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Paleo-environmental effects of the Mid-Pleistocene transition in the tropical Atlantic and equatorial Africa : = Mileu-veranderingen in de tropische Atlantische Oceaan en equatoriaal Afrika tijdens de Midden-Pleistocene klimaatsovergang (2003)

Schefuß, Enno

Utrecht : Univ.

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Schlagwort(e): climate change ; Dissertation ; Pleistocene ; environmental change ; Atlantic Ocean ; Africa ; Hochschulschrift ; Paläoklimatologie ; Mittelpleistozän ; Tropenklima ; Atlantischer Ozean Süd ; Zentralafrika

Materialart: Buch

Seiten: 187 S , graph. Darst., Kt

ISBN: 9057440814

Serie: Geologica Ultraiectina 223

Sprache: Englisch

Anmerkung: Zsfassung in niederländ. und dt. Sprache , Zugl.: Utrecht, Univ., Diss., 2003

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Pollen analyses of sediment core GeoB9508-5 (2012)

Bouimetarhan, Ilham ; Prange, Matthias ; Schefuß, Enno ; [weitere]

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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

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Publikationsdatum: 2023-06-27

Beschreibung: 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.

Schlagwort(e): 293; Center for Marine Environmental Sciences; GeoB9508-5; Gravity corer (Kiel type); M65/1; MARUM; Meteor (1986); SL

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Format: application/zip, 5 datasets

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Stable hydrogen isotopic composition (dD) and stable carbon isotopic composition (δ¹³C) of sediment core GeoB9508-5 off Senegal

Niedermeyer, Eva M ; Schefuß, Enno ; Sessions, Alex L ; [weitere]

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In: Supplement to: Niedermeyer, Eva M; Schefuß, Enno; Sessions, Alex L; Mulitza, Stefan; Mollenhauer, Gesine; Schulz, Michael; Wefer, Gerold (2010): Orbital- and millennial-scale changes in the hydrologic cycle and vegetation in the western African Sahel: Insights from individual plant wax delta D and d13C. Quaternary Science Reviews, 29(23-24), 2996-3005, https://doi.org/10.1016/j.quascirev.2010.06.039

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Publikationsdatum: 2023-06-27

Beschreibung: To reconstruct variability of the West African monsoon and associated vegetation changes on precessional and millennial time scales, we analyzed a marine sediment core from the continental slope off Senegal spanning the past 44,000 years (44 ka). We used the stable hydrogen isotopic composition (dD) of individual terrestrial plant wax n-alkanes as a proxy for past rainfall variability. The abundance and stable carbon isotopic composition (d13C) of the same compounds were analyzed to assess changes in vegetation composition (C3/C4 plants) and density. The dD record reveals two wet periods that coincide with local maximum summer insolation from 38 to 28 ka and 15 to 4 ka and that are separated by a less wet period during minimum summer insolation. Our data indicate that rainfall intensity during the rainy season throughout both wet humid periods was similar, whereas the length of the rainy season was presumably shorter during the last glacial than during the Holocene. Additional dry intervals are identified that coincide with North Atlantic Heinrich stadials and the Younger Dryas interval, indicating that the West African monsoon over tropical northwest Africa is linked to both insolation forcing and high-latitude climate variability. The d13C record indicates that vegetation of the western Sahel was consistently dominated by C4 plants during the past 44 ka, whereas C3-type vegetation increased during the Holocene. Moreover, we observe a gradual ending of the Holocene humid period together with unchanging ratio of C3 to C4 plants, indicating that an abrupt aridification due to vegetation feedbacks is not a general characteristic of this time interval.

Schlagwort(e): 293; Center for Marine Environmental Sciences; GeoB9508-5; Gravity corer (Kiel type); M65/1; MARUM; Meteor (1986); SL

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Format: application/zip, 5 datasets

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Plant-wax, alkenone and major element analyses of ODP Site 659 for the Last Glacial cycle and associated coretop data (2013)

Küchler, Rony R ; Schefuß, Enno ; Beckmann, Britta ; [weitere]

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In: Supplement to: Küchler, Rony R; Schefuß, Enno; Beckmann, Britta; Dupont, Lydie M; Wefer, Gerold (2013): NW African hydrology and vegetation during the Last Glacial cycle reflected in plant-wax-specific hydrogen and carbon isotopes. Quaternary Science Reviews, 82, 56-67, https://doi.org/10.1016/j.quascirev.2013.10.013

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Publikationsdatum: 2024-01-09

