المؤلفون: Ana Lúcia Lindroth Dauner, Gesine Mollenhauer, Jens Hefter, Márcia Caruso Bícego, Michel Michaelovitch de Mahiques, César de Castro Martins

المصدر: Frontiers in Marine Science, Vol 9 (2022)

مصطلحات موضوعية: continental slope, marine productivity, mass accumulation rates, organic proxies, paleoceanography, South Brazil Bight, Science, General. Including nature conservation, geographical distribution, QH1-199.5

الوصف: Despite the increased number of paleoceanographic studies in the SW Atlantic in recent years, the mechanisms controlling marine productivity and terrestrial material delivery to the South Brazil Bight remain unresolved. Because of its wide continental shelf and abrupt change in coastline orientation, this region is under the influence of several environmental forcings, causing the region to have large variability in primary production. This study investigated terrestrial organic matter (OM) sources and marine OM sources in the South Brazil Bight, as well as the main controls on marine productivity and terrestrial OM export. We analyzed OM geochemical (bulk and molecular) proxies in sediment samples from a core (NAP 63-1) retrieved from the SW Atlantic slope (24.8°S, 44.3°W, 840-m water depth). The organic proxies were classified into “terrestrial-source” and “marine-source” groups based on a cluster analysis. The two sources presented different stratigraphical profiles, indicating distinct mechanisms governing their delivery. Bulk proxies indicate the predominance of marine OM, although terrestrial input also affected the total OM deposition. The highest marine productivity, observed between 50 and 39 ka BP, was driven by the combined effects of the South Atlantic Central Water upwelling promoted by Brazil Current eddies and fluvial nutrient inputs from the adjacent coast. After the last deglaciation, decreased phytoplankton productivity and increased archaeal productivity suggest a stronger oligotrophic tropical water presence. The highest terrestrial OM accumulation occurred between 30 and 20 ka BP, with its temporal evolution controlled mainly by continental moisture evolution. Sea level fluctuations affected the distance between the coastline and the sampling site. In contrast, continental moisture affected the phytogeography, changing from lowlands covered by grasses and saltmarshes to a landscape dominated by mangroves and the Atlantic Forest. Our results suggest how the OM cycle in the South Brazil Bight may respond to warmer and dryer climate conditions.

وصف الملف: electronic resource

العلاقة: https://www.frontiersin.org/articles/10.3389/fmars.2022.924556/fullTest; https://doaj.org/toc/2296-7745Test

الوصول الحر: https://doaj.org/article/dab1a2a9c1334234938dbefdba81bcfcTest

المؤلفون: Dauner, Ana Lucia Lindroth, Mollenhauer, Gesine, Hefter, Jens, Bicego, Marcia Caruso, de Mahiques, Michel Michaelovitch, Martins, Cesar de Castro

المساهمون: Environmental Change Research Unit (ECRU), Ecosystems and Environment Research Programme

مصطلحات موضوعية: continental slope, marine productivity, mass accumulation rates, organic proxies, paleoceanography, South Brazil Bight, stratigraphical zones, terrestrial matter, BRAZILIAN UPPER SLOPE, ORGANIC-MATTER, CONTINENTAL-MARGIN, LATE QUATERNARY, SEA-SURFACE, N-ALKANES, SEDIMENTS, CLIMATE, SHELF, DRIVEN, 1172 Environmental sciences, 1171 Geosciences, 1181 Ecology, evolutionary biology

الوصف: Despite the increased number of paleoceanographic studies in the SW Atlantic in recent years, the mechanisms controlling marine productivity and terrestrial material delivery to the South Brazil Bight remain unresolved. Because of its wide continental shelf and abrupt change in coastline orientation, this region is under the influence of several environmental forcings, causing the region to have large variability in primary production. This study investigated terrestrial organic matter (OM) sources and marine OM sources in the South Brazil Bight, as well as the main controls on marine productivity and terrestrial OM export. We analyzed OM geochemical (bulk and molecular) proxies in sediment samples from a core (NAP 63-1) retrieved from the SW Atlantic slope (24.8 degrees S, 44.3 degrees W, 840-m water depth). The organic proxies were classified into "terrestrial-source" and "marine-source" groups based on a cluster analysis. The two sources presented different stratigraphical profiles, indicating distinct mechanisms governing their delivery. Bulk proxies indicate the predominance of marine OM, although terrestrial input also affected the total OM deposition. The highest marine productivity, observed between 50 and 39 ka BP, was driven by the combined effects of the South Atlantic Central Water upwelling promoted by Brazil Current eddies and fluvial nutrient inputs from the adjacent coast. After the last deglaciation, decreased phytoplankton productivity and increased archaeal productivity suggest a stronger oligotrophic tropical water presence. The highest terrestrial OM accumulation occurred between 30 and 20 ka BP, with its temporal evolution controlled mainly by continental moisture evolution. Sea level fluctuations affected the distance between the coastline and the sampling site. In contrast, continental moisture affected the phytogeography, changing from lowlands covered by grasses and saltmarshes to a landscape dominated by mangroves and the Atlantic Forest. Our results suggest how the OM cycle in the ...

