Attractors and bifurcation diagrams in complex climate models

The climate is a complex non-equilibrium dynamical system that relaxes toward a steady state under the continuous input of solar radiation and dissipative mechanisms. The steady state is not necessarily unique. A useful tool to describe the possible steady states under different forcing is the bifurcation diagram, that reveals the regions of multi-stability, the position of tipping points, and the range of stability of each steady state. However, its construction is highly time consuming in climate models with a dynamical deep ocean, interactive ice sheets or carbon cycle, where the relaxation time becomes larger than thousand years. Using a coupled setup of MITgcm, we test two techniques with complementary advantages. The first is based on the introduction of random fluctuations in the forcing and permits to explore a wide part of phase space. The second reconstructs the stable branches and is more precise in finding the position of tipping points.Comment: 9 pages, 5 figures, Supplemental Material, accepted for publication in Phys. Rev.

Olenekian sulfur isotope records: Deciphering global trends, links to marine redox changes and faunal evolution

The sulfur (S) isotope composition of carbonate associated sulfate (CAS) in carbonate rocks has been used to assess variations in paleo-oceanographic redox conditions and its relationship to biotic changes in Earth’s history, including the Smithian – Spathian transition. However, previous CAS studies of the Olenekian are mostly based on nearshore continental shelf sections and report highly variable δ34S values mostly offset from those of contemporaneous evaporites, casting doubt on the utility of the CAS proxy during this interval. The current study presents new CAS isotopic data from three well-dated carbonate successions which were deposited in continental shelf (Qiakong) and offshore marine (Wadi Musjah and Jebel Aweri) environments during the Olenekian (Smithian – Spathian). The aim of the study was to constrain the temporal and spatial variations in sulfur cycling and its relation to marine redox and faunal changes across the Smithian – Spathian transition (ca. 250.5 – 248.8 Ma). The CAS dataset is complemented by rare earth element (REE) concentration data and thin section petrography. Using a suite of optical and geochemical techniques, the preservation of near-primary CAS isotopic information in the studied samples is evaluated. Results indicate that of the three sections investigated, the offshore sections mostly preserve near-primary marine sulfate S-isotope compositions while the continental shelf Qiakong section suffers from post-depositional alteration of CAS. Comparisons of our new, as well as previously published CAS δ34S data, with the evaporite δ34S record suggests that although Olenekian CAS δ34S values may have been modified by abiotic factors such as ocean-atmosphere oxygenation levels. Keywords: sulfur isotopes, SSB, sulfur cycle, seawater sulfate, marine redox, CA

Attractors and Bifurcation Diagrams in Complex Climate Models

AbstractData required to generate the figures in the manuscript by Brunetti and Ragon entitled "Attractors and Bifurcation Diagrams in complex Climate Models

Robustness of competing climatic states

The climate is a non-equilibrium system undergoing the continuous action of forcing and dissipation. Under the effect of a spatially inhomogeneous absorption of solar energy, all the climate components dynamically respond until an approximate steady state (or attractor) is reached. However, multiple steady states can co-exist for a given forcing and with the same boundary conditions. Here, we apply the Thermodynamic Diagnostic Tool (TheDiaTo) to investigate the statistical properties of five co-existing climates, ranging from a snowball to an ice-free aquaplanet, obtained in MITgcm coupled simulations. The aim is to explore the multistability of the climate model setup by highlighting differences in competing steady states and their characteristic signatures regarding the meridional transport of heat and water mass, the Lorenz energy cycle and the material entropy production. We also investigate how such attractors change when the model configuration is varied. We consider, in particular, the effect of changing the representation of the cloud albedo, and of implementing an improved closure of the energy budget. We find that, even if the dynamics remains on the same attractor, state variables are modified. The set of metrics in TheDiaTo quantify such modifications and represent a valuable tool for model evaluation

High Pressure Inside Nanometer-Sized Particles Influences the Rate and Products of Chemical Reactions

International audienceThe composition of organic aerosol has a pivotal influence on aerosol properties such as toxicity and cloud droplet formation capability, which could affect both climate and air quality. However, a comprehensive and fundamental understanding of the chemical and physical processes that occur in nanometer-sized atmospheric particles remains a challenge that severely limits the quantification and predictive capabilities of aerosol formation pathways. Here, we investigated the effects of a fundamental and hitherto unconsidered physical property of nanoparticles-the Laplace pressure. By studying the reaction of glyoxal with ammonium sulfate, both ubiquitous and important atmospheric constituents, we show that high pressure can significantly affect the chemical processes that occur in atmospheric ultrafine particles (i.e., particles < 100 nm). Using high-resolution mass spectrometry and UV-vis spectroscopy, we demonstrated that the formation of reaction products is strongly (i.e., up to a factor of 2) slowed down under high pressures typical of atmospheric nanoparticles. A size-dependent relative rate constant is determined and numerical simulations illustrate the reduction in the production of the main glyoxal reaction products. These results established that the high pressure inside nanometer-sized aerosols must be considered as a key property that significantly impacts chemical processes that govern atmospheric aerosol growth and evolution