitute an efficient transport agent for (larvae of) marine faunas, while the circulation of water masses in the ocean interior drives nutrient redistribution, ventilates the ocean and contributes to shaping surface biological productivity and the benthic redox landscape. Therefore, a robust understanding of ocean circulation, b...

The Ordovician global cooling trend observed by several temperature proxies, which coincides with one of the most significant evolutionary diversifications on Earth, is yet to be fully understood. This study presents new simulations of pCO2 and surface temperatures using a spatially resolved climate-carbon cycle Earth system model fed with refined...

The fossil record of marine invertebrates has long fuelled the debate as to whether or not there are limits to global diversity in the sea1–5. Ecological theory states that, as diversity grows and ecological niches are filled, the strengthening of biological interactions imposes limits on diversity6,7. However, the extent to which biological intera...

This article describes a suite of global climate model output files that provide continental climatic conditions (monthly temperatures, precipitation, evaporation, precipitation minus evaporation balance, runoff) together with the calculated Köppen–Geiger climate classes and topography, for 28 evenly spaced time slices through the Phanerozoic (Camb...

The first forests appeared on the continents during the Givetian stage of the Devonian. The fossil record shows that, by the end of the Devonian, vascular plants and forests were common and widespread in the wet lowlands. Although the impact of this major event on chemical weathering of the continents is reasonably known, the coeval change in physi...

The global ocean circulation plays a pivotal role in the regulation of the Earth's climate. The specific pattern and strength of circulation also determines how carbon and nutrients are cycled and via the resulting distribution of dissolved oxygen, where habitats suitable for marine animals occur. However, from data and models, transitions in circu...

The fossil record of marine invertebrates has long fueled the debate on whether or not there are limits to global diversity in the sea1–4⁠. Ecological theory states that as diversity grows and ecological niches are filled, the strengthening of biological interactions imposes limits on diversity5–7⁠. However, the extent to which biological interacti...

Significance The decline in extinction rates through geologic time is a well-established but enigmatic feature of the marine animal fossil record. We hypothesize that this trend is driven largely by secular changes in the oxygenation of the atmosphere and oceans, as physiological principles predict that marine animals would have been more vulnerabl...

The early evolutionary and much of the extinction history of marine animals, is thought to be driven by changes in dissolved oxygen concentrations ([O 2 ]) in the ocean1–3. In turn, [O 2] is widely assumed to be dominated by the geological history of atmospheric oxygen ( p O 2 )4,5. Here, in contrast, we show via a series of Earth system model expe...

The latitudinal diversity gradient (LDG) — the decline in species richness from the equator to the poles — is classically considered as the most pervasive macroecological pattern on Earth, but the timing of its establishment, its ubiquity in the geological past, and explanatory mechanisms remain uncertain. By combining empirical and modeling approa...

[https://zenodo.org/record/4506617#.YN3VJBMzaCf] These files contain the necessary data and R scripts for the manuscript "Quantitative comparison of geological data and climate simulations constrains early Cambrian geography and climate". The files include the NetCDF output of early Cambrian global climate simulations conducted using the coupled o...

The Phanerozoic period covers the last 542 million years of Earth’s history, about 12% of the history of our planet. With regard to the evolution of life, the Phanerozoic experienced major events such as the rapid diversification of multicellular organisms which first appeared in the Cambrian (541–485 Ma), the colonization of continental surfaces b...

A new and innovative workflow predicts presence, type and thickness of marine carbonates through geological Time and Space. It couples exhaustive data mining, accurate paleogeography and deep time paleoclimate modeling to reveal the waning and waxing of carbonate deposition throughout geological history with many, yet unmapped, implications for geo...

For more than a century, a number of ammonite taxa of supposed Tethyan origin or affinity have been reported from the Berriasian condensed deposits of Russia (referred to as ‘Ryazanian’). These occurrences have been used to constrain long-distance correlation and palaeobiogeographic interpretation of the Russian Platform during the earliest Cretace...

These files contain the output of Cretaceous global climate simulations conducted using the coupled ocean-atmosphere FOAM general circulation model. They are available every 10 Myrs between 150 Ma and 60 Ma, both included. For each time slice, numerous CO2 levels were used. Files are provided in netcdf format, fully compatible with GIS softwares,...

Platform carbonates are among the most voluminous of Cretaceous deposits. The production of carbonate platforms fluctuated through time. Yet, the reasons for these fluctuations are not well understood, and the underlying mechanisms remain largely unconstrained. Here we document the long-term trend in Cretaceous carbonate platform preservation based...