وصف الملف: application/pdf

العلاقة: This study was supported by FAPESP (Sao Paulo Science Foundation; 2010/06147-5 and 2015/21834-2 research grants) and CNPq (Brazilian National Council for Scientific and Technological Development; 300962/2018-5 and 305763/2011-3 research grants). CM also would like to thank CAPES-PrInt for financial support (88887.311742/2018-00). AD would like to thank Helsinki University Library for the financial support for open access publication fees.; Dauner , A L L , Mollenhauer , G , Hefter , J , Bicego , M C , de Mahiques , M M & Martins , C D C 2022 , ' Late Pleistocene to Holocene variations in marine productivity and terrestrial material delivery to the western South Atlantic ' , Frontiers in Marine Science , vol. 9 , 924556 . https://doi.org/10.3389/fmars.2022.924556Test; ORCID: /0000-0002-9686-6241/work/123143851; d2985c6e-e833-4847-97da-1382e7b5af0f; http://hdl.handle.net/10138/350794Test; 000872792000001

الإتاحة: http://hdl.handle.net/10138/350794Test

المؤلفون: Capo, Eric, Rydberg, Johan, 1976, Tolu, Julie, 1985, Domaizon, Isabelle, Debroas, Didier, Bindler, Richard, 1963, Bigler, Christian

المصدر: Frontiers in Ecology and Evolution. 7

مصطلحات موضوعية: varved sediment record, sedimentary DNA, protists, metabarcoding, meteorological data, inorganic geochemistry, organic proxies, paleolimnology

الوصف: To assess the sensitivity of lakes to anthropogenically-driven environmental changes (e.g., nutrient supply, climate change), it is necessary to first isolate the effects of between-year variability in weather conditions. This variability can strongly impact a lake's biological community especially in boreal and arctic areas where snow phenology play an important role in controlling the input of terrestrial matter to the lake. Identifying the importance of this inherent variability is difficult without time series that span at least several decades. Here, we applied a molecular approach (metabarcoding on eukaryotic 18S rRNA genes and qPCR on cyanobacterial 16S rRNA genes) to sedimentary DNA (sed-DNA) to unravel the annual variability of microbial community in 40 years' sediment record from the boreal lake Nylandssjon which preserve annually-laminated sediments. Our comparison between seasonal meteorological data, sediment inorganic geochemistry (X-ray fluorescence analyses) and organic biomarkers (pyrolysis-gas chromatography/mass spectrometry analyses), demonstrated that inter-annual variability strongly influence the sediment composition in Nylandssjon. Spring temperature, snow and ice phenology (e.g., the percentage of snow loss in spring, the timing of lake ice-off) were identified as important drivers for the inputs of terrestrial material to the lake, and were therefore also important for shaping the aquatic biological community. Main changes were detected in the late-80s/mid-90s and mid-2000s associated with increases in algal productivity, in total richness of the protistan community and in relative abundances of Chlorophyta, Dinophyceae as well as Cyanobacteria abundance. These changes could be linked to a decline in terrestrial inputs to the lake during the snow melt and run-off period, which in turn was driven by warmer winter temperatures. Even if our data shows that meteorological factors do affect the sediment composition and microbial communities, they only explain part of the variability. This is most likely a consequence of the high inter-annual variability in abiotic and biotic parameters highlighting the difficulty to draw firm conclusions concerning drivers of biological changes at an annual or sub-annual resolution even with the 40-year varved sediment record from Nylandssjon. Hence, it is necessary to have an even longer time perspective in order to reveal the full implications of climate change.

