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  • 1
    Keywords: Forschungsbericht
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (21 Seiten, 8,86 MB) , Diagramme, Illustrationen
    Language: German
    Note: Förderkennzeichen BMBF 01DH16030 , Verfasser dem Berichtsblatt entnommen , Laufzeit des Vorhabens: 01.12.2016 - 30.11.2019; Berichtszeitraum: 01.12.2016 - 30.11.2019 , Unterschiede zwischen dem gedruckten Dokument und der elektronischen Ressource können nicht ausgeschlossen werden
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  • 2
    Publication Date: 2021-02-08
    Description: The semi-arid northeastern (NE) Brazil vegetation is largely dominated by Caatinga, one of the largest and richest dry forests in the world. Caatinga is a strategic biome, since it has borders with Cerrado, Atlantic forests and the Amazon, acting as a potential corridor (or barrier) for biotic interchange between these regions during evolutionary times. Therefore, accurate reconstructions of past vegetation, ecological and hydrological changes in this area are critical to understanding the dynamics of biome boundaries that may play an important role in dispersal and diversification mechanisms and, more specifically, the link between the long-term climate variability and tropical biodiversity. Here, we present high-resolution palynological and elemental data from marine core GeoB16205-4 retrieved off the Parnaíba River mouth (NE Brazil) mainly covering the Younger Dryas (YD). We show that the YD interval was predominantly wet in NE Brazil, yet it was not homogenous and two distinct phases could be distinguished. A marked intensification of wet conditions between ∼12.3 and 11.6 cal kyr BP was recorded by the expansion of tropical rainforest and tree ferns. These results are in agreement with the transient TraCE-21k coupled climate model simulation. We infer that the second pluvial phase of the YD is related to a weak AMOC due to meltwater pulses in the North Atlantic, which forces a southward shift of the Intertropical Convergence Zone and its associated rainfall. Our records provide new evidence on the establishment of an “eastern forest corridor” in the nowadays semi-arid Caatinga allowing for past biotic interchanges of plant species.
    Type: Article , PeerReviewed
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  • 3
    Publication Date: 2017-06-18
    Description: In order to investigate a possible connection between tropical northeast (NE) Atlantic primary productivity, Atlantic meridional overturning circulation (AMOC), and drought in the Sahel region during Heinrich Stadial 1 (HS1), we used dinoflagellate cyst (dinocyst) assemblages, Mg/Ca based reconstructed temperatures, stable carbon isotopes (δ13C) and geochemical parameters of a marine sediment core (GeoB 9508-5) from the continental slope offshore Senegal. Our results show a two-phase productivity pattern within HS1 that progressed from an interval of low marine productivity between ~ 19 and 16 kyr BP to a phase with an abrupt and large productivity increase from ~ 16 to 15 kyr BP. The second phase is characterized by distinct heavy planktonic δ13C values and high concentrations of heterotrophic dinocysts in addition to a significant cooling signal based on the reconstructions of past sea surface temperatures (SSTs). We conclude that productivity variations within HS1 can be attributed to a substantial shift of West African atmospheric processes. Taken together our results indicate a significant intensification of the North East (NE) trade winds over West Africa leading to more intense upwelling during the last millennium of HS1 between ~ 16 and 15 kyr BP, thus leaving a strong imprint on the dinocyst assemblages and sea surface conditions. Therefore, the two-phase productivity pattern indicates a complex hydrographic setting suggesting that HS1 cannot be regarded as uniform as previously thought.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
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    PANGAEA
    In:  Supplement to: Bouimetarhan, Ilham; Prange, Matthias; Schefuß, Enno; Dupont, Lydie M; Lippold, Jörg; Mulitza, Stefan; Zonneveld, Karin A F (2012): Sahel megadrought during Heinrich Stadial 1: evidence for a three-phase evolution of the low- and mid-level West African wind system. Quaternary Science Reviews, 58, 66-76, https://doi.org/10.1016/j.quascirev.2012.10.015
    Publication Date: 2024-05-27
    Description: Millennial-scale dry events in the Northern Hemisphere monsoon regions during the last Glacial period are commonly attributed to southward shifts of the Intertropical Convergence Zone (ITCZ) associated with an intensification of the northeasterly (NE) trade wind system during intervals of reduced Atlantic meridional overturning circulation (AMOC). Through the use of high-resolution last deglaciation pollen records from the continental slope off Senegal, our data show that one of the longest and most extreme droughts in the western Sahel history, which occurred during the North Atlantic Heinrich Stadial 1 (HS1), displayed a succession of three major phases. These phases progressed from an interval of maximum pollen representation of Saharan elements between ~19 and 17.4 kyr BP indicating the onset of aridity and intensified NE trade winds, followed by a millennial interlude of reduced input of Saharan pollen and increased input of Sahelian pollen, to a final phase between ~16.2 and 15 kyr BP that was characterized by a second maximum of Saharan pollen abundances. This change in the pollen assemblage indicates a mid-HS1 interlude of NE trade wind relaxation, occurring between two distinct trade wind maxima, along with an intensified mid-tropospheric African Easterly Jet (AEJ) indicating a substantial change in West African atmospheric processes. The pollen data thus suggest that although the NE trades have weakened, the Sahel drought remained severe during this time interval. Therefore, a simple strengthening of trade winds and a southward shift of the West African monsoon trough alone cannot fully explain millennial-scale Sahel droughts during periods of AMOC weakening. Instead, we suggest that an intensification of the AEJ is needed to explain the persistence of the drought during HS1. Simulations with the Community Climate System Model indicate that an intensified AEJ during periods of reduced AMOC affected the North African climate by enhancing moisture divergence over the West African realm, thereby extending the Sahel drought for about 4000 years.
