Marine records of Holocene glacier variability in the Kerguelen Islands (South Indian Ocean): sedimentology, chronology, and paleoclimatic drivers
(19/04/2021)
ULaval, GEODE, UT2J, Comue de Toulouse, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, IGE, IRD, INSU - CNRS, CNRS, Fédération OSUG, UGA, Grenoble INP, UGA, CEREGE, IRD, AMU, CdF (institution), INSU - CNRS, CNRS, INRAE, ELI, UCLouvain, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Hydroclimate and atmospheric circulation over North Africa through the last two climatic cycles reconstructed from dust deposited off West Africa
(19/04/2021)
GEOPS, INSU - CNRS, CNRS, LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France], EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Revisiting the marine reservoir age in Baja California continental margin sediments using 14C and 210Pb dating
Knowledge of the Marine Reservoir Effect (MRE) correction is fundamental in palaeoceanographic research to establish an accurate age-depth model for marine sedimentary records. However, during the last decades different MRE corrections have been applied in inconsistent ways for the same locality and same sediment cores, at Soledad Basin, Baja California, Mexico, creating confusion about the proper correction value of the marine reservoir effect (ΔR) to be applied. In contrast with the empirical approach previously used for assessing the ΔR value in Soledad Basin, in this study we applied an analytical approach based on the concurrent application of AMS-14 C and 210 Pb xs dating techniques made on sedimentary total organic carbon and foraminifera to determine new regional ΔR values from newly collected sediment cores from this site. Our results from Soledad Basin show a ΔR of 206 ± 32 years for foraminifera and 706 ± 42 years for organic carbon. Modeled ages using these results, and compared with those previously applied for the basin, highlight the relevance of the correct use of the local reservoir age as it can generate an offset of approximately 150 years if the other published ΔR were used. These differences can shift core chronologies by several decades and thus yield significant errors in palaeoceanographic reconstructions, which will be important to remedy in future work.
(Quaternary Geochronology. vol. 66, n° 1871-1014, 17/04/2021)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
The MALINA oceanographic expedition: how do changesin ice cover, permafrost and UV radiation impactbiodiversity and biogeochemical fluxesin the Arctic Ocean?
The MALINA oceanographic campaign was conducted during summer 2009 to investigate the carbon stocks and the processes controlling the carbon fluxes in the Mackenzie River estuary and the Beaufort Sea. Dur- ing the campaign, an extensive suite of physical, chemical and biological variables was measured across seven shelf–basin transects (south-north) to capture the meridional gradient between the estuary and the open ocean.Key variables such as temperature, absolute salinity, radiance, irradiance, nutrient concentrations, chlorophyll-a concentration, bacteria, phytoplankton and zooplankton abundance and taxonomy, and carbon stocks and fluxes were routinely measured onboard the Canadian research icebreaker CCGS Amundsen and from a barge in shallow coastal areas or for sampling within broken ice fields. Here, we present the results of a joint effort to tidy and standardize the collected data sets that will facilitate their reuse in further studies of the changing Arctic Ocean.
(Earth System Science Data. vol. 13, n° 1866-3508, pp. 1561–1592, 15/04/2021)
ULaval, INSU - CNRS, CNRS, TAMU, LOV, INSU - CNRS, SU, CNRS, IMEV, INSU - CNRS, SU, CNRS, SBR, SU, CNRS, NIOZ, SZN, UQAR, SEOE, ISMER, UQAR, LATMOS, UVSQ, INSU - CNRS, SU, CNRS, CEFREM, UPVD, INSU - CNRS, CNRS, SKLEG, CAS, BU, TJU, MIO, IRD, AMU, INSU - CNRS, UTLN, CNRS, IAEA-EL, LOMIC, INSU - CNRS, SU, CNRS, OOB, SU, CNRS, FR2424, SBR, SU, CNRS, INRS - ETE, INRS, UFZ, GSFC, UdeS, UdeS, UWF | CEDB, UWF, CIAS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, OCEANIS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, IUEM, IRD, INSU - CNRS, UBO EPE, CNRS, CADIC, CONICET, ICPA, UNTDF, DGD.REVE, MNHN, LOCEAN-VOG, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité, CMES, UVI, IRD, SHOM, IFREMER, CNRS, GEOTOP, EPM, UdeM, UQAT, UQAR, UQAM, EPS, AWI, HIFMB, OFFIS, MPL, SIO - UC San Diego, UC San Diego, UC, OSU ECCE TERRA, ENS-PSL, PSL, INSU - CNRS, SU, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, MEL, TJU, LARGE, UA, ASE, NTU, CSIRO-MAR, CSIRO, UTAS, VU, STAR, NESDIS, NOAA, ESSIC, UMD
Late Holocene Paleonvironmental Evolution of Two Coastal Lakes in Mediterranean Chile and Its Implications for Conservation Planning
Paleolimnological reconstructions from the mid and high latitudes in the Southern Hemisphere are still relatively scarce. Anthropogenic impacts have evidenced trophic state changes and an increase in cyanobacterial blooms in the lacustrine system of San Pedro de la Paz in the last decades. Here, we reconstructed primary production and sedimentological changes spanning the past 2500 years in two coastal lakes in Mediterranean Chile. A multiproxy approach including sedimentological, biogenic silica, carbon and nitrogen isotopes and fossil pigments analysis in sediment cores was performed in Laguna Grande (LGSP) and Laguna Chica de San Pedro (LCSP). A marked change in the sedimentology of the lakes, likely related to the terrigenous sediment inputs derived by a transition from an arid condition in the mid-Holocene to a more humid condition in the late Holocene that favoured arboreal forest establishment at 100 BC–AD 150. A period of low primary production was identified between 850 to 1050 AC for LCSP, suggesting moist and cold conditions that were possibly related to La Niña events. In recent decades, there have been increases in primary production, probably resulting from anthropogenic disturbances. These likely include the clearance of native vegetation, the introduction of exotic tree species, and urbanisation, which in turn, resulted in nutrient inputs and hence eutrophication. We conclude that an integrated management program for both lakes is urgently needed