وصف الملف: electronic

الوصول الحر: https://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-161823Test
https://doi.org/10.3389/fevo.2019.00245Test
https://umu.diva-portal.org/smash/get/diva2:1342108/FULLTEXT01.pdfTest

المؤلفون: Ana Lúcia Lindroth Dauner, Gesine Mollenhauer, Jens Hefter, Márcia Caruso Bícego, Michel Michaelovitch de Mahiques, César de Castro Martins

مصطلحات موضوعية: Oceanography, Marine Biology, Marine Geoscience, Biological Oceanography, Chemical Oceanography, Physical Oceanography, Marine Engineering, continental slope, marine productivity, mass accumulation rates, organic proxies, paleoceanography, South Brazil Bight, stratigraphical zones, terrestrial matter

الوصف: Despite the increased number of paleoceanographic studies in the SW Atlantic in recent years, the mechanisms controlling marine productivity and terrestrial material delivery to the South Brazil Bight remain unresolved. Because of its wide continental shelf and abrupt change in coastline orientation, this region is under the influence of several environmental forcings, causing the region to have large variability in primary production. This study investigated terrestrial organic matter (OM) sources and marine OM sources in the South Brazil Bight, as well as the main controls on marine productivity and terrestrial OM export. We analyzed OM geochemical (bulk and molecular) proxies in sediment samples from a core (NAP 63-1) retrieved from the SW Atlantic slope (24.8°S, 44.3°W, 840-m water depth). The organic proxies were classified into “terrestrial-source” and “marine-source” groups based on a cluster analysis. The two sources presented different stratigraphical profiles, indicating distinct mechanisms governing their delivery. Bulk proxies indicate the predominance of marine OM, although terrestrial input also affected the total OM deposition. The highest marine productivity, observed between 50 and 39 ka BP, was driven by the combined effects of the South Atlantic Central Water upwelling promoted by Brazil Current eddies and fluvial nutrient inputs from the adjacent coast. After the last deglaciation, decreased phytoplankton productivity and increased archaeal productivity suggest a stronger oligotrophic tropical water presence. The highest terrestrial OM accumulation occurred between 30 and 20 ka BP, with its temporal evolution controlled mainly by continental moisture evolution. Sea level fluctuations affected the distance between the coastline and the sampling site. In contrast, continental moisture affected the phytogeography, changing from lowlands covered by grasses and saltmarshes to a landscape dominated by mangroves and the Atlantic Forest. Our results suggest how the OM cycle in the South Brazil Bight ...

العلاقة: https://figshare.com/articles/dataset/DataSheet_1_Late_Pleistocene_to_Holocene_variations_in_marine_productivity_and_terrestrial_material_delivery_to_the_western_South_Atlantic_pdf/20631633Test

الإتاحة: https://doi.org/10.3389/fmars.2022.924556.s001Test
https://figshare.com/articles/dataset/DataSheet_1_Late_Pleistocene_to_Holocene_variations_in_marine_productivity_and_terrestrial_material_delivery_to_the_western_South_Atlantic_pdf/20631633Test

المؤلفون: Eric Capo, Johan Rydberg, Julie Tolu, Isabelle Domaizon, Didier Debroas, Richard Bindler, Christian Bigler

المساهمون: Umeå University, Swiss Federal Insitute of Aquatic Science and Technology [Dübendorf] (EAWAG), Centre Alpin de Recherche sur les Réseaux Trophiques et Ecosystèmes Limniques (CARRTEL), Institut National de la Recherche Agronomique (INRA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry]), Laboratoire Microorganismes : Génome et Environnement (LMGE), Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS), Region Rhone-Alpes, EC2CO INSU program (France), Swedish Research Council 90432301

المصدر: Frontiers in Ecology and Evolution, Vol 7 (2019)
Frontiers in Ecology and Evolution
Frontiers in Ecology and Evolution, 2019, 7, ⟨10.3389/fevo.2019.00245⟩
Frontiers in Ecology and Evolution, Frontiers Media S.A, 2019, 7, ⟨10.3389/fevo.2019.00245⟩
Frontiers in Ecology and Evolution (7), . (2019)

