Pollen abundance in Late Quaternary sediment cores off West Africa

The pollen record of three marine late Quaternary cores off Senegal shows a juxtaposition of Mediterranean, Northern Saharan, Central Saharan elements, which are considered transported by the trade winds from a winter-rainfall area, and Sahelian, Soudanese, Soudano-Guinean elements, considered transported both by winds and mostly by the Senegal River, and coming from the monsoonal, summer tropical rainfall area of southern West Africa. Littoral vegetation is either the edaphically dry and saline Chenopodiaceae from sebkhas at the time of the main regression, or the warm tropical humid mangrove with Rhizophora during the humid optimum period. Four stratigraphic zones reflect, from basis to top: Zone 4. A semi-arid period with a balanced pollen input. Zone 3. A very arid period with the disappearance of monsoonal pollen, probably from the disappearance of the Senegal River, a very saline littoral plain with Chenopodiaceae, a larger input of northern Saharan pollen from intensified trade winds. Zone 2. A quite humid period, much more so than today, very suddenly established, with a northward extension of the monsoonal areas, a rich littoral mangrove, and weakening of the trade winds. Zone l. A slow and steady evolution toward the present semi-humid conditions with regression of the mangrove, and of the monsoonal areas toward the south. Tentative datations and correlations with the Tchad area suggested: zone 4: 22,500 to 19,000 years BP; zone 3: 19,000 to 12,500 years BP; zone 2: 12,500 to 5,500 years BP; zone 1: 5,500 years BP to top of core. Dinoflagellate cysts display a tropical assemblage with mostly estuarine neritic elements and also a weak oceanic component, mostly in the lower slope core 47. Cosmopolitan taxa dominate the assemblage and only a few species point to more specialized environments. Quantitative variations of the assemblage are the basis of stratigraphy which is not similar to the pollen stratigraphy, and an inshore-outshore gradient has to be taken into account to correlate the three cores.

Pollen analysis of surface sediments from the Gulf of Guinea and offshore NW-Africa

The areas of marine pollen deposition are related to the pollen source areas by aeolian and fluvial transport regimes, whereas wind transport is much more important than river transport. Pollen distribution patterns of Pinus, Artemisia, Chenopodiaceae-Amaranthaceae, and Asteraceae Tubuliflorae trace atmospheric transport by the northeast trades. Pollen transport by the African Easterly Jet is reflected in the pollen distribution patterns of Chenopodiaceae-Amaranthaceae, Asteraceae Tubuliflorae, and Mitracarpus. Grass pollen distribution registers the latitudinal extension of Sahel, savannas and dry open forests. Marine pollen distribution patterns of Combretaceae-Melastomataceae, Alchornea, and Elaeis reflect the extension of wooded grasslands and transitional forests. Pollen from the Guinean-Congolian/Zambezian forest and from the Sudanian/Guinean vegetation zones mark the northernmost extension of the tropical rain forest. Rhizophora pollen in marine sediments traces the distribution of mangrove swamps. Only near the continent, pollen of Rhizophora, Mitracarpus, Chenopodiaceae-Amaranthaceae, and pollen from the Sudanian and Guinean vegetation zones are transported by the Upwelling Under Current and the Equatorial Under Current, where those currents act as bottom currents. The distribution of pollen in marine sediments, reflecting the position of major climatic zones (desert, dry tropics, humid tropics), can be used in tracing climatic changes in the past.

Pollen distribution of sediment core MD96-2048 from the Western Indian Ocean

Glacial-interglacial fluctuations in the vegetation of South Africa might elucidate the climate system at the edge of the tropics between the Indian and Atlantic Oceans. However, vegetation records covering a full glacial cycle have only been published from the eastern South Atlantic. We present a pollen record of the marine core MD96-2048 retrieved by the Marion Dufresne from the Indian Ocean ~120 km south of the Limpopo River mouth. The sedimentation at the site is slow and continuous. The upper 6 m (spanning the past 342 Ka) have been analysed for pollen and spores at millennial resolution. The terrestrial pollen assemblages indicate that during interglacials, the vegetation of eastern South Africa and southern Mozambique largely consisted of evergreen and deciduous forests. During glacials open mountainous scrubland dominated. Montane forest with Podocarpus extended during humid periods was favoured by strong local insolation. Correlation with the sea surface temperature record of the same core indicates that the extension of mountainous scrubland primarily depends on sea surface temperatures of the Agulhas Current. Our record corroborates terrestrial evidence of the extension of open mountainous scrubland (including fynbos-like species of the high-altitude Grassland biome) for the last glacial as well as for other glacial periods of the past 300 Ka.

Pollen flux off Cape Blanc

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.

Pollen record of sediment core GeoB1008-3 from the Congo fan

Palynological investigation of the marine core, GeoB1008-3, from near the mouth of the Congo river (6°35.6'S/10°19.1'E), provides information about the changes in vegetation and climate in West Equatorial Africa during the last 190 ka. The pollen diagram is divided into zones 1-6 which are considered to correspond in time with the marine isotope stages 1-6. Oscillations in temperature and moisture are indicated during the cold stage 6. During stage 5, two cooler periods (5d and 5b) can be shown with an expansion of Podocarpus forests to lower elevations on the expense of lowland rain forest. Extended mangrove swamps existed along the coast in times of high sea level (stages 5 and 1).

Evaluating potential olive orchard sugar food sources for the olive fly parasitoid Psyttalia concolor

Olive fruit fly Bactrocera oleae (Rossi) (Diptera: Tephritidae) is a major olive pest in the Mediterranean basin where increasing insecticide resistance has enhanced damage and necessitates more reliance on other control strategies, such as biological control. Provision of floral resources has been reported to improve the effectiveness of natural enemies. Here, we tested the effect of six plant nectars and two honeydew sources on the survival of Psyttalia concolor (Szépligeti) (Hymenoptera: Braconidae), a parasitoid wasp used in the biological control of olive fruit fly. Our results showed a positive effect on survival associated with nectars of Anchusa azurea Mill., Rosmarinus officinalis L., Lavatera cretica L. and Calamintha nepeta (L.) Savi, while honeydew proved to be a valuable alternative food source. When offering flowers directly to insects, Anchusa azurea, Lavatera cretica, and Foeniculum vulgare L. were found to be the most beneficial species, indicating also that P. concolor feeds predominantly on shallow corollas.