(Applied Sciences. vol. 11, n° 2076-3417, 13/04/2021)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Fire regime changes in the Mediterranean climate region during the last 8500 last years using microcharcoal preserved in marine sediments from the Gulf of Lion
Nowadays, the Mediterranean region is strongly impacted by fires. Projected warming scenarios suggest increasing fire risk in this region considered as hot-spot of the climate change (Liu et al., 2010; Pechony and Shindell, 2010). However, models based on modern-day statistical relationships do not properly account for interactions between climate, vegetation, and fire. In addition, process-based models must be tested not only against modern observations but also under different past climate conditions reflecting the range of climate variability projected for the next centuries (Hantson et al. 2016). Marine sediments are a major source of fire history of nearby land masses. Here, we present a unique 8,500 yr long record of biomass burning changes from southeastern France based on a marine microcharcoal sedimentary record from the Gulf of Lion, located in the subaqueous Rhone river delta. Sediment delivery to the Gulf of Lion comes mainly from the Rhône River draining a large watershed in southeast France (ca.100,000 km2). Due to the direction of dominant winds blowing from the North-North-West (Mistral and Tramontane) and carrying fine particles from the land to the sea, the microcharcoal record likely reflects the biomass burning in the Rhone watershed and South-East of France. Our results show multi-centennial to millennial changes in biomass burning with a periodicity of 1000 years for the full record and between 500 and 700 years before 5,000 cal BP and after 3,000 cal BP. Large peaks of biomass burning are associated with marked dry periods observed in the region. Burning of biomass is higher when the region is dominated by xerophytic vegetation than when mesophyte vegetation dominates. The trend and periodicity of the biomass burning record suggest a predominant climatic control of fire occurrences since 8,500 cal BP in this region.
(13/04/2021)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LOCEAN-VOG, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité
Calibrating microcharcoal in recent marine sediments: implications to reconstruct paleofire regimes on African continent
(13/04/2021)
USV, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Diagnostiquer et réduire à la source les micropolluants -Retour d'expérience du projet Regard (Bordeaux Métropole)
Les micropolluants (MP) représentent un enjeu environnemental et sanitaire important. Identifier leurs sources pour ensuite réduire leurs rejets est la stratégie privilégiée au niveau français pour lutter contre cette pollution. C’est aussi la démarche qui a été mise en oeuvre dans le projet Regard (réduction et gestion des micropolluants sur la métropole bordelaise). La première phase du projet correspondait ainsi à la réalisation d’un diagnostic territorial, global et intégré couplant à la fois des analyses chimiques et biologiques du milieu naturel et du réseau d’assainissement depuis les points de rejets (station de traitement des eaux usées, exutoires pluviaux, by-pass) jusqu’aux sources d’émission (domestique, industrielle, hospitalière et pluviale). En complément, une caractérisation sociale des sources a été faite afin de comprendre les pratiques, les produits et les usages à l’origine des rejets de MP et d’identifier des leviers d’action pour réduire ces rejets. Les points forts de ce diagnostic sont la complémentarité des approches (sciences de l’ingénieur et sciences sociales, analyses chimiques et biologiques, étude des eaux usées et pluviales) et le nombre important de sites d’étude. La seconde phase du projet correspondait à la mise en oeuvre d’actions de réduction pour les tester et les évaluer du point de vue environnemental (efficacité pour réduire la quantité, la diversité et l’effet des MP), social (appropriation et satisfaction vis-à-vis des solutions) et économique (aide à l’orientation de l’action publique). Les actions ayant eu les meilleurs résultats sont (i) l’action « Familles EAU Défi » sur la source domestique, (ii) les actions de dératisation mécanique, de démoussage des terrains de tennis et d’enherbement des cimetières pour la source collectivité et (iii) l’action de traitement des eaux pluviales strictes en conditions réelles à l’échelle d’un pilote. Le présent retour d’expérience sur ce qui a été fait doit aider les collectivités qui souhaiteraient effectuer une telle démarche à ne pas commettre les mêmes « erreurs » et, au contraire, à mettre en oeuvre directement les actions qui donnent des résultats satisfaisants.