مصطلحات موضوعية: 0106 biological sciences, 0301 basic medicine, Naturgeografi, Biodiversité et Ecologie, meteorological data, lcsh:Evolution, Climate change, 010603 evolutionary biology, 01 natural sciences, Paleolimnology, Biodiversity and Ecology, 03 medical and health sciences, Nutrient, inorganic geochemistry, sedimentary DNA, lcsh:QH540-549.5, lcsh:QH359-425, 14. Life underwater, organic proxies, skin and connective tissue diseases, Ecology, Evolution, Behavior and Systematics, protists, Ecology, paleolimnology, varved sediment record, metabarcoding, 15. Life on land, 030104 developmental biology, Boreal, Physical Geography, 13. Climate action, Environmental science, Sedimentary rock, sense organs, Physical geography, lcsh:Ecology, [SDE.BE]Environmental Sciences/Biodiversity and Ecology

الوصف: International audience; To assess the sensitivity of lakes to anthropogenically-driven environmental changes (e.g., nutrient supply, climate change), it is necessary to first isolate the effects of between-year variability in weather conditions. This variability can strongly impact a lake's biological community especially in boreal and arctic areas where snow phenology play an important role in controlling the input of terrestrial matter to the lake. Identifying the importance of this inherent variability is difficult without time series that span at least several decades. Here, we applied a molecular approach (metabarcoding on eukaryotic 18S rRNA genes and qPCR on cyanobacterial 16S rRNA genes) to sedimentary DNA (sed-DNA) to unravel the annual variability of microbial community in 40 years' sediment record from the boreal lake Nylandssjon which preserve annually-laminated sediments. Our comparison between seasonal meteorological data, sediment inorganic geochemistry (X-ray fluorescence analyses) and organic biomarkers (pyrolysis-gas chromatography/mass spectrometry analyses), demonstrated that inter-annual variability strongly influence the sediment composition in Nylandssjon. Spring temperature, snow and ice phenology (e.g., the percentage of snow loss in spring, the timing of lake ice-off) were identified as important drivers for the inputs of terrestrial material to the lake, and were therefore also important for shaping the aquatic biological community. Main changes were detected in the late-80s/mid-90s and mid-2000s associated with increases in algal productivity, in total richness of the protistan community and in relative abundances of Chlorophyta, Dinophyceae as well as Cyanobacteria abundance. These changes could be linked to a decline in terrestrial inputs to the lake during the snow melt and run-off period, which in turn was driven by warmer winter temperatures. Even if our data shows that meteorological factors do affect the sediment composition and microbial communities, they only explain part of the variability. This is most likely a consequence of the high inter-annual variability in abiotic and biotic parameters highlighting the difficulty to draw firm conclusions concerning drivers of biological changes at an annual or sub-annual resolution even with the 40-year varved sediment record from Nylandssjon. Hence, it is necessary to have an even longer time perspective in order to reveal the full implications of climate change.

وصف الملف: application/pdf

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::27f4b3adb04128078f2603cc0c246304Test
https://www.frontiersin.org/article/10.3389/fevo.2019.00245/fullTest

المؤلفون: Eric Capo, Johan Rydberg, Julie Tolu, Isabelle Domaizon, Didier Debroas, Richard Bindler, Christian Bigler

مصطلحات موضوعية: Evolutionary Biology, Ecology, Invasive Species Ecology, Landscape Ecology, Conservation and Biodiversity, Behavioural Ecology, Community Ecology (excl. Invasive Species Ecology), Ecological Physiology, Freshwater Ecology, Marine and Estuarine Ecology (incl. Marine Ichthyology), Population Ecology, Terrestrial Ecology, varved sediment record, sedimentary DNA, protists, metabarcoding, meteorological data, inorganic geochemistry, organic proxies, paleolimnology

الوصف: To assess the sensitivity of lakes to anthropogenically-driven environmental changes (e.g., nutrient supply, climate change), it is necessary to first isolate the effects of between-year variability in weather conditions. This variability can strongly impact a lake's biological community especially in boreal and arctic areas where snow phenology play an important role in controlling the input of terrestrial matter to the lake. Identifying the importance of this inherent variability is difficult without time series that span at least several decades. Here, we applied a molecular approach (metabarcoding on eukaryotic 18S rRNA genes and qPCR on cyanobacterial 16S rRNA genes) to sedimentary DNA (sed-DNA) to unravel the annual variability of microbial community in 40 years' sediment record from the boreal lake Nylandssjön which preserve annually-laminated sediments. Our comparison between seasonal meteorological data, sediment inorganic geochemistry (X-ray fluorescence analyses) and organic biomarkers (pyrolysis-gas chromatography/mass spectrometry analyses), demonstrated that inter-annual variability strongly influence the sediment composition in Nylandssjön. Spring temperature, snow and ice phenology (e.g., the percentage of snow loss in spring, the timing of lake ice-off) were identified as important drivers for the inputs of terrestrial material to the lake, and were therefore also important for shaping the aquatic biological community. Main changes were detected in the late-80s/mid-90s and mid-2000s associated with increases in algal productivity, in total richness of the protistan community and in relative abundances of Chlorophyta, Dinophyceae as well as Cyanobacteria abundance. These changes could be linked to a decline in terrestrial inputs to the lake during the snow melt and run-off period, which in turn was driven by warmer winter temperatures. Even if our data shows that meteorological factors do affect the sediment composition and microbial communities, they only explain part of the variability. This is ...

