Holocene paleotemperatures reconstruction of the coniferous boreal forest of western Québec based on a multi-proxy approach.

Un futur climat planétaire plus chaud avec une sècheresse plus marquée durant toute l’année est aujourd’hui prévus, en particulier pour les hautes latitudes de l’hémisphère nord. Ces changements environnementaux seraient marqués par des fréquences et des intensités plus importantes des perturbations naturelles, qui pourraient menacer l’intégrité de certains écosystèmes forestiers boréaux. L’une des conséquences prévisibles serait une augmentation significative de l’occurrence des feux de forêt qui est déjà et deviendrait davantage encore l’élément perturbateur majeur de ces écosystèmes. Le devenir des écosystèmes boréaux suscite donc de nombreuses interrogations et des incertitudes, ce qui amène à souligner la nécessité d’une bonne caractérisation des changements climatiques spatio-temporels et de leurs conséquences sur ces écosystèmes.Afin de maintenir ces paysages forestiers dans les limites de leur variabilité naturelle, le Ministère des Forêts, de la Faune et des Parcs du Québec (MFFP) se propose, dans un contexte d’aménagement écosystémique durable, d’établir un Registre des états de référence. Dans cette perspective, l’objectif de recherche de cette thèse était de produire des reconstitutions des paléotempératures holocènes les plus robustes possibles au sein de la pessière à mousses de l’ouest du Québec. La recherche a porté sur une approche multi-indicateurs incluant les Chironomidae et le pollen contenus dans les sédiments des deux lacs retenus. Les résultats mettent en évidence la pertinence des capsules céphaliques de Chironomidae pour reconstituer à haute résolution temporelle, les paléotempératures holocènes du mois d’août provenant du Lac Aurélie à l’aide de deux Fonctions de Transfert (FT). La FT Est canadienne s’est avérée plus en accord avec le signal régional que la FT canadienne. De surcroit, les assemblages de Chironomidae du Lac Lili ont donné une reconstitution surestimée des paléotempératures en raison de la faible profondeur de ce lac. Enfin, la reconstitution quantitative combinée (Chironomidae et pollen) des paléotempératures du mois d’août a souligné trois périodes principales: (i) 8500-4500 ans AA, identifiée comme le Maximum Thermique de l’Holocène (HTM) durant laquelle les températures d’août sont plus chaudes que les températures actuelles; (ii) 4500-1000 ans AA, marquée par le début de la période Néoglaciaire froide, où les températures oscillent autour des valeurs actuelles et (iii) les derniers 1000 ans AA, caractérisés par une diminution générale des températures. Plusieurs événements climatiques courts ont également été identifiés pour chaque période : (i) l’évènement froid de 8200 ans AA; (ii) l’évènement chaud de 4200 ans AA; (iii) la période chaude dite Romaine (RWP, 1900-1700 ans AA) ; (iv) la période froide de l’Âge Sombre (DACP, 1700-1500 ans AA) ; (v) l’Anomalie Climatique Médiévale (MCA, 1100 ans AA) et (vi) le Petit Âge Glaciaire (LIA, 500-250 ans AA). Une série d’événements froids est également observée vers 5900, 4300, 2800 et 400 ans AA, se référant probablement aux évènements « Bond ». La durée et l’amplitude observées des événements climatiques rejoignent les enregistrements régionaux, nord-américains et plus largement ceux de l’Hémisphère Nord. Par ailleurs, la synthèse soulignant les relations entre climat-végétation-feu confirme l’influence d’une instabilité climatique sur les changements des régimes des feux, principalement causée par les variations saisonnières des précipitations et de l'irrégularité des épisodes de sécheresse. Toutefois, notre reconstitution combinée des paléotempératures indique que les grands feux coïncident avec l’évènement ponctuel de 4200 ans AA et ceux survenus à partir de 2000 ans (RWP, DACP, MCA et LIA). La température estivale conjuguée à d’autres variables climatiques (sécheresse estivale, ensoleillement estival, et précipitations annuelles) joue donc un rôle important dans la variation du régime des feux à l’ouest du Québec.A future warmer global climate with more severe annual drought has been predicted, especially for the high latitudes of the Northern Hemisphere. Such an environmental change would be marked by higher frequencies and intensities of natural disturbances, which could threaten the integrity of some boreal forest ecosystems. One of the foreseeable consequences would be a significant increase in the occurrence of wildfires, which is already the major disruptive element of these ecosystems. The future of boreal ecosystems thus raises many questions and uncertainties, highlighting the need for a good characterization of spatio-temporal climate changes and its consequences on these ecosystems.In order to maintain these forest landscapes within the limits of their natural variability, the Ministère des Forêts, de la Faune et des Parcs du Québec (MFFP) proposes, in a context of sustainable ecosystem management, to establish a registry of reference states. In this perspective, the research objective of this thesis was to produce the most possible robust reconstructions of Holocene temperatures within the spruce-moss forest of western Québec. The research focused on a multi-indicator approach including Chironomidae and pollen deposited in the sediments of two selected lakes.The results highlight the relevance of Chironomidae head capsules to reconstruct at high temporal resolution the August Holocene temperatures from Lac Aurélie using two Transfer Functions (TF). The East Canadian TF was more in agreement with the regional signal than the Canadian TF. In addition, chironomid assemblages from Lac Lili gave an overestimated paleotemperature reconstruction due to the specific shallowness of this lake. Finally, the combined quantitative reconstruction (Chironomidae and pollen) of the August palaeotemperatures suggested three distinct periods: (i) 8500-4500 years BP, identified as the Holocene Thermal Maximum (HTM) during which the August temperatures are warmer than modern temperatures; (ii) 4500-1000 cal BP, marked by the beginning of the cold Neoglacial period, where the temperatures oscillate around the current values and (iii) the last 1000 cal BP, characterized by a general decrease of the temperatures. Several short climatic events were also identified for each period: (i) the 8200 cal BP cold event; (ii) the 4200 cal BP warm event; (iii) the Roman Warm Period (RWP, 1900-1700 cal BP); (iv) the Dark Age Cold Period (DACP, 1700-1500 cal BP); (v) Medieval Climate Anomaly (MCA, 1100 cal BP) and (vi) the Little Ice Age (LIA, 500-250 cal BP). A series of cold events is also observed around 5900, 4300, 2800 and 400 cal BP, probably corresponding to the "Bond" events. The observed duration and amplitude of climate events are consistent with regional, North American records, and more widely those of the Northern Hemisphere. In addition, the synthesis highlighting climate-vegetation-fire relationships confirms the influence of climatic instability on changes in fire regimes mainly driven by seasonal variations in rainfall and frequency of drought events. However, our paleotemperatures combined reconstitution indicated that large fires coincide with the occasional event of 4200 cal BP and those occurring from 2000 cal BP onwards (RWP, DACP, MCA and LIA). Summer temperatures combined with other climatic variables (summer drought, summer insolation, and annual precipitation) play an important role in the variation of the fire regime in western Québec