(TSM. Techniques Sciences Méthodes, n° 0299-7258, pp. 13-28, 08/04/2021)
LyRE, INERIS, CIRSEE, LyRE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR ETBX, INRAE, LabPsy, UB, UB, ENSAP Bordeaux, UBM, CNRS
Karst hydrological changes during the Late-Holocene in Southwestern China
The frequent alternation between droughts and floods in the karst regions of Southwestern China has a serious impact on the ecological environment and socio-economic development. Although some high-resolution records for this region have been published, there is a lack of multi-proxy geological records that could be used to reconstruct the relationships between the changes in the Asian summer monsoon (ASM) and the regional hydrology and ecological environment since the Late Holocene. In this study, the history of the ASM from 3109 to 694 yr BP with a mean temporal resolution of 2.5 yr is reconstructed based on 47 high-precision 230Th dating results (mean 2-sigma error of ±14 yr), 959 pairs of δ18O/δ13C data, and multiple trace element analyses of a stalagmite from Shijiangjun (SJJ) Cave in the karst area of Southwestern China. The positive δ18O and δ13C excursions accurately recorded eight interdecadal-centennial weak summer monsoon events at ∼779, 1013–911, 1282–1172, 1736–1638, 1961–1864, 2472–2375, 2931–2818, and 3050–3014 yr BP. The cross-wavelet spectrum analysis of the δ18O and δ13C of stalagmite SJJ7 indicates that they have similar periods. The 7 yr period of the δ18O record was determined to have the maximum contribution rate (36.8%) to the periods using ensemble empirical mode decomposition (EEMD) analysis. In the Late Holocene, the weak ASM events were dominated by the southward shift of the Intertropical Convergence Zone (ITCZ) and the frequent El Niño events on an interdecadal-centennial timescale. The southward migration of the ITCZ lead to frequent El Niño events, and the resultant Hadley Circulation and Walker Circulation were weakened, leading to a weak ASM and changes in the hydrological conditions in the monsoon region. The δ13C values of the stalagmite changed relatively slowly compared with the δ18O values, which may indicate that the degradation and restoration of the regional ecological environment caused by abrupt changes in the climate is a relatively slow process. When the summer monsoon decreased, the stalagmite’s Mg/Ca and Sr/Ca ratios were relatively high due to CO2 degassing, and the prior calcite precipitation (PCP)/prior aragonite precipitation (PAP) increased in the karst zone. However, the Mg/Ca ratio increased and the Sr/Ca ratio rapidly decreased during the calcite deposition due to differences in the crystal structures and partition coefficients of aragonite and calcite. The dark layers in stalagmite SJJ7 correspond to transition from heavy to light δ18O values, reflecting the transition in the ASM. The pulsed increases in the elements (Mn, Fe, Al, and Si) in the dark layers reflect the stronger mechanical transport caused by more rainfall. The multi-proxy analysis of this stalagmite may reflect the interactions between the changes in the ASM and the atmosphere-hydrosphere-pedosphere-biosphere-lithosphere in the karst critical zone during the Late Holocene.
(Quaternary Science Reviews. vol. 258, n° 0277-3791, pp. 106865, 01/04/2021)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Fire slightly decreases the competitive effects of a thorny cushion shrub in a semi‐arid mountain steppe in the short term
AbstractQuestionsStudies in alpine environments have highlighted dominant facilitative effects of cushion species for diversity. Many fewer studies have assessed the effects of cushion shrubs in drier and less cold mountain habitats and how these effects vary within the shrub canopy and with increasing drought stress with exposure and disturbance by fire.LocationA mountain steppe of the Golestan National Park in the semi‐arid climate of northeast Iran.MethodsWe quantified the cover of understorey species at the center and edge of the canopy of the thorny cushion shrub Onobrychis cornuta and in paired open areas, in north and south exposures and unburned and burned plots, two years after a fire. Soil chemical variables and moisture were measured in treatments. We quantified cushions’ center and edge effects on understorey species cover with the Relative Interaction Index (RII). Treatment effects on RII cover were analyzed with generalized linear mixed‐effects models (GLMM) and species composition with Correspondence Analysis.ResultsIn unburned plots, competition for cover was very high at cushion centers and strongly decreased at cushion edges. Exposure stress did not affect competition in unburned plots. Fire slightly decreased competition but only at center cushion shrub position and at south exposure. Species composition was mostly affected by exposure and fire treatments, although there was subtle variation in species composition among patches due to fire. Cushion position, fire and exposure treatments affected soil moisture and chemical variables, but soil changes did not explain cushion effects on understorey cover and their variations along treatments.ConclusionsThe effects of the cushion shrub were highly negative and in particular at cushion center, likely due to interference and competition for light in a dry and not too cold environment. Fire only slightly decreased competition in the short term, likely due to the delayed response of understorey species to disturbance induced by fire.
(Applied Vegetation Science. vol. 24, n° 1402-2001, 01/04/2021)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS