XXI. On the conversion of animal matter into new substances by the action of sulphuric acid

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Two functionally different muscle fibre types in some salps?

This paper describes the structure and operation of the fibres in the locomotor muscle bands of several salp species. In many species, for example Thalia democratica or Pegea confoederata, all the muscle fibres of the locomotor muscle bands are similar in width and structure. In others, for example Salpa fusiformis and S. maxima, although fibre structure is similar, the marginal fibres edging the bands may be some 3-4 times the width of those in the centre of the band. In Ihlea punctata, not only is there a more striking difference in width between the marginal and central fibres of the bands, but also the two differ in structure. The marginal fibres are up to 10 times the width of the central fibres and the two differ in myofibrillar and mitochondrial content. Intracellular recordings from the fibres show that the normally compound spike potentials do not overshoot resting potentials (up to -70 mV), and are decremental. The two types of fibre may be separately activated. It is suggested that in Ihlea punctata, the wide marginal fibres may be involved in slow swimming, the central narrow fibres in `escape´ swimming.No disponibl

PMIP4 simulations: what is new?

The Paleoclimate Modeling Intercomparison Project (PMIP) enters its fourth phase. Five PMIP periods have been retained for tier one simulations as part of CMIP6 (coupled model intercomparison project, phase 6): the last millennium, the mid-Holocene (6ka BP), the Last Glacial maximum (21ka BP), the Last Interglacial (127ka BP) and the Pliocene (3 Ma BP). The talk will review the rationale behind these simulations and highlight what would be needed from the paleoclimate community to fully benefit from this huge simulation effort.  The discussion will also discuss how this suite of PMIP4CMIP6 experiments is connected to several other periods and sensitivity experiments as part of PMIP. I propose to illustrate some of the new challenges that can now be tackled to improve the understanding of the rate of climate change, major feedbacks and the interplay between climate trends and climate variability</p

Modulation of Mid‐Holocene African Rainfall by Dust Aerosol Direct and Indirect Effects

Climate model simulations of the mid‐Holocene (MH) consistently underestimate northern African rainfall for reasons not fully understood. While most models incorporate orbital forcing and vegetation feedbacks, they neglect dust reductions associated with greater vegetation cover. Here we simulate the MH climate response to reduced Saharan dust using CESM CAM5‐chem, which resolves direct and indirect dust aerosol effects. Direct aerosol effects increase Saharan and Sahel convective rainfall by ~16% and 8%. In contrast, indirect aerosol effects decrease stratiform rainfall, damping the dust‐induced total rainfall increase by ~13% in the Sahara and ~59% in the Sahel. Sensitivity experiments indicate the dust‐induced precipitation anomaly in the Sahara and Sahel (0.27 and 0.18 mm/day) is smaller than the anomaly from MH vegetation cover (1.19 and 1.08 mm/day). Although sensitive to dust radiative properties, sea surface temperatures, and indirect aerosol effect parameterization, our results suggest that dust reductions had competing effects on MH African rainfall.Plain Language SummarySix thousand years ago, changes in Earth’s orbit led to greater summer season solar radiation over northern Africa. The increase in energy resulted in higher rainfall amounts, widespread vegetation, and reduced dust aerosols over regions that today are desert. In this study we use a climate model, CESM CAM5‐chem, that accounts for the ways dust aerosols interact with sunlight and cloud droplets to examine how the reduction in Saharan dust during this past humid time affected rainfall. When dust aerosols are reduced in the model, more sunlight reaches the surface, the Sahara warms, and convective rainfall from the West African Monsoon increases. However, through dust‐cloud droplet interactions, the same reduction in dust decreases nonconvective rainfall, which is less prevalent during the monsoon season but still important, and thus dampens the total rainfall increase. Overall, dust reduction leads to a rainfall response that is dependent on rainfall type. Lastly, we compare the rainfall response of reducing dust to that of increasing vegetation cover and find that while important, the response from dust is considerably weaker.Key PointsChanges in direct dust aerosol effects from reduced mid‐Holocene Saharan dust loading increase convective rainfall in northern AfricaChanges in indirect dust aerosol effects weaken total precipitation increases by limiting stratiform rainfall, particularly in the SahelThe African rainfall response to total dust aerosol effects is lower than a previous study and substantially less than vegetation forcingPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149324/1/grl58759-sup-0001-2018GL081225-SI.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/149324/2/grl58759_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/149324/3/grl58759.pd

