Pollen and Spores in Marine Sediments from the East Atlantic -A View from the Ocean into the African Continent

Dupont, Lydie M

doi:10.1007/978-3-642-58646-0_22

Cited by 15 publications

(13 citation statements)

References 58 publications

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“…During the subsequent sea-level rise, only pioneer species from the Amaranthaceae, tolerating highly saline environments with a permanent tidal influence and having good colonizing abilities, could expand under these stressful conditions. The development of mangroves at ∼ 14.8 kyr BP might reflect either the expansion of mangrove vegetation along the Rufiji Delta or the erosion of mangrove peat during sea-level rise (Hooghiemstra and Agwu, 1986;Dupont and Agwu, 1991;Lézine at al., 1995Lézine at al., , 1996Dupont, 1999;Kim et al, 2005;Scourse et al, 2005). Mangroves are most common in wetter habitats and swamps where brackish water accumulates.…”

Section: Expansion Of the Salt Marshes And Mangroves: Deglacial Ecolomentioning

confidence: 99%

Northern Hemisphere control of deglacial vegetation changes in the Rufiji uplands (Tanzania)

et al. 2015

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Abstract. In tropical eastern Africa, vegetation distribution is largely controlled by regional hydrology, which has varied over the past 20 000 years. Therefore, accurate reconstructions of past vegetation and hydrological changes are crucial for a better understanding of climate variability in the tropical southeastern African region. We present high-resolution pollen records from a marine sediment core recovered offshore of the Rufiji River delta. Our data document significant shifts in pollen assemblages during the last deglaciation, identifying, through changes in both upland and lowland vegetation, specific responses of plant communities to atmospheric (precipitation) and coastal (coastal dynamics and sea-level changes) alterations. Specifically, arid conditions reflected by a maximum pollen representation of dry and open vegetation occurred during the Northern Hemisphere cold Heinrich event 1 (H1), suggesting that the expansion of drier upland vegetation was synchronous with cold Northern Hemisphere conditions. This arid period is followed by an interval in which forest and humid woodlands expanded, indicating a hydrologic shift towards more humid conditions. Droughts during H1 and the shift to humid conditions around 14.8 kyr BP in the uplands are consistent with latitudinal shifts of the intertropical convergence zone (ITCZ) driven by high-latitude Northern Hemisphere climatic fluctuations. Additionally, our results show that the lowland vegetation, consisting of well-developed salt marshes and mangroves in a successional pattern typical for vegetation occurring in intertidal habitats, has responded mainly to local coastal dynamics related to marine inundation frequencies and soil salinity in the Rufiji Delta as well as to the local moisture availability. Lowland vegetation shows a substantial expansion of mangrove trees after ∼ 14.8 kyr BP, suggesting an increased moisture availability and river runoff in the coastal area. The results of this study highlight the decoupled climatic and environmental processes to which the vegetation in the uplands and the Rufiji Delta has responded during the last deglaciation.

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Section: Expansion Of the Salt Marshes And Mangroves: Deglacial Ecolomentioning

confidence: 99%

Northern Hemisphere control of deglacial vegetation changes in the Rufiji uplands (Tanzania)

et al. 2015

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“…Previous high-resolution geochemical studies at site GeoB 1008 on the southern Congo deep-sea fan [Schneider et al, , 1997b suggest that organic sedimentation over the last 200 kyrs was governed by orbital-forced fluctuations in atmospheric circulation that triggered upwelling and marine productivity along the western equatorial African continental margin as well as continental aridity-humidity cycles [Pokras and Mix, 1985;deMenocal, 1995]. The dominance of precessionalforced insolation changes on African climate and thus on the distribution of vegetation zones has been confirmed by numerous marine pollen records from the eastern equatorial Atlantic [e.g., Frédoux, 1994;Ning and Dupont, 1997;Jahns et al, 1998;Dupont, 1999;Dupont et al, 2000]. The general link between organic sedimentation and orbital forcing persisted over the past 1.2 Myrs on the Congo deep-sea fan [Holtvoeth et al, 2001].…”

Section: Introductionmentioning

confidence: 95%

Organic matter in river‐influenced continental margin sediments: The land‐ocean and climate linkage at the Late Quaternary Congo fan (ODP Site 1075)