العلاقة: https://figshare.com/articles/dataset/Data_Sheet_1_How_Does_Environmental_Inter-annual_Variability_Shape_Aquatic_Microbial_Communities_A_40-Year_Annual_Record_of_Sedimentary_DNA_From_a_Boreal_Lake_Nylandssj_n_Sweden_xlsx/8851673Test

الإتاحة: https://doi.org/10.3389/fevo.2019.00245.s001Test
https://figshare.com/articles/dataset/Data_Sheet_1_How_Does_Environmental_Inter-annual_Variability_Shape_Aquatic_Microbial_Communities_A_40-Year_Annual_Record_of_Sedimentary_DNA_From_a_Boreal_Lake_Nylandssj_n_Sweden_xlsx/8851673Test

المؤلفون: Eric Capo, Johan Rydberg, Julie Tolu, Isabelle Domaizon, Didier Debroas, Richard Bindler, Christian Bigler

مصطلحات موضوعية: Evolutionary Biology, Ecology, Invasive Species Ecology, Landscape Ecology, Conservation and Biodiversity, Behavioural Ecology, Community Ecology (excl. Invasive Species Ecology), Ecological Physiology, Freshwater Ecology, Marine and Estuarine Ecology (incl. Marine Ichthyology), Population Ecology, Terrestrial Ecology, varved sediment record, sedimentary DNA, protists, metabarcoding, meteorological data, inorganic geochemistry, organic proxies, paleolimnology

الوصف: To assess the sensitivity of lakes to anthropogenically-driven environmental changes (e.g., nutrient supply, climate change), it is necessary to first isolate the effects of between-year variability in weather conditions. This variability can strongly impact a lake's biological community especially in boreal and arctic areas where snow phenology play an important role in controlling the input of terrestrial matter to the lake. Identifying the importance of this inherent variability is difficult without time series that span at least several decades. Here, we applied a molecular approach (metabarcoding on eukaryotic 18S rRNA genes and qPCR on cyanobacterial 16S rRNA genes) to sedimentary DNA (sed-DNA) to unravel the annual variability of microbial community in 40 years' sediment record from the boreal lake Nylandssjön which preserve annually-laminated sediments. Our comparison between seasonal meteorological data, sediment inorganic geochemistry (X-ray fluorescence analyses) and organic biomarkers (pyrolysis-gas chromatography/mass spectrometry analyses), demonstrated that inter-annual variability strongly influence the sediment composition in Nylandssjön. Spring temperature, snow and ice phenology (e.g., the percentage of snow loss in spring, the timing of lake ice-off) were identified as important drivers for the inputs of terrestrial material to the lake, and were therefore also important for shaping the aquatic biological community. Main changes were detected in the late-80s/mid-90s and mid-2000s associated with increases in algal productivity, in total richness of the protistan community and in relative abundances of Chlorophyta, Dinophyceae as well as Cyanobacteria abundance. These changes could be linked to a decline in terrestrial inputs to the lake during the snow melt and run-off period, which in turn was driven by warmer winter temperatures. Even if our data shows that meteorological factors do affect the sediment composition and microbial communities, they only explain part of the variability. This is ...

العلاقة: https://figshare.com/articles/dataset/Table_1_How_Does_Environmental_Inter-annual_Variability_Shape_Aquatic_Microbial_Communities_A_40-Year_Annual_Record_of_Sedimentary_DNA_From_a_Boreal_Lake_Nylandssj_n_Sweden_docx/8851679Test

الإتاحة: https://doi.org/10.3389/fevo.2019.00245.s002Test
https://figshare.com/articles/dataset/Table_1_How_Does_Environmental_Inter-annual_Variability_Shape_Aquatic_Microbial_Communities_A_40-Year_Annual_Record_of_Sedimentary_DNA_From_a_Boreal_Lake_Nylandssj_n_Sweden_docx/8851679Test

المؤلفون: Alfama Lopes dos Santos, R.