Les mots du climat

Le climat de la Terre se réchauffe, un réchauffement particulièrement marqué sur les cinq dernières décennies. Une vaste communauté scientifique s’est organisée à l’échelle mondiale pour percer les causes et les mécanismes de ce réchauffement afin de pouvoir anticiper l’avenir du climat et concevoir les moyens de le contenir et d’en maîtriser les conséquences. La société civile n’est pas en reste dans ses efforts pour inciter les décideurs à prendre les mesures appropriées pour que l’évolution du climat reste dans des limites gérables. Il en résulte une profusion de publications, tant dans les revues scientifiques que dans la grande presse et les divers médias. Comme tout domaine spécialisé, les sciences du climat ont leur jargon propre, soit des termes spécifiques au domaine, soit des mots et expressions du langage courant mais avec des significations différentes. Ainsi, alors qu’en langage courant un puits est une source d’eau ou de pétrole, pour le climatologue, un puits de CO2, c’est le milieu ou le processus qui enlève du CO2 à l’atmosphère. Le jargon des climatologues est largement repris par les médias qui n’en explicitent pas systématiquement le sens. Dans ce livre, le lecteur trouvera quelques quatre cents définitions de termes concernant le climat et son évolution, explications présentées avec le contexte d’utilisation de ces termes. Pour mieux situer les choses, dix-huit encadrés tout au long du livre détaillent des processus climatiques et des moyens mis en œuvre pour les étudier

Science directions in a post-COP21-world of transient climate change: enabling regional to local predictions in support of reliable climate information

During recent decades, through theoretical considerations and analyses of observations andmodel simulations, the scientific community has fundamentally advanced our understanding of thecoupled climate system, thereby establishing that humans affect the Earth’s climate. Resulting from thisremarkable accomplishment, the COP21 agreement marks a historic turning point for climate research bycalling for actionable regional climate change information on time scales from seasonal to centuries for thebenefit of humanity, as well as living and nonliving elements of the Earth environment. Out of the underlyingUnited National Framework Convention on climate Change process, improving seamless regional climateforecast capabilities emerges as a key challenge for the international research community. Addressing itrequires a multiscale approach to climate predictions. Here we offer a vision that emphasizes enhancedscientific understanding of regional to local climate processes as the foundation for progress. The scientificchallenge is extreme due to the rich complexity of interactions and feedbacks between regional andglobal processes, each of which affects the global climate trajectory. To gain the necessary scientific insightand to turn it into actionable climate information require technical development, international coordination,and a close interaction between the science and stakeholder communities

The use of paleoclimate simulations to refine the environmental and chronological context of archaeological/paleontological sites

This study illustrates the strong potential of combining paleoenvironmental reconstructions and paleoclimate modeling to refine the paleoenvironmental and chronological context of archaeologicaland paleontological sites. We focus on the El Harhoura 2 cave (EH2), an archeological site located on the North-Atlantic coast of Morocco that covers a period from the Late Pleistocene to the mid-Holocene. On several stratigraphic layers, inconsistencies are observed between species- and isotope-based inferences used to reconstruct paleoenvironmental conditions. The stratigraphy of EH2 also shows chronological inconsistencies on older layers between age estimated by Optical Stimulated Luminescence (OSL) and Combination of Uranium Series and Electron Spin Resonance methods (combined US-ESR). We performed paleoclimate simulations to infer the global paleoclimate variations over the EH2 sequence in the area, and we conducted a consistency approach between paleoclimatereconstruction estimated from simulations and available from EH2 paleoenvironmental inferences. Our main conclusion show that the climate sequence based on combined US-ESR ages is more consistent with paleoenvironmental inferences than the climate sequence based on OSL ages. We also evidence that isotope-based inferences are more congruent with the paleoclimate sequence than species-based inferences. These results highlight the difference in scale between the information provided by each ofthese paleoenvironmental proxies. Our approach is transferable to other sites due to the increase number of available paleoclimate simulations.1 Introduction 2 Material and methods 2.1 El Harhoura 2 cave 2.1.1 Presentation of the site 2.1.2 Chronostratigraphy and dating hypotheses 2.1.3 Paleoenvironmental variables 2.2 Paleoclimate reconstruction 2.2.1 Climate model 2.2.2 Paleoclimate simulations 2.2.3 Sea-surface boundary conditions 2.2.4 A subset of key paleoclimate variables 2.3 Consistency analyses 3 Results 3.1. Simulated climate changes 3.2 Consistency between paleoclimate simulations and paleoenvironmental inferences 3.2.1 Association of paleoclimate simulations and stratigraphic layers 3.2.2 Consistency analyses 4 Discussion 4.1 Paleoclimate variation and underlying forcings 4.2 Paleoclimate simulations and chronostratigraphy 4.3 Paleoclimate simulations and paleoenvironmental inferences 5 Conclusion

