ALBERT

Description: Throughout the history of complex life, Earth's climate and biogeochemical cycles have been perturbed by Large Igneous Province (LIP) volcanism, with several LIP episodes correlating with major mass extinction events. Yet many aspects of the interplay between geological, climatic and ecological processes in the Earth System during these times of global upheaval remain poorly understood. This study focuses on the Central Atlantic Magmatic Province and the associated extinction event in the latest Triassic, about 201 million years ago. Although climate and carbon cycle models successfully reproduce aspects of the end-Triassic environmental changes, many questions regarding the causal and temporal relations behind them remain unresolved. Here, we report an effort to model and quantify the dynamic response of the Earth System to short pulses of volcanogenic volatile emissions for an ensemble of emission scenarios. For the first time in the context of the end-Triassic events, this is done with a coupled climate model and under consideration of both carbon and sulfur emissions. Tested are pulses with ∼1−6 kyr duration during which 2500 - 7500 GtC are emitted and 0 - 500 GtS form stratospheric sulfate aerosols. The simultaneous emission of carbon and sulfur during one pulse of volcanic activity causes climatic fluctuations on annual to millennial timescales: A sequence of transient global cooling and subsequent sustained warming, overprinted with high interannual variability. The simulated maximum global warming ranges from +1.8 to +4.4 °C, while the amplitude of cooling is considerably higher in the upper range of the tested sulfur emission scenarios. The magnitude of temperature change varies regionally, being lowest in the Tethys realm. Changes in steric sea level (∼1−3 m) and ocean overturning strength, a surface ocean pH decrease (∼0.2−0.4) and a drop of the carbonate saturation especially in the Tethys are also obtained from the simulations during each emission pulse. By evaluating the simulated temperature changes against thermal tolerance limits of stony corals in a simplified manner, we find that these are not clearly transgressed on a global scale in the simulated warming scenarios. However, the climatic variability potentially introduced by the volcanic forcing would have represented significant stress for marine organisms. This study represents a significant step towards integrating multiple volcanic forcing mechanisms and environmental response processes in space and time to yield a more complete picture of impacts of CAMP volcanism and LIPs in general.

Description: Tropical rainforests are recognized as one of the terrestrialtipping elements which could have profound impacts on the global cli-mate, once their vegetation has transitioned into savanna or grasslandstates. While several studies investigated the savannization of, e.g., theAmazon rainforest, few studies considered the influence of fire. Fire isexpected to potentially shift the savanna-forest boundary and henceimpact the dynamical equilibrium between these two possible vegeta-tion states under changing climate. To investigate the climate-inducedhysteresis in pan-tropical forests and the impact of fire under future cli-mate conditions, we employed the Earth system model CM2Mc, whichis biophysically coupled to the fire-enabled state-of-the-art dynamicglobal vegetation model LPJmL. We conducted several simulation ex-periments where atmospheric CO2concentrations increased (impactphase) and decreased from the new state (recovery phase), each withand without enabling wildfires. We find a hysteresis of the biomassand vegetation cover in tropical forest systems, with a strong regionalheterogeneity. After biomass loss along increasing atmospheric CO2concentrations and accompanied mean surface temperature increase ofabout 4°C (impact phase), the system does not recover completely intoits original state on its return path, even though atmospheric CO2concentrations return to their original state. While not detecting large-scale tipping points, our results show a climate-induced hysteresis intropical forest and lagged responses in forest recovery after the climatehas returned to its original state. Wildfires slightly widen the climate-induced hysteresis in tropical forests and lead to a lagged response inforest recovery by ca. 30 years.

Description: There is increasing evidence linking the mass-extinction event at the Cretaceous-Paleogene boundary to an asteroid impact near Chicxulub, Mexico. Here we use model simulations to explore the combined effect of sulfate aerosols, carbon dioxide and dust from the impact on the oceans and the marine biosphere in the immediate aftermath of the impact. We find a strong temperature decrease, a brief algal bloom caused by nutrients from both the deep ocean and the projectile, and moderate surface ocean acidification. Comparing the modeled longer-term post-impact warming and changes in carbon isotopes with empirical evidence points to a substantial release of carbon from the terrestrial biosphere. Overall, our results shed light on the decades to centuries after the Chicxulub impact which are difficult to resolve with proxy data.

Description: The Mesozoic era (∼252 to 66 million years ago) was a key interval in Earth's evolution toward its modern state, witnessing the breakup of the supercontinent Pangaea and significant biotic innovations like the early evolution of mammals. Plate tectonic dynamics drove a fundamental climatic transition from the early Mesozoic supercontinent toward the Late Cretaceous fragmented continental configuration. Here, key aspects of Mesozoic long-term environmental changes are assessed in a climate model ensemble framework. We analyze so far the most extended ensemble of equilibrium climate states simulated for evolving Mesozoic boundary conditions covering the period from 255 to 60 Ma in 5 Myr timesteps. Global mean temperatures are generally found to be elevated above the present and exhibit a baseline warming trend driven by rising sea levels and increasing solar luminosity. Warm (Triassic and mid-Cretaceous) and cool (Jurassic and end-Cretaceous) anomalies result from pCO2 changes indicated by different reconstructions. Seasonal and zonal temperature contrasts as well as continental aridity show an overall decrease from the Late Triassic-Early Jurassic to the Late Cretaceous. Meridional temperature gradients are reduced at higher global temperatures and less land area in the high latitudes. With systematic sensitivity experiments, the influence of paleogeography, sea level, vegetation patterns, pCO2, solar luminosity, and orbital configuration on these trends is investigated. For example, long-term seasonality trends are driven by paleogeography, but orbital cycles could have had similar-scale effects on shorter timescales. Global mean temperatures, continental humidity, and meridional temperature gradients are, however, also strongly affected by pCO2.

Description: The simulations of the end‐Cretaceous climate and the effects of the impact are carried out with a coupled climate model consisting of a modified version of the ocean general circulation model MOM3, a dynamic/thermodynamic sea ice model, and a fast statistical‐dynamical atmosphere model. Our impact simulations are based on a climate simulation of the end‐Cretaceous climate state using a Maastrichtian (70 Ma) continental configuration. The solar constant is scaled to 1354 W/m2, based on the present‐day solar constant of 1361 W/m2 and a standard solar model. A baseline simulation with 500 ppm of atmospheric CO2 and a sensitivity experiment at 1000 ppm CO2 concentration. The impact is assumed to release 100 Gt sulfur and 1400 Gt CO2. We simulate stratospheric residence times of 2.1 y, 4.3 y and 10.6 y. More information about the model can be found in the manuscript (https://doi.org/10.1002/2016GL072241).

Description: In “Investigating Mesozoic Climate Trends and Sensitivities with a Large Ensemble of Climate Model Simulations” we study global trends in the climatic evolution through the Mesozoic era (252-66 Ma). The data presented here is the model output on which the results of this manuscript are based. Also included are different boundary condition model input files and scripts to generate the included figures (using the Python programming language in a Jupyter Notebook). The model output is provided in different netcdf files. The data is generated using the coupled ocean-atmosphere model CLIMBER3alpha (Montoya et al. 2005) which models climate globally on a 3.75° x 3.75° (ocean, lon.x lat.) and 22.5° x 7.5° (atmosphere) grid. Please note that data from other research that is shown in the figures in Landwehrs et al. (2021a) is not included in this data publication to avoid copyright issues. Methods The data is model input and output for/from the coupled ocean-atmosphere model CLIMBER3alpha which models climate globally on a 3.75° x 3.75° (ocean, lon.x lat.) and 22.5° x 7.5° (atmosphere) grid.

Description: In "A pronounced spike in ocean productivity triggered by the Chicxulub impact" we study the combined effect of sulfate aerosols, carbon dioxide and dust on the oceans and the marine biosphere after the Chicxulub impact using simulations with a climate model including ocean biogeochemistry. The data presented here is the model output the results of this manuscript are based on. Additionally, the figures of the publication and scripts (Python) to analyse the model output and generate the figures are contained. The model output is provided in different netcdf files. The structure of the model output is explained in a readme file. The data is generated using the coupled ocean-atmosphere model CLIMBER-3α+C which models climate globally on a 3.75° x 3.75° (ocean) and 22.5° (longitude) x 7.5° (latitude) (atmosphere) grid. More information about the model can be found in the manuscript and the README of this data publication.

Description: The past and future evolution of the Antarctic Ice Sheet is largely controlled by interactions between the ocean and floating ice shelves. To investigate these interactions, coupled ocean and ice sheet model configurations are required. Previous modelling studies have mostly relied on high resolution configurations, limiting these studies to individual glaciers or regions over short time scales of decades to a few centuries. We present a framework to couple the dynamic ice sheet model PISM with the global ocean general circulation model MOM5 via the ice-shelf cavity module PICO. Since ice-shelf cavities are not resolved by MOM5, but parameterized with the box model PICO, the framework allows the ice sheet and ocean model to be run at resolution of 16 km and 3 degree, respectively. This approach makes the coupled configuration a useful tool for the analysis of interactions between the entire Antarctic Ice Sheet and the Earth system over time spans on the order of centuries to millennia. In this study we describe the technical implementation of this coupling framework: sub-shelf melting in the ice sheet model is calculated by PICO from modeled ocean temperatures and salinities at the depth of the continental shelf and, vice versa, the resulting mass and energy fluxes from the melting at the ice-ocean interface are transferred to the ocean model. Mass and energy fluxes are shown to be conserved to machine precision across the considered model domains. The implementation is computationally efficient as it introduces only minimal overhead. The framework deals with heterogeneous spatial grid geometries, varying grid resolutions and time scales between the ice and ocean model in a generic way, and can thus be adopted to a wide range of model setups.

Description: Model code for the GMD publication: CM2Mc-LPJmL v1.0: Biophysical coupling of a process-based dynamic vegetation model with managed land to a general circulation model, Drüke et al. (https://doi.org/10.5194/gmd-2020-436). Further information is provided in README-CM2Mc-LPJmL-v1.0.html.