Reconstitution des paléotempératures holocènes de la forêt boréale coniférienne de l'ouest du Québec basée sur une approche multi-indicateurs

A future warmer global climate with more severe annual drought has been predicted, especially for the high latitudes of the Northern Hemisphere. Such an environmental change would be marked by higher frequencies and intensities of natural disturbances, which could threaten the integrity of some boreal forest ecosystems. One of the foreseeable consequences would be a significant increase in the occurrence of wildfires, which is already the major disruptive element of these ecosystems. The future of boreal ecosystems thus raises many questions and uncertainties, highlighting the need for a good characterization of spatio-temporal climate changes and its consequences on these ecosystems.In order to maintain these forest landscapes within the limits of their natural variability, the Ministère des Forêts, de la Faune et des Parcs du Québec (MFFP) proposes, in a context of sustainable ecosystem management, to establish a registry of reference states. In this perspective, the research objective of this thesis was to produce the most possible robust reconstructions of Holocene temperatures within the spruce-moss forest of western Québec. The research focused on a multi-indicator approach including Chironomidae and pollen deposited in the sediments of two selected lakes.The results highlight the relevance of Chironomidae head capsules to reconstruct at high temporal resolution the August Holocene temperatures from Lac Aurélie using two Transfer Functions (TF). The East Canadian TF was more in agreement with the regional signal than the Canadian TF. In addition, chironomid assemblages from Lac Lili gave an overestimated paleotemperature reconstruction due to the specific shallowness of this lake. Finally, the combined quantitative reconstruction (Chironomidae and pollen) of the August palaeotemperatures suggested three distinct periods: (i) 8500-4500 years BP, identified as the Holocene Thermal Maximum (HTM) during which the August temperatures are warmer than modern temperatures; (ii) 4500-1000 cal BP, marked by the beginning of the cold Neoglacial period, where the temperatures oscillate around the current values and (iii) the last 1000 cal BP, characterized by a general decrease of the temperatures. Several short climatic events were also identified for each period: (i) the 8200 cal BP cold event; (ii) the 4200 cal BP warm event; (iii) the Roman Warm Period (RWP, 1900-1700 cal BP); (iv) the Dark Age Cold Period (DACP, 1700-1500 cal BP); (v) Medieval Climate Anomaly (MCA, 1100 cal BP) and (vi) the Little Ice Age (LIA, 500-250 cal BP). A series of cold events is also observed around 5900, 4300, 2800 and 400 cal BP, probably corresponding to the "Bond" events. The observed duration and amplitude of climate events are consistent with regional, North American records, and more widely those of the Northern Hemisphere. In addition, the synthesis highlighting climate-vegetation-fire relationships confirms the influence of climatic instability on changes in fire regimes mainly driven by seasonal variations in rainfall and frequency of drought events. However, our paleotemperatures combined reconstitution indicated that large fires coincide with the occasional event of 4200 cal BP and those occurring from 2000 cal BP onwards (RWP, DACP, MCA and LIA). Summer temperatures combined with other climatic variables (summer drought, summer insolation, and annual precipitation) play an important role in the variation of the fire regime in western Québec.Un futur climat planétaire plus chaud avec une sècheresse plus marquée durant toute l’année est aujourd’hui prévus, en particulier pour les hautes latitudes de l’hémisphère