المساهمون: Schouten, S., Sinninghe Damsté, J.S., University Utrecht

المصدر: PhD+Thesis.+Universiteit+Utrecht%3A+%5Bs.l.%5D.+ISBN+978-94-6203-218-7.+145+pp.+%3Ca+href%3D%22http%3A%2F%2Fhdl.handle.net%2F1874%2F258158%22+target%3D%22_blank%22%3Ehttp%3A%2F%2Fhdl.handle.net%2F1874%2F258158%3C%2Fa%3E

مصطلحات موضوعية: NW Africa, SE Australia, productivity, vegetation, organic proxies [keywords], paleoclimate, Earth Sciences, organic proxies, SST

الوصف: NW Africa and SE Australia are regions which are particularly vulnerable to climate change. In this thesis, organic proxies are used from marine sediment cores to reconstruct past environmental conditions from these areas. In sediments from NW Africa, the UK'37 showed an efficient proxy for sea surface temperature (SST) reconstruction, while the TEXH86 reconstructed thermocline temperatures. The UK'37 and TEXH86 records for the last 192 ka showed that periods of reduced AMOC coincide with a reduction in the vertical temperature gradient. Thus, variations in AMOC strength is a driver of the thermocline structure in the tropical Atlantic. Three independent organic proxies (UK’37,TEXH86 and LDI) were used to reconstruct SSTs for the last 135 ka in sediments from offshore SE Australia. Comparison with SST estimates based on foraminiferal assemblages shows that LDI temperatures compared well with the temperature of the warmest month, TEXH86 with the temperature of the coolest month and UK’37 with mean annual temperature. Thus, the application of these 3 proxies together at this area enables the reconstruction of SST variations from different seasons. Accumulation rates and concentrations of biomarkers from marine plankton classes were used to examine the changes in productivity at the above mentioned sites during the late Quaternary. In NW Africa, a positive correlation was observed between TOC content, productivity proxies (for dinoflagellates, eustigmatophytes, haptophytes) and the sedimentary Fe, in particular during periods of high aridity on the continent. Thus, the productivity in this area is considerably influenced by the fertilization effect of the Sahara dust, while in SE Australia, Proboscia diatom productivity seems to be controlled by the transport of silicic acid to this area as increases in its productivity matched increased diatom productivity observed at some sites of the tropical equatorial Pacific. To assess changes in the vegetation of NW Africa and SE Australia, the d13C of the n-alkanes from plant leaf waxes were analysed. Sediments from the NW Africa reveal three periods (early Holocene, 50–45 and 120–110 ka) during the past 192 ka when the central Sahara/Sahel contained a higher percentage of C3 plants, indicating wetter conditions than at present. A remarkably close correlation between d13C of benthic foraminifera and n-alkanes indicates a connection between variability in AMOC strength and vegetation type in the Sahara/Sahel region. The n-alkane d13C record from SE Australia reveals an extensive period (68-31ka) of high C4 plant abundance that is punctuated by a sharp increase in C3 vegetation at ~43 ka. This sharp increase in C3 vegetation lasts ~5 ka and is characterized by increased levels of biomass burning. Thus, this vegetation change was likely caused by increased burning events and/or by reduced herbivory as it follows the main period of the late Quaternary megafauna extinction in Australia. This thesis demonstrates the benefit of applying multiple organic proxies on marine sediments to assess marine and terrestrial paleoenvironmental changes and it has thereby provided new insights in the cause and effect of environmental changes in marine and continental areas of NW Africa and SE Australia.

وصف الملف: text/plain; application/pdf

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=dedup_wf_001::247061173cccdb89744db5a0059a33edTest
https://dspace.library.uu.nl/handle/1874/258158Test

المؤلفون: Weiyan eWu, Chuanlun eZhang, Huanye eWang, Liu eHe, Wenjun eLi, Hailiang eDong

المصدر: Frontiers in Microbiology
Frontiers in Microbiology, Vol 4 (2013)

مصطلحات موضوعية: Microbiology (medical), Ecology, pH, Ph control, lcsh:QR1-502, chemistry.chemical_element, temperature, hot springs, Context (language use), Yunnan, Biology, biology.organism_classification, Nitrogen, Sulfur, Microbiology, Archaea, lcsh:Microbiology, chemistry, Environmental chemistry, GDGTs, Dominance (ecology), Water chemistry, Original Research Article, organic proxies

