Moisture variability over the Indo-Pacific region and its influence on the Indian summer monsoon rainfall

The Indo-Pacific Ocean (i.e. region between 30°E and 150°E) has been experiencing a warming since the 1950s. At the same time, the large-scale summer monsoon rainfall over India and the moisture over the East Africa/Arabian Sea are both decreasing. In this study, we intend to investigate how the decrease of moisture over the East Africa/Arabian Sea is related to the Indo-Pacific Ocean warming and how this could affect the variability of the Indian summer monsoon rainfall. We performed the analysis for the period 1951–2012 based on observed precipitation, sea surface temperature and atmospheric reanalysis products and we verified the robustness of the result by comparing different datasets. The decreasing trend of moisture over the East Africa/Arabian Sea coincides with an increasing trend of moisture over the western Pacific region. This is accompanied by the strengthening (weakening) of the upward motion over the western Pacific (East Africa/Arabian Sea) that, consequently, contributes to modulate the western Pacific-Indian Ocean Walker circulation. At the same time, the low-level westerlies are weakening over the peninsular India, thus contributing to the reduction of moisture transport towards India. Therefore, rainfall has decreased over the Western Ghats and central-east India. Contrary to previous decades, since 2003 moisture over the East Africa/Arabian Sea started to increase and this is accompanied by the strengthening of convection due to increased warming of sea surface temperature over the western Arabian Sea. Despite this moisture increase over the Arabian Sea, we found that moisture transport is still weakening over the Indian landmass in the very recent decade and this has been contributing to the decreased precipitation over the northeast India and southern part of the Western Ghats

Réparation de l'ADN et mutagenèse dans les mitochondries des vertébrés : preuve de l'asymétrie de l'héritage des brins d'ADN

International audienceA variety of endogenous and exogenous factors induce chemical and structural alterations in cellular DNA in addition to the errors occurring throughout DNA synthesis. These types of DNA damage are cytotoxic, miscoding or both and are believed to be at the origin of cancer and other age-related diseases. A human cell, aside from nuclear DNA, contains thousands of copies of mitochondrial DNA (mtDNA), a double-stranded, circular molecule of 16,569 bp. It has been proposed that mtDNA is a critical target of reactive oxygen species: by-products of oxidative phosphorylation that are generated in the organelle during aerobic respiration. Indeed, oxidative damage to mtDNA is more extensive and persistent as compared to that to nuclear DNA. Although transversions are the hallmark of mutations induced by reactive oxygen species, paradoxically, the majority of mtDNA mutations that occur during ageing and cancer are transitions. Furthermore, these mutations show a striking strand orientation bias: T→C/G→A transitions preferentially occur on the light strand, whereas C→T/A→G on the heavy strand of mtDNA. Here, we propose that the majority of mtDNA progenies, created after multiple rounds of DNA replication, are derived from the heavy strand only, owing to asymmetric replication of the DNA strand anchored to the inner membrane via the D-loop structure.Divers facteurs endogènes et exogènes induisent des altérations chimiques et structurelles dans l'ADN cellulaire, en plus des erreurs qui se produisent tout au long de la synthèse de l'ADN. Ces types de dommages à l'ADN sont cytotoxiques, dus à un mauvais codage ou aux deux, et on pense qu'ils sont à l'origine du cancer et d'autres maladies liées à l'âge. Une cellule humaine, outre l'ADN nucléaire, contient des milliers de copies de l'ADN mitochondrial (ADNmt), une molécule circulaire double brin de 16 569 pb. Il a été proposé que l'ADNmt soit une cible critique des espèces réactives de l'oxygène : des sous-produits de la phosphorylation oxydative qui sont générés dans l'organelle pendant la respiration aérobie. En effet, les dommages oxydatifs de l'ADNmt sont plus étendus et plus persistants que ceux de l'ADN nucléaire. Bien que les transversions soient la marque des mutations induites par les espèces réactives de l'oxygène, paradoxalement, la majorité des mutations de l'ADNmt qui se produisent au cours du vieillissement et du cancer sont des transitions. De plus, ces mutations présentent un biais d'orientation des brins frappant : A→G/G→A transitions se produisent de préférence sur le brin léger, tandis que T→C/A→G sur le brin lourd de l'ADNmt. Ici, nous proposons que la majorité des descendants de l'ADNmt, créés après plusieurs cycles de réplication de l'ADN, soient dérivés du brin lourd uniquement, en raison de la réplication asymétrique du brin d'ADN ancré à la membrane interne via la structure en boucle D.Traduit avec www.DeepL.com/Translator (version gratuite

Support for global climate reorganization during the "Medieval Climate Anomaly"

Widely distributed proxy records indicate that the Medieval Climate Anomaly (MCA; *900–1350 AD) was characterized by coherent shifts in large-scale Northern Hemisphere atmospheric circulation patterns. Although cooler sea surface temperatures in the central and eastern equatorial Pacific can explain some aspects of medieval circulation changes, they are not sufficient to account for other notable features, including widespread aridity through the Eurasian sub-tropics, stronger winter westerlies across the North Atlantic and Western Europe, and shifts in monsoon rainfall patterns across Africa and South Asia. We present results from a full-physics coupled climate model showing that a slight warming of the tropical Indian and western Pacific Oceans relative to the other tropical ocean basins can induce a broad range of the medieval circulation and climate changes indicated by proxy data, including many of those not explained by a cooler tropical Pacific alone. Important aspects of the results resemble those from previous simulations examining the climatic response to the rapid Indian Ocean warming during the late twentieth century, and to results from climate warming simulations—especially in indicating an expansion of the Northern Hemisphere Hadley circulation. Notably, the pattern of tropical Indo-Pacific sea surface temperature (SST) change responsible for producing the proxy-model similarity in our results agrees well with MCA-LIA SST differences obtained in a recent proxy-based climate field reconstruction. Though much remains unclear, our results indicate that the MCA was characterized by an enhanced zonal Indo-Pacific SST gradient with resulting changes in Northern Hemisphere tropical and extra-tropical circulation patterns and hydroclimate regimes, linkages that may explain the coherent regional climate shifts indicated by proxy records from across the planet. The findings provide new perspectives on the nature and possible causes of the MCA—a remarkable, yet incompletely understood episode of Late Holocene climatic change