nord. Ces changements environnementaux seraient marqués par des fréquences et des intensités plus importantes des perturbations naturelles, qui pourraient menacer l’intégrité de certains écosystèmes forestiers boréaux. L’une des conséquences prévisibles serait une augmentation significative de l’occurrence des feux de forêt qui est déjà et deviendrait davantage encore l’élément perturbateur majeur de ces écosystèmes. Le devenir des écosystèmes boréaux suscite donc de nombreuses interrogations et des incertitudes, ce qui amène à souligner la nécessité d’une bonne caractérisation des changements climatiques spatio-temporels et de leurs conséquences sur ces écosystèmes.Afin de maintenir ces paysages forestiers dans les limites de leur variabilité naturelle, le Ministère des Forêts, de la Faune et des Parcs du Québec (MFFP) se propose, dans un contexte d’aménagement écosystémique durable, d’établir un Registre des états de référence. Dans cette perspective, l’objectif de recherche de cette thèse était de produire des reconstitutions des paléotempératures holocènes les plus robustes possibles au sein de la pessière à mousses de l’ouest du Québec. La recherche a porté sur une approche multi-indicateurs incluant les Chironomidae et le pollen contenus dans les sédiments des deux lacs retenus. Les résultats mettent en évidence la pertinence des capsules céphaliques de Chironomidae pour reconstituer à haute résolution temporelle, les paléotempératures holocènes du mois d’août provenant du Lac Aurélie à l’aide de deux Fonctions de Transfert (FT). La FT Est canadienne s’est avérée plus en accord avec le signal régional que la FT canadienne. De surcroit, les assemblages de Chironomidae du Lac Lili ont donné une reconstitution surestimée des paléotempératures en raison de la faible profondeur de ce lac. Enfin, la reconstitution quantitative combinée (Chironomidae et pollen) des paléotempératures du mois d’août a souligné trois périodes principales: (i) 8500-4500 ans AA, identifiée comme le Maximum Thermique de l’Holocène (HTM) durant laquelle les températures d’août sont plus chaudes que les températures actuelles; (ii) 4500-1000 ans AA, marquée par le début de la période Néoglaciaire froide, où les températures oscillent autour des valeurs actuelles et (iii) les derniers 1000 ans AA, caractérisés par une diminution générale des températures. Plusieurs événements climatiques courts ont également été identifiés pour chaque période : (i) l’évènement froid de 8200 ans AA; (ii) l’évènement chaud de 4200 ans AA; (iii) la période chaude dite Romaine (RWP, 1900-1700 ans AA) ; (iv) la période froide de l’Âge Sombre (DACP, 1700-1500 ans AA) ; (v) l’Anomalie Climatique Médiévale (MCA, 1100 ans AA) et (vi) le Petit Âge Glaciaire (LIA, 500-250 ans AA). Une série d’événements froids est également observée vers 5900, 4300, 2800 et 400 ans AA, se référant probablement aux évènements « Bond ». La durée et l’amplitude observées des événements climatiques rejoignent les enregistrements régionaux, nord-américains et plus largement ceux de l’Hémisphère Nord. Par ailleurs, la synthèse soulignant les relations entre climat-végétation-feu confirme l’influence d’une instabilité climatique sur les changements des régimes des feux, principalement causée par les variations saisonnières des précipitations et de l'irrégularité des épisodes de sécheresse. Toutefois, notre reconstitution combinée des paléotempératures indique que les grands feux coïncident avec l’évènement ponctuel de 4200 ans AA et ceux survenus à partir de 2000 ans (RWP, DACP, MCA et LIA). La température estivale conjuguée à d’autres variables climatiques (sécheresse estivale, ensoleillement estival, et précipitations annuelles) joue donc un rôle important dans la variation du régime des feux à l’ouest du Québec