Holtvoeth

Wagner

Schubert

2003

Geochem Geophys Geosyst

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[1] Late Quaternary sections (1.2 Ma) of ODP-Site 1075 from the Congo deep-sea fan are investigated to reconstruct variations of terrigenous organic matter supply to the eastern equatorial Atlantic. To characterize the organic matter (OM) with regard to marine and terrigenous amounts we used elemental analysis (C, N, S), stable carbon isotopes (bulk d 13 C org ), Rock-Eval pyrolysis, and terrigenous biomarkers (lignin phenols from CuO oxidation). The records of total organic carbon (TOC) contents, C org /N tot ratios, bulk OM degradation rates (C org /C org *), and the ratios of hydrocarbons (HC) from low-mature versus HC from high-mature OM (lm/hm) reveal pronounced cyclic changes in OM abundance, preservation, and reactivity that are closely related to the precessional controlled record of insolation, and thus, to variations in upwelling intensity and fluvial run-off. Primary productivity off the Congo is stimulated by both, enhanced nutrient supply in response to trade-induced upwelling during arid African climates (insolation minima) and fluvial nutrient delivery during humid stages (following insolation maxima), especially due to the contribution of dissolved silica that is taken up preferably by diatoms. However, results stemming from a multiparameter approach reveal that the fluvial supply of degraded OM and black carbon (BC) associated with fine-grained sediments from soil erosion is a decisive factor for the preservation of marine OM and, in addition, significantly influences the geochemical signature of bulk and terrigenous OM. Riverine and eolian supply of C 4 plant matter, as well as enhanced concentrations of BC, during arid and arid-to-humid transitional climate stages, may lead to a severe underestimation of terrigenous organic carbon, if its amount is calculated from bulk isotopic ratios using binary end-member models. During the humid stages, it is the massive supply of 13 C-enriched soil OM with low C org /N tot ratios that may suggest a mainly marine composition of bulk OM. In fact, terrigenous OM governs bulk OM geochemical signatures in the sediments of the Congo deep-sea fan, a result that is contradictory to earlier studies, especially to the conventional interpretation of the bulk d 13 C org signal.

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“…While the 700-and 500-hPa levels represent the area and the upper boundary of the SAL [Kubatzki and Claussen, 1998;Diedhiou et al, 1999], the latter marks the upper boundary of the trade winds [Schuetz, 1980]. These trajectories have been calculated with a global 2-dimensional trajectory isobaric model, a modification of a previously developed model by the Norwegian Meteorological Institute [Eliassen, 1977]. The model computes 4-day isobaric backward trajectories from zonal and meridional components.…”

Section: Methodsmentioning

confidence: 99%

“…Interdisciplinary studies focusing on the connection between sources, transport and deposition of windblown material in marine sediments are rather scarce. In this regard, trap-collected freshwater diatoms, phytoliths and pollen can be used as potential source markers of land-derived material over the tropical northeast Atlantic [Dupont, 1999;Romero et al, 1999a].…”

Section: Introductionmentioning

confidence: 99%

“…It has been widely demonstrated that changes in the allochthonous microfossil assemblages in tropical northeast Atlantic sediments provide information on the eolian input from northwest Africa and the wind system involved. Therefore, it documents continental paleoenvironments and biostratigraphy during Quaternary times, and contribute significantly to the reconstruction of paleoclimatic events in Northern Africa [e.g., Pokras and Mix, 1985;Gasse et al, 1989Gasse et al, , 1990Pokras, 1991;de Menocal et al, 1993;Dupont, 1999]. However, if we wish to interpret the paleoatmospheric circulation and its relationship with the paleoclimate, it is necessary to assess the present-day deposition rates of landderived material, in order to establish likely source areas, as well as to identify the transport agent and its seasonal variability.…”

Section: Introductionmentioning

confidence: 99%

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Temporal variability of fluxes of eolian‐transported freshwater diatoms, phytoliths, and pollen grains off Cape Blanc as reflection of land‐atmosphere‐ocean interactions in northwest Africa

Romero

2003

J. Geophys. Res.

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Fluxes of airborne freshwater diatoms (FD), phytoliths (PH), and pollen grains (PO) collected with sediment traps off Cape Blanc, northwest Africa, from 1988 till 1991 are presented. Both continental rainfall variations and wind mean strength and direction play a key role in the temporal fluctuations of the fluxes of eolian traces in the pelagic realm. Drier conditions in Northern Africa in 1987 could have preceded the high lithogenic input and moderate FD flux in 1988. The PH peak in summer 1988 was probably caused by increased wind velocity. Wetter rainy seasons of 1988/89 might have promoted a significant pollen production in summer 1989, and FD in late 1989 and early 1990, as well as contributed to the reduction of the lithogenic flux in 1989/90. Decreased fluxes of FD, PH and PO, and higher contribution of the 6–11 μm lithogenic fraction in 1991 would mainly reflect minor intensity and decreased amount of continental trade winds. Air‐mass backward trajectories confirm that the Saharan Air Layer is predominantly involved in the spring/summer transport. Trade winds play a decisive role in the fall/winter months, but also contribute to the transport during late spring/summer. Origin of wind trajectories does not support a direct relationship between transporting wind‐layers and material source areas in Northern Africa. High winter fluxes of eolian tracers and high amount of trade winds with continental origin in summer warn against a simplistic interpretation of the seasonal eolian signal preserved in the sediments off Cape Blanc, and the wind layer involved in its transport.

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Pollen and Spores in Marine Sediments from the East Atlantic -A View from the Ocean into the African Continent

Cited by 15 publications

References 58 publications

Northern Hemisphere control of deglacial vegetation changes in the Rufiji uplands (Tanzania)

Northern Hemisphere control of deglacial vegetation changes in the Rufiji uplands (Tanzania)

Organic matter in river‐influenced continental margin sediments: The land‐ocean and climate linkage at the Late Quaternary Congo fan (ODP Site 1075)

Temporal variability of fluxes of eolian‐transported freshwater diatoms, phytoliths, and pollen grains off Cape Blanc as reflection of land‐atmosphere‐ocean interactions in northwest Africa

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