الوصف: In culture experiments and many low temperature environments, the distribution of isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) commonly shows a strong correlation with temperature; however, this is often not the case in hot springs. We studied 26 hot springs in Yunnan, China, in order to determine whether temperature or other factors control the distribution of GDGTs in these environments. The hot springs ranged in temperature from 39°C to 94°C, and in pH from 2.35 to 9.11. Water chemistry including nitrogen-, sulfur- and iron species was also determined. Lipids from the samples were analyzed using LC-MS (liquid chromatography-mass spectrometry). Distributions of GDGTs in these hot springs were examined using cluster analysis, which resulted in two major groups. Group 1 was characterized by the lack of dominance of any individual GDGTs, while Group 2 was defined by the dominance of GDGT-0 or thaumarchaeol. Temperature was the main control on GDGT distribution in Group 1, whereas pH played an important role in the distribution of GDGTs in Group 2. However, no correlations were found between the distribution of GDGTs and any of the nitrogen-, sulfur- or iron species. Results of this study indicate the predominance of temperature or pH control on archaeal lipid distribution, which can be better evaluated in the context of lipid classification.

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::92b56858cb2000dd91d65ac9de23f73dTest
http://europepmc.org/articles/PMC3812992Test

مصطلحات موضوعية: NW Africa, SE Australia, productivity, vegetation, paleoclimate, organic proxies, SST

الوصف: NW Africa and SE Australia are regions which are particularly vulnerable to climate change. In this thesis, organic proxies are used from marine sediment cores to reconstruct past environmental conditions from these areas. In sediments from NW Africa, the UK'37 showed an efficient proxy for sea surface temperature (SST) reconstruction, while the TEXH86 reconstructed thermocline temperatures. The UK'37 and TEXH86 records for the last 192 ka showed that periods of reduced AMOC coincide with a reduction in the vertical temperature gradient. Thus, variations in AMOC strength is a driver of the thermocline structure in the tropical Atlantic. Three independent organic proxies (UK’37,TEXH86 and LDI) were used to reconstruct SSTs for the last 135 ka in sediments from offshore SE Australia. Comparison with SST estimates based on foraminiferal assemblages shows that LDI temperatures compared well with the temperature of the warmest month, TEXH86 with the temperature of the coolest month and UK’37 with mean annual temperature. Thus, the application of these 3 proxies together at this area enables the reconstruction of SST variations from different seasons. Accumulation rates and concentrations of biomarkers from marine plankton classes were used to examine the changes in productivity at the above mentioned sites during the late Quaternary. In NW Africa, a positive correlation was observed between TOC content, productivity proxies (for dinoflagellates, eustigmatophytes, haptophytes) and the sedimentary Fe, in particular during periods of high aridity on the continent. Thus, the productivity in this area is considerably influenced by the fertilization effect of the Sahara dust, while in SE Australia, Proboscia diatom productivity seems to be controlled by the transport of silicic acid to this area as increases in its productivity matched increased diatom productivity observed at some sites of the tropical equatorial Pacific. To assess changes in the vegetation of NW Africa and SE Australia, the d13C of the n-alkanes from plant leaf waxes were analysed. Sediments from the NW Africa reveal three periods (early Holocene, 50–45 and 120–110 ka) during the past 192 ka when the central Sahara/Sahel contained a higher percentage of C3 plants, indicating wetter conditions than at present. A remarkably close correlation between d13C of benthic foraminifera and n-alkanes indicates a connection between variability in AMOC strength and vegetation type in the Sahara/Sahel region. The n-alkane d13C record from SE Australia reveals an extensive period (68-31ka) of high C4 plant abundance that is punctuated by a sharp increase in C3 vegetation at ~43 ka. This sharp increase in C3 vegetation lasts ~5 ka and is characterized by increased levels of biomass burning. Thus, this vegetation change was likely caused by increased burning events and/or by reduced herbivory as it follows the main period of the late Quaternary megafauna extinction in Australia. This thesis demonstrates the benefit of applying multiple organic proxies on marine sediments to assess marine and terrestrial paleoenvironmental changes and it has thereby provided new insights in the cause and effect of environmental changes in marine and continental areas of NW Africa and SE Australia.

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=dris___00893::d56bdec3cf5f729eea91559354b524f6Test
https://hdl.handle.net/1874/258158Test