A chironomid-inferred Holocene temperature record from a shallow Canadian boreal lake: potentials and pitfalls

International audienceThe biodiversity of shallow (zmax <5–7 m) lakes is sensitive to water-level and climate changes, but few such aquatic ecosystems have been studied in the context of quantitative climate reconstruction. Lac Lili (unofficial name) is located in the boreal forest of western Quebec, Canada, and was chosen for its shallowness (zmax = 1.40 m) to assess if chironomid assemblages in the sediments could be used to reconstruct Holocene temperature fluctuations quantitatively. Inferred temperatures displayed a decreasing trend from a maximum value ca. 8000–3500 cal year BP, slight warming between ca. 3500 and 3000 cal year BP, followed by cooling to the present. Although chironomid assemblages were influenced by factors other than climate, primarily water depth and changes in macrophyte richness, the reconstructed Holocene temperature pattern was very similar to the known regional climate history. Temperature inferences derived from the chironomid assemblages were, however, warmer than the two reference periods. This deviation was likely a consequence of three factors: (1) shallowness of the lake, which favoured littoral taxa with warmer-than-today temperature optima, (2) the low number of lakes warmer than 16°C in the training set, and (3) the absence of shallow lakes in the training set

Locating North African microrefugia for mountain tree species from landscape ruggedness and fossil records

International audienceIn order to optimize conservation policies for endangered plant species in North Africa and minimize the investment of the public resources we explore the capacity of a mountain plant species to persist locally in restricted natural areas. Palaeoecological studies have shown that plant species survived major global climate changes within refugia which offered suitable condition for their long term persistence. Our study aims at identifying potential mountains areas which may play the role of modern microrefugia for preserving locally endangered plant species.We analysed the mountain ruggedness of an area in the North-East of the Middle Atlas mountains where a population of an endangered plant species, Cedrus atlantica, is isolated today around lake Tameda. In addition, we collected a sediment core in the lake to investigate the recent history of the species with the local environmental changes. We compared the terrain and fossil analyses with an area in the Rif mountains where the terrain rugosity is lighter than in the Middle Atlas and where Atlas cedar populations occur as well.Our results show that the Atlas cedar is better preserved in terrains with high rugosity because they offer a wider panel of suitable microclimates for the species persistence and they restrict the number of inhabitants as well which, de facto, reduces the anthropogenic disturbances.We have carried out this analysis at a very small scale (less than 40km2). A more exhaustive analysis of the terrain rugosity over the Atlas and Rif mountains, combined with historical data, will help to identify more suitable refugial areas for preserving the species at a larger scale. Protecting these refugial areas over decades from any anthropogenic activity should be possible at a minimal cost and would represent an immediate response to the ongoing climate change for preserving endangered species

Major postglacial summer temperature changes in the central coniferous boreal forest of Quebec (Canada) inferred using chironomid assemblages

International audienceChironomid head capsules preserved in lake sediments were used to reconstruct 8200 years of summer temperatures in the boreal forest of northeastern Canada. Two training sets were used derived from Canadian and Eastern Canadian transfer functions. Both models reconstructed similar climate patterns, but the Canadian model provided temperatures generally 2-3 ˚C lower than the Eastern Canadian model. Three main thermal changes inferred by chironomids were: (i) the Holocene Thermal Maximum, which occurred between 8 and 5k cal a BP, with temperatures generally higher than today's, maximum temperatures between 8 and 6.5k cal a BP, and an average of þ 0.9 ˚C; (ii) the Medieval Climate Anomaly around 1.1-1.2k cal a BP with an amplitude of þ 0.7 ˚C; and (iii) a colder period reconstructed between the 14th and 19th centuries, corresponding to the Little Ice Age, with summer temperatures on average À0.5 ˚C lower than the climate normal. For each of these three climatic events, the timing and the amplitude of changes were similar with other published regional, North American and Northern Hemisphere records

Guidelines for the use and interpretation of palaeofire reconstructions based on various archives and proxies

International audienceWe present a comparative analysis of fire reconstructions from tree rings and from wood charcoal preserved in forest soils, peat and lake sediments. Our objective is to highlight the benefits and limits of different archives and proxies to reconstruct fire histories. We propose guidelines to optimize proxy and archive choice in terms of spatial and temporal scales of interest. Comparisons were performed for two sites in the boreal forest of northeastern North America. Compared to others archives, tree-ring analysis remains the best choice to reconstruct recent fires (<1000 years). For longer periods (from several centuries to millennia), lake charcoal can be used to reconstruct regional or local fire histories depending on the method used, but the focus should be on historical trends rather than on the identification of individual fire events. Charcoal preserved in peat and soils can be used to identify individual fire, but sometimes cover shorter time periods than lake archives

Polyclonal expansion of TCR Vb 21.3 + CD4 + and CD8 + T cells is a hallmark of multisystem inflammatory syndrome in children