    Keywords: 293; Center for Marine Environmental Sciences; GeoB9508-5; Gravity corer (Kiel type); M65/1; MARUM; Meteor (1986); SL
    Type: Dataset
    Format: application/zip, 5 datasets
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  • 6
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    In:  Supplement to: Bouimetarhan, Ilham; Marret, Fabienne; Dupont, Lydie M; Zonneveld, Karin A F (2009): Dinoflagellate cyst distribution in marine surface sediments off West Africa (6-17°N) in relation to sea-surface conditions, freshwater input and seasonal coastal upwelling. Marine Micropaleontology, 71(3-4), 113-130, https://doi.org/10.1016/j.marmicro.2009.02.001
    Publication Date: 2024-05-27
    Description: An organic-walled dinoflagellate cyst analysis was carried out on 53 surface sediment samples from West Africa (17-6°N) to obtain insight in the relationship between their spatial distribution and hydrological conditions in the upper water column as well as marine productivity in the study area. Multivariate analysis of the dinoflagellate cyst relative abundances and environmental parameters of the water column shows that sea-surface temperature, salinity, marine productivity and bottom water oxygen are the factors that relate significantly to the distribution patterns of individual species in the region. The composition of cyst assemblages and dinoflagellate cyst concentrations allows the identification of four hydrographic regimes; 1) the northern regime between 17 and 14°N characterized by high productivity associated with seasonal coastal upwelling, 2) the southern regime between 12 and 6°N associated with high-nutrient waters influenced by river discharge 3) the intermediate regime between 14 and 12°N influenced mainly by seasonal coastal upwelling additionally associated with fluvial input of terrestrial nutrients and 4) the offshore regime characterized by low chlorophyll-a concentrations in upper waters and high bottom water oxygen concentrations. Our data show that cysts of Polykrikos kofoidii, Selenopemphix quanta, Dubridinium spp., Echinidinium species, cysts of Protoperidinium monospinum and Spiniferites pachydermus are the best proxies to reconstruct the boundary between the NE trade winds and the monsoon winds in the subtropical eastern Atlantic Ocean. The association of Bitectatodinium spongium, Lejeunecysta oliva, Quinquecuspis concreta, Selenopemphix nephroides, Trinovantedinium applanatum can be used to reconstruct past river outflow variations within this region.