Beschreibung: We present a hydrologic reconstruction of the Sahara-Sahel transition, covering the complete last glacial cycle (130 ka), based on a combination of plant-wax-specific hydrogen (dD) and carbon isotopes (d13C). The dD and d13C signatures of long-chain n-alkanes from ODP Site 659 off NW Africa reveal a significant anti-correlation. Complementary to published pollen data, we infer that this plant-wax signal reflects sensitive responses of the vegetation cover to precipitation changes in the Sahel region, as well as varying contributions from biomes north of the Sahara (C3 domain) by North-East Trade Winds (NETW). During arid phases, especially the northern parts of the Sahel likely experienced crucial water stress, which resulted in a pronounced contraction of the vegetation cover, thus reducing the amount of C4 plant waxes from the region. The increase in NETW strength during dry periods further promoted a more pronounced C3-plant-wax signal derived from the North African C3 plant domain. During humid periods, the C4-dominated Sahelian environments spread northward into the Saharan realm, in association with lower NETW inputs of C3 plant waxes. Arid-humid cycles deduced from plant-wax dD are in accordance with concomitant changes in weathering intensity reflected in varying major element distributions. Environmental shifts are generally linked to periods with large fluctuations in Northern Hemisphere summer insolation. During Marine Isotope Stages 2 and 3, when insolation variability was low, coupling of the hydrologic regime to alkenone-based estimates of NE Atlantic sea-surface temperatures becomes apparent.

Schlagwort(e): Center for Marine Environmental Sciences; MARUM; Ocean Drilling Program; ODP

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Format: application/zip, 3 datasets

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Specific microbial biomarker signatures from Congo fan sediments of ODP site 175-1075, Congo soils, wetland and estuary sediments (2014)

Talbot, Helen M ; Handley, Luke ; Spencer-Jones, Charlotte L ; [weitere]

PANGAEA

In: Supplement to: Talbot, Helen M; Handley, Luke; Spencer-Jones, Charlotte L; Dinga, Bienvenu Jean; Schefuß, Enno; Mann, Paul James; Poulsen, John R; Spencer, Robert GM; Wabakanghanzi, Jose N; Wagner, Thomas (2014): Variability in aerobic methane oxidation over the past 1.2Myrs recorded in microbial biomarker signatures from Congo fan sediments. Geochimica et Cosmochimica Acta, 133, 387-401, https://doi.org/10.1016/j.gca.2014.02.035

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Publikationsdatum: 2024-02-02

Beschreibung: Methane (CH4) is a strong greenhouse gas known to have perturbed global climate in the past, especially when released in large quantities over short time periods from continental or marine sources. It is therefore crucial to understand and, if possible, quantify the individual and combined response of these variable methane sources to natural climate variability. However, past changes in the stability of greenhouse gas reservoirs remain uncertain and poorly constrained by geological evidence. Here, we present a record from the Congo fan of a highly specific bacteriohopanepolyol (BHP) biomarker for aerobic methane oxidation (AMO), 35-aminobacteriohopane-30,31,32,33,34-pentol (aminopentol), that identifies discrete periods of increased AMO as far back as 1.2 Ma. Fluctuations in the concentration of aminopentol, and other 35-aminoBHPs, follow a pattern that correlates with late Quaternary glacial-interglacial climate cycles, with highest concentrations during warm periods. We discuss possible sources of aminopentol, and the methane consumed by the precursor methanotrophs, within the context of the Congo River setting, including supply of methane oxidation markers from terrestrial watersheds and/or marine sources (gas hydrate and/or deep subsurface gas reservoir). Compound-specific carbon isotope values of -30 per mil to -40 per mil for BHPs in ODP 1075 and strong similarities between the BHP signature of the core and surface sediments from the Congo estuary and floodplain wetlands from the interior of the Congo River Basin, support a methanotrophic and likely terrigenous origin of the 35-aminoBHPs found in the fan sediments. This new evidence supports a causal connection between marine sediment BHP records of tropical deep sea fans and wetland settings in the feeding river catchments, and thus tropical continental hydrology. Further research is needed to better constrain the different sources and pathways of methane emission. However, this study identifies the large potential of aminoBHPs, in particular aminopentol, to trace and, once better calibrated and understood, quantify past methane sources and fluxes from terrestrial and potentially also marine sources.

Schlagwort(e): Center for Marine Environmental Sciences; MARUM; Ocean Drilling Program; ODP

Materialart: Dataset

Format: application/zip, 3 datasets

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