International audienceMultisystem inflammatory syndrome in children (MIS-C) is a delayed and severe complication of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection that strikes previously healthy children. As MIS-C combines clinical features of Kawasaki disease (KD) and toxic shock syndrome (TSS), we aimed to compare the immunological profile of pediatric patients with these different conditions. We analyzed blood cytokine expression and the T cell repertoire and phenotype in 36 MIS-C cases, which were compared with 16 KD, 58 TSS, and 42 coronavirus disease 2019 (COVID-19) cases. We observed an increase of serum inflammatory cytokines (IL-6, IL-10, IL-18, TNF-α, IFN-γ, sCD25, MCP1, and IL-1RA) in MIS-C, TSS, and KD, contrasting with low expression of HLA-DR in monocytes. We detected a specific expansion of activated T cells expressing the Vβ21.3 T cell receptor β chain variable region in both CD4 and CD8 subsets in 75% of patients with MIS-C and not in any patient with TSS, KD, or acute COVID-19; this correlated with the cytokine storm detected. The T cell repertoire returned to baseline within weeks after MIS-C resolution. Vβ21.3 + T cells from patients with MIS-C expressed high levels of HLA-DR, CD38, and CX3CR1 but had weak responses to SARS-CoV-2 peptides in vitro. Consistently, the T cell expansion was not associated with specific classical HLA alleles. Thus, our data suggested that MIS-C is characterized by a polyclonal Vβ21.3 T cell expansion not directed against SARS-CoV-2 antigenic peptides, which is not seen in KD, TSS, and acute COVID-19

Inborn errors of OAS–RNase L in SARS-CoV-2–related multisystem inflammatory syndrome in children

International audienceMultisystem inflammatory syndrome in children (MIS-C) is a rare and severe condition that follows benign COVID-19. We report autosomal recessive deficiencies of OAS1 , OAS2 , or RNASEL in five unrelated children with MIS-C. The cytosolic double-stranded RNA (dsRNA)–sensing OAS1 and OAS2 generate 2′-5′-linked oligoadenylates (2-5A) that activate the single-stranded RNA–degrading ribonuclease L (RNase L). Monocytic cell lines and primary myeloid cells with OAS1, OAS2, or RNase L deficiencies produce excessive amounts of inflammatory cytokines upon dsRNA or severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) stimulation. Exogenous 2-5A suppresses cytokine production in OAS1-deficient but not RNase L–deficient cells. Cytokine production in RNase L–deficient cells is impaired by MDA5 or RIG-I deficiency and abolished by mitochondrial antiviral-signaling protein (MAVS) deficiency. Recessive OAS–RNase L deficiencies in these patients unleash the production of SARS-CoV-2–triggered, MAVS-mediated inflammatory cytokines by mononuclear phagocytes, thereby underlying MIS-C

The risk of COVID-19 death is much greater and age dependent with type I IFN autoantibodies

International audienceSignificance There is growing evidence that preexisting autoantibodies neutralizing type I interferons (IFNs) are strong determinants of life-threatening COVID-19 pneumonia. It is important to estimate their quantitative impact on COVID-19 mortality upon SARS-CoV-2 infection, by age and sex, as both the prevalence of these autoantibodies and the risk of COVID-19 death increase with age and are higher in men. Using an unvaccinated sample of 1,261 deceased patients and 34,159 individuals from the general population, we found that autoantibodies against type I IFNs strongly increased the SARS-CoV-2 infection fatality rate at all ages, in both men and women. Autoantibodies against type I IFNs are strong and common predictors of life-threatening COVID-19. Testing for these autoantibodies should be considered in the general population

The risk of COVID-19 death is much greater and age dependent with type I IFN autoantibodies

International audienceSignificance There is growing evidence that preexisting autoantibodies neutralizing type I interferons (IFNs) are strong determinants of life-threatening COVID-19 pneumonia. It is important to estimate their quantitative impact on COVID-19 mortality upon SARS-CoV-2 infection, by age and sex, as both the prevalence of these autoantibodies and the risk of COVID-19 death increase with age and are higher in men. Using an unvaccinated sample of 1,261 deceased patients and 34,159 individuals from the general population, we found that autoantibodies against type I IFNs strongly increased the SARS-CoV-2 infection fatality rate at all ages, in both men and women. Autoantibodies against type I IFNs are strong and common predictors of life-threatening COVID-19. Testing for these autoantibodies should be considered in the general population