    Keywords: 286; 287; 288; 289; 290; 291; 293; 295; 297; 298; 300; 301; 302; 303; 304; 305; 306; 307; 310; 311; 312; 313; 314; 316; 317; 318; 319; 320; 321; 322; 323; 324; 326; 327; 329; 330; 331; 371; 376; 388; Atlantic Ocean; Center for Marine Environmental Sciences; Eckernfoerder Bay; GeoB9501-4; GeoB9502-5; GeoB9503-3; GeoB9503-5; GeoB9504-4; GeoB9505-3; GeoB9506-3; GeoB9508-4; GeoB9510-3; GeoB9512-4; GeoB9513-5; GeoB9515-2; GeoB9516-4; GeoB9517-5; GeoB9518-4; GeoB9519-6; GeoB9520-4; GeoB9521-3; GeoB9522-2; GeoB9525-5; GeoB9526-4; GeoB9527-6; GeoB9528-1; GeoB9529-1; GeoB9531-2; GeoB9532-1; GeoB9533-3; GeoB9534-4; GeoB9535-5; GeoB9536-4; GeoB9537-4; GeoB9538-5; GeoB9539-1; GeoB9541-1; GeoB9542-1; GeoB9544-1; GeoB9545-1; GeoB9546-1; GEOTROPEX 83, NOAMP I; Giant box corer; GIK16402-1; GIK16404-1; GIK16405-1; GIK16407-1; GIK16414-1; GIK16421-1; GIK16425-1; GIK16437-3; GIK16558-1; GIK16755-1; GIK16764-1; GIK16765-1; GIK16766-1; GIK16767-1; GIK16768-1; GIK16769-1; GKG; Gravity corer (Kiel type); LI198x; Littorina; M6/5; M65; M65/1; MARUM; Mauritania Canyon; Meteor (1964); Meteor (1986); MUC; MultiCorer; off Guinea; SL; van Veen Grab; VGRAB
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 7
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    PANGAEA
    In:  Supplement to: Bouimetarhan, Ilham; Dupont, Lydie M; Schefuß, Enno; Mollenhauer, Gesine; Mulitza, Stefan; Zonneveld, Karin A F (2009): Palynological evidence for climatic and oceanic variability off NW Africa during the late Holocene. Quaternary Research, 72(2), 188-197, https://doi.org/10.1016/j.yqres.2009.05.003
    Publication Date: 2024-05-27
    Description: Pollen and organic-walled dinoflagellate cyst assemblages from core GeoB 9503-5 retrieved from the mud-belt ( 50 m water depth) off the Senegal River mouth have been analyzed to reconstruct short-term palaeoceanographic and palaeoenvironmental changes in subtropical NW Africa during the time interval from ca. 4200 to 1200 cal yr BP. Our study emphasizes significant coeval changes in continental and oceanic environments in and off Senegal and shows that initial dry conditions were followed by a strong and rapid increase in humidity between ca. 2900 and 2500 cal yr BP. After ca. 2500 cal yr BP, the environment slowly became drier again as indicated by slight increases in Sahelian savannah and desert elements in the pollen record. Around ca. 2200 cal yr BP, this relatively dry period ended with periodic pulses of high terrigenous contributions and strong fluctuations in fern spore and river plume dinoflagellate cyst percentages as well as in the fluxes of pollen, dinoflagellate cysts, fresh-water algae and plant cuticles, suggesting "episodic flash flood" events of the Senegal River. The driest phase developed after about 2100 cal yr BP.
    Keywords: 288; Center for Marine Environmental Sciences; GeoB9503-5; Gravity corer (Kiel type); M65/1; MARUM; Meteor (1986); SL
    Type: Dataset
    Format: application/zip, 3 datasets
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  • 8
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    PANGAEA
    In:  Supplement to: Zhao, Xueqin; Dupont, Lydie M; Schefuß, Enno; Bouimetarhan, Ilham; Wefer, Gerold (2017): Palynological evidence for Holocene climatic and oceanographic changes off western South Africa. Quaternary Science Reviews, 165, 88-101, https://doi.org/10.1016/j.quascirev.2017.04.022
    Publication Date: 2024-05-27
    Description: Atmospheric and oceanographic interactions between the Atlantic and Indian Oceans influence upwelling in the southern Benguela upwelling system. In order to obtain a better knowledge of paleoceanographic and paleoenvironmental changes in the southern Benguela region during the Holocene, 12 marine surface sediment samples and one gravity core GeoB8331-4 from the Namaqualand mudbelt off the west coast of South Africa have been studied for organic-walled dinoflagellate cysts in high temporal resolution. The results are compared with pollen and geochemical records from the same samples. Our study emphasizes significantly distinct histories in upwelling intensity as well as the influence of fluvial input during the Holocene. Three main phases were identified for the Holocene. High percentages of cysts produced by autotrophic taxa like Operculodinium centrocarpum and Spiniferites spp. indicate warmer and stratified conditions during the early Holocene (9900-8400 cal. yr BP), suggesting reduced upwelling likely due to a northward shift of the southern westerlies. In contrast, the middle Holocene (8400-3100 cal. yr BP) is characterized by a strong increase in heterotrophic taxa in particular Lejeunecysta paratenella and Echinidinium spp. at the expense of autotrophic taxa. This indicates cool and nutrient-rich waters with active upwelling probably caused by a southward shift of the southern westerlies. During the late Holocene (3100 cal. yr BP to modern), Brigantedinium spp. and other abundant taxa interpreted to indicate fluvial nutrient input such as cyst of Protoperidinium americanum and Lejeunecysta oliva imply strong river discharge with high nutrient supply between 3100 and 640 cal. yr BP.