The widespread demise of the Urgonian rudistid-platform ecosystem in the Mediterranean Tethys was so far considered as a progressive phenomenon starting at the Barremian–Aptian transition and culminating in the mid-early Aptian in concert with the Oceanic Anoxic Event (OAE) 1a. The re-assignment of the final demise of the Urgonian-type peri-Voconti...

A striking feature of the marine fossil record is the variable intensity of extinction during superficially similar climate transitions. Here we combine climate models and species trait simulations to explore the degree to which differing palaeogeographic boundary conditions and differing magnitudes of cooling and glaciation can explain the relativ...

Prediction of carbonate distributions at a global scale through geological time represents a challenging scientific issue, which is critical for carbonate reservoir studies and the understanding of past and future climate changes. Such prediction is even more challenging because no numerical spatial model allows for the prediction of shallow-water...

Shallow-water carbonates are a major component of the Earth System but their spatial distribution through geological times is difficult to reconstruct, due to the incompleteness of the geological record, sampling heterogeneity and their intrinsic complexity (i.e. the “conundrum” of Pomar & Hallock, 2008). Beyond this complexity, carbonates are not...

Platform carbonates are a major component of the Earth system, but their spatial distribution through geological times is difficult to reconstruct, due to the incompleteness of geological records, sampling heterogeneity, and their intrinsic complexity. Beyond this complexity, carbonates are not randomly distributed in the world oceans, neither in t...

In the past fifteen years, a number of ammonite taxa of supposed Tethysian origin or affinity were reported from the Berriasian condensed deposits of Central Russia (regionally referred to as "Ryazanian''). These occurrences have been used to constrain long-distance correlation and paleobiogeographic interpretation of the Russian Platform during th...

Platform carbonates are a major component of the Earth System but their spatial extent through geological time is difficult to reconstruct, due to the incompleteness of the geological record, sampling heterogeneity and their intrinsic complexity. Here we use coupled ecological niche modeling and deep-time general circulation models to predict the o...

The Toarcian Oceanic Anoxic Event (T-OAE, ∼183 Myr) was a long-lasting episode of ocean deoxygenation during the Early Jurassic. The event is related to a period of global warming and characterized by major perturbations to the hydrological and carbon cycles with high rates of organic matter burial in shelf seas. Ocean circulation during the Toarci...

The Hirnantian glacial acme (445–444 Ma) represents the glacial maximum of the long-lived Ordovician glaciation. The ensuing deglaciation and associated transgression deeply affected depositional environments and critically impacted marine living communities, contributing to the Late Ordovician Mass Extinction. In the absence of a better model, thi...

The oceans of the early Cambrian (~541 to 509 million years ago) were the setting for a marked diversification of animal life. However, sea temperatures—a key component of the early Cambrian marine environment—remain unconstrained, in part because of a substantial time gap in the stable oxygen isotope (δ¹⁸O) record before the evolution of euconodon...

Following the appearance of numerous animal phyla during the ‘Cambrian Explosion’, the ‘Great Ordovician Biodiversification Event’ (GOBE) records their rapid diversification at the lower taxonomic levels, constituting the most significant rise in biodiversity in Earth's history. Recent studies suggest that the rapid rise in phytoplankton diversity...

The Ordovician-Silurian transition (∼ 455-430 Ma) is characterized by repeated climatic perturbations, concomitant with major changes in the global oceanic redox state best exemplified by the periodic deposition of black shales. The relationship between the climatic evolution and the oceanic redox cycles, however, remains largely debated. Here, usi...

It has been hypothesized that predecessors of today's bryophytes significantly increased global chemical weathering in the Late Ordovician, thus reducing atmospheric CO2 concentration and contributing to climate cooling and an interval of glaciations. Studies that try to quantify the enhancement of weathering by non-vascular vegetation, however, ar...

Supplementary Figure 1, Supplementary Note 1 and Supplementary References.

KEY POINTS • Earth system model providing the first detailed simulation of Mid-Late Ordovician land-ice growth. • Model/data comparison suggests a Darriwilian age for glacial onset. • A single ice sheet of large extent covered Gondwana during the Hirnantian glacial maximum. ABSTRACT The Ordovician glaciation represents the acme of one of only thre...

The Ordovician Period (485–443 Ma) is characterized by abundant evidence for continental-sized ice sheets. Modeling studies published so far require a sharp CO2 drawdown to initiate this glaciation. They mostly used non-dynamic slab mixed-layer ocean models. Here, we use a general circulation model with coupled components for ocean, atmosphere, and...