The use of paleoclimatic simulations to refine the environmental and chronological context of archaeological/paleontological sites

To reconstruct the paleoenvironmental and chronological context of archaeological/paleontological sites is a key step to understand the evolutionary history of past organisms. Commonly used method to infer paleoenvironments rely on varied proxies such as faunal assemblages and isotopes. However, those proxies often show some inconsistencies. Regarding estimated ages of stratigraphic layers, they can vary depending on the dating method used. In this paper, we tested the potential of paleoclimate simulations to address this issue and contribute to the description of the environmental and chronological context of archaeological/paleontological sites. We produced a set of paleoclimate simulations corresponding to the stratigraphy of a Late-Pleistocene Holocene site, El Harhoura 2 (Morocco), and compared the climatic sequence described by these simulations to environmental inferences made from isotopes and faunal assemblages. Our results showed that in the studied site combined US-ESR ages were much more congruent with paleoenvironmental inferences than OSL ages. In addition, climatic variations were found to be more consistent with isotopic studies than faunal assemblages, allowing us to discuss unresolved discrepancies to date. This study illustrates the strong potential of our approach to refine the paleoenvironmental and chronological context of archaeological and paleontological sites.1 Introduction 2 Material and methods 2.1 El Harhoura 2 cave 2.2 Paleoclimate simulations 2.2.1 Pre-existing ensemble of simulations 2.2.2 Model 2.2.3 Sea-surface boundary conditions 2.3 Climate variations through EH2 sequence 3 Results 3.1 Paleoclimate simulations 3.2 Climate variations through EH2 sequence 4 Discussion 5 Conclusio

Holocene evolution of summer winds and marine productivity in the tropical Indian Ocean in response to insolation forcing: data-model comparison

The relative abundance of &lt;i&gt;Globigerinoides bulloides&lt;/i&gt; was used to infer Holocene paleo-productivity changes on the Oman margin and at the southern tip of India. Today, the primary productivity at both sites reaches its maximum during the summer season, when monsoon winds result in local Eckman pumping, which brings more nutrients to the surface. On a millennium time-scale, however, the % &lt;i&gt;G. bulloides&lt;/i&gt; records indicate an opposite evolution of paleo-productivity at these sites through the Holocene. The Oman Margin productivity was maximal at ~9 ka (boreal summer insolation maximum) and has decreased since then, suggesting a direct response to insolation forcing. On the contrary, the productivity at the southern tip of India was minimum at ~9 ka, and strengthened towards the present. &lt;br&gt;&lt;br&gt; Paleo-reconstructions of wind patterns, marine productivity and foraminifera assemblages were obtained using the IPSL-CM4 climate model coupled to the PISCES marine biogeochemical model and the FORAMCLIM ecophysiological model. These reconstructions are fully coherent with the marine core data. They confirm that the evolution of particulate export production and foraminifera assemblages at our two sites were directly linked with the strength of the upwelling. Model simulations at 9 ka and 6 ka BP show that the relative evolution between the two sites since the early Holocene can be explained by the weakening but also the southward shift of monsoon winds over the Arabian Sea during boreal summer