    Keywords: Center for Marine Environmental Sciences; MARUM; RAiN; Regional Archives for Integrated iNvestigations
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 9
    Publication Date: 2024-05-27
    Keywords: 1; 21; 22; 23; 3; AFRIDEEP; Aluminium; BC; Box corer; Bromine; Calcium; Center for Marine Environmental Sciences; Chromium; Copper; DEPTH, sediment/rock; ECT-10-1; ECT-10-2; ECT-1-1; ECT-11-2; ECT-1-2; ECT-12-2; ECT-12-3; ECT-12-4; ECT-1-3; ECT-14-1; ECT-14-2; ECT-15-3; ECT-15-4; ECT-16-1; ECT-16-3; ECT-17-2; ECT-17-3; ECT-18-1; ECT-19-2; ECT-20-1; ECT-2-1; ECT-21-1; ECT-2-2; ECT-22-2; ECT-23-2; ECT-23-3; ECT-24-1; ECT-25-1; ECT-26-1; ECT-27-2; ECT-27-3; ECT-3-1; ECT-5-1; ECT-5-2; ECT-6-1; ECT-6-2; ECT-7-2; ECT-8-1; ECT-9-1; ECT-9-2; Event label; GeoB20602-1; GeoB20604-1; GeoB20607-1; GeoB20608-2; GeoB20609-1; GeoB20610-1; GeoB20611-1; GeoB20613-1; GeoB20615-1; GeoB20619-1; GeoB20624-2; GeoB20625-1; GeoB20628-1; GeoB9301-1; GeoB9302-5; GeoB9312-2; GeoB9313-3; GeoB9314-1; Gourits River; Iron; Limpopo Fan; M123; M123_161-1; M123_163-1; M123_166-1; M123_167-2; M123_168-1; M123_169-1; M123_170-1; M123_172-1; M123_174-1; M123_178-1; M123_183-2; M123_184-1; M123_187-1; M63/1; Magnesium; Manganese; MARUM; Meteor (1986); MUC; MultiCorer; Nickel; North of Tugela Cone; Potassium; Rubidium; Sample ID; Silicon; South of Limpopo Fan; South of Tugela Cone; Strontium; Sulfur, total; Titanium; VC; Vibro corer; Zinc; Zirconium
    Type: Dataset
    Format: text/tab-separated-values, 1062 data points
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  • 10
    Publication Date: 2024-05-27
    Keywords: Acacia; Acanthaceae; Aizoaceae; Amaranthaceae/Chenopodiaceae; Apiaceae; Argania spinosa; Artemisia; Aruncus-type; Asphodelus-type; Asteroideae; Brassicaceae; Caryophyllaceae; Cedrus; Centaurea-type; Center for Marine Environmental Sciences; Cichorioideae; Combretaceae; Concentricystes; Convolvulaceae; Corylus; Cyperaceae; ECHo1-1a2; ECHo1-1a3; ECHo1-1a4; ECHo1-2a1; ECHo1-2a2; ECHo1-2a3; ECHo2-1a1; ECHo2-1a2; ECHo2-1a3; ECHo2-2a2; ECHo2-2a3; ECHo2-3a1; ECHo2-4a1; ECHo2-4a2; ECHo2-4a3; ECHo3-1a1; ECHo3-1a2; ECHo3-1a3; ECHo3-3a1; ECHo3-4a1; ECHo3-4a2; Ephedra; Ericaceae; Euphorbia; Euphorbiaceae; Event label; Fabaceae; Indeterminata; Jasminum; Juglans; Juniperus/Tetraclinis; Justicia-type; Labiatae; Leguminosae; Lotus-type; Marker, added; Marker, found; MARUM; Mass; Myrtaceae; Olea; Pentzia-type; Phillyrea; Pinus; Plantago; Poaceae; Pollen, total; Polygalaceae; Polygonaceae; Polygonum; Quercus ilex-type; Quercus robur-type; Rhamnus; Rhus; Rumex; Salix; Selaginella; Solanaceae; Spores; Spores, monolete; Spores, trilete; Tamarix; Tribulus; Typha; Ulmus; Urticaceae; Xanthium-type
    Type: Dataset
    Format: text/tab-separated-values, 1344 data points
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